United States
Environmental Protection
Agency
United Nations
Environment Programme
August 1986
vvEPA
EFFECTS OF CHANGES IN STRATOSPHERIC
OZONE AND GLOBAL CLIMATE
Volume I: Overview 170OPPE861
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Library of Congress Cataloging - in - Publication Data
Effects of changes in stratospheric ozone and global climate.
Proceedings of a conference convened by the United Nations Environment
Programme and the U.S. Environmental Protection Agency.
Contents: v. 1. Overview — v. 2. Stratospheric ozone — v. 3. Climate
change. — v. 4. Sea level rise
1. Atmospheric ozone—Reduction—Congresses. 2. Stratosphere—Con-
gresses. 3. Global temperature changes—Congresses. 4. Climatic
changes—Congresses. 5. Sea level—Congresses. 6. Greenhouse effect,
Atmospheric—Congresses. 7. Ultraviolet radiation—Congresses. I.
Titus, James G II. United States Environmental Protection Agency. III.
United Nations Environment Programme.
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EFFECTS OF CHANGES IN STRATOSPHERIC
OZONE AND GLOBAL CLIMATE
Volume 1: Overview
Edited by
James G. Titus
U.S. Environmental Protection Agency
This report represents the proceedings of the INTERNATIONAL CON-
FERENCE ON HEALTH AND ENVIRONMENTAL EFFECTS OF
OZONE MODIFICATION AND CLIMATE CHANGE sponsored by the
United Nations Environment Programme and the U.S. Environmental
Protection Agency. The purpose of the conference was to make available
the widest possible set of views. Accordingly, the views expressed herein
are solely those of the authors and do not represent official positions of
either agency. Mention of trade names or commercial products does not
constitute endorsement or recommendation for use.
U.S. EnvirosE&rtsl Frr/tec-tira
Great Lakes National rro£ra,u
GLKPO Li
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PREFACE
This report examines the possible consequences of projected changes in
stratospheric ozone and global climate resulting from emissions of chloro-
fluorocarbons, carbon dioxide, methane, and other gases released by human
activities. During the week of June 16-20, the United Nations Environment
Programme and the U.S. Environmental Protection Agency sponsored an
International Conference on the Health and Environmental Effects of Ozone
Modification and Climate Change, which was attended by scientists and
officials from approximately twenty countries from all areas of the world.
The four volumes of this report comprise the proceedings of that conference.
Volume 1 provides an overview of the issues as well as the introductory
remarks and reactions from top officials of the United Nations Environment
Programme and the United States Environmental Protection Agency, two U.S.
Senators, and representatives from industry, academia, and environmental
groups. Volumes 2, 3, and 4 provide more detailed investigations on the
effects of ozone depletion, climate change, and the rise in sea level that
might result from a global warming.
We wish to thank the many people who helped us to publish this report on
time. Mary Dalrymple and Wendy Martin of Technology Applications,
Incorporated (TAI) coordinated a team of copy editors that included Karen
Spear, Linda Stiles, June Leatherman, and Susan MacMillan. Sandra Miller
directed a team of word processors that included Lynette Dunaway, Felicia
Jenkins, and Patricia Maddox. All of these people worked many long nights.
We also wish to thank Maria Tikoff and Stephen Seidel, who coordinated
the presentations at the conference and whose perpetually good nature helped
keep us enthusiastic, and Judy Salmon of TAI who coordinated the logistics for
the conference. Peter Usher of UNEP and John Hoffman of EPA provided overall
guidance.
With the exception of the papers by Lee Thomas and Genady Golubev, this
report does not present the official views of either the U.S. Environmental
Protection Agency or the United Nations Environment Programme.
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TABLE OF CONTENTS
INTRODUCTION
Overview of the Effects of Changing the Atmosphere
James G. Titus and Stephen Seidel 3
Global Environmental Change: The UNEP Perspective
Genady N. Golubev 21
Global Environmental Change: The EPA Perspective
Lee Thomas 27
Global Environmental Change: The International Perspective
Richard E. Benedick 31
Man's Impact on Earth's Atmosphere
James P. Bruce 35
The Importance of Knowing Sooner
John S. Hoffman 53
Our Global Environment: The Next Challenge
John H. Chafee 59
The Greenhouse Effect
Albert Gore, Jr 63
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OZONE MODIFICATION AND SUMMARY OF UV-B EFFECTS
Atmospheric Ozone
Robert T. Watson 69
Ozone Perturbations Due to Increases in NpO, CHj, and Chlorocarbons:
Two-Dimensional Time Dependent Calculations
Frode Stordal and Ivar S.A. Isaksen 83
The Ultraviolet Radiation Environment of the Biosphere
John E. Frederick 121
Health Effects of Ultraviolet Radiation
Edward A. Emmett 129
Ozone Depletion and Ocular Risks from Ultraviolet Radiation
Morris Waxier : 14?
Overview of Our Current State of Knowledge of UV Effects on Plants
Alan H. Teramura 165
The Effect of Solar UV-B Radiation on Aquatic Systems: An Overview
R.C. Worrest 175
CLIMATE CHANGE
The Greenhouse Effect: Projections of Global Climate Change
J. Hansen, A. Lacis, D. Rind, G. Russell, I. Fung,
P. Ashcraft, S. Lebedeff, R. Ruedy, and P. Stone 199
The Causes and Effects of Sea Level Rise
James G. Titus 219
Reduction in Summer Soil Wetness Induced by an Increase in Atmospheric
Carbon Dioxide
S. Manabe and R.T. Wetherald 249
Effects of Climatic Changes on Agriculture and Forestry:
An Overview
Martin L. Parry and Timothy R. Carter 257
The Water Resource Impact of Future Climate Change and Variability
Max Beran 299
VI
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REVIEW AND ASSESSMENT
Determining the Options - The Role of UNEP in Addressing Global Issues
Peter Usher [[[ 331
The Policy Context
Gus Speth [[[ 335
The Need for Responsible CFC Policy
Richard Barnett [[[ 341
Cooling the Chemical Summer: Some Policy Responses to Ozone-
Destroying and Greenhouse Gases
David D. Doniger and David A. Wirth .....................................
Climate Change and Stratospheric Ozone Depletion:
Need for More Than the Current Minimalist Response
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INTRODUCTION
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Overview of the Effects of Changing the Atmosphere
James G. Titus and Stephen R. Seidel
Environmental Protection Agency
Washington, DC USA
INTRODUCTION
Society is conducting a global experiment on the earth's atmosphere.
Human activities are increasing the worldwide atmospheric concentrations of
chlorofluorocarbons, carbon dioxide, methane, and several other gases. A
growing body of scientific evidence suggests that if these trends continue,
stratospheric ozone may decline and global temperature may rise. Because the
ozone layer shields the earth's surface from damaging ultraviolet radiation
(UV) future depletion could increase the incidence of skin cancer and other
diseases, reduce crop yields, damage materials, and place additional stress on
aquatic plants and animals. A global warming from the "greenhouse effect"
could also threaten human health, crop yields, property, fish, and wildlife.
Precipitation and storm patterns could change, and the level of the oceans
could eventually rise.
To improve the world's understanding of these and other potential
implications of global atmospheric changes, the United Nations Environment
Programme (UNEP) and the U.S. Environmental Protection Agency (EPA) sponsored
an International Conference on the Health and Environmental Effects of Ozone
Modification and Climate Change during the week of June 16-20, 1986. The
conference brought together over three hundred researchers and policy makers
from approximately twenty nations. This four-volume report presents the
seventy-three papers that were delivered at the conference by over eighty
speakers, including two U.S. Senators, top officials from UNEP and EPA, some
of the leading scientists investigating the implications of atmospheric
change, and representatives from industry and environmental groups. In
addition to this summary of the entire report, Volume 1 presents a series of
overview papers describing each of the major areas of research on the effects
of atmospheric change, as well as policy assessments of these issues by well-
known leaders in government, industry, and the environmental community.
Volumes 2, 3, and 4 present the more specialized papers on the impacts of
ozone modification, climate change, and sea level rise, respectively, and
provide some of the latest research in these areas.
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OZONE MODIFICATION
Atmospheric Processes
The ozone in the upper part of the atmosphere—known as the strato-
sphere—is created by ultraviolet radiation. Oxygen (02) is continuously
converted to ozone (Oo) and back to 02 by numerous photochemical reactions
that take place in the stratosphere, as Stordal and Isaksen (Volume 1)
describe. Chlorofluorocarbons and other gases released by human activities
could alter the current balance of creative and destructive processes.
Because CFCs are very stable compounds, they do not break up in the lower
atmosphere (known as the troposphere). Instead, they slowly migrate to the
stratosphere, where ultraviolet radiation breaks them down, releasing
chlorine.
Chlorine acts as a catalyst to destroy ozone; it promotes reactions that
destroy ozone without being consumed. A chlorine (Cl) atom reacts with ozone
(Oo) to form CIO and 02. The CIO later reacts with another 0, to form two
molecules of Op, which releases the chlorine atom. Thus, two molecules of
ozone are converted to three molecules of ordinary oxygen, and the chlorine is
once again free to start the process. A. single chlorine atom can destroy
thousands of ozone molecules. Eventually, it returns to the troposphere,
where it is rained out as hydrochloric acid.
Stordal and Isaksen point out that CFCs are not the only gas released by
human activities that might alter the ozone balance. Increasing
concentrations of methane in the troposphere increase the water vapor in the
stratosphere, which helps create ozone. Carbon dioxide and other greenhouse
gases (discussed below) warm the earth's surface but cool the upper
atmosphere; cooler stratospheric temperatures slow the process of ozone deple-
tion. Nitrous oxide (N20) reacts with both chlorine and ozone.
Stordal and Isakson present results of possible ozone depletion over
time, using their two-dimensional atmospheric-chemistry model. Unlike one-
dimensional models which provide changes in ozone in the global average, this
model calculates changes for specific latitutdes and seasons. The results
show that if concentrations of the relevant trace gases grow at recent levels,
global average ozone depletion by 2030 would be 6.5 percent. However,
countries in the higher latitudes (60°N) would experience 16 percent depletion
during spring. Even in the case of constant CFC emissions, where global
average depletion would be 2 percent by 2030, average depletion would be 8
percent in the high northern latitudes.
Watson (Volume 1) presents evidence that ozone has been changing recently
more than atmospheric models had predicted. As Plate 1 shows, the ozone over
Antarctica during the month of October appears to have declined over 40
percent in the last six to eight years. Watson also discusses observations
from ozone monitors that suggest a 2 to 3 percent worldwide reduction in ozone
in the upper portion of the stratosphere (thirty to forty kilometers above the
surface), which is consistent with model predictions. Finally, he presents
preliminary data showing a small decrease since 1978 in the total (column)
ozone worldwide. However, he strongly emphasizes that the data have not yet
been fully reviewed and that it is not possible to conclusively attribute
observed ozone depletion to the gases released by human activities. While
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there are several hypotheses to explain why ozone concentrations have
declined, none have been adequately established; nor did any of the
atmospheric models predict the measured loss of ozone over Antarctica.
Ultraviolet Radiation
Many of the chemical reactions investigated by atmospheric scientists
take place only in the stratosphere because they are caused by types of
radiation only found in the upper atmosphere. As Frederick (Volume 1)
explains, the sun emits radiation over a broad range of wavelengths, to which
the human eye responds in the region from approximately 400 to 700 nanometers
(nm). Wavelengths from 320 to 400 nm are known as UV-A; wavelengths from 280
to 320 nm are called UV-B, and wavelengths from 200 to 280 nm are known as
UV-C.
Frederick explains why attention has primarily focused on the UV-B part
of the spectrum. The atmosphere absorbs virtually all UV-C, and is expected
to continue to do so under all foreseeable circumstances. On the other hand,
UV-A is not absorbed by ozone. . By contrast, UV-B is partially absorbed by
ozone, and future depletion would reduce the effectiveness of this shield.
We now examine the potential implications of such changes on human
health, plants, aquatic organisms, materials, and air pollution.
Effects on Human Health
The evidence suggests that solar ultraviolet radiation induces skin
cancer, cataracts, suppression of the human immune response system, and
(indirectly through immunosuppression) the development of some cutaneous
infections, such as herpes. Emmett (Volume 1) discusses the absorption of UV
radiation by human tissue and the mechanisms by which damage and repair may
occur.
Emmett also examines UV radiation as the cause of aging of the skin and
both basal and squamous skin cancers. In reviewing the role of UV radiation
in melanoma (the most frequently fatal skin cancer), he states that some
evidence suggests this link, but that currently there is no acceptable animal
model that can be used to explore or validate this relationship. He concludes
that future studies must focus on three major factors—exposure to solar
radiation, individual susceptibility, and personal behavior. Waxier (Volume
1) presents evidence of a link between UV-B exposure and cataracts.
Volume 2 presents specific research results and provides more detail on
many of the aspects covered in this volume. Scotto presents epidemiological
evidence linking solar radiation with skin cancers, other than melanoma. His
analysis suggests that Caucasians in the United States have a 12 to 30 percent
chance of developing these cancers within their lifetimes, even without ozone
depletion. Armstrong examines the role of UV-B exposure to melanoma in a
study of 511 matched melanoma patients and control subjects in Western
Australia. He shows that "intermittent exposure" to sunlight was closely
associated with this type of cancer.
However, $2 an<* ^ reflect some UV-A back to space.
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In a paper examining nonmelanoma skin cancer in Kuwait, Kollias and Baqer
(Volume 2) show that despite the presence of protective pigmentation, 75
percent of cancers occur on the 10 percent of the skin exposed to sunlight. A
second paper on skin cancer presents experimental evidence suggesting that the
mechanism by which skin cancer could occur involves disruption of the
cytoskeleton from exposure to UV-A and UV-B light (Zamansky and Chow,
Volume 2).
The pathways by which suppression of the immune response might be
triggered are explored in papers by DeFabo and Noonan, Daynes et al., and
Elmets et al (all Volume 2). Davies and Forbes (Volume 2) show that mice
exposed to UV-B radiation had a decrease in lifetime that was proportional to
the quantity of radiation and not directly related to the incidence of skin
cancer.
Possible implications of immune suppression of diseases and the
mechanisms by which it occurs are still uncertain. However, several papers in
Volume 2 suggest that in addition to skin cancer and contact hypersensitivity,
diseases influenced by UV-B induced immune suppression include leishmaniasis
and herpes infections. Fisher et. al (Volume 2) show that at least one
sunscreen effectively protects mice exposed to UV-B radiation from sunburn;
but it does not stop the immune suppression from interfering with a contact
hypersensitivity (allergic) reaction.
Effects on Plants
The effects of increased exposure to UV-B radiation on plants has been a
primary area of research for nearly a decade. Teramura (Volume 1) reports
that of the two hundred plants tested for their sensitivity to UV-B radiation,
over two-thirds reacted adversely; peas, beans, squash, melons, and cabbage
appear to be the most sensitive. Given the complexities in this area of
research, he warns that these results may be misleading. For example, most
experiments have used growth chambers. Studies of plants in the field have
shown them to be less sensitive to UV-B. Moreover, different cultivars of the
same plant have shown very different degrees of sensitivity to UV-B
radiation. Finally, Teramura suggests that potential effects from multiple
stresses (e.g., UV-B exposure plus water stress or mineral deficiency) could
substantially alter a plant's response to changes in UV-B alone.
In Volume 2, Teramura draws extensively from the results of his five
years of field tests on soybeans. His data show that a 25 percent depletion
in ozone could result in a 20 to 25 percent reduction in soybean yield and
adverse impacts on the quality of that yield. Because soybeans are the fifth
largest crop in the world, a reduction in yields could have serious
consequences for world food supplies. However, some soybean cultivars appear
to be less susceptible to UV-B radiation, which suggests that selective crop
breeding might reduce future losses, if it does not increase vulnerability to
other environmental stresses.
BJorn (Volume 2) examines the mechanisms by which plant damage occurs.
His research relates specific wavelengths with those aspects of plant growth
that might be susceptible, including the destruction of chloroplast, DMA, or
enzymes necessary for photosynthesis.
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Aquatic Organisms
Aquatic plants would also be adversely affected by increased ultraviolet
radiation. Worrest (Volume 1) points out that most of these plants, which are
drifters (phytoplankton), spend much of their time near the surface of the
water (the euphotic zone) and are therefore exposed to ultraviolet
radiation. A reduction in their productivities would be important because
these plants directly and indirectly provide the food for almost all fish.
Furthermore, the larvae of many fish found in the euphotic zone would be
directly affected, including crabs, shrimp, and anchovies. Worrest points out
that fish account for 18 percent of the animal protein that people around the
world consume, and 40 percent of the protein consumed in Asia.
An important question is the extent to which current UV-B levels are a
constraint on aquatic organisms. Calkins and Blakefield (Volume 2) conclude
that some species are already exposed to as much UV-B as they can tolerate.
Thomson (Volume 2) shows that a 10 percent decrease in ozone could increase
the number of abnormal larvae as much as 18 percent. In a study of anchovies,
a 20 percent increase in UV-B radiation over a 15-day period caused the loss
of all the larvae within a 10-meter mixed layer in April and August.
Many other factors could affect the magnitude of the impacts on specific
species, ecosystems, and the food chain. An important mechanism by which
species could adapt to higher UV-B incidence would be to reduce their exposure
by moving further away from the water's surface during certain times of the
day or year when exposure is greatest. Haeder (Volume 2) suggests, however,
that for certain species such avoidance may be impaired by UV-B radiation.
Even for those organisms that could move to avoid exposure, unwanted
consequences may result. Calkins and Blakefield present model results showing
that movement by phytoplankton away from sunlight to reduce exposure to a 10
percent increase in UV-B would result in a 2.5 to 5 percent decrease in
exposure to the photosynthetically active radiation on which their growth
depends. Increased movement requires additional energy consumption, while
changes in location may affect the availability of food for zooplankton, which
could cause other changes in shifts in the aquatic food chain.
To a certain extent, losses within a particular species of plankton may
be compensated by gains in other species. Although it is possible that no net
change in productivity will occur, questions arise concerning the ecological
impacts on species diversity and community composition (Kelly, Volume 1).
Reductions in diversity may make populations more susceptible to changes in
water temperatures, nutrient availability, diseases, or pollution. Changes in
community composition could alter the protein content, dry weight, or overall
food value of the initial stages of the aquatic food chain.
Polymer Degradation and Urban Smog
Current sunlight can cause paints to fade, transparent window glazing to
yellow, and polymer automobile roofs to become chalky. These changes are
likely to occur more in places closer to the equator where UV-B radiation is
greater. They are all examples of degradation that could accelerate if
depletion of the ozone layer occurs. Andrady and Horst (Volume 2) present a
case study of the potential magnitude of loss due to increased exposure to
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UV-B radiation on polyvinyl chloride (PVC). This chemical is used in outdoor
applications where exposure to solar radiation occurs over a prolonged
period. It is also used in the construction industry in siding and window
frames and as a roofing membrane.
To analyze the potential economic impact of future ozone depletion on
PVC, the authors assumed that the future service life of polymers would be
maintained by increasing the quantity of light stabilizers (titanuim dioxide)
used in the product. As a result, the costs associated with increased UV-B
radiation would be roughly equal to the costs of increased stablizers.
Preliminary results show that for a 26 percent depletion by 2075, the
undiscounted costs would be $4.7 billion (1984 dollars).
Increased penetration of UV-B radiation to the earth's surface could play
an important role in the formation of ground level oxidants (smog). UV-B
affects smog formation through the photolysis of formaldehyde, from which
radicals are the main source for deriving chain reactions that generate
photochemical smog. Whitten and Gery (Volume 2) analyze the relationship
between UV-B, smog, and warmer temperatures. The results of this preliminary
study of Nashville, Philadelphia, and Los Angeles show that large depletions
in stratospheric ozone and increases in temperature would increase smog by as
much as 50 percent. In addition, because oxidants would form earlier in the
day and closer to population centers (where emissions occur), risks from
exposure could increase by an even higher percentage increase. Whitten and
Gery also report a sensitive relationship between UV-B and hydrogen peroxide,
an oxidant and precursor to acid rain.
CLIMATE CHANGE
The Greenhouse Effect
Concern about a possible global warming focuses largely on the same gases
that may modify the stratospheric ozone: carbon dioxide, methane, CFCs, and
nitrous oxide. The report of a recent conference convened by UNEP, the World
Meteorological Organization, and the International Council of Scientific
Unions concluded that if current trends in the emissions of these gases
continue, the earth could warm a few degrees (C) in the next fifty years
(Villach 1985). In the next century, the planet could warm as much as five
degrees (MAS 1983), which would leave the planet warmer than at any time in
the last two million years.
A planet's temperature is determined primarily by the amount of sunlight
it receives, the amount of sunlight it reflects, and the extent to which the
atmosphere retains heat. When sunlight strikes the earth, it warms the
surface, which then reradiates the heat as infrared radiation. However, water
vapor, COp, and other gases in the atmosphere absorb some of the energy rather
than allowing it to pass undeterred through the atmosphere to space. Because
the atmosphere traps heat and warms the earth in a manner somewhat analogous
to the glass panels of a greenhouse, this phenomenon is commonly known as the
"greenhouse effect." Without the greenhouse effect of the gases that occur
naturally in the atmosphere, the earth would be approximately 33°C colder than
it is currently (Hansen et al. 1984).
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In recent decades, the concentrations of greenhouse gases have been
increasing. Since the beginning of the industrial revolution, the combustion
of fossil fuels, deforestation, and a few other activities have released
enough COp to raise atmospheric concentrations by 20 percent; concentrations
have risen 8 percent since 1958 (Keeling, Bacastow, and Whorf 1982). More
recently, Ramanathan et al. (1985) examined the greenhouse gases other than
C02 (such as methane, CFCs, and nitrous oxide), and concluded that these other
gases are likely to double the • warming caused by C02 alone. Using these
results, the Villach Conference estimated that an "effective doubling" of C02
is likely by 2030.
Hansen et al. (Volume 1) and Manabe & Wetherald (Volume 1) present the
results that their climate models predict for an effective doubling of COp.
Both models consider a number of "climatic feedbacks" that could alter the
warming that would directly result from COp and other gases released by human
activities. Warmer temperatures would allow the atmosphere to retain more
water vapor, which is also a greenhouse gas, thereby resulting in additional
warming. Ice and snow cover would retreat, causing sunlight that is now
reflected by these bright surfaces to be absorbed instead, causing additional
warming. Finally, a change in cloud cover might result, which could increase
or decrease the projected warming. Although the two models differ in many
ways, both conclude that an effective doubling of greenhouse gases would warm
the earth's surface between two and four degrees (C).
Hansen et al. project the doubling to occur between 2020 and 2060. They
also provide estimates of the implications of temperature changes for
Washington, D.C., and seven other U.S. cities for the middle of the next
century. For example, Washington would have 12 and 85 days per year above
38°C (100°F) and 32°C (90°F), respectively, compared with 1 and 35 days above
those levels today. While evenings in which the thermometer fails to go below
27°C (80°F) occur less than once per year today in that city, they project
that such evenings would occur 19 times per year. (See Plates 2 and 3 for
worldwide maps of historical and projected temperature changes.)
Water Resources
Manabe and Wetherald (Volume 1) focus on the potential changes in
precipitation patterns that might result from the greenhouse warming. They
project substantial increases in summer dryness at the middle latitudes that
currently support most of the world's agriculture. Their model also projects
increased rainfall for late winter.
Beran (Volume 1) reviews the literature on the hydrological and water
resource impacts of climate change. He expresses some surprise that only
twenty-one papers could be found that address future water resource impacts.
One of the problems, he notes, is that there is a better scientific
understanding of how global average temperatures and rainfall might change,
than for the changes that specific regions may experience. Nevertheless, he
Studies on the greenhouse effect generally discuss the impacts of a carbon
dioxide doubling. By "effective doubling" we refer to any combination of
increases in concentrations of the various gases that causes a warming
equal to the warming of a doubling of carbon dioxide alone.
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demonstrates that useful information can be extracted by studying the
implications of particular scenarios.
Nicholson (Volume 3) shows how historical changes in water availability
have caused problems for society in the past. The best lesson of climatic
history, she writes, "is that agricultural and economic systems must be
flexible enough to adapt to changing conditions and, in the face of potential
water scarcity, systems must be designed that require minimum use of
resources." Wilhite (Volume 3) examines drought policies in Australia and the
United States, concluding that the lack of national drought plans could
substantially impair the ability of these two nations to successfully adapt to
hydrologic changes resulting from the greenhouse warming.
Cohen (Volume 3) examines the potential implications of the global
warming for water levels in the Great Lakes that separate Canada from the
United States. Using results from the models of both Hansen et al. and Manabe
& Wetherald, he concludes that lake levels could drop 10 to 30 centimeters.
This drop would significantly reduce the capacity of ocean-going vessels that
enter the Great Lakes. On the other hand, such a drop might be viewed as a
benefit by the owners of critically eroding property whose homes are currently
threatened by historically high lake levels. Street-Perrott et al. (Volume 3)
discuss the historic impacts of changes in climate on the levels of lakes in
North America, South America, Australia, and Africa.
Gleick (Volume 3) uses scenarios from the Hansen et al. and Manabe &
Wetherald models (as well as a third developed by the National Center for
Atmospheric Research) to drive a water-balance model of the Sacramento Basin
in California. He finds that reductions in runoff could occur even in months
where precipitation increases substantially, because of the increased rates of
evaporation that take place at higher temperatures. He also points out that
the models predict that changes in monthly runoff patterns will be far more
dramatic than changes in annual averages. For seven of ten scenarios, soil
moisture would be reduced every month of the year; for the other three cases,
slight increases in moisture are projected for winter months. Mather (Volume
3) conducts a detailed analysis for southern Texas and northern Mexico;
examines in less detail twelve regions around the world; and projects shifts
in global vegetation zones.
Agriculture and Forestry
The greenhouse warming could affect agriculture by altering water
availability, length of growing season, and the number of extremely hot
days. Increased COp concentrations could also have two direct impacts
unrelated to climate change: At least the laboratory, plants grow faster (the
COp fertilization effect) and retain moisture more efficiently. The extent to
which these beneficial effects offset the impacts of climate change will
depend on the extent to which global warming is caused by COp as opposed to
other greenhouse gases, which do not have these positive impacts.
Parry (Volume 1) provides an overview of the potential impacts of climate
change on agriculture and forestry. He points out that commercial farmers
plan according to the average year, while family and subsistence farmers must
ensure that even in the worst years they can make ends meet. Thus, the
commercial farmer would be concerned about the impact of future climate change
10
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on average conditions and average yields, while farmers at the margin would be
most concerned with changes in the probability of (for example) a severe
drought that causes complete crop failure. Parry notes that the probability
of two or more anomalous years in a row could create disproportionately
greater problems for agriculture. -For example, a persistent drought in the
U.S. Great Plains from 1932 to 1937 contributed to about two hundred thousand
farm bankruptcies.
Parry discusses a number Of historical changes in climate. The Little
Ice Age in western Europe (1500-1800 A.D.) resulted in the abandonment of
about half the farms in Norway, an end to cultivation of cereals in Iceland,
and some farmland in Scotland being permanently covered with snow. Concerning
the late medieval cooling (1250-1500) he writes: "The failure to adapt to the
changing circumstances is believed to explain much of the Norse decline. The
Norse continued to emphasize stock-raising in the face of reduced capacity of
the already limited pastures. The option of exploiting the rich seas around
them, as the Inuit (Eskimos) successfully did, was not taken up ... This is
an extreme example of how governments can fail to identify and implement
appropriate policies of response." It also suggests that effective responses
can reduce damages from climate change.
The paper reviews a number of studies that project impacts of climate
change on agriculture. "Warming appears to be detrimental to cereals in the
core wheat-growing areas of North America and Europe." If no precipitation
changes take place, a one-degree warming would decrease yields 1 to 9 percent
while a two-degree (C) warming would decrease yields 3 to 17 percent. Parry
also discusses how particular crop zones might shift. A doubling of COp would
substantially expand the wheat-growing area in Canada due to higher winter
temperatures and increased rainfall. In Mexico, however, temperature stresses
would increase, thereby reducing yields.
A number of studies have been conducted using the models of Hansen et
al., Manabe & Wetherald, and others. Although these projections cannot be
viewed as reliable forecasts, they do provide consistent scenarios that can be
useful for examining vulnerability to climate change. Parry indicates that
investigations of Canada, Finland, and the northern USSR using the model by
Hansen et al. show reduced yields of spring-sown crops such as wheat, barley,
and oats, due to increased moisture stress early in the growing period.
However, switching to winter wheat or winter rye might reduce this stress.
Parry goes on to outline numerous measures by which farmers might adapt to
projected climate change.
Waggoner (Volume 3) points out that the global warming would not affect
plants uniformly. Some are more drought-resistant than others, and some
respond to higher COg concentrations more vigorously than others. C^ plants,
such as wheat, respond to increased COp more than Ch plants such as maize.
Thus, the COp fertilization effect woula not help the farmer growing C^ crops
accompanied by Co weeds. Waggoner also examines the impact of future climate
change on average crop yields and pests, and the probability of successive
drought years. He concludes that although projections of future changes are
useful, historical evidence suggests that surprises may be in store, and that
"agricultural scientists will be expected to aid rather than watch mankind's
adaptation to an inexorable increase in C02 and its greenhouse effect."
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The impact of future climate change on yields for spring wheat in
Saskatchewan, Canada, is the subject of the paper by Stewart (Volume 3).
Using the output from the Hansen et al. model (Volume 1), which projects that
the effective doubling of carbon dioxide would increase average annual
temperatures in that region by 4.7°C, he estimates that the growing season
would start two or three weeks earlier and end three or four weeks later.
Although average precipitation during the growing season would increase, he
also finds that the area would become more prone to drought. The impact of
climatic change would be to reduce yields 16 to 26 percent. Stewart estimates
that the fertilization effect of a COp doubling would reduce the losses to 6
to 15 percent. Cooter (Volume 3) examines the economic impact of projected
climate change on the economy of Oklahoma, concluding that the Gross State
Product would decline 75 to 300 million dollars. (The state's gross product
in 1985 was approximately 50 billion dollars.)
Fritts (Volume 3) examines tree rings to assess how past changes in
climate have affected forests, and concludes that tree rings are useful for
estimating past changes in climate. Solomon and West (Volume 3) discuss the
results of their efforts to model the future impacts. Considering the impact
of climate change caused by doubled C02 without the fertilization effect, they
find that "biomass (for boreal forests) declines for 50-75 years as warming
kills off large boreal forest species, before new northern hardwoods can grow
into the plot."
"Warming at the transition site causes an almost immediate response in
declining biomass from dieback of mature trees, and in decline of tree mass as
large trees die and are temporarily replaced by small young trees," they
write. "The deciduous forest site . . . results in permanent loss of dense
forest. One might expect the eventual appearance of subtropical forests
similar to those in Florida today, but the real difficulty is the moisture
balance (which is) more similar to those of treeless Texas today, than to
those of southern Florida." Solomon and West go on to show how the
fertilization effect from increased concentrations of C02 could offset part
but not all of the drop in forest productivity.
Sea Level Rise
One of the most widely recognized consequences of a global warming would
be a rise in sea level. As Titus (Volume 1) notes, global temperatures and
sea level have fluctuated over periods of one hundred thousand years, with
temperatures during ice ages being three to five degrees (C) lower and sea
level over one hundred meters lower than today. By contrast, the last
interglacial period (one hundred thousand years ago) was one or two degrees
warmer than today, and sea level was five to seven meters higher.
The projected global warming could raise sea level by heating and thereby
expanding ocean water, melting mountain glaciers, and by causing polar
glaciers in Greenland and Antarctica to melt and possibly slide into the
oceans. Thomas (Volume 4) presents new calculations of the possible
contribution of Antarctica and combines them with previous estimates for the
other sources, projecting that a worldwide rise in sea level of 90 to 170
centimeters by the year 2100 with 110 centimeters most likely. However, he
also estimates that if the global warming is substantially delayed, the rise
in sea level could be cut in half. Such a delay might result either from
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actions to curtail emissions or from the thermal lag induced by the oceans'
ability to absorb heat.
On the other hand, Thomas also estimates that if a warming of four
degrees results from a C02 doubling, (which the model of Hansen et al.
projects) and concentrations continue to grow after 2050, the rise could be as
great as 2.3 meters. He also notes that an irreversible deglaciation of the
West Antarctic Ice Sheet might, begin in the next century, which would raise
sea level another six meters in the following centuries.
Titus (Volume 1) notes that these projections imply that sea level could
rise 30 centimeters by 2025, in addition to local subsidence trends that have
been important in Taipei, Taiwan; Venice, Italy; the Nile Delta, Egypt; and
most of the Atlantic and Gulf Coasts of the United States. The projected rise
in sea level would inundate low-lying areas, destroy coastal marshes and
swamps, erode shorelines, exacerbate coastal flooding, and increase the
salinity of rivers, bays, and aquifers.
Bruun (Volume 4) argues that with a combination of coastal engineering
and sound planning, society can meet the challenge of a rising sea. He
discusses a number of engineering options, including dikes (levees) and
seawalls, and adding sand to recreational beaches that are eroding, with a
section on the battle that the Dutch have fought with the sea for over one
thousand years. Goemans (Volume 4) describes the current approach of the
Dutch for defending the shoreline, and estimates that the cost of raising
their dikes for a one meter rise in sea level would be 10 billion guilders,
which is less than 0.05 percent of their Gross National Product for a single
year.
Goemans concludes that there is no need to anticipate such a rise because
they could keep up with it. However, he is more concerned by the two-meter
scenario: "Almost immediately after detection, actions would be required. It
is not at all certain that decision-makers act that fast. . . . The present
flood protection strategy came about only after the tragic disaster of 1953.
When nobody can remember a specific disaster, it is extremely difficult to
obtain consensus on countermeasures." For his own country, Goemans sees one
positive impact: Referring to the unique experience of Dutch engineering
firms in the battle with the sea, he suggests that "a rising sea may provide a
new global market for this expertise." But he predicts that "the question of
compensation payments may come up," for the poorer countries who did not cause
climate change but must face its consequences.
Broadus et al. (Volume 4) examine two such countries in detail: Egypt
and Bangladesh. The inhabited areas of both countries are river deltas, where
low-lying land has been created by the sediment washing down major rivers. In
the case of Egypt, the damming of the Nile has interrupted the sediment, and
as the delta sinks, land is lost to the Mediterranean Sea. Broadus et al.
estimate that a 50-centimeter rise in global sea level, when combined with
subsidence and the loss of sediment, would result -in the loss of 0.3 to 0.4
percent of the nation's land area; a 200-centimeter rise would flood 0.7
percent. However, because Egypt's population is concentrated in the low-lying
areas, 16 and 21 percent of the nation's population currently reside in the
areas that would be lost in the two scenarios.
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The situation would be even more severe in Bangladesh. As Plate 4 shows,
this nation, which is already overcrowded, would lose 12 to 28 percent of its
total area, which currently houses 9 to 27 percent of its population.
Moreover, floods could penetrate farther inland, which could leave the nation
more vulnerable to the type of tropical storm that killed 300,000 people in
the early 1970s, especially if the frequency of tropical storms doubled due to
warmer water temperatures, which deSylva (Volume 4) projects. Broadus et al.
conclude that the vulnerability of Bangladesh to a rise in sea level will
depend in large measure on whether future water projects disrupt land-creating
sediment washing down the Ganges.
Bird (Volume 4) examines the implications of sea level rise for other
African and Asian nations, as well as Australia. While holding back the sea
may be viable in Australia, he shows areas in New Guinea where people live in
small cottages on the water's edge on a barrier island that almost certainly
would be unable to justify construction of a dike. He also points to the
Philippines, where many people have literally "taken to the water," living in
small boats and maintaining fishing nets in their own plots of bay instead of
land. Current wetlands, he suggests, may convert to these shallow bays, with
people converting to a more water-based economy.
Leatherman (Volume 4) examines the implications of sea level rise for
South America. He notes that such popular resorts as Copacabana Beach,
Brazil; Punta del Este, Uruguay; and Mar del Plata, Argentina, are already
suffering serious erosion. He concludes that because of the economic
importance of resorts, governments will allocate the necessary funds to
maintain their viability. However, he predicts that "coastal wetlands will
receive benign neglect" and be lost.
Park et al. (Volume 4) focus on the expected drowning of coastal wetlands
in the United States. Using a computer model of over 50 sites, they project
that 40-75 percent of existing U.S. coastal wetlands could be lost by 2100.
Although these losses could be reduced to 20-55 percent if new wetlands form
inland as sea level rises, the necessary wetland creation would require
existing developed areas to be vacated as sea level rises, even though
property owners would frequently prefer to construct bulkheads to protect
their property. Because coastal wetlands are important for many commerically
important seafood species, as well as birds and furbearing animals, Park et
al. conclude that even a one-meter rise in sea level would have major impacts
on the coastal environment.
DeSylva (Volume 4) also examines the environmental implications of sea
level rise, noting that in addition to wetlands being flooded, estuarine
salinity would increase. Because 66 to 90 percent of U.S. fisheries depend on
estuaries, he writes that these impacts could be important. He also suggests
that coral reefs could become vulnerable because of sea level rise, increased
temperatures, and the decrease in the pH (increased acidity) of the ocean.
Kuo (Volume 4) examines the implications of sea level rise for flooding
in Taipei, Taiwan, and coastal drainage in general. Although Taipei is
upstream from the sea, Kuo concludes that projected sea level rise would cause
serious problems, especially because Taiwan is also sinking. He recommends
that engineers around the world take "future sea level rise into consideration
... to avoid designing a system that may become prematurely obsolete."
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Gibbs (Volume 4) estimates that sea level rise could result in economic
damages in Charleston, South Carolina, equal to as much as 25 percent of the
annual product of the community. Anticipatory measures, however, could reduce
these impacts by half. Gibbs finds that in some areas actions should be taken
today, in spite of the current uncertainty regarding future rates of sea level
rise, while for other areas it would be more prudent to wait until uncertain-
ties are resolved.
Ken Smith, a realtor from coastal New Jersey, reacts to the other papers
presented in Volume 4. He argues that the issue of sea level rise should be
taken seriously today, but laments the fact that many of his fellow realtors
make comments such as "What do you care? You won't be around to see it!" and
the scientific community is "a bunch of eggheads who don't want us (to build
on the coast) anyway." Smith suggests that part of the resistance to taking
the issue seriously is that there are a number of "naturalists" who oppose
building near the shore, and "most of the discussion seems to come from the
'naturalist' camp." Nevertheless, Smith argues that "the solutions—if there
are any—should be contemplated now as part of a concerted global effort.
This is a beautiful world, and we are its stewards."
Human Health and Ecological Impacts
Climate and weather have important impacts on human health. A global
warming would increase the stresses due to heat, decrease those due to cold,
and possibly enable some disease that require warm year-round temperatures to
survive at higher latitudes. Kalkstein et al. (Volume 3) present a
preliminary statistical assessment of the relationship of mortality rates to
fluctuations in temperature in New York City. They find that a two to four
degree (C) warming would substantially increase mortality rates in New York
City, if nothing else changed. However, they caution that if New Yorkers are
able to acclimatize to temperatures as well as people who currently live in
U.S. cities to the south, fewer deaths would occur. Kalkstein et al. write
that knowledgeable observers disagree about whether and how rapidly people
adapt to higher temperatures; some people undoubtedly adjust more readily than
others.
Although people may be able to adapt to changes in climate, other species
on the planet would also be affected and may not be as able to control their
habitats. Peters and Darling (Volume 3) examine the possibility that changes
in climate would place multiple stresses on some species which would become
extinct, resulting in a significant decline in biodiversity. (Mass extinc-
tions appear to have accompanied rapid changes in temperatures in the past.)
Throughout the world reserves have been set aside where targeted species
can remain relatively free of human intrusion. Peters and Darling ask: Will
these reserves continue to serve the same function if the climate changes? In
some cases, it will depend on whether the reserve's boundaries encompass areas
to which plants and animals could migrate. Some species may be able to
migrate "up the mountain" to find cooler temperatures; coastal wetlands could
migrate inland. A northerly migration of terrestrial species would be
possible in the undeveloped arctic regions of Alaska, Canada, and the Soviet
Union; but human development would block migration of larger animals in many
areas.
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POLICY RESPONSES
Papers by UNEP Deputy Director Genady Golubev and EPA Administrator Lee
Thomas (both in Volume 1) provide official views on the nature of the effects
from projected changes in the atmosphere and the role of their institutions in
addressing those changes. Golubev notes that while "the global issues are
complex, uncertainty exceeds understanding, and patience is prudence," there
is an other side to the story: "Our legacy to the future is an environment
less benign than that inherited from our forbearers. The risks are sufficient
to generate a collective concern that forebodes too much to wait out the
quantifications of scientific research. Advocating patience is an invitation
to be a spectator to our own destruction."
Golubev also points out that UNEP has worked for the achievement of the
Vienna Convention for the Protection of the Ozone Layer, in which many nations
have agreed to act in concert to address an environmental issue whose impacts
have not yet been detected. Yet he notes that the agreement is for coopera-
tion in research and does not yet bind nations to observe limits in production
and emissions of gases that could deplete stratospheric ozone.
Thomas points out that both the potential depletion of ozone and the
global warming from the greenhouse effect are examples of environmental
problems that involve the "global commons." Because all nations contribute to
the problem and experience the consequences, only an international agreement
is likely to be effective. He urges scientists around the world to discuss
this issue with their colleagues and key officials.
Richard Benedick, Deputy Assistant Secretary in the U.S. Department of
State (Volume 1), describes the emerging international process addressing the
ozone issue. Although the process for addressing climate change has not yet
proceeded as far, he writes, "from my perspective as a career diplomat, it
appears that the greenhouse effect has all the markings of becoming a high
visibility foreign policy issue. . . . How we address this issue internation-
ally depends to a great extent on our success or failure in dealing with the
ozone depletion issue."
J.P. Bruce (Volume 1) of Environment Canada presents the issue of
atmospheric change in the context of air pollution in general. He writes that
ozone modification and climate change are "urgent issues," especially because
important long-term decisions are being made today whose outcomes could be
strongly affected by changes in climate and the ozone layer. Bruce recommends
that emissions of CFCs be reduced, and concludes that "a new approach, a new
ethic towards discharging wastes and chemical materials into the air we all
breathe must soon be adopted on a international scale."
Two U.S. Senators also provide their reactions. John Chafee from Rhode
Island (Volume 1) describes hearings that his Subcommittee on Environmental
Pollution held June 10-11, 1986. "Why are policy makers demanding action
before the scientists have resolved all of the questions and uncertainties?"
he asks. "We are doing so because there is a very real possibility that
society—through ignorance or indifference, or both—is irreversibly altering
the ability of our atmosphere to perform basic life support functions for the
planet." Albert Gore, Jr. from Tennessee, who has chaired three congressional
hearings on the greenhouse effect, explains why he has introduced a bill in
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the U.S. Senate to establish an International Year of the Greenhouse Effect.
"The legislations would coordinate and promote domestic and international
research efforts on both the scientific and policy aspects of this problem,
identify strategies to reduce the increase of carbon dioxide and trace gases,
investigate ways to minimize the impact of the greenhouse effect, and
establish long-term research plans." Senator Gore closes by quoting Sherwood
Rowland (discussed below): "What's the use of having developed a science well
enough to make predictions, if in the end all we're willing to do is stand
around and wait for them to come true?" Both Senators call for immediate
action to reduce global use of CFCs.
John S. Hoffman (Volume 1) emphasizes the inertia of the atmosphere and
oceans. Because there are time lags between changes in emission rates,
atmospheric concentrations, and changes in ozone and global warming
temperatures, the types of management strategies must be different from those
that are appropriate for controlling, for example, particulate pollution,
where the problem goes away as soon as emissions are halted. CFC emissions
would have to be cut 80 percent simply to keep concentrations from
increasing. Although constant concentrations would prevent ozone depletion
from worsening, Hoffman points out that even if we hold the concentrations of
greenhouse gases constant once the earth has warmed one degree, the planet
would warm another degree as the oceans come into equilibrium. Thus it might
be impossible to prevent a substantial warming if we wait until a small
warming has taken place.^
The final section of this volume presents the papers from the final day
of the conference. Peter Usher of UNEP recounts the evolution of the ozone
issue. Following Rowland and Molina's hypothesis that chlorofluorocarbons
could cause a depletion of stratospheric ozone in 1974, UNEP held a conference
in 1977 that led to a world plan of action to assess the issue and quantify
risks. Since that time, UNEP has held numerous coordinating meetings leading
up the the Vienna Convention. However, Usher suggests that motivating inter-
national effort on the greenhouse effect will be more difficult: "Prohibition
of nonessential emissions of relatively small amounts (to control ozone
depletion) is one thing, limiting emissions of carbon dioxide from coal- and
oil-burning is quite another."
Dudek and Oppenheimer of the Environmental Defense Fund (U.S.) analyze
some of the costs and benefits of controlling emissions of CFCs. They
estimate that by holding emissions constant, 1.65 million cases of nonmelanoma
skin cancers could be prevented worldwide, and that the cost of these controls
would be 196 to 455 million dollars, depending on the availability of alterna-
tive chemicals.
Two former high-ranking environmental officials in the United States
argue that we should be doing more to address these problems. John Topping
recommends that CFCs in aerosol spray cans, egg cartons, fast-food containers,
and other nonessential uses be phased out, and that people recognize that
Titus (Volume 1) and Thomas (Volume 4) also explore inertia, noting that
even if temperatures remained constant after warming somewhat, sea level
would rise at an accelerated rate as the oceans, mountain glaciers, and ice
sheets came into equilibrium with the new temperature.
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along with energy conservation, nuclear power is the most likely alternative
to fossil fuels over the next" generation or two. He also recommends that
society take steps to minimize the impacts of climate change and sea level
rise, for example, by requiring environmental impact statements to consider
the likely impacts.
Gus Speth, president of the World Resources Institute, recommends
international efforts to stop tropical deforestation; a production cap for
chlorofluorocarbons; increased energy conservation; advanced technologies for
producing electricity from natural gas; and tighter regulations to limit
carbon monoxide from automobiles, which would indirectly limit increases in
atmospheric methane. He agrees with Topping that environmental impact
statements for projects that could contribute to or be affected by climate
change or ozone modification should consider these impacts.
Doniger and Wirth, from the Natural Resources Defense Council (U.S.),
argue that the current uncertainties are no longer a reason to wait for
additional information: "With the stakes so high, uncertainty is an even more
powerful argument for taking early action." These authors conclude that sharp
reductions in CFCs are necessary, pointing out that even with a production
cap, atmospheric concentrations of these gases will continue to grow.
Therefore, Doniger and Wirth propose an 80 percent cut in production over the
next five years for CFCs 11 and 12, the halons, and perhaps some other
compounds, with a complete phaseout in the next decade.
Richard Barnett of the Alliance for a Responsible CFC Policy (which
represents CFC using industries) agrees that we should not delay all action
until the effects of ozone depletion and climate change are felt; but he
"would hardly characterize the activities over the last twelve years as 'wait
and see' . . . The science, as we currently understand it, however, tells us
that there is additional time in which to solidify international consensus.
This must be done through discussion and negotiation, not through unilateral
regulation."
Barnett adds that industry should "take precautionary measures while
research and negotiations continue at the international level. We will
continue to examine and adopt such prudent precautionary measures as
recapturing, recycling, and recovery techniques to control CFC emissions;
transition to existing alternative CFCs that are considered to be more
environmentally acceptable; practices to replace existing systems at the
expiration of their useful lives to equipment using other CFC formulations;
practices in the field to prevent emissions where possible; encouragement of
CFC users to look for processes or substances that are as efficient, safe, and
productive—or better—than what is presently available."
Barnett concludes that "these environmental concerns are serious, but
their successful resolution will require greater global cooperation in con-
ducting the necessary research and monitoring, and in developing coordinated,
effective, and equitable policy decisions for all nations."
We hope that this paper has provided the reader with a "road map" through
the papers of this four-volume report on the potential effects of changing the
atmosphere. But we have barely scratched the surface of each, just as the
existing research has barely scratched the surface in discovering and
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demonstrating the possible risks of ozone modification and climate change. A
continual evolution of our understanding will be necessary for our knowledge
to stay ahead of the global experiment that society is conducting.
REFERENCES
Hansen, J.E., A. Lacis, D. Rind, and G. Russell. 1984. Climate sensitivity to
increasing greenhouse gases. In Greenhouse effect and sea level rise: A
challenge for this generation, eds. M.C. Earth and J.G. Titus. New York:
Van Nostrand Reinhold.
Keeling, C.D., R.B. Bacastow, and T.P. Whorf. 1982. Measurements of the
concentration of carbon dioxide at Mauna Loa, Hawaii. Carbon Dioxide
Review 1982. 377-382, ed. by W. Clark. New York: Oxford University Press,
Unpublished data from NOAA after 1981.
NAS. 1983. Changing Climate. Washington, D.C.: National Academy Press.
Nordhaus, W.D., and G.W. Yohe. 1983. Future carbon dioxide emissions from
fossil fuels. In Changing Climate. Washington, D.C.: National Academy
Press.
Villach. 1985. International assessment of the role of carbon dioxide and of
other greenhouse gases in climate variations and associated impacts.
Conference Statement. Geneva: United Nations Environment Program.
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Global Environmental Change: The UNEP Perspective
Genady N. Golubev
Office of Environment Programs
United Nations Environment Programme
Nairobi, Kenya
It is, perhaps, paradoxical that the global environmental threat, with
the potential to influence for good or ill the lives of every individual on
the planet, should generate such ambivalent attitudes among people with so
much at stake.
It has been constantly said, and will be said again: the global issues
are complex; uncertainty exceeds understanding; and patience is prudence.
That coin has another side. The issue, stripped to its essentials, is
simple and unequivocal in its message, our legacy to the future is an environ-
ment less benign that that inherited from our forebearers. The risks are
sufficient to generate a collective concern that forebodes too much to wait
out the quantifications of scientific research. Advocating patience is an
invitation to be a spectator to our own destruction.
One approach, adopted by the United Nations Environment Programme, aids
the selection of an appropriate course of action. This concerns the concept
of "outer limits," which postulates that the biosphere has only a limited
tolerance to the demands placed upon it.
Two global outer limits have preoccupied UNEP during the last decade:
the risk to the ozone layer and the issue of climate change occurring in
response to increasing concentrations of trace gases in the atmosphere due to
the actions of humanity. Of course, all environmental sectors have an outer
limit of exploitation, but in this paper, I restrict my comments to the
vulnerability of the atmosphere and its climatic processes to possible
changes. The role of this report and the associated conference, as seen by
UNEP, can be expressed in terms far beyond a mere exchange of scientific
information and viewpoints on the subject of ultraviolet radiation damage or
of climatic variability. It is looked upon more as a necessary step in
formulating international policy to protect the common atmospheric heritage.
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In 1974, the possibility of stratospheric ozone depletion was first
noticed. Simple chemical formulae for the catalytic destruction of the
earth's ozone shield were unfolded to an astonished world. The repercussions
of a weakened ozone layer are as significant as any threat we are ever likely
to face. It does not need hyperbole to emphasize its significance for man-
kind. Human health, fish and animals, plants and food crops are at risk. The
principal suspect is the family of manmade chemicals, chlorofluorocarbons, of
benign property (at least in the lower atmosphere), and of vast commercial
usefulness. The enormity of the issue and the seemingly contradictory results
of the scientific examination of the ozone depletion hypothesis have to some
extent been counterproductive to attempts to deal with the problem. Ozone
depletion estimates have ranged from 5% in the mid-1970s to more than 20% a
few years later. Indeed, some scenarios have produced estimates indicating
increases in the total ozone column. Such divergences have bred skepticism
and fear that subjective and selective interpretation are being introduced
into scientific analysis to accommodate rapidly polarizing viewpoints of
different nations (and factions) on the problem of the ozone layer. You have
read the headlines; perhaps you have even written them: "The ozone problem is
no problem" or "The end of the world is nigh."
I am happy to report that UNEP, at least, kept its head in the midst of
controversy and, supported by its Governing Council and most of the inter-
national community, established a program of activities that has, in the
shortest possible time, led to a unique milestone in the annals of inter-
national legislation: the Vienna Convention for the Protection of the Ozone
Layer. This covenant represents an agreement among nations to act in concert
to address an environmental issue still awaiting scientific confirmation of
its actuality. Impressive as this agreement is, it remains a tenuous response
to the potential threat posed by a changing ozone layer. In present form, it
represents an agreement to cooperate in research and in monitoring the ozone
layer and other gaseous constituents of the atmosphere and in information
exchange regarding production, emissions, usage, trade, and national legisla-
tion on substances suspected of modifying the ozone layer. It does not bind
states to observe limits in production and emission of these substances, which
will require a specific protocol to the Convention and for nations to be party
to both the protocol and the Convention—a thorny path still to be nego-
tiated.
Let us look briefly at the program UNEP is operating regarding the
atmosphere, which will explain the reason why it cosponsored the "Effects
Conference" and this report. In 1977, in response to calls for a rational
approach to the ozone layer issue, UNEP convened an International Conference
on the Ozone Layer in Washington, D.C. A main purpose was to elaborate a
world plan of action on the ozone layer. Under the plan, coordination of the
research effort was to be the province of UNEP and, to assist it in this task,
UNEP established a Coordinating Committee on the Ozone Layer (CCOL) composed
of international, governmental, and nongovernmental organizations with active
ozone layer research programs. This committee makes and publishes through
UNEP, assessments of ozone layer modification and its impact based on national
research results reported to it. To date, the CCOL has met eight times to
refine its estimate of projected ozone layer change. As I noted above, the
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CCOL's predictions have shown wide variations from year to year. Over the
last five years, predictions have moved in a much narrower range and even the
most skeptical of governments accept the validity of UNEP's approach to the
problem.
I have referred to the UNEP role as coordination and catalysis. I might
add that the UNEP approach to an environmental problem is to assess the nature
and scale of the issue and, based on the assessment, to provide advice on the
range of managerial options available to address the problem. In the case of
ozone, the assessment is a continuing one and one that has yet to resolve the
many uncertainties that still exist. Let us not minimize these uncertainties:
A statistically significant depletion of ozone has been observed at 40 km
consistent with the theory of ozone modification. Yet we may still be a
generation away from finally confirming or denying ozone modification as fact.
The assessment of the physical state of the atmosphere and, in
particular, of the ozone layer, has taken a giant step forward over the past
year and a half. Nine national and international organizations cosponsored
and cooperated in a giant—there is no other appropriate word—assessment
orchestrated by the U.S. National Aeronautics and Space Administration
(NASA). The CCOL drew on this assessment to make its own estimation of ozone
layer change. The committee did not, however, address the issue of effects of
ozone layer modification. UNEP will next arrange for the summarizing of the
conference findings by experts for consideration by government experts at a
special session of the CCOL later in 1986 with a view to preparing an
assessment of impacts of ozone layer depletion equivalent to that already
produced on the physical ozone layer.
But assessment, in the UNEP context, is to be followed by rational
environmental management. An ad hoc working group of legal and technical
experts was convened by UNEP in 1982 and met seven times before agreeing on
the framework for an international convention for the protection of the ozone
layer. This group is now to be reconvened to determine the need for and the
form of a protocol of chlorofluorocarbons to the Vienna Convention. Technical
information on chlorofluorocarbons will become available from a two-part
workshop on aspects of production, use and release of those chemicals, and the
consequences and policies of their control. The first workshop took place in
May 1986 in Rome. The second part will be in Washington, B.C. in September
1986.
If there is need of a protocol on CFCs, the Vienna Group, for that is how
it is known, will determine it; hopefully, the agreed protocol will be adopted
by diplomatic conference in 1987.
It is a long road, full of pitfalls, demanding goodwill and indeed
sacrifice in the form of agreements to limit national industrial activity,
trade, and a loss of convenience that CFCs currently provide. Forget the
frivolous cosmetic aerosol use of the chemicals—refrigeration, rigid and
flexible foams for - insulation, packaging and upholstery, solvents for the
electronic industry, and pharmaceutical products also depend on the CFC
industry. More than thirty-five million tons of these non-toxic, non-
reactive, convenient gases have already been emitted to the atmosphere to
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remain there for tens or even hundreds of years. Each molecule has the poten-
tial to dissociate as many as four hundred of the essential ozone molecules in
the fragile shield protecting us from the ravages of unrestrained ultraviolet
radiation.
The Convention was a necessary and timely precaution and UNEP will
encourage any measure—such as the elaboration of suitable protocols—that
will ensure its effectiveness in protecting the environment.
I believe that the goodwill of most nations supports UNEP in its objec-
tive; but it needs more than goodwill. Adherence to the spirit as well as to
the letter of the Convention and its protocols will be necessary prerequisites
for its effectiveness. My concern here arises from a request by UNEP for
factual data on current production capacity, production, emissions, use, and
regulatory measures concerning chlorofluorocarbons to all member states of the
United Nations, all regional economic groups, and relevant non-governmental
organizations. The purpose of the request was to make available necessary
background information to the Workshop on Chlorofluorocarbons. The response
was extremely poor. Only twenty relevant replies were received out of the
more than 170 requests sent. It hardly provided a representative sample of
the nations involved in the chlorofluorocarbon industry—hardly enough to
promote useful analyses of the use, trade, and emission patterns. Probably
all countries use CFCs even if they do not manufacture them. After all, the
substances are widely used in refrigeration and air conditioning. Can the
lack of replies be attributed to ignorance of the extent of trade and use in
CFC containing products, to the designation of low priority to the issue by
states with more pressing environmental problems begging attention? UNEP will
do all it can to raise the consciousness of individuals and nations to the
potential gravity of the situation. But meanwhile, the ozone problem is still
"up in the air." The improvement of scientific knowledge is the
responsibility of you, your fellow scientists, and others who care for our
environment.
I have focused on the ozone layer problem mainly because it is at the
center of an intense effort by UNEP at the present time; but it is not the
only global issue receiving the attention of the international community. Nor
even is the ozone issue a problem addressed independently of other atmospheric
environment problems. UNEP is active in the fields of long-range trans-
boundary air pollution, acid deposition, and the greenhouse effect climate
change issue. Carbon dioxide is generally regarded as the agent of climate
change; but ozone, projected to increase in the troposphere, and ozone modify-
ing gases, such as methane and the ubiquitous chlorofluorocarbons, are also
greenhouse gases. Despite their relatively low concentrations compared with
carbon dioxide, some are vastly more efficient absorbers of infrared radiation
than COp. UNEP operates a major program on the greenhouse gas issue, parallel
and closely interwoven with the ozone layer program. Indeed, action to pro-
tect the ozone layer, for example, by limiting emissions of chlorofluoro-
carbons, will surely have a profound impact upon the rate of climatic change.
If anything, the climate change issue is more resistant to solution than
ozone modification. Although there is already scientific consensus on the
probable future consequences of doubling carbon dioxide or its equivalent in
other greenhouse gases—at least in the global sense—the understanding of
regional climatic change is closer to speculation rather than scientific
24
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prediction. Nevertheless, preparations for a future climate change need to
begin now and UNEP is developing a program that will address the socioeconomic
consequences of climate change and of the range of policy alternatives that
governments might consider in response. Whether there will be a need for a
future legislative process similar to that developed under the Risks to the
Ozone Layer Programme is not yet known. One major difference between the two
issues is that the consequences of ozone depletion are universally harmful;
climatic change, on the other hand, will provide benefits to some as well as
disadvantages to others. Some countries, for instance, those with densely
populated low-lying coastal areas or with agricultural areas postulated to
receive less rainfall, may be big losers. Increased rainfall or longer grow-
ing seasons in the present marginal areas for crop production can only be
greeted with delight by the affected countries. Again, while regulations of
the emissions and use of CFCs are likely to be relatively easy, the price of
regulating COp emissions through energy controls may be too high a price to
pay, and the future lies in adaptation to rather than in prevention of climate
change. UNEP's present role in this issue is the provision of international
assessments. It does so in cooperation with its partners, the World Meteoro-
logical Organization (WHO) and the International Council of Scientific Unions
(ICSU), the three organizations that implement the World Climate Program. In
October 1985, UNEP, WHO, and ICSU held a second conference on the issue at
Villach, Austria, where a new assessment of the issue was made (the first was
also made at Villach, five years earlier).
A recommendation of the Conference is the establishment of an Advisory
Group on greenhouse gases, composed of a small group of eminent scientists, to
advise the international organizations on a program to address the greenhouse
gas/climate change issue. This group of "seven wise men" will meet in Geneva
during the first few days of July. However, no matter what program they
suggest to the international community, it will again require an enormous
complementary scientific effort. Most importantly, there is need of a part-
nership of effort involving all nations to consider the consequences of green-
house gas-induced climate change and to respond in concert to provide whatever
solution may be required.
In the face of these global issues, the world's commitment to the
environment is on trial. I trust in the final analysis that commitment will
not be found wanting.
25
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Global Environmental Change: The EPA Perspective
Lee Thomas
Administrator, Environmental Protection Agency
Washington, DC USA
This report focuses on two global environmental problems that might
result from the worldwide emissions of certain gases: the depletion of
stratospheric ozone and a global warming from the "greenhouse effect." Both
issues are clear examples of a "global commons" environmental problem. All
nations are responsible for contributing to recent changes in our atmosphere—
although the industrially developed nations must shoulder most of the
responsibility. All nations will be affected by depletion of the ozone layer
and by global climate changes.
Based on our current understanding, we believe that a small change in the
amount of UV-B radiation striking the earth and/or a change in the earth's
mean temperature could have significant environmental and health
consequences. The fundamental scientific uncertainty is no longer "are these
phenomena real?" but rather, "at what rate are they likely to occur?" We
need to better understand the full nature of the impact of these changes and
the possible options, both in the near and long term, for managing these
risks. We do not yet have complete answers to these questions, although
recent efforts have resulted in substantial progress.
It was only after extended discussion and considerable thought that the
United Nations Environment Programme (UNEP) and the Environmental Protection
Agency chose to proceed with a conference on both ozone depletion and climate
change. As the other papers in this volume show, our understanding of
atmospheric science tells us that ozone depletion and global warming are
inexorably interconnected. However, the domestic and international politics
surrounding each issue are separate and unique. Combining the two in one
conference had the potential to confuse and compound the political controversy
surrounding each issue. Separating the issues would fail to address their
physical interdependence. In the end the choice was clear: we resolved this
issue by recognizing that this conference is first and foremost a scientific
meeting, not a political one, and therefore it should be organized around our
understanding of the science.
27
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As a scientific meeting our objective was not to find solutions to the
problems but rather to do the best we can to organize and present the current
state of science. In trying to achieve this goal the conference was not an
isolated event but part of a sequence of environment meetings intended to
systematically build our understanding of these problems.
In October 1985 in Villach, Austria, atmospheric scientists and
government officials prepared a major document summarizing the scientific
consensus that is gradually emerging regarding the greenhouse effect. That
conference, sponsored by the World Meteorological Organization (WHO), the
International Council of Scientific Unions (ICSU), and UNEP, provided a sound
scientific foundation for this report's discussion of the effects of global
climate change.
In February 1986 in Nairobi, Kenya, UNEP sponsored a meeting of the
Coordinating Committee on the Ozone Layer (CCOL) to explore the state of
knowledge on the atmospheric science of ozone depletion. A text was
unanimously adopted based extensively on the NASA Assessment Report. The CCOL
Report and the NASA documents both serve as the foundation for this report's
discussions on the effects of ozone depletion.
Finally, in May 1986 in Rome, UNEP held another meeting that focused on
projections of future chlorofluorocarbon production and emissions.
Information from that meeting will help us to address the problem of ozone
depletion.
This sequence of meetings is no accident. Each meeting is part of a
conscious effort to build a common understanding among the nations of the
world about the nature of these problems before we sit down to talk about
possible solutions. At the U.S. Environmental Protection Agency, we recognize
that it is important to separate the process of risk assessment from the
decision-making task that we call "risk management." Risk assessment refers
to the gathering of scientific data in order to understand what type of
problems may confront us if we fail to intervene. Risk management refers to
the evaluation of options to avert those potential problems. Although various
interests may have different points of view regarding the level of action that
may be appropriate, it is my strong belief that the process will be more
constructive if everyone works from a common understanding of the scientific
facts. We rely on the separation of these tasks as a basic approach to most
of the major environmental decisions. Before we can sit down together to find
a common solution to a problem, we must first have a common understanding of
the problem we are trying to solve.
In the last decade we made major advances in assessing the risks of ozone
depletion and the greenhouse effect. This report presents and summarizes the
major portion of our understanding of these two problems.
However, before we move too quickly into the task of risk management I
must raise a word of caution. If the risk management part of the process is
to work effectively, environmental policy-makers from each of our countries
must be made aware of and understand the science involved in these issues. If
not, then much of the progress we have made in developing a common
understanding of those problems will be lost. It serves no useful purpose to
have decision-makers like myself approach problems such as these with either
28
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an inflated or deflated view of the problem, and it is only through the
patient but persistent efforts of the experts that decision-makers like myself
can get the facts we need to make intelligent decisions. I urge the reader to
actively share this information with your colleagues and key officials. Tell
them what we know, what we don't know, and what we are likely to understand
soon. Let them know where we have consensus and where we disagree. Let me
also ask you to share with us your data and scientific information.
In the U.S. we are still gathering the facts; we are still in the role of
risk assessor. Domestically, we have committed ourselves to making a decision
on the need for further regulations of CFCs in the fall of next year, and we
have committed ourselves to actively supporting and participating in the
Vienna Convention process for the protection of the ozone layer. Our
commitment to this process should not be seen as a precedent to a particular
outcome. At the same time we have not made any decisions either as to the
need for additional domestic regulation or the content of an international
protocol. In both cases we will wait until we have completed the risk
assessment, before we make the risk management decision.
We recognize that several important facts must not be overlooked. To the
extent that action is needed, it is essential that the international community
move forward to deal with these issues together. Our analysis must include
all trace gases that may modify the ozone layer and not just CFCs. CFCs are
extremely important chemicals used across a broad spectrum of industrial and
consumer goods. For some uses, no effective alternative chemical currently
exists. Finally, the potential risks we face are generally long-term; if
action proves warranted, any regulatory approach selected should be structured
in a way that minimizes costs and disruption to producers and users.
I am deeply concerned about the potential environmental risks associated
with these issues and the complexity of developing a response that effectively
addresses their unique characteristics. Despite these complexities, we are
moving forward in a timely manner to responsibly address these issues. I am
committed to making a decision even in the face of the many uncertainties that
are likely to persist for the next several years.
29
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Global Environmental Change:
The International Perspective
Richard E. Benedick
Deputy Secretary of State for Environment,
Health and Natural Resources
Washington, DC USA
As a career diplomat who deals with scientific issues, and who strongly
believes in their growing relevance to foreign policy, I appreciate the
opportunity to present my views. I will briefly sketch how the international
community can confront such complex, long-term issues as global climate change
and ozone layer modification.
International law is relatively well equipped for dealing with trans-
boundary environmental problems, where one nation can be identified as "the
polluter" and the other as "the polluted." But in the case of global environ-
mental problems, such as ozone depletion and climate change, the international
community is in fact entering uncharted territory.
This emerging set of problems contains a number of unique elements.
First, almost every nation is both perpetrator and victim: many nations are
producers and/or consumers of chlorofluorocarbons (CFCs), most nations burn
fossil fuels or otherwise emit carbon dioxide, and all nations will be
affected by ozone depletion and climate change. Secondly, the adverse
impacts, and the costs of mitigating those impacts, are not distributed
equally among nations—nor necessarily in proportion to each nation's
contribution to the problem. Finally, for both ozone depletion and climate
change the time-lag between cause and effect spans decades—which is longer
than the normal policy-making horizon of most governments.
Given these factors, designing an efficient and equitable control system
would be exceedingly difficult, even as a theoretical exercise; in practice, a
new paradigm for international cooperation likely will be needed.
But what form might this paradigm take? To answer this question, I think
it would be useful to look at international activities of the last decade that
relate to the ozone depletion issue and—with the benefit of hindsight—to
reflect on what has worked and what has not.
31
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International attention to the question of stratospheric ozone depletion
began shortly after Rowland and Molina published their now-famous theoretical
paper. A number of international meetings were held on this subject during
the late 1970s, at the same time as several nations began to issue domestic
CFC regulations. In 1980, the Governing Council of the United Nations
Environment Programme decided to convene a Working Group of Experts to discuss
appropriate international action to address this potential problem.
The UNEP Working Group decided early in their deliberations to develop a
convention—that is, an international treaty—on the ozone layer. Four years
and several long negotiating sessions later, they completed their work on such
a treaty. In March 1985, at a Plenipotentiary Conference in Vienna, Austria,
where I represented the United States, twenty-one nations signed the Con-
vention for the Protection of the Ozone Layer. This was a landmark event: it
was the first time that the international community acted in concert on an
environmental issue before substantial damage to the environment and health
was done—in effect, acting together in anticipation of potential problems.
The "Vienna Convention" creates a framework for international cooperation
on research, monitoring, and information exchange concerning the ozone
layer. It also creates general obligations to protect the ozone layer and
provides procedures for eventually adopting protocols to the Convention, which
could contain specific measures to control, limit, prevent, or reduce emis-
sions of ozone-modifying substances—should such measures be deemed neces-
sary. In the United States, the Senate has held hearings on the Convention,
and we expect it to be ratified soon. After twenty nations have ratified it,
the Convention becomes international law.
The question of a control protocol was the subject of considerable debate
during the UNEP Working Group negotiations. In April 1983, Norway, Finland,
and Sweden tabled a draft protocol for controlling all CFC uses. In October
1983, the United States voiced its support for that part of the "Nordic
Proposal" dealing with CFCs used as aerosol propellants. Eventually the
Nordics, along with Canada and Switzerland, joined us in supporting an
international aerosol ban protocol.
On the other side of the debate, the nations of the European Economic
Community—who represented the other major source of CFC production—were
initially opposed to any further controls on CFCs. However, they eventually
supported a. protocol—but, like us, and not surprisingly, they supported one
that mirrored what they already had in place: a 30 percent reduction in
aerosol use and a cap on future CFC production capacity.
During the debate on these two alternative control approaches, we pointed
out many of the problems with their approach, and they in turn noted many of
the flaws in our approach. The result was total gridlock, and there was no
possibility for agreement on a protocol text at the Vienna Conference.
However, because most of the disagreement near the end of the negotia-
tions had centered on the economic and policy aspects of alternative control
strategies, participants generally agreed that a series of international
workshops—outside of a formal negotiating context—would be useful to these
questions in detail. All parties also agreed to approach these workshops with
an open mind, unwedded to their previous negotiating positions. This
32
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certainly represents the U.S. position: we are prepared to re-examine the
costs and benefits of various protocol options, ranging from no further
controls to a full cap on production or use.
The first international workshop was held in Rome during the last week of
May 1986. A second international workshop was planned for September 1986 in
the United States to evaluate alternative strategies for international
control. After the workshops, the next round of protocol negotiations was
planned for November 1986, with a second Diplomatic Conference scheduled for
April 1987.
Scientific assessments are proceeding on a parallel track: earlier in
1986, the National Aeronautics and Space Administration (NASA), the World
Meteorological Organization (WMO), UNEP, and other organizations completed two
years of work on an international assessment of atmospheric processes. The
UNEP Coordinating Committee on the Ozone Layer met in January 1986 to review
the state of the science and will meet again in August. The International
Conference on the Effects of Ozone Modification and Climate Change further
contributed to this process.
Where have we come on the ozone layer internationally? Looking back with
the benefit of hindsight on the past round of negotiations, I believe that the
international community may have tried to put the cart before the horse: we
were trying, in effect, to make a risk management decision before conducting a
risk assessment.
The first part of this approach, risk assessment, involves identifying
the range of potential adverse effects and the affected population, estimating
the timing and magnitude of those effects, and assessing the attendant
uncertainties. The second step, risk management, entails developing a set of
possible regulatory options, analyzing the efficacy of these options in
reducing the risks identified, evaluating the economic and social costs and
benefits of the various options, and then choosing the most efficient option.
Some of the virtues of this approach are that it recognizes cost/benefit
analysis as an integral part of decision-making, but it separates such analy-
sis from assessment of the risk. It recognizes the need to assess scientific
and other uncertainties, but it does not allow the existence of uncertainties
per se to automatically stop the decision-making process.
The two-part UNEP workshop uses a format similar to that prescribed by
the "risk assessment-risk management" approach. As far as I am aware, this is
the first time that such a process has been deliberately established at the
international level and, as such, it is truly an innovative approach.
Whether this approach will work is at this point an open question. A
primary aim of the first part of the workshop was to try to find a reasonable
range of estimates of future growth in CFCs and the other trace gases, which
could then be plugged into the various global atmospheric models to give us
estimates of the timing and magnitude of ozone depletion.
The Rome workshop was only partially successful in this regard. Although
I wasn't there, I gather that the Workshop's limited success was due in large
part to the view of some delegations that because making future projections
33
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inherently entails uncertainties, nothing can be said about the future. The
pitfalls inherent in this kind of all-or-nothing thinking should be obvious.
For example, the notion that "future risk cannot be estimated with certainty"
is sometimes translated, by a curious leap of faith, into the assertion that
"there is no future risk"—when that may not be the case!
We should suspend judgement on whether this approach can in fact work on
the international level until after Part II of the Workshop. However, if it
does work, I believe that the international community could adopt this
paradigm in order to come to grips with the issue of global climate also.
As noted at the UNEP/WMO/International Conference on Scientific Unions
(ICSU) Conference on Climate Change last fall in Villach, Austria, it is well
established scientifically that the earth's average surface temperature will
rise as the result of increasing concentrations of "greenhouse" gases. But
how much warming will occur, and when, is less certain. And what global
warming will mean for regional temperature and rainfall patterns is still very
much uncertain.
Our knowledge of the impacts of climate change is thus a few years behind
that of ozone depletion. It is therefore probably too early for the kind of
structured workshops that we are undertaking with respect to the ozone layer
issue to be undertaken to deliberate climate change. In the meantime, I
believe that we should follow the Villach Conference recommendation to give
higher priority to researching and assessing the impacts of climate change.
From my perspective as a career diplomat, it appears that the greenhouse
effect has all the markings of becoming a high visibility foreign policy
issue. The time scale between cause and effect, between policy action and
desired result is distressingly long. Somehow, political leaders and
government processes and budget makers must accustom themselves to a new way
of thinking. The scientific issues are complex, interrelating many different
scientific disciplines, often at the frontiers of discovery. The uncertain-
ties are still a subject of debate. How we address this issue internationally
depends to a great extent on our success or failure in dealing with the ozone
depletion issue. And how we deal with global climate change may in turn
influence how we deal with other similar international issues.
Thus, the activities in which we are engaged—including this report and
the International Conference on the Effects of Ozone Modification and Climate
Change—are of no small consequence to the world. I wish these efforts
success and wise counsel.
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Man's Impact on Earth's Atmosphere
James P. Bruce
Atmosphere Environment Service
Downsview, Ontario, Canada
The astonishing thing about earth is that it is alive in a corner of the
cosmos where all other bodies are lifeless. This was never more dramatically
demonstrated than 17 years ago, when men first walked on the moon and sent
home those marvellous photographs of earth-rise over the dead moon. Our
beautiful planet home is blue with water, green and brown with vegetation and
land, and wreathed in bands of white clouds of our atmosphere. This atmo-
sphere, "as thin as the dew on an apple" (Watson 1984), makes the rest
possible.
We now know that our species has the capability of modifying, in a major
way, the constituents of the atmosphere and the climate it produces. We have
inadvertently assumed a great responsibility. If we are to continue to alter
the atmospheric balances, we should be sure we can predict and understand the
consequences and be sure that these changes are tolerable.
REGIONAL ATMOSPHERIC CHANGES
More than three decades ago, the great climatologist R. Geiger (1950)
wrote: "the blue sky laughs over the landscape, while in the city all is
covered with grey and the sun shines along with a weak yellowish-red light.
Outside, it is possible to see church towers several kilometers away; inside,
the houses on long streets soon disappear in impenetrable grey. The larger
the city, the denser, heavier and more resistant is its haze hood."
Thirty-five years after Geiger's observations, the Organization for
Economic Cooperation and Development (OECD 1985) was able to list twenty-one
cities in its industrialized member countries where the situation had changed
drastically. In these major cities between 1975 and 1983, sulphur dioxide
concentrations have declined by 19$ to 65% (the latter figure for Newcastle
and Oslo), with only one, Rome, showing an increase in concentrations. Simi-
lar trends are evident in concentration of carbon monoxide and particulate
matter, but trends are not so positive for nitrogen oxides and photochemical
oxidants, such as tropospheric ozone.
35
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These reductions have been achieved by enforcing pollution control
measures; by reducing economic activity over the measured period in the heavy,
most polluting, industries; and by building higher stacks to carry the air-
borne wastes beyond the cities. So while the. air quality in our cities has
generally improved, there has been a growing realization that much of this
improvement may be causing contamination of a large part of the earth's atmo-
sphere as well as environmental damage in the countryside far removed from
urban centers. How much the situation has deteriorated in the regions away
from cities is difficult to tell, since very few measurements of rural air or
precipitation quality go back before the 1970s.
However, we do know that some of the effects of airborne pollutants on
lakes and soils are cumulative year after year; we know that many chemical
species are increasing in the whole global atmosphere; and we know that stag-
nant weather conditions, with high pressure systems over the industrial
regions of Europe and eastern North America, result in "megalopolitan plumes"
of smog that can blanket half a continent. With these newer perceptions, much
of the scientific and regulatory attention on air pollution has shifted from
the cities, becoming global and regional in scale. We are now concerned about
what Watson (1984) has called the "international trade in pollutants" brought
about by "the democracy of world winds."
We are altering the chemical balances of the earth's atmosphere and the
relationship between our veil of air and the earth's biological systems.
These biological communities, which sustain our species, have grown in harmony
with the air we breathe. Or if you are a follower of Lovelock and the Gaia
hypothesis, the biota have largely created the atmosphere, over the millenia,
with a chemical composition designed to sustain the life forms of earth. But
we are upsetting the balances in a relatively short time. What are some of
the ways our activities have been changing the air we live in and what are
some of the consequences?
PRECIPITATION CONTAMINATION AND EXCHANGE WITH WATER BODIES
At a conference on the Great Lakes in 1970, I felt justified, after
reviewing some data on chemical contamination of precipitation of the basin,
in saying that it was no longer a compliment in Toronto to say that a woman
was "as pure as the driven snow." Chemical composition of precipitation
reflects contamination that is carried by the winds for both short distances
and distances of thousands of kilometers. Furthermore, evidence of serious
contamination of the rain and snow has accumulated alarmingly over the past 15
years.
The major concern of the media, and with justification, has been acid
rain, a problem in large regions such as eastern North America and Europe, and
an increasing global concern. The pH of "clean" rain is about 5.6 with
present COp concentrations in the atmosphere. But major areas of the Northern
Hemisphere have been experiencing for some years—probably decades—precipita-
tion with acidity averaging lower than 4.6 and as low as 4.2—ten to forty
times as acidic as "clean" rain. The main contributor to the suite of acids
is sulphuric acid derived from sulfur dioxide (SO^) emissions from thermal
power plants and smelters. The relationship between low pH areas and high
sulfate deposition is very strong in Europe and eastern North America.
36
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The data from the Background Air Pollution Monitoring Network (BAPMoN) of
the World Meteorological Organization, part of the Global Environmental Moni-
toring System (GEMS) sponsored by the U.N. Environment Programme, has been
used to assess the sulfur in precipitation on a global scale. The areas with
average values greater than 1.5 to 2.0 mg/1 in 1980-82 include eastern North
America; much of Europe; central USSR on both sides of the Ural mountains; a
region in the Far East over eastern China, Japan, Taiwan and the Philippines;
the east coast of South America between Sao Paulo and Rio de Janeiro; and a
smaller less well documented area in southern Africa. It is hardly surprising
that high rates of sulfur deposition in rain and snow are becoming nearly
global, if one considers the tenfold increase in anthropogenic sulfur
emissions since 1900 (see Figure 1).
The acidification of unbuffered lakes is of course closely related to
sulfur deposition. Many lakes in Canada, the northeastern USA, and
Scandinavia have become too acidic to sustain fish. Recent findings that the
droplets at the base of clouds and in some fogs, for example in Japan, are
often ten times as acidic as the rain have generated concern about damage to
forests and vegetation at high elevations that are frequently shrouded in
clouds and fog for long periods.
But it is not just acidic substances that are contaminating the rain;
toxic metals and organics do so as well. The next newspaper headlines will
probably feature "toxic rain." For example, atmospheric loadings of toxic
contaminants are known to be the dominant source of some pollutants in the
Great Lakes, particularly PCBs, lead, zinc, and copper (see Figure 2).
Recent evidence suggests that in addition to being a source of toxic
contaminants for the lakes, the atmosphere is also a "sink," at least tempo-
rarily, for toxic substances volatilized to the atmosphere from the waters
(see Figure 3). In fact, recent studies of the budget of chlorinated benzenes
introduced by the Niagara River into Lake Ontario suggest that more than 80$
of these compounds are volatilized into the atmosphere. As much as 50% of the
PCBs that get into Lake Ontario water may return to the atmosphere by
volatilization. What is most disturbing is that measurements of a highly
toxic contaminant such as Mirex, known to have been only discharged directly
into Lake Ontario waters, have been measured in crops, cattle, and milk from
land areas surrounding the lake. These represent a far more important vehicle
by which toxic chemicals are likely to be consumed by most people living in
the basin than the fish and treated drinking water. Thus, the scientific
questions of the volatilization processes and their implications for the toxic
chemical budget of the region are under intensive research.
GLOBAL ATMOSPHERIC CHANGES
These problems of contamination of rain by acidic and toxic substances,
while gradually becoming global, tend to be concentrated regionally. However,
there are a number of atmospheric contaminants that have a nearly uniform
worldwide distribution and are beginning to have global effects, particularly
on the earth's climate, on the vertical temperature distribution of the
atmosphere, on stratospheric ozone, and on the total amount of ozone in a
column above the earth at any location. These increases in contamination of
the earth's atmosphere are probably decreasing the health-protecting ozone
layer and can cause an unprecedented global warming. Let us review, briefly,
37
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Tg S/y»or
100-
90-
80
70
60-
50-
40
30
20-1
10
® Cullis ond Hirschler (1980)
© Katz (1956)
x Robinson ond Rabbins (1971)
®
O©
0X
1860 70 80 90190010 20 30 40 50 60 70 80 yeor
Figure 1. Estimates of Global Anthropogenic Emissions of Sulfur
into the Atmosphere (millions of metric tons per year)
38
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Metric tons
per year
500 -
(9158)
Municipal
point sources
Rural runoff
Urban runoff
Atmospheric
Industrial
point sources
Lead Zinc Copper
Industrial loadings are not indicated for lead, zinc, and copper.
Cadmium
Figure 2. Metal Loadings to the Great Lakes, by Source
Source: Great Lakes Basin Commission and
Great Lakes Science Advisory Board
39
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t-,
O
a.
n
i
CD
O
S-.
3
O
to
40
-------
some of the wonderful things humanity has achieved so far in changing the air
around us.
The substances of primary concern in bringing about ozone and climate
changes are carbon dioxide (COp), the chlorofluorocarbons (CFCs), methane
(CH|j), and the nitrogen oxides (NO ). These are all increasing on a global
scale and current annual rates of increase in the atmosphere are very large.
The most important of the CFCs are increasing at 5% to 1% per year; C02 is
increasing at about 0.5% per year and methane at about 1%. To compound the
problem, the residence times of some of these gases are very long; CFClo,
CFpCl2, and nitrous oxide remain in the atmosphere 75 to 150 years. C02 re-
mains even longer. These long lifetimes imply that annual increases are
cumulative over a long period of time and that any changes in climate or ozone
distribution brought about by such substances will last for centuries even if
remedial actions are taken.
To complicate matters, other gases introduced into the atmosphere by
human activities or formed in the atmosphere by reactions involving anthro-
pogenic substances also have direct or indirect effects on temperatures and on
ozone formation or dissipation. These include the hydroxyl radical (OH),
which reacts with carbon monoxide (CO) and methane (CH|j). With increases in
both CO and CH^ the cycle between these gases and the hydroxyl radical may be
reducing OH concentrations, and thus the capacity of the troposphere to remove
many gases may be reduced.
The increase in methane concentrations is particularly interesting
because of difficulties in determining why it is occurring. The data on the
upward trend summarized in Figure 4 indicate a 1.\% increase per year between
1976 and 1985. Methane concentrations are affected by natural microbiological
processes in water-logged soils and in the intestines of herbivores, and by
industrial activities involving the use of natural gas, burning of biomass,
and burning of coal. Figure 5 (Bolle, Seiler, and Bolin 1985) shows the
probability that increases in atmospheric CHjj are caused by both industrial
activities and society's impact on natural processes. The figure shows the
close parallel between world population trends and CHj, mixing ratios for the
past 600 years, as determined from ice cores in Greenland. Table 1 gives
estimates by various workers of the range of values of emissions from the
various sources. Increasing numbers of ruminants and rice paddies, as well as
biomass and natural gas exploitation, are the main sources of increased
methane in the atmosphere. Increased methane concentrations will certainly
add to the greenhouse effect, but may also decrease chlorine (Cl) concentra-
tions in the stratosphere, which would slightly reduce the rate of ozone
depletion resulting from CFC emissions.
Nitrous oxide (N20) is also increasing in the atmosphere but at a con-
siderably slower rate. The source is primarily microbial processes in soil
and water, with both denitrification and nitrification contributing to release
of N20. Production is enhanced by application of fertilizers of mineral
nitrogen, especially ammonia-based fertilizers, and from increases in the use
of lands for agriculture. Both sources are significantly affected by farming
activities. Natural processes in the oceans and fossil fuel burning are also
N20 emission sources. Global emissions over the past century have increased
about 55% (see Figure 6). In addition to its relatively small effect as a
41
-------
1.85
1.80
1.75
1.70
o
1 1.65
.£• 1.60
o
1.55
NORTHERN HEMISPHERE
40-60°
1976 1977 1978 1979 1980 1981 1982 1983 1984 1985
TIME
Figure 4. Trend of tropospheric CHh mixing ratios (concentration)
observed at midlatitudes of the Northern Hemisphere. Data are obtained from
measurements carried out on aircrafts (circles), on ships (squares), and at
different land based stations during clean air conditions (triangles). The
figure includes data (dots) measured by Rowland and colleagues (see Blake
1984) at similar latitudes in air from the Pacific Ocean (from Bolle, Seller,
and Bolin 1985).
CH4 MIXING RATIO [ ppmv ]
0.6 0.8 1.0 1.2 U 1.6 1.8
PRESENT
o Rasmussen and Kham. 1984
Craig and Chou. 1982
* Robbing et al.,1973
• Present day level
d1300
1.0 2.0 "3.0 4.0
WORLD POPULATION
Figure 5. Growth of Human Population (in billions) and Increase of Atmo-
spheric Cfy Mixing Ratios (concentrations) During the Last 600 years (from
Bolle, Seiler, and Bolin 1985).
42
-------
Table 1. Estimated Trend of CHjj Emission Rates from Individual Ecosystems
(Tg per Year) (from Bolle, Seller, and Bolin 1985).
Sources
Ruminants
Rice paddies
Swamps/Marshes
Other biogenic
Biomass burning
Natural gas
Coal mining
Total
1940
53.5
64.5
79
15.5
49
2
19
283
1950
58
74.5
73
18
57
5
19
305
I960
68.5
89
63
20.5
65
11.
26
343
1970
78.5
105
54
23
71
24.5
29
385
1975
84
115
51
24
75
30
31
410
1980
86
117
47
25
79
34.5
35
423
1880 1890 1900 1910 1920 1930 19^0 1950 1960 1970 1980
TIME [years]
Figure 6. Trend of Estimated Total N20 Emission Rates Between 1880 and 1980
(from Bolle, Seller, and Bolin 1985).
43
-------
"greenhouse" gas, it also reduces stratospheric ozone through chemical reac-
tions that form nitric oxide. It is estimated that a doubling of the N20
concentration alone would reduce stratospheric ozone by 3% to 5%.
Increases in carbon dioxide caused primarily by burning fossil fuels are
well documented from the Pacific to the Atlantic, and from the North to the
South Pole (see Figure 7). Projection of future CCU concentrations has become
one of the favorite indoor sports of scientists and economists. Eighty per-
cent of the global energy demand is currently met by burning fossil fuel.
Projections of energy demand and of the mix of energy sources that will be
used are uncertain. As a result, estimates of when C02 concentrations will
double the preindustrial levels of about 275 ppm are uncertain, ranging from
the middle to the end of the next century.
The chlorofluorocarbons (CFCs)-used as refrigerants, solvents, propel-
lants for spray cans, and in other ways-are exclusively manmade. Since the
mid-1970s they have been identified as a source of chlorine in the strato-
sphere, and thus as a threat to the ozone layer. The most important of the
CFCs are CFClo (F11) and CF2C12 (F12). Global emissions of F11 and F12
increased rapidly until the early 70s, followed by a slight decline caused by
restrictions on spray can uses in North America and Scandinavia (see Figure
8). However, other uses have continued to increase and as noted, concentra-
tions in the atmosphere of these long-lived substances grow by 5% to 1% per
year (see Figure 9).
The effects of these changes on ozone in the troposphere and stratosphere
have been observed. Ozone is a radiatively active gas that shields the earth
from ultraviolet B (UV-B) radiation from the sun. A 1$ decrease in ozone in
the atmosphere results in a 2% increase in UV-B radiation, which in turn would
cause a 4% increase in skin cancer. There are considerable uncertainties in
trends in ozone concentrations since individual measurements at times require
significant corrections and since the limited number of individual measure-
ments for large segments of the troposphere or stratosphere may not be
entirely representative. The data available, for example, from Resolute, NWT,
and Hohenpeissenberg, Germany (see Figure 10), strongly suggest that an
increase in ozone near the ground in the middle and high latitudes of the
Northern Hemisphere has occurred over the past few decades because of indus-
trial activities at a rate of 1% to 2% per year. At the same time, strato-
spheric ozone concentrations between 28 and 35 km above the ground appear to
be declining; satellite data suggest that levels have declined as much as 5%
at the 45-km (1 mb) level. Because about 90% of the atmosphere's ozone is in
the stratosphere, some estimates of total column ozone indicate that small
decreases have occurred since 1960.
However, the most startling change in stratospheric ozone has been
observed over Antarctica. The Dobson spectrophotometer at Halley Bay (76°S)
operated by British scientists has shown decreases in ozone in the Southern
Hemisphere spring, especially since the early 70s, amounting to more than 40%
for the month of October. Recent satellite measurements from-Nimbus 7 indi-
cate that this is a much more widespread effect than suspected and that the
decline appears to extend over the whole area of the winter polar vortex.
While several workers have suggested that this is caused, at least in part, by
chlorine increases in the stratosphere from the chemicals discussed
previously, the modeling of the mechanisms to explain such a rapid decline
remains a major scientific problem.
44
-------
350
345
o
— 335
• 330
u
«
O
o
325
320
315
31O
1955
1860
1870
1976
1880
1985
Figure 7. Carbon Dioxide Concentrations
CFC 1 1 Rl
WORLD PI
1000
- 900
O
£
_! B00
J
£ 700
z 600
O
K 500
u
§ «••
o:
"• 300
§ 200
Z
a 100
0
1 9
sJD CFC12: X^«-
RODUCTION XREROaoL
^ NON-PERO30U
-
J,
X
^
[JP*
/
/
/ v
x£
>^
/\
/^
/
r
S\
s/^
X
/S'k^H
V*
^\
X
r«-«
^
^*
60 1965 1970 1975 1980 1 985
YERK
SOUHCC: cut* ttaayjt KRND 119001;
us t re ri96f-i9au
Figure 8. World production has remained nearly constant since the mid-
1970s. While aerosal production has steadily declined, nonaerosol production
has consistently increased.
-------
CFCLi IS) RAGGED POINT, BARBADOS
7210
1 200
2 190
2 180
Z 170
5 160
1978 1979
1980
1981
1982
1983 1984
CF,CL, RAGGED POINT. BARBADOS
s. 350
a
2 23°
5 310
1C
O 290
5 270
5
.1
ill
Hii'"
,asjKOj'«SKj.as:»Cjfn8n.jiSON3Jf»s«Jj»SOKOjf«»»jjl>SON|Jjf"»"jji>ii:NOjf«ai'j
1978 1979 1980 1981 1982 1983 1984
CH,CCL, RAGGED POINT, BARBADOS
a 130
2,20
s. 110
o
5 100
x
I 90
1978 1979
1980
1981
1982
1983 1984
CCU RAGGED POINT, BARBADOS
g 130
< 120
O 110
B 100
II, m,,,""""""1"""1
1978 1979
1*80
1981
1982
1983 1984
Figure 9. Monthly Mean Mixing Ratios (concentrations) and Monthly Vari-
ances of CFC-11, CFC-12, CHoCClo, and CCljj Measured Four Times Daily on a Gas
Chromatograph at the Ragged Point, Barbados ALE/GAGE Station During the First
Six Years of the ALE/GAGE Network (parts per trillion volume).
Source: NASA Assessment Report
46
-------
RESOLUTE
100
HOHENPEISSENBERG
1/70-12/83
1000
-2
A OZONE (%yr"1}
Figure 10. Percent increase or decrease in ozone at various altitudes
(expressed as pressure in millibars) at Resolute (75°N, Canada, 1966-1979) and
Hohenpei-ssenberg (47°N, Germany, 1970-1983). The horizontal bars give the 90$
confidence interval. The shaded area shows the range of the tropopause
heights (from Logan 1985).
Source: NASA Assessment Report
47
-------
Models of ozone changes caused by these atmospheric contaminants indicate
that the maintenance of stratospheric ozone is critically dependent on the
rate of growth of CFC use. If CFC emissions could be returned to and main-
tained at the 1980 levels, the models predict only very small changes in total
column ozone. Increases of 1.5% per year and 3% per year make increasingly
large depletions likely. However, two-dimensional models show strong latitu-
dinal difference with depletions throughout the stratosphere north of 40°N and
some ozone increases in the lower stratosphere nearer the tropics. Polar
depletions in the ozone column are predicted to be two to four times those at
the equator.
The future concentrations of gases affecting the ozone layer and climate
are difficult to predict since they depend on regulatory decisions by govern-
ments, energy policies and consumption, and other human interventions as well
as a more thorough understanding of physical and chemical atmospheric process-
es. However, it is easier to predict what concentrations of some substances
will be if people and governments take no action. Ramanathan and colleagues
in 1985 published a comprehensive set of projections of concentrations of
forty-seven trace gases of the atmosphere that affect radiation balances.
Many of these have a very minor role to play. The relative importance of
these gases to the "greenhouse" effect is summarized in Figure 11, which
gives the cumulative equilibrium surface temperature warming caused by these
gases from 1980 to 2030 as computed from a one-dimensional model following
Ramanathan's work. Because of positive feedbacks predicted by general circu-
lation models, the most probable temperature changes at the earth's surface
are one and a half to two times those given in the diagram. The figure shows
that CFCs are next in importance to carbon dioxide; that methane, nitrous
oxide, and ozone are significant contributors; and that the forty or so other
radiatively active trace gases add little to the total. Carbon dioxide is
about half the story.
In October 1985 in Villach, Austria, a group of nearly 100 of the world's
leading scientists and policy analysts in the field gathered to assess the
present state of knowledge of greenhouse gases and climate change. The con-
ference concluded that "The role of greenhouse gases other than C02 in chang-
ing the climate is already as important as that of C^. If present trends
continue, the combined concentrations of atmospheric COp and other greenhouse
gases would be radiatively equivalent to a doubling of COp from pre-industrial
levels possibly as early as the 2030's." Hansen et al. tthis volume) suggest
a date as early as the 2020s.
The consensus of the results from general circulation models about the
effects of such a doubling of COp was also reviewed at Villach. It was
concluded that the models indicate that the global mean equilibrium surface
temperature would rise by 3°C ± 1.5°C. In the shorter term, a further 1°C
rise beyond the 0.5°C of the past century could occur within the next two
decades, making the earth's climate warmer than at any time in the past
100,000 years. However, the scientists working with these models are quick to
point out imperfections of and problems with the models, particularly that the
hydrologic cycle, clouds, and ocean-atmosphere interactions are not modeled
with much confidence. Thus, while model results are converging on the range
of values indicated, uncertainties in the modeling make many of the scientists
most involved cautious about the results. They believe that we can use the
-------
2.5f
01
CD
O)
a.
e
QJ
u
ra
s_
ZJ
U~l
0.5
Other trace
gases -^
Ozone
Nitrous oxide
Methane
Chi orof1uorocarbons
Carbon dioxide
2.5
Range of
uncerta inty
1 .5
0.5
Figure 11. Cumulative Equilibrium Surface Temperature Warming Due to
Increase in Carbon Dioxide and Other Trace Gases from 1980 to 2030 AD as
Computed by a One-Dimensional Model (after Ramanathan et al. 1985). Due to
positive feedback mechanisms as revealed by general circulation models, actual
warming may be 1.5 to 2 times the values given in this figure (from Bolle,
Seller, and Bolin 1985).
49
-------
outcome as some indication of what may happen, but not as a fully reliable
prediction.
In addition, the models do not agree on regional distribution patterns of
temperature changes or on changes in regional precipitation. The indications
are, however, that the larger temperature increases will be in high latitudes
in winter and autumn and that summer dryness may become more frequent in the
midlatitude Northern Hemisphere (see Manabe and Wetherald, this volume). The
Villach projection of sea-level rise, based simply on extrapolation of past
experience, is that for global temperature increases from 1.5° to 4.5°C sea
level would rise 20 to 140 centimeters (see Titus, this volume, and Thomas,
Volume 3).
This has been a very brief and simplified overview of a very complex
matter, i.e., the changes in the global atmosphere. It might be useful to
reflect on the implications of the present state of knowledge for all of us
and especially for those concerned with public policy. Four main points
should be considered.
First, these are not, as some have assumed, problems for the next gener-
ation, but urgent issues for us today. The protective stratospheric ozone
layer is decreasing, and preventive measures taken so far have been inadequate
to arrest the global increases in the substances causing the change. Climate
warming caused by greenhouse gases appears to be under way and is likely to
reach very significant proportions in the first half of the next century, even
if the inertia of the system caused by the oceans delays warming by a decade
or two. As the Villach Conference statement says, "Many important economic
and social decisions are being made today on long-term projects—in irrigation
and hydro-power; combatting of drought; land use; agriculture; structural
designs; coastal engineering projects; and energy planning." The statement
points out that even if the consequences of global warming are ignored, the
projects are based on some assumption about the climate of the next 50 to 100
years. It is a matter of real urgency to be able to provide more reliable
predictions and guidance.
Second, the need is great for governments and funding agencies to support
research on the changing atmospheric composition and its effects. Uncertain-
ties in our predictions of climate change and ozone layer modification
continue to be disturbing. It is especially important that major inter-
national efforts such as the World Climate Research Programme, the Global
Tropospheric Chemistry Program, and the proposed International Geosphere-
Biosphere Programme be adequately supported.
Third, remedial, or at least preventive, measures seem to be possible.
As the Villach meeting noted, "The rate and degree of future warming could be
profoundly affected by governmental policies on energy conservation, use of
fossil fuels, and the emission of some greenhouse gases." I am reminded of
the debate of the early 70s on how to control the rate of eutrophication of
lakes. A number of nutrients were over-stimulating algal growth in many of
our lakes, but one key nutrient, phosphorus, was most readily controllable.
In our present case, CFCs are one group of substances that clearly have major
impacts on both climate and on the ozone layer. Some of their uses for spray
cans and foam blowing can hardly be considered essential and are therefore
controllable. It is my view that governments should move quickly to a CFC
50
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control protocol under the Vienna Convention on the Ozone Layer, and that
individual governments and companies should be urged to limit their use of
these chemicals. To advance the development of such an international control
program, the directors of environmental programs from many countries need to
be briefed on these issues and should discuss international remedial action.
An S02 control protocol signed in Helsinki, July 1985, by twenty countries
under the Economic Commission for Europe and ministerial meetings in Ottawa
and Munich were essential steps in moving the process forward. If the scien-
tists and bureaucrats make little progress in achieving a CFC control program
by early 1987, we should ensure that the most senior elected and politically
appointed officials become involved.
Finally, we must accelerate acceptance of a more comprehensive view of
the earth's atmosphere and the need to protect its beneficial charac-
teristics. The problems of the ozone layer, of greenhouse gases and climate
change, of long-range transport of acidic and toxic substances are closely
interrelated. They are all problems caused by human contamination of the
atmosphere—the only one we have. A new approach, a new ethic, towards dis-
charging wastes and chemical materials into the air we all breathe must soon
be adopted on an international scale. Without this we will do irreparable
damage to our earthly home.
REFERENCES
Bolle, H.J., W. Seller, B. Bolin. 1985. Other greenhouse gases and aerosols.
In Greenhouse Gases and Climate Change: An Assessment For Villach
Conference 1985. Stockholm: IMI, (to be SCOPE publication).
Geiger, R. 1950. The Climate Near The Ground. Cambridge, MA: Harvard
University Press.
National Aeronautics and Space Administration (with WMO). 1986. An Assessment
Report: Processes That Control Ozone And Other Climatically Important
Trace Gases. NASA Ref. Publ. No. 1162.
Organization for Economic Cooperation and Development. July 1985. The State
Of The Environment 1985. OECD Observer No. 135.
Wallen, C.C. 1986. Sulphur and Nitrogen In Precipitation: An Attempt To Use
BAPMoN And Other Data To Show Regional And Global Distribution.
Environmental Pollution Monitoring and Research Programme, Publication No.
26, Geneva: World Meteorological Organization.
Watson, Lyall. 1984. Heaven's breath: A Natural History Of The Wind. U.K.:
Coronet Books.
World Meteorological Organization. 1986. Report of the International Con-
ference on Assessment of the Role of Carbon Dioxide and of Other Green-
house Gases in Climate Variations and Associated Impacts. WMO publication
No. 661. Villach, Austria: WMO.
51
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The Importance of Knowing Sooner
John S. Hoffman
U.S. Environmental Protection Agency
Washington, DC USA
ABSTRACT
Unlike most environmental problems, the greenhouse warming and ozone
depletion are global in extent, possess enormous momentum for change, and may
be almost irreversible once they occur. Recent scientific assessments
uniformly agree that the changes that are likely to occur in this century will
exceed the range of natural variation experienced in the whole last century.
Given our relative ignorance of the possible effects of these changes, it
would appear that the value of knowing about effects sooner is substantial.
INTRODUCTION
The relative paucity of scientific research that has been undertaken to
understand the health and environmental effects of ozone depletion and global
warming can, in part, be explained by the belief that has been held that these
phenomena were relatively distant and uncertain. Clearly, that view is now in
doubt. Recent scientific reviews sponsored by the World Meteorological
Organization, the United Nations Environment Programme, and others indicate
that the speed of atmospheric change has been greater than thought (NASA 1986;
WMO 1986a; WMO 1986b). These reviews contend that the magnitudes of ozone
depletion and global warming are likely to be large enough to emerge above the
level of natural variations that have occurred within this century, which for
climate, at least, has been quite large.
In this volume, papers by Hansen et al. and Stordal and Isaksen
strengthen that message by presenting some important new results. Both
research teams used, for the first time, the most complex models to simulate
atmospheric change with realistic time-dependent scenarios of emissions.
Their models predict not just global average changes in ozone and climate but
the changes that will occur through time at different latitudes. The
results indicate that at some latitudes, changes will be much larger than
many had expected. As such, these results are certain to heighten our concern
53
-------
about environmental and health effects of ozone depletion and climate
change. As such, a new sense of urgency is likely to develop about the need
to understand the effects of global atmospheric change.
Two other important justifications exist for understanding effects
sooner. A large amount of momentum has developed for ozone depletion and
global warming, and these phenomena may be essentially irreversible once they
occur. Momentum is relevant because the more that exists, the harder it is to
stop. Irreversibility is important because if one cannot go backwards,
momentum threatens to take one forever beyond the point one wishes to go.
This paper explores the forces that create momentum and irreversibility for
global atmospheric systems.
MOMENTUM
Most pollution problems are local in character and can be quickly solved
by reducing emissions. For example, if the concentration of particulates in a
locality is judged too high, the emissions from sources that contribute to
pollution in that area can be reduced proportionally to the reduction in
concentrations desired. Within days of turning on the controls, the problem
will be solved. The situation for global atmospheric problems is radically
different.
Chlorofluorocarbons (CFCs) 11, 12, and 113; nitrous oxide; and the
halons have long lifetimes (NASA 1986). Emissions of these gases do not leave
the atmosphere quickly, but linger for decades or more. In fact, for CFCs 11,
12, and 113; halons 1211 and 1301; and nitrous oxide, the only real sink (loss
mechanism) is the stratosphere itself, where high energy ultraviolet radiation
is capable of photodissociating these gases. Consequently, for any level of
emissions into the atmosphere, concentrations will increase in the lower
atmosphere until the point in time that the transport to the stratosphere
equals the global emissions. We are currently far from that point. Thus, if
current emissions did not grow, concentrations would continue to increase for
over one hundred years, as shown in Figure 1 for CFC 12. If we wanted to
stabilize the concentration of CFC 12, total emissions in the world would have
to be reduced approximately 85 percent immediately, as shown in Figure 2.
This disequilibrium between emissions and concentrations constitutes a
kind of momentum for change in the world. Change is built into the status
quo. Putting on the "brake," except in the most extreme case, would not
prevent change, but would only slow it down. (Figure 3 shows the results of
various reductions in emissions on the increase in 2 concentrations.
In point of fact, the world is still gathering momentum. Emissions have
been increasing and are likely to continue to do so according to most studies.
Figure 4 shows fifteen year projections of CFC 11 and 12 for a variety of
papers presented at the UNEP conference in May. In developed nations, many
uses of CFCs are growing faster than the economy—production of personal
computers, in which CFC 113 is used as a solvent for the chips, is just one
example. Insulation is another. In many developing nations, current
consumption can be expected to grow faster than the economy, as segments of
54
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CFC-12: Constant Emissions
(mill kg)
500
400
300
200
100
0
CFC12: Atmospheric Concentrations
(ppbv)
1930
1985
2100
1930
2100
Figure 1. If future emissions of CFC-12 were held constant at today's
levels (Figure 1a), atmospheric concentrations would continue to rise for over
one hundred years (Figure 1b).
CFC-12: Emissions
(mill kg)
500
400
300
200
100
0
1930
1985
2100
CFC-12 Atmospheric Concentrations
(ppbv)
0.40
0.30
0.20 -
0.10 -
0
1930
1985
2100
Figure 2. Atmospheric concentrations of CFC-12 are far from equili-
brium. Only if emissions were cut 85% and not permitted to increase (Figure
2a) could atmospheric concentrations be held constant (Figure 2b).
55
-------
CFC-12: Atmospheric Concentrations
from Different Emission Trajectories
(ppbv)
Constant
emissions
15% Cut
50% Cut
85% Cut
1930
1985
2100
Figure 3. Atmospheric concentrations of CFC-12 will continue to rise
unless emissions are cut. Holding emissions constant at today's level or even
15$ or 50% lower would still allow atmospheric concentrations to grow. Only a
cut of 85% or more could stablize atmospheric concentrations.
SHORT TERM
Nonaerosol Projections: CFC-11 and CFC-12
(1985-2000)
AUTHORS
A
B
C
D
E
F
G
H
1
J
COUNTRIES
Bevlngton f^
EFCTC
Gibbs
Hammil
Hi
Hedenstrom [_
Knollys
EEC
Sweden
World
Japan
West
U S
Kurosawa 1'""* 1 Canada
Nordhau
s
Sltellteld
PC"*"
B
B
H
0.0 1.0 2.0 3.0 4.0 5.0
Annual Rate of Change (%)
6.0
7.0
8.0
Figure 4. A variety of researchers have estimated future demand for CFCs
in various countries and regions. Despite their diversity of methods and
data, they are in substantial agreement that short-term demand for CFCs in
non-aerosol uses will continue to increase.
56
-------
the populations reach the state of being able to afford goods that use CFCs or
other chemicals. People are likely to want refrigerators, air conditioning,
and electronics as their wealth increases. As populations and economies grow
we can expect the demand for goods and.services to grow in developed nations
too, including those that use potential ozone depleting chemicals. This
process creates a major source of momentum for accelerated atmospheric change.
Another form of momentum exists for global warming. At the present time
the earth has not experienced all the warming that would be expected from past
increases in greenhouse gases. Instead, some of the infrared energy trapped
by past increases in greenhouse gases has been used to heat up the upper
layers of the ocean (MAS 1979). While this effect has retarded the speed of
the warming to date, eventually we can expect ocean and atmosphere
temperatures to rise to their equilibrium values. The current difference
between the realized and equilibrium temperature constitutes a major form of
momentum for global warming—a form that is inescapable. For the model
simulation of global warming performed by Hansen et al. in this volume, the
temperature change realized by 2000 is 1°C. The unrealized warming also turns
out to be 1°C. This means that even if the concentrations of greenhouse gases
were totally stabilized by that year the world would eventually experience a
2°C average global warming.
IRREVERSIBILITY
Clearly momentum makes it difficult to stop any system quickly. It is a
different question whether it is possible to go back once one has stopped. As
it turns out, however, restoring lost ozone or cooling the world would be
difficult. As discussed earlier, the gases likely to cause these phenomena
have long lifetimes. Even if emissions are totally eliminated, it could take
decades for the concentrations to fall. A total elimination of emissions
seems unlikely, but if it did occur in the case of ozone depletion, one would
expect to eventually see the concentrations of ozone restored, all other
things being equal. For global warming, this may not be the case. It may be
that warming makes it impossible for all things to go back to what they
were. In particular, the water vapor that has entered the atmosphere and
amplified the radiative warming from other greenhouse gases may not just
disappear from the atmosphere. If it resides in the atmosphere permanently,
it will continue to enhance global temperature, perhaps forever. Regardless
of whether this happens, the warming will last a long time.
CONCLUSION
A system that is hard to stop and that may be impossible to reverse pre-
sents a very different issue from those facing decisionmakers currently in the
environmental arena. A problem that is global in nature, in which any change
can expose billions of people, all ecosystems, and all outside materials to
change, raises issues that are also very different from environmental problems
in localized systems. It is not difficult to imagine that as recognition of
the unique aspects of global atmospheric change becomes more widespread,
decisionmakers will begin to focus on the effect of depletion and warming,
recognizing the importance of knowing sooner.
57
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REFERENCES
National Academy of Sciences (MAS). 1979. Carbon dioxide and climate: A
scientific assessment. Washington, D.C.: MAS.
National Aeronautics and Space Administration (NASA). 1986. Present state of
knowledge of the upper atmosphere: An assessment report. Processes that
control ozone and other climatically important trace gases. Wash ing ton,
D.C.: NASA.
World Meteorological Organization (WHO). 1986. Atmospheric ozone 1985:
Assessment of our understanding of the processes controlling its present
distribution and change. WHO Global Ozone Research and Monitoring
Project Report No. 16. To be published.
World Meteorological Organization (WMO). 1986. Report of the International
Conference on the Assessment of the Role of Carbon Dioxide and of Other
Greenhouse Gases in Climate Variations and Associated Impacts. WMO No.
661. Villach, Austria: WMO.
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Our Global Environment: The Next Challenge
John H. Chafee
United States Senate
Washington, DC USA
The problems associated with ozone depletion, the greenhouse effect, and
climate change have extraordinary ramifications for the world we inhabit.
Although these problems have not yet been elevated to the same level of public
awareness as toxic waste or acid rain, more and more people are becoming aware
and concerned about them. The press that these issues received in the second
week of June 1986 is evidence of mounting awareness and concern. There have
been stories and editorials in newspapers across the country and in Canada,
national television, radio, and magazines like Newsweek and The New Yorker.
On June 10 and 11, 1986 we conducted two days of hearings before the
Senate Subcommittee on Environmental Pollution to explore the nature of these
problems and to examine what is being done by the U.S. government, domesti-
cally and internationally, to both improve our understanding of these matters
and to respond to them. Why did we decide to spend time on these problems?
Why is all of this so important? Why are the policymakers demanding action
before the scientists have resolved all of the questions and uncertainties?
We are doing so because there is a very real possibility that society—through
ignorance or indifference, or both—is irreversibly altering the ability of
our atmosphere to perform basic life support functions for the planet.
This is not a matter of Chicken Little telling us the sky is falling. At
our hearings, we heard graphic, powerful and disturbing testimony from distin-
guished scientists such as Bob Watson and Jim Hansen of NASA, Sherry Rowland,
George Woodwell, Stephen Leatherman, and Carl Wunsch. The scientific evidence
is telling us we have a problem, a serious problem. There is much that we
know. There is a great deal that we can predict with a fair amount of
certainty.
As evidenced by the October 1985 Villach Conference, there is now an
international consensus among the scientific community. Although there will
always be dissenters—those who claim, for example, that the earth is actually
cooling, not warming—the scientific community has told us with unusual
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clarity that we have a problem. We must not allow their message to fall on
deaf ears.
It is true that we lack the tools to close all of the scientific gaps.
We don't completely understand our climate systems and we cannot predict
precise outcomes. But we will always be faced with a level of uncertainty.
The current gaps in scientific knowledge may not be closed for many years.
Scientists have characterized our treatment of the greenhouse effect as a
global experiment. It strikes me as a form of planetary Russian roulette.
We should not be experimenting with the earth's life support systems
until we know that when the experiment is concluded, the results will be
benign. As Russell Peterson (former Chairman of the President's Council on
Environmental Quality) who worked as a chemist for twenty-six years has said,
"We cannot afford to give chemicals the same constitutional rights that we
enjoy under the law ... chemicals are not innocent until proven guilty."
By not making policy choices today, by sticking to a "wait and see"
approach, we may in fact be making a passive choice. By allowing the so-
called "greenhouse" gases to continue to build up in the atmosphere, this
generation may be committing all of us to severe economic and environmental
disruption without ever having decided that the value of "business as usual"
is worth the risks.
Those who believe that these are problems to be left to future genera-
tions are misleading themselves. Human activities to date may have already
committed us to some level of temperature change. If historical evidence is
any guide, a slight warming may be enough to turn productive, temperate
climates into deserts. To quote from a recent Department of Energy report,
"large changes in both precipitation and the extent of deserts and grasslands
can be associated with relatively small variations in the global mean tempera-
ture."
The path that society is following today is much like driving a car
towards the edge of a cliff. We have a choice. We can go ahead, take no
action and drive off the edge—figuring that, since the car will not hit the
bottom of the canyon until our generation is already long gone, the problem of
coping with what we have made inevitable is a problem for future
generations. We can hope that they will learn how to adapt. On the other
hand, we can put the brakes on now, before the car gets any closer to the edge
of the cliff and before we reach a point where momentum will take us over the
edge.
What do we do about all of this?
First, it is important to focus attention on the potential effects of
ozone modification and climate change. Simply telling people that there will
be a change is not enough. They need to understand how they will be affected
by it. The International Conference on the Effects of Ozone Modification and
Climate Change was an excellent step in that direction. Many people came a
long way to participate in that gathering.
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In addition, we must begin to consider the choices that will have to be
made if we are going to avoid further build-up of harmful gases in the
atmosphere. All of us must recognize that these are no longer just science
issues. They are not policy issues. They demand solutions.
Many of the government witnesses who appeared before my Subcommittee
argued that we need more studies. They contend that there are too many scien-
tific uncertainties to warrant action. Only EPA Administrator Lee Thomas
recognized what is at stake here'. He was the only decisionmaker from the
government who appreciated the fact that there will always be scientific
uncertainty and that policymakers and those who make regulatory decisions
cannot allow themselves to be paralyzed by these gaps in knowledge.
Sure, we can continue to study the problem—and we should continue our
studies—but we cannot wait until these studies are completed. We need
action.
Those who argue against action like to recite the caveats, uncertainties,
and margins of error that accompany scientific reports and projections in this
area. For those people, it is worth noting that the margins of error usually
associated with the greenhouse effect are in terms of decades. The issues of
magnitude and timing need to be resolved but they do not need to be resolved
before we take action. It is important to talk about projections of, for
example, global warming over the next 50 to 100 years. But disagreements over
the accuracy of projections for that time frame obscure the issue: Do we have
the right to pollute the atmosphere today in a manner that will wreak havoc in
as few as 100 to 300 years?
Obviously, no single step is going to solve the multitude of problems
associated with these matters. But we must not let the enormity of the task
keep us from taking a series of small steps.
The growing use of chlorofluorocarbons (CFCs) is a prime candidate for
controls. Given the risks associated with ozone modification and climate
change, a treaty that limits the availability of CFCs would seem to be a
sensible course to pursue. The good news is that, under the leadership of the
United Nations Environment Programme, negotiations aimed at developing an
international agreement to limit future growth in CFCs—to impose controls—
are currently underway. The not-so-good news is that we don't have an
agreement yet.
At the Environmental Pollution Subcommittee hearings, Dr. Rowland raised
an interesting suggestion that I intend to examine more closely: In addition
to imposing controls on the use of CFCs generally, why don't we redesign
equipment such as car air-conditioners to use alternative, less harmful forms
of CFCs? Although CFCs are not the only source of the problem, they are a
significant factor and controlling them would represent a major accomplish-
ment.
The need for international cooperation in addressing these matters is
obvious. We are dealing with a global issue. But the difficulty of getting
international agreement should not keep the United States from taking action
unilaterally. By taking such action, we can move once again into the role we
once proudly held: we can be world leader in environmental protection. We
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can set the example. A country as large and as powerful as the United States
can afford to make temporary sacrifices that ultimately will benefit all of
mankind.
The importance of these issues is matched only by the complexity of
them. But we have created complex problems before and we have responded to
them with creative solutions. There is no reason to believe that the only
answer is to throw up our hands and wait for the inevitable.
We lose so very little by trying. We lose everything by doing nothing.
Tough choices need to be made and we should start what promises to be a
long, sometimes frustrating process of making policy choices and regulatory
decisions. All of us will have key roles to play in that process. By working
together, we can attempt to minimize the disruptions that go along with
changes in the status quo. But there will be changes. Present and future
generations of all life forms depend on our making the right choices.
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The Greenhouse Effect
Albert Gore, Jr.
United States Senate
Washington, DC USA
I am pleased to have the opportunity to join the other authors of this
report to accelerate our progress on the global problems of climate change.
In order to resolve these issues, we will need the kind of international
cooperation and leadership that organizations like the United Nations
Environment Programme and the U.S. Environmental Protection Agency can
provide. Let me briefly discuss one of our gravest climatic concerns—and
perhaps the most significant environmental problem of the next century—the
greenhouse effect.
The buildup of atmospheric carbon dioxide and other trace gases is
causing a global warming that could have disastrous results on sea level,
agriculture, and the climate in general. Other papers present some of the
forecasts—a 3 to 8 degree (F) temperature increase by 2030, a 10 percent
decrease in crop yields, more frequent tropical storms. And if today's worst
case scenarios come true we may have only a few decades left in which to
decrease these impacts.
My interest in the greenhouse effect goes back several years, and I have
chaired three congressional hearings on the phenomenon. During the first
hearing in 1981, a number of prominent scientists, including Professor Roger
Revelle of the University of California, testified that the greenhouse effect
was not a hypothesis but a reality. This marked perhaps the first time that
the scientific community had reached a consensus on this point.
The evidence to substantiate that conclusion was not long in coming. In
19§2, Dr. James Hansen of NASA and Professor George Kukla of Columbia
University testified that the rise in carbon dioxide levels could be
correlated very closely with a rise in the earth's mean temperature, a
shrinking of glacial ice, and the resulting rise in the earth's mean sea
level. At that time the Washington Post, in an editorial, stated that the
greenhouse effect was no longer just something for the "sandals and granola"
crowd; it was in the mainstream of scientific thought.
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The most comprehensive evaluations of the greenhouse effect were
presented at the third hearing in 1984. One was an EPA report predicting a
global temperature increase of 3.6 degrees Fahrenheit by the year 2040, and a
rise of as much as 9 degrees Fahrenheit by the year 2100. This would result
in sea level increases ranging from 4.5 to 7 feet by the end of the next
century.
A 1983 report from the National Academy of Sciences was more conservative
in its projections. The WAS predicted a 2 to 8 degree Fahrenheit rise in
temperature along with a "modest" 2.5 foot rise in the sea levels by the year
2100. The major difference between the two studies was that EPA included the
impact of all the greenhouse gases, including CFCs and methane, as well as
carbon dioxide. The Academy projections were based solely on increased carbon
dioxide concentrations.
In October 1985, a conference on the greenhouse effect brought scientists
from twenty-nine countries to Villach, Austria. These scientists concluded
that "...greenhouse gases are likely to be the most important cause of climate
change over the next century." They went on to recommend that governments
should "...take into account the results of this assessment in their policies
on social and economic development, environmental programs, and control of
emissions of radiatively active gases."
We must explore measures to prevent and mitigate the impact of the
greenhouse effect. If there is to be an effective global effort to address
this major environmental problem, then all nations must coordinate their
activities.
To address this issue, I have introduced Senate Concurrent Resolution
96. The bill calls for an International Year on the Greenhouse Effect and
would be the beginning of a long-term cooperative effort by scientists from
all over the world.
The legislation would coordinate and promote domestic and international
research efforts on both the scientific and policy aspects of this problem,
identify strategies to reduce the increase of carbon dioxide and trace gases,
investigate ways to minimize the impact of the greenhouse effect, and
establish long-term research plans.
The concept of an international year of study has been used successfully
in the past. In fact, the best and most complete collection of data based on
atmospheric concentrations of carbon dioxide began in 1957 as a result of the
International Geophysical Year. At that time a sampling station was
established on Mona Loa, Hawaii. Today scientists are still collecting data
from that station.
I believe this legislation will markedly improve national and
international research efforts. In time, it will produce the vital data that
the United States and other nations need to establish a long-term workable
corrective policy.
Paul Brodeur pointed out in the June 9, 1986 issue of the New Yorker that
we have known about the greenhouse effect and ozone depletion for over a
decade, yet our efforts to develop corrective solutions have been minimal. He
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quotes Professor Sherwood Rowland of the University of California at Irvine
who discovered the impact of chlorofluorocarbons on the ozone layer,
"...what's the use of having developed a science well enough to make
predictions, if in the end all we're willing to do is stand around and wait
for them to come true?"
The greenhouse effect is complicated and worrisome, and seems too
overwhelming to resolve. But its potential impact is far too disastrous to
ignore. The longer we wait, the worse the impact will be because the effect
of the greenhouse gases is cumulative. If we wait much longer to act, it may
be too late.
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OZONE MODIFICATION AND
SUMMARY OF UV-B EFFECTS
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Atmospheric Ozone
Robert T. Watson
Office of Space Science and Applications
National Aeronautics and Space Administration
Washington, DC USA
INTRODUCTION
For several decades scientists have sought to understand the complex
interplay among the chemical, radiative, and dynamical processes that govern
the structure of the earth's atmosphere. During the last decade or so there
has been particular interest in studying the processes that control atmo-
spheric ozone, since it has been predicted that human activities might cause
harmful effects to the environment by modifying the total column amount and
vertical distribution of atmospheric ozone. Most of the ozone in the earth's
atmosphere resides in a region of the atmosphere known as the stratosphere.
The stratosphere extends from about 8 km at the poles and 17 km at the
equator, to about 50 km above the earth's surface. Ozone is the only gas in
the atmosphere that prevents harmful solar ultraviolet radiation from reaching
the surface of the earth. The total amount of ozone in the atmosphere would,
if compressed to the pressure at the earth's surface, be a layer about one-
eighth of an inch thick. Figure 1 schematically illustrates the vertical
distribution of ozone and temperature. Unlike some other more localized
environmental issues (e.g., acid deposition) ozone layer modification is a
global phenomenon that affects the well-being of every country in the world.
Changes in the total column amount of atmospheric ozone would modify the
amount of biologically harmful ultraviolet radiation penetrating to the
earth's surface, resulting in potential adverse effects on human health (skin
cancer and suppression of the immune response system) and on aquatic and
terrestrial ecosystems. Changes in the vertical distribution of atmospheric
ozone, along with changes in the atmospheric concentrations of other infrared-
active (greenhouse) gases, could contribute to a change in climate on a
regional and global scale by modifying the atmospheric temperature structure,
which could lead to changes in atmospheric circulation, in precipitation
patterns, and in sea level. (See Hansen et al; Titus; and Manabe and
Witherald, all in this volume, for discussion of the greenhouse effect and
consequences of global warming.)
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OZONE CONCENTRATION
10'° 10" 101
10'
140
120
100
• 80
< 60
40
20
I
I
THERMOSPHERE
TROPOSPHERE
I
100
200 300
TEMPERATURE (K)
400 500
Figure 1. Temperature Profile and Distribution of Ozone
(molecules per cubic centimeter) in the Atmosphere
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The ozone issue and the greenhouse warming issue are strongly coupled
because ozone itself is a greenhouse gas, and because the same gases that are
predicted to modify ozone are also predicted to produce a climatic warming.
These gases include carbon monoxide (CO), carbon dioxide (COo), methane (CH^,),
nitrous oxide (NpO), and several chlorofluorocarbons (CFCs), including
chlorofluorocarbons 11 (CFClo) and 12 (CFpCl2), and are precursors to the
hydrogen, nitrogen, and chlorine oxides, which can catalyze the destruction of
ozone in the stratosphere by a series of chemical reactions. Concentrations
of these gases in the parts per billion range control the abundance of ozone
whose concentration is in the parts per million range. (For example, one
molecule of a chlorofluorocarbon destroys thousands of molecules of ozone.)
CO and C02 can affect ozone indirectly. CO controls the concentration of the
hydroxyl radical (OH) in the troposphere, which itself controls the
atmospheric concentrations of some of the gases that can affect stratospheric
chemistry. C02 plays a key role in controlling the temperature structure of
the stratosphere, which is itself important in controlling the rates at which
the hydrogen, nitrogen, and chlorine oxides destroy ozone.
TRENDS IN THE CHEMICAL COMPOSITION OF ATMOSPHERE
There is now compelling observational evidence that the chemical
composition of the atmosphere is changing at a rapid rate and on a global
scale. The atmospheric concentrations of C02, CHh, NpO, and CFCs 11 and 12
are currently increasing at rates ranging from 0.2% to 5.0% per year (Figure 2
shows the trends for four chlorinated gases, and Figure 3 shows the global
trend for methane). The concentrations of other gases important in the ozone
depletion and global warming issues are also increasing, some at an even
faster rate. These changes in atmospheric composition reflect in part the
metabolism of the biosphere and in part a broad range of human activities,
including agricultural and combustion practices. It should be noted that the
only known source of CFCs is industrial production. CFCs are used for a
variety of applications, including aerosol propellants, refrigerants, foam
blowing agents, and solvents. At present one of our greatest difficulties in
accurately predicting future changes in ozone concentrations or global climate
is our inability to predict the future evolution of the atmospheric
concentrations of these gases. We need to understand the role of the
biosphere, and the impact of human activities upon it, in regulating the
emissions to the atmosphere of gases such as CH^, C02, N20, and methyl
chloride (CH^Cl) and we need to know the most probable future industrial
release rates of gases such as the CFCs, NpO, CO, and COp, which depend upon
economic, social, and political factors.
One important aspect of the ozone and global warming issues is that the
atmospheric lifetimes of gases such as NpO, CFC1,, and CF2C12 are known to be
very long. Consequently, if there is a change in atmospheric ozone or climate
caused by increasing atmospheric concentrations of these gases, the full
recovery of the system will take decades or centuries after the emission of
these gases into the atmosphere is terminated.
THEORETICAL PREDICTIONS OF OZONE MODIFICATION
Numerical models are used as tools to predict to what extent human
activities will modify atmospheric ozone and climate. The types of models
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CFCI, (S) RAGGED POINT, BARBADOS
>210
a 200
2 190
K 180 I
a '
2 1701
*
S 160
1978 1979
1980
1982
CF2CI2 RAGGED POINT, BARBADOS
1983 1984
U 350
S I
0 330
L_ 1
< 310
oc
0 290
X 270
1111
1978 1979 1980
CH3CCI3 RAGGED POINT, BARBADOS
1982
1983 1984
7 140
3 130
2 120
<
1C 110
C3
* 100
X
S 90
T
1
t t I I 1 I 1
i ,, III,!'! 1,1 'I
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i
i i
JHSONOJFflRMJJRSSNOjFMHMJJflSCNQjFflflHJJRSONOJFMRMJjRSONOJFMflHJJRSONOJFHRrtJ
CCU RAGGED POINT, BARBADOS
S. 140
^
g 130
< 120
E
O 110
X 100
£
111 i I I' III'''' 11,1'
1978 1979
1980
1981
1983 1984
Figure 2. Monthly-mean mixing ratios and monthly variances of CFC-11,
CFC-12, CFUCClo and CCln measured 4-times-daily on a gas chromatograph at the
Ragged Point, Barbados ALE/GAGE station during the first six years of the
ALE/GAGE network.
72
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1.65
1.60
1.55
1.50
PPMV
CH4
I I I I
I I I I
1977 1978 1979
1980 1981 1982 1983 1984 1985
YEAR
Figure 3. Globally averaged concentrations of CH^ from 1977 to 1985.
73
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most commonly used to predict ozone modification are known as one- and two-
dimensional photochemical models. One-dimensional models predict changes in
the column content and vertical distribution of ozone, but cannot predict
variations in ozone modification with latitude, longitude, or season. Major
progress has been made over the past few years to develop two-dimensional
models which can predict the variation of ozone change as a function of season
and latitude.
Three-dimensional models which include longitudinal variations are being
developed to study the coupling between the chemical, radiative, and dynamical
processes that control the distribution of ozone, but these models are not yet
ready to perform perturbation calculations.
Because it is now well recognized that the chemical effects of these
gases on atmospheric ozone are strongly coupled and should not be considered
in isolation, the most realistic calculations of ozone change take into
account the impact of simultaneous changes in the atmospheric concentrations
of C02, CHh, N20, the CFCs, and possibly other gases, such as CO, oxides of
nitrogen (NO ), and bromine-containing substances. The effects of these trace
gases on ozone are not simply additive. Increased atmospheric concentrations
of CFCs and NpO are predicted to decrease the column content of ozone, whereas
increased atmospheric concentrations of C02 and CHn are predicted to increase
the column content of ozone. Therefore, it can be seen that the effects of
increasing concentrations of CFCs and NpO are to some degree offset by
increasing concentrations of COp and CHjj as shown in Figure 4. This is in
contrast to the global warming issue where increased atmospheric
concentrations of the same trace gases are all predicted to increase the
temperature of the atmosphere in an approximately cumulative manner (see
Figure 7).
One-dimensional model calculations have been performed to predict how
ozone would change with time (assuming that the atmospheric concentrations of
COp, CHh, and N20 continue to increase at their current rates of 0.5%, 1.0%,
and 0.2% per year, respectively, for the next 100 years) in conjunction with
three different assumptions for annual increase rates in the emission of CFCs
11 and 12 to the atmosphere (i.e., 0.0%, 1.5%, and 3.0%). For CFC emission
increases of up to 1.5% per year, the ozone column changes were calculated to
be less that 3% over the next 70 years. With a CFC growth rate of 3.0% per
year, the predicted ozone depletion is 10% for the next 70 years and rapidly
increasing thereafter (see Figure 5). The results of these calculations
demonstrate the strong chemical coupling between these gases and the time
scale on which ozone changes are predicted to occur. In essence, when the
growth rates of the CFCs are less than the growth rates of CHh and COp only
small column ozone changes are predicted because the CFC efffects on ozone are
temporarily masked. However, when the growth rates of the CFCs exceed those
of CHh and C02, these gases can no longer offset the impact of the CFCs—and
large ozone depletions are predicted.
Even when the predicted column ozone changes are small, and hence little
change is expected in the amount of ultraviolet radiation reaching the earth's
surface, major changes in the vertical distribution of ozone are still
predicted, which may have potential consequences for climate. Figure 6 shows
that ozone is predicted to decrease in the middle to upper stratosphere—
-------
Figure 4. Ozone depletion for particular changes in atmospheric con-
centrations, as estimated by the Lawrence Livermore model.
2
1
0
-1
i -2
I "3
5 -4
-5
-6
-7
-8
-9
-10
I I
LLIML 1-D MODEL
WITH TEMPERATURE FEEDBACK
10 20 30 40 50 60
YEARS FROM PRESENT
70 80 90 100
Figure 5, Calculated changes in ozone column with time for time-
dependent scenarios: A (CFC flux continues at 1980 level, CH^ increased \% per
yr, NoO increases 0.25$ per yr, and CO^ increases according to the DOE
scenario); B (CFC emissions begin at 1980 rates and increase at 1.5$ per yr,
other trace gases change as with A); C (same as B except CFC emissions
increase at 3% per yr).
75
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55
50
45
40
35
E 30
Q
t 25
20
15
10
100
0
-50
LLNL 1-D MODEL
WITH TEMPERATURE FEEDBACK
-40 -30 -20 -10 0 10
CHANGE IN LOCAL OZONE. (%)
20 30
Figure 6. Calculated percentage change in local ozone at selected times
5 to 100 years in the future (scenario B of Figure 5).
76
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primarily because of increasing concentrations of CFCs—and to increase in
the troposphere primarily because of increasing concentrations of CH^.
Two-dimensional models predict a significant variation in the ozone
column, with the greatest depletions occuring at high latitudes. Depending
upon the exact trace-gas scenario used to predict ozone change, the pole-to-
equator ratio of ozone depletion can range from a factor of two to ten.
Seasonal effects are predicted but are somewhat less pronounced than the
latitudinal effects. For a given trace-gas scenario the two-dimensional
models predict larger column ozone depletions at mid- and high-latitudes, but
less in the tropics, than the global average predicted by one-dimensional
models.
One important question that has been debated during the last couple of
years is whether the magnitude of the predicted ozone change is a linear or
non-linear function of atmospheric chlorine concentration. The issue is still
somewhat unresolved, although it now appears from most one- and two-
dimensional model calculations that ozone change is a linear function of
atmospheric chlorine for atmospheric concentrations of chlorine of 25 parts
per billion or less. Thus, sudden catastrophic global ozone depletions are
unlikely if only small changes occur in the atmospheric concentrations of
chlorine. However, this statement assumes that the models accurately
represent the real world, yet prudence tells us that we should remember that
these models are not perfect and that they cannot explain the observed large
changes that are currently occurring in ozone over Antarctica during
springtime, which we discuss below.
ATMOSPHERIC OZONE OBSERVATIONS
A crucial task for scientists is to assess the extent to which changes in
global ozone have already taken place, and to compare the changes to what has
been predicted by theory. The search for global ozone trends involves looking
for small secular changes amidst the large natural variations that occur on
many time scales. Observations of the total column content and the vertical
distribution of ozone have been made for several decades using networks of
different measurement techniques. Unfortunately, each of these observational
techniques has certain limitations, which tends to restrict our confidence in
the results. These limitations arise from factors such as the lack of
continuity of reliable calibration and the uneven geographic distribution of
stations. Statistical analyses of the data are required to identify small
trends amongst high natural variability using data from relatively few
stations.
In general, analyses for the trends in the total global column content of
ozone, using data from the ground-based Dobson spectrophotometer network, show
no statistically significant trend since 1970, which is in agreement with
model predictions for the same period when the changes in all of the trace
gases are taken into account. It should be noted that the values of total
global column ozone in the last three years have exhibited significant vari-
ability. Abnormally low values of total column ozone were observed in 1983
following the eruption of El-Chichon and the largest El-Nino event this
century. However, the values of total column ozone recovered in 1984, only to
decrease significantly in 1985.
77
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Trend estimates have also been made for the altitude profile of ozone
from the network of stations using the Umkehr technique. Deriving an accurate
trend for changes in the vertical distribution of ozone is more difficult than
for the total column because there are fewer stations and the Umkehr measure-
ments are very sensitive to the presence of aerosols in the atmosphere.
Recent volcanic eruptions, such as that of El-Chichon, have deposited large
quantities of aerosols into the stratosphere, and thus the Umkehr data must be
corrected. After correcting the derived ozone amounts for the aerosol inter-
ference, an estimate of the ozone trend in the middle and upper stratosphere
(30-40 km) gives a 2% to 3% decrease for the period 1970-80. The magnitude of
the change is broadly consistent with the predictions of photochemical models,
which predict that chlorine will have its maximum effect at this altitude.
A recent preliminary analysis of Nimbus 7 satellite Solar Backscatter
Ultra-Violet (SBUV) data has indicated that there has been a statistically
significant change in both the total column content (a decrease) and the
vertical distribution (a decrease in the middle and upper stratosphere) of
atmospheric ozone between 1978 and 1984. Further analysis of the data
indicates that most of the change has occurred since 1981. It is crucial to
evaluate whether the decrease is due to natural causes, such as a decrease in
solar radiation, the 1982 eruption of El-Chichon, or the 1982 El-Nino event,
or whether it is due to human activities such as the use of chlorofluoro-
carbons. At this time, any of these explanations are plausible.
Important new observational evidence on ozone changes has recently been
obtained. Data from a single Dobson instrument at Halley Bay 76°S, 27°W has
indicated a considerable decrease (greater than 40$) in the total column
content of ozone above Antarctica during the spring period (late August to
early November) since 1957, with most of the decrease occurring since the mid-
1970s. Satellite measurements using both the Nimbus 7 Total Ozone Monitoring
System (TOMS) and the SBUV instruments have verified this trend over
Antarctica since 1979 and have demonstrated the spatial and temporal
variations in this feature. Plate 1 shows the decrease in the monthly mean
concentrations of the column amount of ozone over Antarctica in the month of
October from 1979 to 1985. Similar ozone changes are not observed over the
Arctic. Satellite measurements of the vertical distribution of ozone,
nitrogen dioxide, water vapor, and aerosols over Antarctica during the 1985
spring period have been obtained using the Stratospheric Aerosol and Gas
Experiment (SAGE), which was launched in 1984 on the Earth Radiation Budget
Satellite (ERBS). This data is now being analyzed and interpreted. It is not
yet evident whether the behavior of ozone above Antarctica is an early warning
of future changes in global ozone or whether it will always be confined to the
Antarctic because of the special geophysical conditions that exist there.
While it has been suggested that these Antarctic ozone decreases are caused by
increasing concentrations of chlorine in the stratosphere, no credible
mechanism has been demonstrated—since the models using present chemical
schemes are unable to simulate this effect. Until the processes responsible
for the decrease in spring-time Antarctic ozone are understood, it will not
be possible to state with any certainty whether it is- a precursor of a global
trend. A number of theories, some chemical, others dynamical, have been
advanced to explain these observations. A major field measurement has been
planned to take place in 1986 to study the ozone layer above Antarctica. This
campaign is being cosponsored and coordinated by NASA, the National Science
78
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Foundation, the National Oceanic and Atmospheric Administration (NOAA), and
the Chemical Manufacturers Associations (CMA).
MODEL RELIABILITY
There are now observations of increases in the atmospheric concentrations
of the gases predicted to affect ozone, and there are observations indicating
that the total column content of ozone has changed significantly on a regional
and, possibly, global scale. In addition, there are indications that the
vertical distribution of ozone may also have changed. The question still
remains concerning the reliability of the model used to predict ozone
change. Given that we cannot directly test the accuracy of a prediction of
the future state of the atmosphere, including the distribution of atmospheric
ozone, we must test the models by trying to simulate the present atmosphere
(including the distribution of atmospheric ozone) or by trying to simulate the
evolution of the atmosphere, in particular ozone, over the past few years.
This is done by comparing model predictions with atmospheric observations.
We should note that nearly all the key chemical constituents that are
predicted to be present in the atmosphere (and that are important in ozone
photochemistry) have now been observed. In general, the models predict the
distribution of the chemical constituents quite well. However, the
measurements are not adequate for critically testing the reliability of the
photochemical models. Close examination of the intercomparison of
measurements and model simulations of the present atmosphere reveal several
disturbing disagreements. One of the major disagreements appears to be that
modelled ozone concentrations are typically 30% to 50% lower than measured
ozone concentrations in the upper stratosphere—where it should be easiest to
predict the concentration of ozone (Figure 7) and where chlorine is predicted
to have its maximum effect. These types of disagreements limit our confidence
in the predictive capability of these models.
In the end, our predictive capability will be tested by measuring the
changes taking place in the atmosphere. This will require careful measure-
ments of critical species to be carried out over long time periods (i.e.,
decades). NASA, NOAA, and the Chemical Manufacturers Association recently
cosponsored a workshop to design an "Early Detection of Stratospheric Change"
system. This system would be designed primarily to provide the earliest
possible detection of changes in the chemical and physical structure of the
stratosphere, and the means to understand them. Implementation of such a
system is a high priority.
CLIMATE CHANGE
As stated earlier, the observed increase in atmospheric concentrations of
the CFCs, CH|j, COp, and N20 also have direct implications for the earth's
radiative balance through the so-called greenhouse effect. These gases absorb
infrared radiation in a part of the spectrum for which the atmosphere is
otherwise transparent. Presently, and in the near future, changes in the
concentrations of trace gases other than COp are thought to be contributing to
the greenhouse warming of the earth's surface and lower atmosphere by an
amount that is about equal to that due to changes in the concentration of COp
(Figure 8). The cumulative effect of the increase in all trace gases for the
period 1850-1980 is a predicted equilibrium warming (ignoring the heat
79
-------
0.8
UJ
-------
o
0.08
0 04
DECADAL INCREMENTS OF GREEENHOUSE FORCING
03
CFCs,
str.
H20
CFCs,
str.
ppm
1850-1960
(PER DECADE)
03
CFCs,
str
H20
• • • J + * •
F,2
CH4
N20
C02
128
ppm
it-
CH4
F"
- lN20
C02
15.6
ppm
03
CFCs,
str
H20
F,2
N2O
CH4
1960's
1970's
1980's
o
<
0.20
0.16
0.12
0.08
0.04
CO2
17.7
ppm
DECADAL INCREMENTS OF GREEENHOUSE FORCING
(1990-2030)
CFCs,
str.
H20
• • • m • • •
F,,
F,2
N20
CH4
CO2
20.6
ppm
03
CFCs,
str.
N2O
CH4
C02
23.9
ppm
03
CFCs,
str
H2O
F,,
F,2
W20
CH4
CO2
27.8
ppm
03
CFCs
str.
H2O
F,,
F,2
N20
CH4
1990's
2000's
2010's
2020's
Figure 8. Decadal additions to global mean greenhouse forcing of the
climate system. AT0 is the computed temperature change at equilibrium
(t -MO ) for the estimated decadal increases in trace gas abundances, with no
climate feedbacks included.
81
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capacity of the oceans) in the range of 0.7°-2.0°C, about half of which
should have occurred to date. Model calculations indicate that the greenhouse
warming predicted to occur during the next 50 years should be about twice that
which has occurred during the previous 130 years. Thus, problems of ozone
change and climate change should be considered together. It is also apparent
that what has been previously thought of as the COp/climate problem should
more properly be thought of as the trace gas/chemistry/climate problem.
SUMMARY
Given what we know about the ozone and trace gas/chemistry/climate
problem, we should recognize that we are conducting a global-scale experiment
on the earth's atmosphere without fully understanding the consequences.
Significant progress has been made in our understanding of the physical and
chemical processes that control the distribution of atmospheric ozone.
However, we must recognize that significant uncertainties in our knowledge
remain, and that these can only be resolved through a vigorous program of
research. It is essential that the U.S. government and industry continue
their strong commitment to study the earth's atmosphere, and that the
scientific agencies continue their close collaboration at both the national
and international level.
82
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Ozone Perturbations Due to Increases
in N2O, CH4, and Chlorocarbons:
Two-Dimensional Time-
Dependent Calculations
Frode Stordal and Ivar SA Isaksen
Institute of Geophysics
Binbern, Oslo, Norway
ABSTRACT
Time-dependent ozone perturbation estimates are performed in a 2-D
diabatic circulation model with ozone photochemistry. Future increases in the
emissions of NpO, CH^, and the Chlorocarbons CFCl^, CFpCl2, CHC1F2, C2Cl^^,
CHqCClo, and Culj, are considered. The altitude variation of the calculated
ozone change in the upper stratosphere is within the uncertainty limits of the
observed trend reported from Umkehr data for the period 1970-80 when the
effect of temperature changes from COp is included. Future ozone predictions
consider only the photochemical response to source gas increases. For the
integrations through the year 2030, four different emission scenarios for
chlorine releases have been used. The average global ozone column would be
reduced by 6.5% in the year 2030 compared to the 1960 level, if chlorine
emissions are increased by 3.0%/yr and the concentrations of N20 and CHn
increase by 0.25 and 1.0/S/yr, respectively.
In a case with low chlorocarbon emissions and a modest reduction in the
total ozone column, the altitude profile is highly distorted. In addition,
the latitude gradients are pronounced. If all the chlorocarbon emissions are
stopped in the year 2000, a minimum in the total ozone column density would be
reduced at different times at low and high latitudes. Although the average
total global density would decrease for almost 10 years, the minimum would be
reached after only 5 years at high latitudes where the depletion in total
ozone would be largest. Accelerated ozone depletion would occur approximately
when the total chlorine exceeds the amount of nitrogen in the stratosphere.
This situation would not occur before the year 2030 in any of the model runs
with the scenarios selected here. Ozone predictions were performed for an
additional period of 50 years for the chlorocarbon scenario with the highest
emissions. In this case, nonlinear growth in ozone depletion was projected to
occur after the middle of the next century.
83
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INTRODUCTION
Possible modifications of stratospheric ozone have attracted considerable
interest in the last decade. Increased concentrations of stratospheric
chlorine from industrial emissions of chlorocarbons, as well as increased
levels of nitrogen accompanying an observed increase in the concentration of
nitrous oxide (^0), have the potential to significantly deplete ozone. An
increase in C02 and other radiatively active trace gases that lead to lower
temperatures in the stratosphere will have the opposite effect through a
decrease in ozone destruction. Enhanced ozone production is believed to take
place in the troposphere due to the observed increase in methane (CHh).
A number of ozone perturbation experiments have been performed using two-
dimensional (2-D) computer models (Brasseur and Bertion 1978; Vupputuri 1979;
Borucki et al. 1980; Haigh and Pyle 1982; Gidel, Crutzen, and Fishman 1983;
Whitten, Bourucki, and Woodward 1983; Haigh 1984; Solomon, Garcia, and Stordal
1985). In a recent study (Isaksen and Stordal 1986) we used the present 2-D
diabatic circulation model for steady-state ozone perturbation studies.
Perturbations due to increases in CHh and NpO, as well as a wide range of
chlorine levels were investigated. The main features in the distribution of
ozone changes were similar to those obtained by the models of Garcia and
Solomon (1983), Solomon and Garcia (1984), and Ko et al. (1985), as presented
in the National Aeronautics and Space Administration/World Meteorological
Organization (NASA/WHO) (1986) compilation. This is not surprising since the
transport representation is similar in the model (as discussed in NASA
1986). It deviates from most 2-D models using the Eulerian transport
formulation with higher diffusion (e.g., Gidel et al. 1983) in important
ways. For instance, a more pronounced latitudinal gradient in the chlorine-
induced reductions of the total ozone column is predicted when the diabatic
circulation and slow diffusion are used for tracer transport. All the above
calculations are based on steady-state assumptions. Time-dependent long-time
simulations have so far been confined to one-dimensional (1-D) models.
In this paper, a set of 2-D time-dependent experiments is described, to
our knowledge the first reported since the experiment of Vupputuri (1979). He
calculated ozone changes through the year 2015 under the assumption of
constant releases of chlorofluoromethanes at 1975 levels. Our understanding
of the photochemistry of the stratosphere has increased considerably over the
last few years, leading to ozone-perturbation estimates that differ
considerably from what Vupputuri obtained. Besides offering a more realistic
tracer transport than 1-D models, 2-D models employ predictions of future
ozone variations at specific latitudes. When the time history of the future
ozone distribution is considered, the difference in latitudinal response is a
main concern since the ozone depletion has been shown to increase
significantly from lower to higher latitudes. As discussed in Stordal,
Isaksen, and Horntveth (1985), the model gives a credible description of the
distributions and lifetimes of long-lived gases, such as Oo, NpO, CHh, CFpClp,
CFC13, and CCljj.
A set of scenarios of the future evolution of some source gases has been
selected for the present study. It has been necessary to restrict the number
of cases. Four different scenarios for the chlorocarbons have been selected
in combination with increases in NpO and CHh. The source gas scenarios
adopted are presented in the Ozone Loss Mechanisms section. As the observed
84
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CHh increase is not well understood, it is far from certain that the present
rate of increase (1% per year) will continue over the time period considered
in these calculations. One of the experiments has therefore been performed
with future CH^ constant at the 1980 level, making a total of five scenarios
that have been selected for model simulations for the time period 1980-2030.
The reference year for the model study is 1960, when the time-dependent
calculations were started.
The present model extends from the surface to 50 km altitude, and
includes the photochemistry of oxygen, hydrogen, nitrogen, and chlorine
compounds. The distribution of ozone-loss rates due to each of these chemical
families is important for the response in ozone to changes in the chemical
composition of the stratosphere. Photochemical terms for the long-lived
tracers are calculated four times a year when fully diurnal computations are
undertaken. The photochemical data have been updated in accordance with the
latest NASA/Jet Propulsion Laboratory (JPL) (1985) recommendations. In the
discussion on ozone balance in the Ozone Loss Mechanisms section, latitudinal
as well as altitudinal variations in the influence of each of the main ozone
loss cycles are demonstrated.
In the middle and lower statosphere, nitrogen species are believed to
contribute largely to the loss of ozone. In our previous study we also
demonstrated that nitrogen compounds have a strong influence on the efficiency
of ozone depletion due to chlorine increases (Isaksen and Stordal 1986). In
light of reports that 2-D diabatic circulation models tend to underestimate
the amount of odd nitrogen present in the lower stratosphere (NASA/WHO 1986;
Ko et al. 1986), we have included a discussion of how well nitrogen is
distributed in the lower stratosphere in the Ozone Loss Mechanisms section.
In the section on the trend in ozone for the period 1970-80, we compare
estimated changes in upper tropospheric ozone as compared to the observed
decadal trend in ozone in the period 1970-80, as reported in NASA/WHO
(1986). Estimated changes in ozone during the decade based on Umkehr
measurements at thirteen observational locations were reported.
Results describing the future evolution of the tropospheric and
stratospheric ozone are described in the section titled Time-Dependent Future
Ozone Experiments. Figures showing the globally and seasonally averaged total
column, latitudinal and yearly variation of the ozone columns, as well as
altitudinal distributions are presented. For some of the scenarios, the
effects of a cease of reductions in chlorine reductions are demonstrated (see
the section on the response in ozone to future regulations in chlorine
releases), which could offer useful information with respect to future
emission control.
All ozone predictions presented in this study represent the photochemical
response to source gas increases except upper stratospheric depletion between
1970 and 1980, which includes cooling effects from (X>2. Feedback from changes
in temperatures and tracer transport have not been considered.
85
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SOURCE GAS SCENARIOS
Chlorocarbons
Observations show that the concentrations of several halocarbons in the
atmosphere are increasing. In an extensive measurement program (Atmospheric
Lifetime Experiment [ALE]), the concentrations of CFClo, CF2C12, CCljj, and
CHoCClo have been monitored at five coastal or island stations exposed to
little polluted air (Prinn et al. 1983a). A steady increase in these
components has been reported at all locations during the observational period
1978-81.
The Chlorocarbons included in the present study are methyl chlorine
(CHoCl), carbon tetrachloride (CClh), methyl chloroform (CHoCClo), and the
chlorofluorocarbons F11-CFC13, F12-CF2C12, F22-CHClFp, and Fl13-C2Clo_F3.
These compounds are believed to be the main sources of future stratospheric
chlorine. The source for these gases (except CH^Cl) is industrial releases.
As the residence times are of the order of 50-100 years (see Stordal, Isaksen,
and Horntveth 1985), except CHoCClo which has a residence time of about 10
years, the present increases are due to past as well as present emissions.
Release rates of Chlorocarbons for the period 1960-80 are taken from:
Cunnold et al. (1983b, CFClo); Cunnold et al. (1983b, CFpCl2); Prinn et al.
(1983b, CHoCClo); and Simmonds et al. (1983, CC1). The atmosphere was
assumed to initially (1960) contain 0.6 ppb of CHoCl and 0.1 ppb of CCl^,
resulting in a 1 ppb in content of stratospheric chlorine. The CHoCl surface
flux needed to obtain the 1960 mixing ratio was kept constant in all the
computations. For CFClo, CFpClp, and CHoCClo, the integrations were started
in 1960 with zero abundances and releases corresponding to amounts accumulated
in the years prior to 1960, which is a reasonable assumption since the
releases were small before 1960.
Scenarios for future industrial releases are necessarily uncertain. We
have performed experiments with four different chlorocarbon scenarios, listed
in Table 1 . Our computations are partly based on the evaluation of Quinn et
al. (1986) from whom we have adopted emissions for CFClo, CF2C12, CHClFp,
C2CloFo, CCljj, and CHoCClo in the period 1985-2030. Based on economic models
that consider industrial usage, competitive products, and economic and
population growth, they developed seven scenarios for the Chlorocarbons. In
our scenario C we have used emission rates between the values in their two
highest scenarios (VI and VII). As can be deduced from Table 2, the releases
of the largest contributions to stratospheric chlorine, CF2C12 and CFClo, are
projected to increase 3.5$ and 5% per year, respectively, until the year
2000. Thereafter the growth rate declines and reaches 2% per year by the end
of the period for both gases. Our scenario D is chosen to be identical to
their scenario II. In this scenario the reduction in emission growth starts
earlier (in the year 1990). By the end of the period in question, the growth
is 1% per year for CFpClp and CFClo. We have also included one scenario with
constant emissions at 198T) levels (scenario A) as well as one with a steady 3%
yearly increase in emissions after 1980 (scenario B). C2CloF3 is not
explicitly represented in the model. The release of this compound is added to
the releases of CFpCl2 (on a Cl base) since the two gases have similar
photochemical characteristics (NASA/JPL 1985). Table 2 demonstrates that the
releases of CpCloFo are modest compared to the CF2C12 releases.
86
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Table 1. Source Gas Scenarios 1980-2030
N20
CHJ(
0.25$/yr increase in the period.
Either 1.0%/yr increase or constant surface mixing
ratio at 1980 level.
Chlorinated source gas emission (10^/yr)
SCENARIO A: Constant releases 1980 level
CFC13
CF2CI2
CHF2C1
CHqCCl:
265
485
82
504
60
SCENARIO B: A 3$/yr increase in the emissions, starting with the
values of scenario A in 1980
SCENARIO C: Emission rates between the values of scenarios VI and
VII in Quinn et al. (1986)
Year
1985
1990
1995
2000
2010
2020
2030
2040
2050
2060
2070
2075
CFC13
325.4
427.6
553.4
716.6
1024.5
1332.5
1637.0
2006.4
2467.6
2936.8
3439.9
3711.1
CF2C12
449.3
528.5
624.9
745.8
994.8
1266.0
1564.1
1919.2
2341.8
2770.4
3226.0
3472.3
CHF2C1 C
52.9
90.8
130.2
176.8
284.1
407.4
543.0
732.7
918.7
1115.5
1310.0
1408.2
2F3C13 c
114.0
142.0
198.2
277.0
334.4
403.6
484.1
573.0
683.0
808.4
956.8
1033.0
:H3cci3
509.7
568.6
634.3
707.5
854.0
1030.9
1235.4
1472.9
1743.4
2063.5
2442.4
2637.6
cci4
153.1
187.7
205.7
225.9
272.6
329.2
382.2
446.8
523.7
613.8
719.4
784.1
SCENARIO D: Emission rates as in scenario II in Quinn et al. (1986)
Year
1985
1990
1995
2000
2010
2020
2030
CFC13
323
421
476
522
594
656
725
.5
.8
.2
.0
.1
.8
.3
CF2C12
446
519
572
611
683
762
852
.1
.3
.7
.0
.2
.7
.7
CHF2C1
57
74
92
111
139
156
172
.3
.5
.4
.3
.2
.6
.1
C2F3C13
114
142
157
180
217
262
317
.0
.0
.0
.0
.5
.9
.7
CH3CC13
509
568
634
707
854
1020
1235
.7
.6
.3
.5
.0
.9
.4
cci4
41.0
41.0
45.0
49.4
58.8
70.1
83.5
87
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Table 2. Source Gas Scenarios 1960-80
N20 : 1980 level 305 ppb, 0.2%/yr increase in the period.
CHjj : 1980 level 1.70 ppm, 1.1$/yr increase in the period.
CHoCl : 1960 level 0.6 ppb, constant surface boundary flux.
Emissions for Chlorine Source Gases Taken From:
: Cunnold et al. (1983a)
: Cunnold et al. (1983b)
. U: Prinn et al. (1983b)
CCI4 : Simmonds et al. (1983)
Chlorocarbons decompose in the stratosphere, where chlorine (Cl) and
chlorine monoxide (CIO) radicals catalytically destroy ozone. Reductions of
the stratospheric ozone layer is therefore presumed to accompany a continued
growth in the chlorocarbon release rates.
Nitrous Oxide
The atmospheric concentrations of nitrous oxide are increasing (e.g.,
Weiss 1981; Khalil and Rasmussen 1983). Natural as well as anthropogenic
sources have been identified. The two main anthropogenic sources are
fertilizers (Crutzen 1974; Logan et al. 1978) and combustion processes (Weiss
and Craig 1976; Pierotti and Rasmussen 1976).
Weiss (1981) observed an increase of about 0.2% per year in the four-year
period 1976-80 and suggested that this increase was due to increasing
anthropogenic releases. In the present study this growth has been adopted for
the entire period 1960-80 (Table 2). Isaksen and Stordal (1986) argued that
the anthropogenic releases constitute only a small fraction of the total N20
source at present. In the future the anthropogenic fraction can be expected
to increase markedly and also play a more significant role in the total N20
budget, causing an accelerated growth in NpO. Despite this speculation, we
take a more conservative approach; a yearly growth of 0.25% is assumed for
future NpO releases in accordance with the recommendation of Quinn et al.
(1986).
NpO has a long atmospheric lifetime (about 150 years, see discussion in
Stordal, Isaksen, and Horntveth 1985) as the loss processes in the troposphere
are very slow. In the stratosphere, NpO decomposes, and is partly converted
to oxides of nitrogen (NO ) which catalytically destroy ozone. Future
increases in nitrous oxide will therefore be associated with ozone reductions
in the stratosphere.
The efficiency of stratospheric chlorine in reducing the atmospheric
ozone layer depends strongly on the level of stratospheric NOX through various
interactions between the NOX and Clx chemistry. N20 increases will therefore
also influence the ozone reduction due to the presence of Clx in the
-------
stratosphere. The rates at which chlorocarbons and nitrous oxide are assumed
to increase in combined scenario experiments thus play an important role in
the estimation of future ozone depletion.
Methane
Atmospheric measurements have clearly established that the concentration
of methane is increasing (Rasmussen and Khalil 1981; Blake et al. 1982; Khalil
and Rasmussen 1982; Ehhalt, Zander, and Lamontagne 1983). Since 1979, methane
data have been obtained from at least six measuring sites, including the
continuous record from the Cape Meares Region (Khalil and Rasmussen 1983).
After an increase of about 1.8$ per year in the period 1979-82, a temporary
decline in methane was obtained at this station. This feature was associated
with an El Nino Southern Oscillation phenomenon (Khalil and Rasmussen 1985)
and reduced the average trend in the period 1979-84 to about 1.0% per year.
The increase in methane prior to about 1979 is more uncertain. From the
period after 1965 values from 0.5% per year (Ehhalt, Zander, and Lamontagne
1983) to 1.7$ per year (Rasmussen and Khalil 1981) have been reported. In
this study we used an annual increase of 1.1$ for the period 1960-80 (see
Table 2).
Our understanding of the global methane budget is still insufficient. An
extensive review of the present knowledge is presented in NASA/WHO (1986).
The total sink is estimated to be approximately 450 TG/year (Isaksen and Hov
1986), due to the loss through reaction with the hydroxyl radical in the
troposphere. Total production of methane should be approximately the same; it
is commonly thought that there is a balance between total production and loss
of methane in the atmosphere. The relative strength of each source is,
however, highly uncertain (Ehhalt and Schmidt 1978; Khalil and Rasmussen 1983;
Seller 1984). The latitudinal distribution of these sources is also poorly
known. It is therefore difficult to explain the current rise in methane, and
predicting future evolution of methane concentrations in the atmosphere is
highly uncertain. We have chosen here to assume a future annual increase of
1.0$ (Quinn et al. 1986) in most of the scenarios, but we have also included a
scenario with constant level of CHj, in the future (see Table 1).
Through methane's interaction with tropospheric chemistry, increases in
emissions will lead to increased ozone concentration in this region of the
atmosphere. Methane also plays an important role in the partitioning between
the chlorine constituent Cl, CIO, and HC1 in the stratosphere. Future methane
changes will therefore also affect chlorine species in the stratosphere and
thereby the depletion of ozone through these species.
OZONE LOSS MECHANISMS
Chemical loss of ozone in the stratosphere is characterized by the
efficiency of chemical cycles involving nitrogen, hydrogen, chlorine, and
oxygen species. To avoid the strong coupling between the individual
components, particularly among the oxygen and nitrogen species, but also in
the chlorine cycles at the enhanced levels expected to appear in the future,
we introduce an odd oxygen family quantity: Ov = 0Q + 0 + 0('D) - NO - Cl.
x j
The rationale for introducing such a numerical quantity is thoroughly
discussed by Hesstvedt and Isaksen (1978) where it was applied to air
89
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pollution modeling to avoid stiffness in the oxygen-hydrogen-nitrogen
system. In our previous studies on stratospheric chemistry (Stordal 1983;
Stordal, Isaksen, and Horntveth 1985; Isaksen and Stordal 1986), chlorine was
added to the quantity, strongly improving the stiffness problem (and thereby
allowing for longer time steps to be used in the chemical calculations). We
have considered the following loss reactions in the oxygen, hydrogen,
nitrogen, and chlorine cycles (the parenthesized number to the left-hand side
of the reaction denotes the number of CL molecules destroyed in the reaction):
X
R1 Oxygen: (2) 0 + 0^ -»• 02 + 02
R2 Hydrogen: (1) OH + Oo •* H02 + 02
R3 (1) H02 + 0^ * OH + 02
R4 (1) OH + 0 -. H + 02
R5 (1) H02 + 0 + OH + 02
R6 Nitrogen: (2) N02 + 0 -»• NO + 02
R7 Chlorine: (2) CIO + 0 * Cl + 02
In our previous paper (Figure 3 in Isaksen and Stordal 1986) we demon-
strated the strong variations with height in the relative importance of the
different chemical families. There are also some marked latitudinal
variations in their relative importances, which are demonstrated in Figures
1a-d, where the relative loss of ozone from the oxygen, hydrogen, nitrogen and
chlorine families is given as a function of latitude and height. Most
important are the latitudinal differences in ozone destruction by the nitrogen
and the chlorine reactions, particularly because the concentrations of these
two families probably will increase noticeably in the future. The figures
represent the situation in 1980 when the chlorine content of the stratosphere
still was low (about 2.3 ppb). Nevertheless it is seen that chlorine
reactions become increasingly important going toward high latitudes, where
they dominate upper stratospheric ozone loss in the present atmosphere (Figure
1d). Ozone loss by nitrogen species is systematically moved to lower
latitudes as we proceed toward high latitudes. This will be of importance,
not only for the response in ozone concentrations to increased levels of NO
or Clx, but also to the latitudinal response in ozone due to simultaneous
changes in NOX and Clx (combined scenario studies). The efficiency of the
chlorine cycle at high latitudes with these moderate Clx levels explains the
fast, high-latitude response in upper stratospheric ozone and in total ozone
to chlorocarbon perturbation that is discussed in this paper. It seems
reasonable in this early state of ozone depletion, before chlorine reactions
are the dominant loss process at low latitude, that the differences in
depletions are largest at high and low latitudes.
The importance of the NOX chemistry for the ozone loss in the middle and
lower troposphere is clearly demonstrated in Figure 1c. In addition, NO
plays a significant role for chlorine-induced ozone depletion through
interaction with- the chlorine chemistry (Isaksen and Stordal 1986). Ozone
perturbation studies from chlorocarbon releases rely heavily on a proper
representation of NO levels in the models used. Unfortunately, 2-D diabatic
circulation models tend to underestimate NO (total odd nitrogen) levels in
the lower stratosphere in equatorial regions compared to observations
(NASA/WMO 1986). At higher latitudes and altitudes the agreement is better.
90
-------
Ko et al. (1986) suggest that the discrepancy between observed and 2-D model
calculated NO values can be removed by taking into account NO production by
lightning. This production is efficient in the upper troposphere in
equatorial regions, where a significant amount (compared to the stratospheric
N0y production from NpO) can be transported up through the troposphere by the
process of diabatic circulation applied in these 2-D models.
The NO distribution in the actual area is very sensitive, for instance,
to the horizontal eddy diffusion coefficients applied in the model at this low
latitude region in the lower stratosphere. Our 2-D diabatic circulation model
tends to give NO levels in better agreement with observations even without a
lightning source.
In Figure 2 we have taken one of Ko et al.'s figures showing the NO
profiles at the Equator from their model along with observations presented by
Callis, Natarajan, and Russell (1985) and included the NOV profile from our
model. In contrast to the model of Ko et al. (1986), our mcrael underestimates
NOV only at very low latitudes. At the important 25-km level there is a very
good agreement between our model and the measurements. The figure shows that
there is in general a higher NO level in our model than in the model of Ko et
al. (1986). The discrepancy between the models increases toward lower
altitudes in the lower stratosphere. This is at least partly due to a balance
between vertical advection and horizontal diffusion which is more in favor of
the latter process in our model than in theirs.
TREND IN OZONE FOR THE PERIOD 1970-80
Trend estimates based on thirteen Umkehr stations indicate that there has
been a statistically significant reduction in ozone between 1970 and 1980 in
the upper stratosphere between approximately 30 and 40 km. This reduction is
estimated to be on the order of 0.2^-0.3/5 per year (NASA 1986), and is most
pronounced in the height regions where the chlorine chemistry has its strong-
est effect on the ozone (Figure 1d).
Although the Umkehr data are hampered by large uncertainties—the result
is particularly sensitive to the corrections made for the aerosol burden in
the stratosphere—they nevertheless represent important indications that
chlorine-induced perturbations can be detected in the stratosphere. For this
reason it is very important to compare the estimated ozone trends based on
observations with model-calculated ozone depletion for the same period.
Figure 3 shows height profiles at 40°N for the decadal depletion from our
2-D model studies. Global trend estimates reported in (NASA/WHO 1986) are
also given in the figure. Estimates with temperature feedback (curve 1) give
upper stratospheric ozone depletion larger than what is deduced from Umkehr
observations. We have, however, also done one model study where we include
temperature changes between 1979 and 1980. The stratospheric temperature
decrease adapted for this period is taken from one-dimensional model studies
by Brasseur, DeRudder, and Tricot (1985). Their calculations are based on a
combined scenario, where temperature decreases in the 1970-80 period are a
result of increases in COp and other trace species. We have assumed that
approximately one-third of the estimated change up to 1983 given by Brasseur,
DeRudder, and Trico (1985) takes place between 1970 and 1980. This gives
temperature decreases of approximately 1°C in the 45-50 km region and less
91
-------
ox
, 198O
•is .
-IB .
26 .
to .
•43-
i~eo . -so
-20 . O . 20 .
LfVTITUDE
SERSON= 2
60 ,
HOX
2S .
-BO
198O
SERSON= 2
-2O . O . 20
LRTITUOE
-»O . 8O . 80
Figure 1. Percentage ozone loss rates due to 0 , HOX, NOX and C10X
chemical cycles, relative to the total loss rates. Results are given as
altitude-latitude contours for near equinox conditions.
-------
NOX
•is
as .
198O
SERSON= 2
«~i-ao. —ao. -to.
-20 . O . 20 ,
LATITUDE
to. so. eo
CLOX
1980
SEflSON= 2
•49 .
«-!_eo. -so,
Figure 1 (Cont).
following reactions:
-tO. -2O. O. 20. to. BO. 80.
LflTJTUOE
The individual loss rates are computed from the
o
NO
Cl
x "
«,i
0
OH
HO
OH
HO
NO
Cl
2
2
8
+ Oo
+ Oo
+ 0
+ 0
+ 0
+ 0
->•
-»•
-»•
->•
-»•
-»•
->•
H§p
OH
H
OH
NO
Cl
+
+
-t-
+
+
+
0
0
2
0
0
0
2
2
°2
2
2
2
9
(times
(times
(times
2)
2)
2)
93
-------
50
45
J40
t30
<25
20
15
» I • i •ii
I
- EQUATOR
/ . . .....I . . I
'.] \ 10 30
MIXING RATIO (ppbv)
Figure 2. Comparison of the calculated NO profile at Equator in this
model (curve 1) and the model of Ko et al. (1986) (curve 2) with the observed
nighttime concentration of NOP+HNO? (Callis et al., 1985; LIMS-data) (curve
3).
MB
1-2
2-4
4-8
8-16
16-32
-8 -6 -4 -2 0
DECADAL OZONE CHANGES
Figure 3. Calculated ozone depletion between 1970 and 1980 without
(curve 1) and with (curve 2) temperature changes from radiatively active gases
in the stratosphere. The adapted temperature change- is taken from a 1-D model
study by Brasseur, DeRudder, and Tricot (1985). Estimated global trends
(Reinsel et al. 1983; Reinsel et al. 1984) are based on Umkehr data (triangles
with error bars). A one-dimensional model calculation by Wuebbles, Luther,
and Penner (1983) is included.
-------
than 1°C below 35 km. When the temperature feedback is considered (curve 2),
ozone depletion becomes approximately two-thirds of the estimated depletion
when no temperature effect is considered.
The calculated profile is in, better agreement with the result of the
trend analysis when temperature effects are considered. However, almost twice
as much depletion in the maximum area at high latitudes takes place than at
low latitudes. Comparisons with observations are therefore strongly dependent
on how representative the Umkehr observations are for mid-latitudes in the
Northern Hemisphere (40°N).
The temperature effect from CCU is estimated to be more pronounced at low
than at high latitudes, thus increasing the latitudinal differences in ozone
depletion when temperature feedback is included. The reason is that nitrogen
reactions that dominate ozone loss at low latitudes become less efficient at
lower temperatures (Isaksen, Hesstevdt, and Stordal 1980), while this is not
the case for chlorine reactions that dominate at high latitudes (see Figure
Temperature changes will have a pronounced effect on the trend in total
ozone as shown in Table 3. Global ozone decrease between 1970 and 1980 is
reduced from 0.62% to 0.22$ when temperature feedback is included. If the
observed methane increase is included there is even a slight increase (+0.03$)
in the total column of ozone. At high latitudes (60°N) the depletion is
pronounced in all three model studies discussed above.
Table 3. Time-dependent 2-D model calculations of ozone column
depletion between 1970 and 1980. The numbers are for March and are
given in %.
Global
60° N
-0.62
-1.84
-0.21
-1.13
+0.03
-0.88
case 1. Without temperature feedback and constant CHn release.
case 2. With temperature feedback and constant CHh release.
case 3. With temperature feedback and 2% annual increase in CHh
releases.
TIME-DEPENDENT FUTURE OZONE EXPERIMENTS
The distribution of ozone at three different points of time, the years
1980, 2000, and 2020, will be used to illustrate some main features in the
development of ozone changes. Figures 4a-4f show the change in the total
ozone column as a function of latitude and time of the year. The depicted
changes result from a model run with a chlorine increase as assumed in
scenario C. Simultaneous increases in N^O and CHn (see Tables 1 and 2) are
assumed. The figures also show latituae-altitude cross sections for the
solstices (Northern Hemisphere winter) in the same years. The latitudinal,
altitudinal, and yearly patterns are similar to those obtained in the steady-
95
-------
state ozone calculations reported earlier with this (Isaksen and Stordal 1986)
and other 2-D models (especially the diabatic type models, WASA/WMO 1986):
Ozone reductions take place in the middle and upper stratosphere as a result
of chlorine chemistry (Figure 4d). The balance between active chlorine
compounds (Cl and CIO), and the inactive compound HC1 is shifted toward higher
values of Cl and CIO. This is due to low CH^ mixing ratios resulting from
downward transport (Cl+CHh -»• HCl+CHo is a main reaction converting active
chlorine to HC1, see Solomon and Garcia 1984; Solomon, Garcia, and Stordal
1985). The maximum reductions are 15$, 40$, and 65% in the years 1980, 2000,
and 2020, respectively. In the lower stratosphere at low and middle
latitudes, increased penetration of UV radiation, resulting in the so-called
self-heating effect, leads to increased levels of ozone. The growth in
methane leads to increases in ozone in the entire troposphere, with maximum
increases in the upper tropical troposphere. The model predicts a steady
increase from 5% to 20$ between the years 1980 and 2020.
In the lower stratosphere, where ozone is mainly transport-dependent, the
isolines for constant percentage change slope poleward and downward due to the
prevailing circulation pattern (see discussion in Solomon, Garcia, and Stordal
1985). This transport feature is the main cause for the marked latitudinal
gradient in changes of the total ozone columns due to increased levels of
chlorine and nitrogen in the stratosphere. Maximum depletions occur at high
latitudes during winter and spring when the poleward and downward transport is
most pronounced.
As Isaksen and Stordal (1986) point out, the latitudinal gradient in
total ozone depletion caused by increases in stratospheric chlorine and
nitrogen is enhanced by the effect of CHj, increases. However, even if the low
latitude ozone columns are only modestly changed, the height distribution of
ozone is highly distorted. These changes are believed to have the potential
for large climatological effects (NASA 1986). In the present (1986)
atmosphere the estimated ozone changes are modest, as discussed in the
section titled Trend in Ozone for the Period 1970-80. The situation may,
however, be quite different already at the turn of the century, when large
depletions in the upper stratosphere are estimated to take place. By that
time, depletion in ozone column densities may exceed 5% at middle and high
latitudes. Toward the year 2020 ozone depletion will continue to grow
strongly, as a result of the pronounced increase in release rates of the
chlorocarbons.
Figure 5 shows the time-dependent depletion in globally and seasonally
averaged total ozone column densities. The curves represent the four chlorine
scenarios (see Table 1). NpO and CHh increases are assumed in all the results
depicted in Figure 5. An ozone reduction of 1$ compared to the 1960 level was
reached between 1980 and 1985. The effect of temperature changes is not
included in the results presented in this and the forthcoming sections. In
the scenario where the chlorine releases are kept constant at 1980 levels, the
ozone continues to deplete to about 2% by 2010. For the rest of the period,
the global ozone is practically unchanged. In the three remaining scenarios
with increasing chlorine releases, ozone columns in the entire period
decrease. At the year 2020 the ozone reductions are 8.5$ in the reference
case, 5.0$ in the low scenario, and 6.5$ in the case with 3$ annual increases
in chlorine emissions. All values refer to average global reductions. These
values can be compared to the time-dependent, 1-D study of Wuebbles (1983)
96
-------
O3 PERT
198O
-20.
-eo.
---•'-I
-I
-80.,
I . 4O . 4 4 . 42 . 4J
03 PERT
198O
SEOSON= 1
Figure 4. Percentage ozone
changes in the year 1980 (see
scenario Table 2) and the
years 2000 and 2020 in the
chlorine emission reference
case with simultaneous
increases in NpO and CH^ (see
Table 1). Panels a, c , and e
depict changes in the total
ozone columns as a function of
latitude and time of the
year. Panels b, d, and f show
altitude-latitude cross
sections of local ozone
changes for solstice condi-
tions.
'-eo. -eo. -HO. -20.
O3 PERT
2OOO
80.
•O.
*0.
5 30.
•*
O.
-zo.
if
\ \
97
-------
O3 PERT
2OOO
SEOSON= 1
O3 PERT
2020
BO .
SO.
•«o.
ji 20.
o.
-zo.
-•»o.
-so.
a. *.
. a.
Figure 4 (Cont.)
03 PERT
2O2O
SEflSON=
--40 .cr
za.
: « .
-••£,"
-to-
—-.o
'-80. -80. --»0. -ZO .
p-
98
-------
GLOBAL OZONE COLUMN
-10
Chlorine Scenarios A, B, C, D
N2O and CH4 Increase
i i i
0
-1
-2
-3
-4
-5
-6
-7
-8
-9
-10
1960
1970
1980
1990
20OO
2010
2020
2030
TIME
Figure 5. Calculated changes in globally and seasonally averaged
ozone column as a function of time for the four chlorine scenarios
(Table 1). Increases in N20 (0.25%/yr) and CH^ (1$/yr) have been
included.
which has been run for our scenario C (Wuebbles 1986, private communication)
with, as well as without, temperature changes. In the latter case the reduc-
tions are slightly less in his model compared to ours. The time evolution is,
however, very similar in the 1-D and 2-D model runs.
Due to considerable uncertainties in the CHh scenario one experiment was
performed with constant CHj, releases (see the Source Gas Scenarios section).
In this case, ozone is depleted substantially after 1980. In the year 2030,
the reduction in the global ozone column density reaches 4.5% (see also Figure
6).
GLOBAL OZONE COLUMN
-9
Chlorine Scenario A
No Chlorine Releases After 2OOO: A'
70%/Yr Red In Chlorine Rel. After 20OO: A"
N2O Growth
CH4 Constant After 1980
1960
1970
1980
1990
20OO
2010
2030
TIME
Figure 6. As Figure 5. Also included are ozone changes after the
year 2000 when either a cease or annual reduction of 10% per year
in emissions is introduced. CHj, is kept constant after 1980.
99
-------
Figure 4 shows a pronounced latitudinal gradient in the ozone changes.
At high latitudes we also find marked seasonal variations. To illustrate the
latitudinal effect we show time variations of ozone column densities at
different latitudes in the constant chlorine release case (Figure 7). The
spring values have been chosen since the latitudinal gradient is largest at
that time of the year (see Figure 4). Even if the globally and seasonally
averaged ozone column densities show small changes toward the year 2030, the
column densities are still decreasing markedly at high latitudes. For
instance, the reduction in the year 2030 is 8.3% at 60°N latitude and 3.8% at
40°N, while the global average reduction is only 2.0$.
The ozone reductions at 60°M latitude during spring are presented in
Figure 8 for the four chlorine scenarios. In all cases NpO and CHh increases
are assumed. Ozone reductions are more than twice as large as the globally
and seasonally averaged reductions shown in Figure 5. Particularly in the
scenario C case, the springtime ozone reduction is pronounced at 60°N. At
this latitude the ozone column density decreases at a rate of approximately
0.4$ per year in the year 2030. Note that high latitude depletion shows
little dependence on the scenarios chosen up to year 2000. The depletion is
pronounced in all four cases, contrary to what is seen for the global average
reductions (Figure 7).
OZONE COLUMNS SPRING
0
-1
-2
-3
-4
-5
£-6
J -7
-8
-9
-10
-11
-12
Chlorine Scenario A
N2O and CH4 Increase
-1
-2
-3
-4
-5
-6
-7
-8
-9
-10
-11
-12
1960
1970
1980
1990 2OOO
TIME
2010
2020
2030
Figure 7. Changes in total ozone column with time for various
latitudes. The results are for the spring in the case of 1980
level constant chlorine emission and growth in 0 and CH.
100
-------
OZONE COLUMN 60°N SPRING
-2
-4
-6
-8
£
o" ~1
-12
-14
-16 -
-18 -
-20
- -10
Chlorine Scenarios A, B, C, D
N2O and CH4 Increase
- -12
-14
- -16
-18
-20
1960 1970 1980 1990 2000 2010 2020 2030
TIME
Figure 8. As Figure 5, but for the ozone column at 60° during spring.
The most dramatic ozone reduction takes place at high latitudes in the
upper stratosphere (see Figure 4). Figure 9 compares local ozone changes with
time at the 43 km level at 60°N during the winter for different scenarios. In
all cases the ozone reduction is more than 30% by the turn of the century, and
the depletion continues towards the year 2030. The reductions range from 45%
in scenario A to 12% in scenario C.
Based on what has been shown in the previous two figures, it can be
concluded that the ozone depletion at high latitudes in the upper stratosphere
will be pronounced toward the beginning of the next century regardless which
scenario unfolds. This statement applies to total column ozone as well as
local depletion.
Temperatures are expected to change in the future as a result of an
altered distribution of radiatively active gases. Predicted ozone reductions
for the middle and upper stratosphere will lead to temperature reductions, as
will COp and other radiatively active gases that are increasing in the
atmosphere (see, e.g., Ramanathan et al. 1985; NASA/WHO 1986). These
temperature changes will influence the ozone distribution, as we have seen in
Figure 3, leading to smaller ozone reductions from increases in stratospheric
chlorine and nitrogen.
101
-------
LOCAL OZONE 6O°N 43 KM WINTER
-10
-20
I -3°
n
o
-40
-50
-60
-70
Chlorine Scenarios A, B, C, D
N20 and CH4 Increases
-10
-20
-30
-40
-50
-60
-70
1960
1970
1980
1990 2000
TIME
2010
2020
2030
Figure 9. As Figure 5, but for local ozone densities at 60° N at
the 43 km level during winter.
It is also likely that when the stratospheric temperature distribution is
altered, changes in atmospheric circulation will take place, which in turn
will influence the calculated ozone distribution. Ozone is jointly controlled
by dynamical and photochemical processes. Even in regions where the ozone
chemistry is fast, the dynamics can be of importance through the distribution
of other long-lived species. The works of Fels et al. (1980) and Schoeberl
and Strobel (1978), however, indicate a thermal rather than dynamical response
to GO and COp temperature perturbations. Their findings support the approach
taken in this study, where we have used fixed dynamics in all the calcula-
tions. In their study, Fels et al. (1980) assumed uniform perturbations in 0^
and COp, making the application of their results somewhat uncertain for the 0^
perturbations presented in this paper.
RESPONSE IN OZONE TO FUTURE REGULATIONS IN CHLORINE RELEASES
The results presented in this and other studies show that large ozone
depletions, especially at high latitudes (see below), will take place early in
the next century if the chlorine emissions continue to grow. Extended
emission control could then be required. In some experiments we have
therefore studied the effect of reductions in chlorine releases. In Figure 10
the effect of stopping all chlorine releases is demonstrated. In two of the
cases, the constant 1980 level release case (scenario A) and the 3% yearly
emission increase case (scenario B), the emissions are assumed to come to a
halt in the year 2000. (However, NpO and CHh are assumed to continue
increasing.) In both cases the globally and seasonally averaged ozone column
density continues to decrease for 5-10 years. The relatively efficient
recovery of the ozone layer after chlorine releases are stopped is a result of
the continued increase in CHh releases after the year 2000.
102
-------
Figure 6 shows that in the case with a constant CH^ concentration the
recovery of the ozone layer is slower. Obviously the future CHh evolution
will have a pronounced influence on the recovery of the ozone column after a
potential stop in chlorine releases. In the experiment described in Figure
6, constant releases of chlorine source gases have been assumed in the period
1980-2000 (scenario A). If chlorine emissions are stopped in the year 2000,
the ozone would not relax back to the 1960 situation, mainly due to NpO
increases that have been assumed (also after the year 2000). In the period
2020-30 in this experiment, ozone continues to recover in the upper
stratosphere due to decreases in stratospheric chlorine. In the middle and
lower stratosphere there is a weak ozone reduction, mainly attributed to the
NpO growth, compensating for the production in the upper stratosphere such
that the globally averaged total column is almost constant throughout the
period.
So far results of a total removal of chlorine emissions have been
demonstrated. A prompt cease in the emissions at a certain time, as we have
assumed in the year 2000, must be considered unlikely. A gradual reduction of
the emissions could be more conceivable. A scenario with a 1% yearly decrease
in CFC emissions starting in the year 2000 (after constant release from 1980,
scenario A) is therefore included in Figure 6 in the constant CHj, case. This
case is identical to scenario IX in the Organization for Economic Cooperation
and Development (OECD) (1981) report. In the particular case it takes about
15 years to reach a minimum in ozone column densities, and the increase
thereafter is extremely slow, in agreement with the 1-D calculations of
Wuebbles (1983). Thirty years after the implementation of an emission
reduction, the global ozone depletion would be 3.1$, compared to 4.5$ in the
case without emission reductions.
As discussed in the previous section (Figure 7), the ozone column is
projected to decay more rapidly at higher than at lower latitudes.
Correspondingly, when chlorine releases are stopped, the increase will be
faster. This is demonstrated in Figure 11, which shows results from 60°
latitude in the experiments where chlorine releases were halted in the year
2000 (scenario B). In the scenario A and C cases, the rate of increase is not
only larger than the globally averaged column; it also starts faster. The
ozone minimum is reached after 5 years, while the corresponding time for the
globally averaged column was shown to be 10-15 years (Figure 10). The local
behavior of ozone at 60° northern latitude at the 43 km level is similar to
the behavior of total ozone. Minimum ozone is obtained 5-6 years after the
emissions are ceased, and ozone recovery is fast thereafter. If emissions are
reduced by 1% per year instead of being completely stopped, the period of
decreasing ozone is prolonged to 13 years, according to our results.
NONLINEAR OZONE REDUCTIONS AT VERY HIGH CHLORINE LEVELS
Since Cicerone, Walters, and Liu (1983) reported a pronounced nonlinear
relationship between ozone reductions and increases in stratospheric chlorine,
this relation has been subject to extensive studies. Cicerone, Walters, and
Liu (1983) found a more rapid growth in ozone reductions than in stratospheric
103
-------
GLOBAL OZONE COLUMN
0
-1
-2
-3
-4
-6
-7
-8
-9
-10
1960
Chlorine Scenarios A, B
No Chlorine Releases After 2000: A', B'
N2O and CH4 Increase
1970
1980
1990 2000
TIME
2010
2020
0
-1
-2
-3
-4
-5
-6
-7
-8
-9
-10
2O30
Figure 10. As Figure 5 for the chlorine scenarios A and B. Also
included is the change in ozone column after a cease in the
chlorine emissions after the year 2000. Growth in NpO and CHh is
included.
chlorine for Cl mixing ratios up to about 10 ppb. Rather, McElroy, and Wofsy
(1985); Herman and McQuillan (1985); and Isaksen and Stordal (1986) found the
relationship to be almost linear in this Cl range. They found, however, a
faster growth in ozone reductions than in Cl mixing ratios from the point
where Cl becomes larger than the amount of stratospheric NO (total odd
nitrogen). It was interesting to see if this situation occurred in the time-
dependent experiments described in this paper. The values for Cl and NO in
case C, the scenario with the largest chlorine emissions, are shown in Figure
12. The Clx concentration increases rapidly after the turn of the century and
reaches 12 ppb in the year 2030, well below the predicted 25 ppb of NO . The
point of accelerating ozone reductions is therefore reached much later than
the year 2030 in all the calculations presented here. As discussed in Isaksen
and Stordal (1986), there is still a considerable uncertainty in the modeled
NO (as well as in NO measurements). The lower the values of NO , the
earlier the accelerated ozone depletion will start. The NO results presented
include an increase in NpO of 0.25$ per year, a growth rate that is somewhat
uncertain. The accompanying increase in NO values is much slower than the
growth in Cl . In the 50-year time period from 1980 to 2030 the stratospheric
level of NO is projected to increase 16.5$.
To study the alterations in the ozone chemistry when Cl reaches the
level of NO , we have run the scenario C case for an additional period of 50
years. The chlorine release rates for this period are also contained in Table
1. The yearly growth in emissions for CF2Clp and CFClo are assured to
decrease from about 2% in the year 2030 to less than 1$ 50 years later. Since
104
-------
OZONE COLUMN 60°N SPRING
-2
-4
-6
-8
-10
-12
-14
-16
-18
-20
Chlorine Scenario B
No Chlorine Releases After 2000:B
Na and CH4 Increase
- -10
- -12
14
-16
- -18
-20
1960 1970 1980 1990 2000 2010 2020 203O
TIME
Figure 11. As Figure 10, but for the ozone column at 60° northern
latitude during spring.
the predicted increases in CH^ and N20 are based on currently observed trends,
we find their scenarios through the middle of the next century to be highly
uncertain. We have therefore assumed constant surface mixing ratios for CHh
and NpO in the period 2030-80. This assumption is also convenient for the
then will exceed the level of
current study since Cl levels
With the adapted scenario, Cl catches up with NO
reaches 34 ppb in the year 2080.
NO earlier.
between 2060 and 2070 and
Isaksen's and Stordal's (1986) steady-state experiments showed that for
high levels of stratospheric chlorine, the most significant ozone reduction
105
-------
Clx and NOy 37 km Equator
12
11
10
9
8
a
~ 6
O
5
4
3
2
Chlorine Scenario C
N2O and CH4 Increase
25
24
»
22
21
20
1960
1970
1980
1990
2000
2010
2020
203O
TIME
Figure 12. Maximum stratospheric levels of Clx and NO as
function of time, in the chlorine scenario C case (see Table 1)
with simultaneous increases in
and CHh
will be in the lower stratosphere. Figures 13a-c illustrate that the time-
dependent calculations confirm this behavior. The absolute changes in ozone
concentration in three different 10-year periods are given as altitude-
latitude contour plots. In the first period, 1980-90, the poleward and
downward transport will result in maximum ozone depletions at high latitudes
in the lower stratosphere. At middle and low latitudes, the largest
depletions would be confined to the middle stratosphere. Forty years later,
in the period 2020-30, the depletions in the middle and low latitudes would be
intensified. The zero line separating the two regions would descend 2-3 km.
As in the former period, the maximum decrease in the upper region (at middle
and low latitudes) would be similar in magnitude to the maximum increase in
the lower region. This is no longer the case in the period 2060-70 when the
nonlinear growth in ozone depletions at low and middle latitudes would
start. Maximum depletions would take place (as in Isaksen and Stordal 1986)
in the 25 km region where the zero line was located 80 years earlier. The
large projected ozone depletions are due to increase in stratospheric
chlorine, which is shown to influence the loss rate of ozone increasingly,
even in the lower stratosphere.
106
-------
O3 RED
199O VS 1980
SERSON= 2
•48 .
•« 4 .
as .
24 .
-O.Z
•-•o. -.o. -«o. -ao. Lfl?fTUDE*°.
a
eo. so,
03 RED
2O3O VS 2O2O
•48
t 1
SB
IB
» ™ V* ^
SEHSON= 2
~~'\-i\o '* .~^*"~ *' '•nr~:—"'"*•. .'-""'I •'•
'^''l.'^^''::<'&:?--=^
:--:::<'"":^'/_ ^ \ \ \,4.* i.-^o <-
-:..-• ^/ KT \ ^.>N:s:.;>
>-ao. —so. -
•to. -20. o. 20.
LHTITUDE
•4O. SO.
Figure 13- Changes in
ozone densities (10 molec
em"-*) as a function of
altitude and latitude in
the experiment discussed in
the section on the response
in ozone to future
regulations in chlorine
releases. The changes are
given for the following 10-
year intervals: 1980-90,
2020-30, and 2060-70.
O3 RED
2O7O VS 2O6O
SERSON= 2
•4S .
SI .
SB.
£29
24
4B .
a.
B .
«-eo.
-ao. -«o. -20. Lf,?fTUDE*°. "o- eo. ao.
107
-------
We now focus on the rather dramatic changes in the chemistry of the lower
stratosphere that are assumed to take place by the year 2080 when the
stratospheric chlorine level becomes very large. Other chlorine reactions
than reaction R7 below must then be considered. Wuebbles and Chang (1981)
listed four different chlorine cycles resulting in 0 destruction (the number
in brackets to the left-hand side of each equation represents the number of 0
molecules lost in the reaction, as described in the section titled Trend in
Ozone for the Period 1970-80).
Cycle 1
R7
R8
(2)
(0)
Net:
(0)
(0)
(0)
(1)
(1)
Net:
CIO +
Cl +
0 +
Cycle
Cl +
NO +
CIO +
C10NO +
N03 +
203
0
°3
°3
2
°3
NlL + M •*•
hu
hu
-»•
Cl + 02
CIO + 02
2 02
CIO + 02
N02 + 02
C10NO + M
Cl + N03
NO + 02
3 02
R8
R9
R10
R11
R12
The dissociation of NOo has an alternative pathway to reaction (R12).
Only the fraction of the dissociation forming NO (1/9, see NASA/JPL 1985)
leads to 0 destruction. The net loss term for cycle 2 is then 2/9 J-i-i ClONOp
since the ClONOp dissociation is the rate-limiting step (see, e.g., Wuebbles
and Chan 1981; Cicerone, Walters, and Liu 1983).
Cycle 3
(0)
(0)
(2)
Net:
Cl +
CIO +
N02 +
0 +
W*5
NO
0
°3
CIO +
Cl +
NO +
2 02
N§p
o22
Cycle 4
(0)
(0)
(1)
(1)
Net:
Cl H
CIO -
OHC1 H
OH
203
H 0,
K H02
i- hu
h °3
CIO +
OHC1 +
OH +
H02 +
* 302
°2
??
°2
R8
R13
R6
R8
R14
R15
R2
108
-------
At very high chlorine levels, OHC1 dissociation (R15) becomes faster than
the rate of the reaction OH+CU (R2). Another reaction is then converting OH
to H02, namely OH+C10, constituting a 5 0 loss cycle:
Cycle 5
(1)
(1)
Cl -
CIO -
OHC1 -
OH -
Cl
1- Oo
H H02
K hu
H CIO
,o3
-*•
->•
-»•
->•
->•
CIO H
OHCL H
OH H
H02 H
CIO H
i- 0
h 02
h Cl
H Cl
H 02
R8
R14
R15
R16
R8
Net: 2
Cycle 1 is the only pure chlorine cycle, while the four remaining cycles
involve nitrogen (2 and 3) and hydrogen (4 and 5) compounds. As noted in
Wuebbles and Chang (1981), the distribution of the ozone loss between the
individual families is then not obvious. We have taken the following approach
in this study:
Cycle 3 has the 0 loss reaction (R6) in common with the pure nitrogen
catalytic cycle:
N02 + 0 ->• NO + Op R6
MO + 03 -* N02 + 02 R17
We distribute the QX loss between the two cycles so that T17/(T1+T17) is
attributed to the pure nitrogen chain and the remaining T13/(T13+T10) to
chlorine cycle (3). Here Tn represents the rate K XY of reaction R with X
and Y as reactants.
The rate-limiting process in cycle r is reaction (R16). The loss rate of
cycle (5) is therefore set to the rate of R16 times two, since two 0 are lost
in each cycling. The OHC1 dissociation (R15) is common for cycles 4 and 5.
The part of the rate of this reaction that exceeds the rate of R16 is
attributed to cycle (4). This cycle has reaction R2 common with the pure
hydrogen loss chain
OH + Oo - H02 -f 02 R2
H02 + 0^ ->- OH + 2 02 R3
Only the part of the rate of R2 that has not been involved in the
chlorine cycles (4) and (5) is attributed to the pure hydrogen caused 0 loss.
A
Figures I4a-f show the fraction of the 0 loss attributed to the various
chlorine cycles in the year 2080. Altitude-latitude cross sections are given
for the season March-May. In the region of chemical control, chlorine cycles
account for at least 80$ of the total loss. The contribution of the pure
hydrogen cycle is reduced to less than 10% except around the stratosphere
where a 10$ influence remains. The influence of the pure nitrogen cycle as
well as the oxygen cycle is also less than 10$. Chlorine cycle (1) is
dominating, even in the lower stratosphere. At low latitudes, this cycle
109
-------
CLOX
CYCLE 1
2080
SEPSON= 2
n .
S «»•
«~»-ao. -eo. --»o. -20. o. 20.
LflTlTUOE
i. ao,
CLOX CYCLE 2 2O8O
SEflSON= 2
ia .
•is .
2S .
2B ,
24.
'"'-•O. -ao . --4O. -2O. O. 2O. -»O .
>O. BO.
Figure 14. Percentage ozone
loss rates due to C10X
cycles (see text, the sec-
tion on nonlinear ozone
reductions at very high
chlorine levels). Altitude-
latitude contours are given
for near equinox conditions
in the year 2080 of the
experiment discussed in the
section on the response in
ozone to future regulations
in chlorine releases.
CLOX CYCLE 3 2O8O
SEflSON= 2
—ao. —eo. —^o. -20. o. 20. -40. BO. ao.
110
-------
CLOX CYCLE 4 2O8O
•46 .
1 4 .
a4 .
SERSON= 2
CLOX CYCLE 5 2O80
JS ««
'"'— *o . -BO. — -«o . — ao . o. ao .
LflTlTUDE
SERSON= 2
»o . BO
Figure 14 (Cont.)
CLOX TOTflL
2O8O
SEnSON= 2
eo. —-»o. -ao. o. ao. -»o. eo
eo .
111
-------
stands for more than 60% of the total loss at the 25 km level. In the middle
stratosphere cycle (3) is the second largest depletion cycle, attaining a
maximum of more than 30%. Below the 25 km level the two cycles involving
OHC1, cycles (4) and (5), gradually increase their influence. Each of these
cycles contributes to the 0 loss with about 1Q%-20% in the transition
region. The chlorine cycle (2) involving chlorine nitrate is effective only
at very low altitudes at high altitudes where contributions of 1Q%-20% are
obtained.
Since the chemistry of 0 in the year 2080 is dominated by the chlorine
cycles, as demonstrated in Figures 15a-d, the explanation to the accelerated
growth in ozone depletion must be sought in the chlorine chemistry. At all
altitudes above the 30 km level more than half of the ozone has vanished in
the year 2080, leading to a slower growth in ozone depletions there.
Accelerated depletion of the total column can only take place due to the
highly nonlinear increase in ozone reductions in the lower stratosphere, which
was demonstrated in Figures 13a-c.
As discussed in Isaksen an Stordal (1986), the explanation for the
accelerated chlorine influence can be found in the changes in the balance
between ozone-depleting components and passive reservoirs in the chlorine
chemistry in the lower stratosphere. The calculations show that HC1 has
effectively been converted mainly to CIO but also ClONOp in the region in the
period 2030-80.
The explanation for the increase in the fraction of CIO must be sought in
changes in components determining the balance between the chlorine components.
Figures 15a-d show the change in the period 2030-80 in some key components as
well as in the ratio between CIO and HC1. The increase in the ratio C10/HC1
is large in the lower stratosphere. At the 25 km level at low latitudes this
ratio has increased by a factor 3-4 in the 50-year period in question. The
ratio can be expressed as a product of the ratios C10/C1 and C1/HC1. The
first of these ratios, C10/C1, increases by a factor of about 2 since the NO
concentrations drop (Figure 15b), lowering the rate of reaction R13. The
C1/HC1 ratio increases by a factor 1.5-2 in the lower stratosphere at low
latitudes, since CHh decreases (Figure 15c) and OH increases (Figure 15d).
Both favor an increase in the decreases since OH increases and since the
reaction Cl + CHh •* HC1 + CHo (R18) becomes a significant loss reaction for
CHn in the upper stratosphere. OH increases due to lowered levels of HNOo and
HOpNOp (Prater et al. 1985) as well as an efficient transformation from H02
via HOC1 (see detailed discussion in Isaksen and Stordal 1986).
The time-dependent experiments described here confirm the point made by
Isaksen and Stordal (1986) that accelerated ozone depletion at high chlorine
levels occurs as a result of the fractional CIO increase. OHC1 and to some
extent ClONOp contribute to the nonlinearity.
According to the present understanding of the chemistry of the
stratosphere (NAS/JPL 1986), the transformation of the active components Cl
and CIO to the main reservoir HC1 takes place through Cl reactions. At high
chlorine levels, when the C1-C10 balance is shifted towards the latter
component, the loss mechanisms for C1+C10 are less efficient. Isaksen and
Stordal (1986) demonstrated, however, that only small yields of reactions like
C10+OH and OHCl+hu for pathways leading to HC1 formation could decrease the
nonlinear ozone depletion significantly.
112
-------
SERSON= 2
4"I-eo. —ao. ~
Lfl?fTUDE2°
so . eo ,
NO
2O8O VS 2O3O
•4S .
« .
B"T
SERSON= 2
T—eo . -so. — -»p
Figure 15. Changes in ratios and components in the period 2030-80 in the
experiment considered in the section on nonlinear ozone reductions at very
high chlorine levels. Altitude-latitudes cross sections for near equinox
conditions are given for the quantities log, (HOQQQ/HPQOQ) where H represents,
firstly, the ratio a) C10/HC1, and secondly, the mixing ratios of b) NO, c)
CH4, and d) OH.
113
-------
CH4
2O8O VS 2O3O
SEflSON= 2
»T.
29
25.
24 .
.^
.. ..... -o.-s
*~T—eo. — eo. -HO. -20.
•4O. so. eo.
OH
2O8O VS 2O3O
SERSON= 2
1 1 1 r-
—eo. --4O. -20.
Lfl?lTUDE20
•40 . 60 . 00 ,
Figure 15 (Cont.)
114
-------
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119
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The Ultraviolet Radiation Environment
of the Biosphere
John E. Frederick
Department of the Geophysical Sciences
University of Chicago
Chicago, Illinois USA
ABSTRACT
The flux of biologically significant ultraviolet radiation that reaches
the surface of the earth varies markedly with season and latitude. A compari-
son of computed UV-B (280 to 320 nm) and UV-A (320 to 400 nm) surface fluxes
shows the greatest latitudinal and temporal gradients at the shorter
wavelengths where atmospheric ozone is an efficient absorber. Calculations
performed for four cities in the United States define the respective roles of
the solar zenith angle and the column ozone amount in determining the
biologically damaging flux of solar radiation incident on the biosphere.
These variables, together with surface elevation, combine to produce
significantly different radiation environments in the cities analyzed.
INTRODUCTION
The amount of solar ultraviolet radiation that reaches the biosphere is
controlled by several factors of which the best known is the amount of atmos-
pheric ozone. This paper defines the major variables required to predict the
flux of biologically relevant solar radiation at the surface of the earth and
shows how they combine to produce large latitudinal and seasonal variations in
the energy received at the ground. The sun emits electromagnetic radiation
over a broad range of wavelengths, of which the human eye responds to the
region from approximately 400 to 700 nm. This work focuses on shorter wave-
lengths located in the near ultraviolet. The region from 320 to 400 nm is
termed the UV-A, while the UV-B lies shortward of this, from 280 to 320 nm.
Absorption of solar radiation by ozone is significant primarily at UV-B wave-
lengths .
One can think of the atmosphere as a filter located between the sun and
the earth's surface. The transmission of this filter for solar radiation is a
very sensitive function of wavelength, geographic location, and time of
year. Figure 1 presents a reference solar spectrum both at the top of the
121
-------
atmosphere and at the earth's surface for conditions typical of afternoon
illumination at a middle latitude site. The extraterrestrial flux represents
a combination of recent rocket and satellite measurements. The total energy
flux incident on the atmosphere over the entire UV-B and UV-A combined is
approximately 109 watts per square meter. This is similar to the power of a
standard 100 watt light bulb being directed onto each square meter of area at
the top of the atmosphere.
The lower curve in Figure 1 illustrates the solar UV-B and UV-A energy
flux reaching the ground for clear sky conditions. The solar zenith angle in
this calculation is 60°. (The solar zenith angle is the angle between the
point directly overhead and the sun. A solar zenith angle of 90° means that
the sun is on the horizon.) The most obvious feature in Figure 1 is the very
sharp decline in energy flux as one moves toward shorter wavelengths from the
UV-A into the UV-B. This is the well-known "ozone cutoff" in which the flux
at the ground drops to negligible levels over a wavelength range of a few
nanometers. For most purposes one does not consider radiation at wavelengths
less than 295 to 300 nm as reaching the surface of the earth. However, the
surface flux in the region of the rapid dropoff is very sensitive to the
atmospheric ozone amount.
At wavelengths longer than 320 nm, absorption by ozone becomes weak. Yet
Figure 1 shows that the radiation flux reaching the ground is still much less
than is incident at the top of the atmosphere. This attenuation arises from
scattering by atmospheric molecules, mainly 0^ an<^ N?* Some of the incoming
solar radiation is backscattered and exits the earth's atmosphere into
space. This constitutes the albedo of the planet in the ultraviolet. Hence,
even in the absence of an ozone layer the earth's surface would be partially
shielded from the sun's ultraviolet emissions. However, in such a circum-
stance the lethal radiation in the UV-B would be vastly greater than the
values to which life is now adapted.
Photobiological responses are sensitive functions of the wavelength of
incident light. This wavelength dependence is described mathematically by a
biological "action spectrum," which is simply a quantitative way of saying
that some wavelengths are more efficient than others at causing a specific
type of photobiological response. Figure 2 is a sample action spectrum for a
type of radiation damage to the DMA molecule (Setlow 1974). This figure shows
that biological sensitivity is greater at the wavelengths where the solar
radiation reaching the ground is smaller and vice-versa. For biological
applications the relevant quantity is the product of an action spectrum and
the solar flux at the ground added over all wavelengths (mathematically, the
"convolution" of the action spectrum with the solar flux). This provides a
single number (rather than a series of numbers at many wavelengths) that
depends on the biological process under study and varies with the radiative
transfer properties of the earth's atmosphere. A combination of the values in
Figures 1 and 2 implies that radiation at wavelengths in the 300 to 315 nm
region is overwhelmingly the most important in damaging the DMA molecule.
This is a region where atmospheric ozone exerts a major influence on the solar
flux reaching the ground.
122
-------
E 10°
10
-2
10
10"'
,-4
1 ' I ' I ' T
-EXTRATERRESTRIAL FLUX
FLUX AT GROUND
(SZA=60 ,R = O.I5
CLEAR SKIES)
UV-A
280 300
320 340 360
WAVELENGTH (nm)
380 400
Figure 1. Reference solar ultraviolet spectrum incident on the top of
the atmosphere (extraterrestrial flux) and at the ground for typical afternoon
conditions and a middle latitude location. The calculations assume a solar
zenith angle (SZA) of 60°, a ground albedo (R) of 15/6, and clear skies.
O)
o
cr !0~2
E '"-4
in
E I
UJ
to
o
CJ3
O
_J
O
03
10
-UV-B-
DNA ACTION SPECTRUM
UV-A-
280 300 320 340 360
WAVELENGTH (nm)
380
400
Figure 2. Action spectrum for damage to the DMA molecule. The vertical
scale is a relative measure of biological sensitivity to radiation at each
wavelength.
123
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The Latitudinal Distribution of Radiation
Figure 3 presents the global distribution of UV-B radiation at the
surface of the earth computed for clear sky conditions. Contours in the
figure are in watts per square meter and appear as functions of latitude and
month. All values refer to a local time of 10:00 A.M. and represent the sum
of all radiation at wavelengths between 280 and 320 nm. The largest energy
fluxes, four watts per square meter, exist in the tropics because the sun is
almost directly overhead, and the atmospheric ozone amounts are relatively
small. The large variation in radiation flux with latitude, especially during
the winter season is illustrated in Figure 3. In the Northern Hemisphere
during December and January, the flux decreases by a factor of ten between the
equator and 50° latitude. If one considered a calculation in which the radia-
tion at each UV-B wavelength is weighted by an action spectrum value, the
gradients in latitude would be still more pronounced than those of Figure 3
because shorter wavelengths, where ozone absorbs most efficiently, would be
relatively more important. During summer the latitudinal changes are much
less pronounced than in winter, and one must move from the tropics to 60° to
experience a factor of two decrease in radiation at the ground. Accompanying
this latitudinal behavior are seasonal variations. In the tropics there is
very little change in the 10:00 A.M. fluxes over the course of a year. At
middle latitudes, however, the seasonal cycle can range between a factor of
two and ten depending on location.
A calculation analogous to Figure 3 could be done for the UV-A spectral
region. Although the contours would be similar in shape, the gradients would
be much less pronounced because of the greatly reduced absorption by ozone at
wavelengths longward of 320 nm. Figure 4 illustrates this behavior with the
contours of the ratio of the UV-B and UV-A fluxes. Clearly, the UV-B flux is
much smaller than the UV-A, with the ratios ranging between 2 and 7.5
percent. The most significant information in Figure 4 is the differing
latitudinal and seasonal gradients shown by the UV-B and UV-A. As one moves
from the tropics to 60° latitude in winter, the UV-B shows a decrease, which
is a factor of three to four greater than the UV-A, while in summer the
relative variation is much less than a factor of two.
Radiation Received by Selected Cities
For many medical applications the relevant quantity is the radiation
received at a specific locality weighted by the action spectrum for the
particular photobiological process under study. The calculations that follow
use the DNA action spectrum of Figure 2, and therefore one must not view the
results as applicable to all cases of biological interest. Figure 5 presents
the annual cycle of "biologically damaging" flux (flux at the ground convolved
with the DNA action spectrum) for four cities in the United States. The
calculations refer to local noon for clear sky conditions, and results appear
in relative units. Miami represents a low latitude site (25.8° N), and
consistent with the global contours of the previous section, the radiation
flux here is significantly larger than that received by the more northerly
locations. Boston is the highest latitude site in Figure 5 (42.3° N). A
comparison of Miami and Boston reveals a factor of 1.5 difference in damaging
radiation during July, and a factor of 8.5 in winter.
124
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N
85
65
45
25
5
-5
-25
-45
-65
-85
Total UV-B Flux at Ground (W-(vf2)
Ratio UV-B UV-A (Units: 10
\
N
N D J F M
A M
Month
J J A S 0
N 0
M A M J J A
Month
S 0
Figure 3. The latitudinal and
monthly distribution of UV-B
radiation at the ground computed for
clear sky conditions and a local
time of 10:00 A.M. Contour values,
in watts per square meter, include
all wave lengths between 280 and
320nm.
Figure 4. The ratio of solar energy
flux in the UV-B (280-320 nm) to that
in the UV-A (320-400 nm) as a function
of latitude and month. Values refer
to radiation reaching the ground for
10.00 A.M. local time and clear sky
conditions. Contours are in percent
(7.5 means that the UV-B energy is 7.5
of that in the UV-A).
MIAMI (25.8°N)
WASHINGTON (38.9°N)
DENVER (39.7°N)
BOSTON (42.3° N)
JFMAMJJASONO
MONTH
Figure 5. Biologically damaging solar flux received at the ground
computed for four cities in the United States during each month of the year.
Results refer to clear skies at local noon. The damaging flux is the
convolution of the solar flux at the ground with the DNA action spectrum.
Values are in relative units, normalized to a maximum of 100.
125
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Denver (39.7° N) and Washington, D.C. (38.9° N) are at similar latitudes,
although based solely on their 0.8° separation one would expect slightly
larger fluxes in Washington (for clear skies and the same local times).
Figure 5 shows that this is not the case, and in July the Denver radiation
level is approximately 12 percent greater than that in Washington. This
offset shrinks to 9 to 10 percent in January. The elevations of the two
metropolitan areas are the source of the computed differences. The surface
atmospheric pressure at Denver is approximately 85 percent of that for
Washington, D.C. This means that over Denver there is less atmospheric mass
available to scatter incoming solar radiation back to space than for
elevations closer to sea level. The result is a greater radiation flux at the
ground. In summer for clear sky noon conditions, a one kilometer increase in
elevation is accompanied by roughly a 7 to 8 percent increase in biologically
damaging flux. In winter the computed change is closer to 6 percent per
kilometer, although the absolute radiation levels are vastly smaller here than
in summer.
Based on the annual cycle in solar zenith angle, one would predict
maximum damaging radiation levels at the summer solstice (June 21). Yet,
inspection of Figure 5 reveals that the peaks lie closer to mid-July. (Note
that the tick marks on the horizontal scale of Figure 5 refer to the centers
of each month.) Figures 6 and 7 allow one to interpret the annual cycles in
radiation. First, Figure 6 illustrates the noon solar zenith angles for the
four cities in each month, where the minimum values obviously occur at the
summer solstice. The annual cycle in radiation flux at the ground clearly
varies inversely with the solar zenith angle. This dependence arises from the
varying slant path taken by the sunlight through the absorbing and scattering
atmosphere during different times of the year. Both absorption by ozone and
scattering by atmospheric molecules act to decrease the flux reaching the
ground as the radiation path through the atmosphere increases (i.e., as the
solar zenith angle increases).
The shift in time between minimum solar zenith angle and maximum radia-
tion flux arises from the annual cycle in atmospheric ozone depicted for each
city in Figure 7. Note that the total ozone in a vertical column of the
atmosphere is not simply related to the solar zenith angle. Although ozone is
produced by the action of ultraviolet sunlight on Op molecules in the upper
atmosphere, much of the ozone that exists in a vertical column has drifted
downward from higher altitudes. At altitudes below thirty kilometers, where
most of the ozone resides, the lifetime before chemical conversion back to $2
is long. The abundance here is controlled by atmospheric transport processes
that carry ozone from low to high latitudes during the winter, leading to the
mid-latitude maxima of Figure 7 in February and March. The rapid decrease in
ozone taking place between 35° and 45°N during late spring and early summer
effectively suppresses a radiation maximum in the time immediately before
summer solstice, and promotes a maximum shortly after solstice. This is the
mechanism that shifts the maximum radiation fluxes of Figure 5 into July.
Note also that the behavior of total ozone over Miami in Figure 7 is more
representative of a tropical than a mid-latitude site. The relatively small
ozone amount combined with an annual behavior different from that at higher
latitudes leads to a seasonal cycle in surface ultraviolet radiation with a
shape distinct from that at more northerly locations.
126
-------
00
UJ
UJ
cc
70
MIAMI (25.8°N)
DENVER (39.7°N)
WASHINGTON (38.9°N)
BOSTON (42.3°N)
O
UJ
S 60
50
40
30
20
10
0
cc
-------
CONCLUSIONS
We can conclude from this analysis that: (a) the gross shape of the
annual cycle in biologically damaging radiation at a given location is deter-
mined by the variation in solar zenith angle; (b) the ozone amount influences
details of the shape shown by the annual radiation cycle and is the major
determinant of the absolute magnitude of the radiation flux for a given solar
zenith angle; and (c) the biologically damaging radiation flux at latitudes
between 35° and 45° varies by approximately an order of magnitude from winter
to summer.
The availability of global scale ozone measurements and accurate informa-
tion concerning the extraterrestrial solar irradiance permits more thorough
studies of the ultraviolet radiation environment of the biosphere than have
been possible in the past. However, a major deficiency of our results is the
neglect of cloudcover and other forms of atmospheric turbidity. Data sets now
exist that could provide valuable information on the reflectivity and trans-
mission of clouds in the near ultraviolet. This information should be
exploited both for applications in atmospheric science and photobiology. In
addition, it is essential that a long-term measurement program be capable of
providing unambiguous evidence of any changes in the global ozone amount.
ACKNOWLEDGEMENTS
Portions of this work were supported by the National Aeronautics and
Space Administration under grant NAGW-873- The author thanks George N.
Serafino (Applied Research Corporation) for many of the calculations shown
here and Daniel Eiblum (University of Chicago) for assistance in data
handling.
REFERENCE
Setlow, R. B. 1974. The wavelengths in sunlight effective in producing skin
cancer: A theoretical analysis. Proceedings of the National Academy of
Science. USA 9:3363-3366.
128
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Health Effects of Ultraviolet Radiation
Edward A. Emmett
Johns Hopkins Medical School
School of Hygiene and Public Health
Baltimore, Maryland USA
SOURCES OF ULTRAVIOLET RADIATION
People are exposed to ultraviolet radiation from both natural sunlight
and artificial sources; the most important source for humans is the sun.
Virtually all of us are exposed to solar radiation at some time in our
lives. In the United States an estimated eight million outdoor workers have
occupational exposure to solar radiation. The sun is a complex source.
Although we refer to "sunlight," solar radiation contains not only visible
rays but also substantial portions of ultraviolet radiation—near, middle, and
far infrared and other portions of the electromagnetic spectrum, including
cosmic rays, microwaves, and radiowaves.
In this paper I present a general introduction to the health effects of
ultraviolet radiation emphasizing photobiologic principles that are necessary
to understand the significance of the work presented at this conference.
Because many scientists have contributed to our knowledge of this field, my
references are not exhaustive and generally direct readers to major reviews.
Ultraviolet radiation, particularly its UV-B component, has major effects on
the skin and eye. Other effects, including systemic effects have been
claimed, but these are not discussed in this paper.
For convenience, we customarily divide the ultraviolet into three wave-
bands, UV-A, UV-B, and UV-C, whose properties are indicated in Table 1. This
table is an oversimplification. The distinction between the wavebands is not
sharp, and shorter UV-A rays can behave like UV-B. Interactions between the
various wavebands of ultraviolet radiation and with other wavebands outside
the ultraviolet may occur, particularly involving ultraviolet radiation and
heat. However, this shorthand notation is convenient and serves to highlight
UV-B, which is the focus of Volume 2.
129
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Table 1. Wavelengths of Ultraviolet
Waveband Properties
UV-A 320-400 nm Not carcinogenic at usual exposure
levels. Present in solar radi-
ation at earth's surface. Respon-
sible for most photosensitivity
reactions.
UV-B 290-320 nm Usually responsible for sunburn
and skin cancer. Present in solar
radiation at earth's surface.
UV-C 200-290 nm Virtually totally removed by
stratospheric ozone. Exposures
occur only from artificial
sources. Can cause erythema and
skin cancer.
Artificial sources of ultraviolet radiation are varyingly rich in
different regions of the ultraviolet. The total population exposed to these
sources to any significant extent is much smaller than for solar radiation.
The sources include welding arcs; germicidal lamps; sunlamps; therapeutic
sources; environmental test chambers; printing, plastic, and paint curing and
drying processes; ultraviolet lasers; plasma torches; and others. Relatively
little is known about their long-term effects on exposed human groups.
Much of our knowledge about the effects of ultraviolet radiation comes
from experiments on cellular systems, whole animals, and a relatively small
number of experiments in human volunteers. The experimental ultraviolet
sources used to develop this information were generally monochromators that
deliver exposures to very narrow wavebands of ultraviolet, fluorescent sources
including sunlamps (UV-C + UV-B + UV-A), germicidal lamps (predominantly 254
nm radiation), blacklights (predominantly UV-A), and xenon arc solar simu-
lators (generally designed to simulate solar radiation in the UV-B but not in
the visible or infrared). Most of our information about deoxyribonucleic acid
(DNA) photochemistry has been generated using germicidal sources. There is an
important discrepancy between solar radiation and the sources generally used
in experimental studies. Furthermore, the spectral distribution of sunlight
is not constant; it constantly varies within certain limits, depending on the
latitude, altitude, time of year, time of day, and atmospheric conditions.
Thus our observations about the effects of ultraviolet radiation- in humans
have been collected mainly through clinical case reports and epidemiologic
studies related to exposure to ambient solar radiation that has a spectral
distribution different from that of sources used for experimental studies.
130
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TRANSMISSION OF UV THROUGH TISSUES
The ultraviolet radiation that reaches target cells in the body depends
not only on the characteristics of the source and the radiation reaching the
surface of the body, but also on the optical properties of the cells and
tissues overlying the biological target. In these overlying tissues ultra-
violet may be reflected, scattered, absorbed, or transmitted.
Figure 1 displays the seminal work of Boettner and Wolter (1962)
measuring the total transmission of direct and scattered radiation through the
tissues of the eye. The figure shows that very little ultraviolet shorter
than 300 nm penetrates the cornea, and that very little radiation shorter than
400 nm penetrates deeper into the eye than the lens, whereas most of the
visible radiation (400-780 nm) reaches the retina. To a large extent this
explains why the effects of UV-C on the eye are virtually confined to the
cornea, which explains why we are concerned about the possible effects of the
longer ultraviolet on the lens. Interestingly, the rabbit eye often used for
experimental studies shows transmission similar to the human eye (Geeraets and
Berry 1968).
100
TOTAL TRANSMITTANCE AT THE
VARIOUS ANTERIOR SURFACES
30O
4OO 500 600 800 10OO 12OO
WAVELENGTH MILLIMICRONS
1600 2000
Figure 1. Total Transmittance at the Various Anterior Surfaces of
Structures Within the Human Eye (from Boettner and Wolter 1986).
In the case of the skin, wavelengths from approximately 250 nm in the
ultraviolet to approximately 3000 nm in the infrared penetrate the surface,
but reach vastly different depths within the tissues (Anderson and Parrish
1982). The optical properties of skin are dynamic and vary with many factors
including humidity, thickness of the skin layers, and the state of
vasodilatation. Epidermal characteristics are of particular significance,
131
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since the cells at greatest risk for ultraviolet carcinogenesis in people
appear to be keratinocytes in the lowest layer and melanocytes within the
lower few layers of the epidermis. An important variable in modulating indi-
vidual susceptibility to ultraviolet is melanin pigmentation which provides
maximum protection against wavelengths shorter than 1200 ran, including the
entire ultraviolet range. Melanin is located primarily in the basal cell
layer of the epidermis in pigment granules which can be seen to directly
overlie the nuclei of many basal cells, like caps protecting the nucleus. It
is very likely that this supranuclear, intracellular, distribution of melanin
results in more protection against nuclear DNA damage than would random
distribution of pigment in the skin.
SEQUENCE LEADING TO ULTRAVIOLET-INDUCED HEALTH EFFECTS
The sequence of events by which ultraviolet produces health effects is
indicated in Table 2. Ultraviolet radiation must be absorbed to produce any
response in tissues. This concept is central to photochemistry and photo-
biology. It was first proposed in 1818 by Grotthus and Draper and is known as
"the first law of photochemistry." Further, as Frederick (this volume)
describes, each absorbing molecule (chromophore) is capable of absorbing
radiation only in specific wavelength ranges, a relationship described by its
absorption spectrum. Each photon or quantum of radiation absorbed activates
one molecule in the excitation step of a photochemical sequence.
Table 2. Sequence by Which Ultraviolet Radiation
Produces a Health Effect
Elapsed Time
Radiation
Absorbed by Chromophore
Excited State
Photochemical Reaction
Biologic Response(s)
Disease
10'9 - 101 sec
10'3 - 1(T7 sec
sees - years
132
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The electromagnetic energy absorbed in the chromophore is converted to
chemical energy, resulting in molecular excitation and an excited electronic
state. Some electronically excited states, notably triplet states, are much
more long lived than others, and these are much more likely to result in
photochemical changes. This electronic energy may be dissipated by heat or
fluorescence, or in the formation of photoproducts either by rearrangement of
the bonds within the excited molecule or by the interaction of the excited
molecule with another molecule. The excited molecule can also initiate a
photosensitized reaction, in which the molecule that absorbed the radiation
transfers the energy to another molecule, which then forms products (Smith
1977).
Photochemical changes occur in many key biologic molecules and structures
following ultraviolet irradiation. These include nucleic acids, proteins,
lipids, steroids, melanin, urocanic acid, and others (Smith 1977; Harber and
Bickers 1981). Damage occurs to the cell nucleus, cytoplasm, organelles, and
membranes. Some (but not all) of the photochemical changes that immediately
follow irradiation are fairly well characterized. However, the subsequent
biologic changes are less understood.
Immediate biologic changes after exposure to ultraviolet include the
release of chemical substances that mediate inflammation, inflammatory
changes, numerous biochemical interactions involving reactive oxygen species,
and immunologic changes including the suppression of certain immune response
and various repair processes. But the precise sequence of these and other
changes leading to the various health effects are not satisfactorily charac-
terized in any instance. Clearly for some effects, such as carcinogenesis,
these changes take place over many years.
ULTRAVIOLET DAMAGE TO DNA AND ITS REPAIR
Lesions in DNA, the essential genetic material in all living organisms,
are of particular interest. The purine and pyrimidine rings of the nucleic
acids, adenine, guanine, thymine, and cytosine, absorb maximally in the 245 to
280 nm range; and the major part of skin absorption of UV-C is by DNA rather
than by protein or other molecules. Because of the extensive absorption of
ultraviolet by DNA, the role of DNA damage in mutagenesis, and DNA's postu-
lated role in carcinogenesis, considerable attention has been given to ultra-
violet-induced DNA damage. Regardless of any long-term effects, ultraviolet
damage to DNA produces substantial short-term effects including blocking the
nucleic acid dependent processes of transcription and translation which are
essential to cellular function and cell division. Above critical levels, this
damage is irreversible and therefore leads to cell death.
Utraviolet-induced photolesions in DNA have been extensively reviewed
(Rahn 1979; Saito et al. 1983). The best studied lesions are those where
ultraviolet radiation causes a linkage of adjacent pyrimidines in DNA giving
rise to cyclobutane-coupled pyrimidine adducts, often called pyrimidine
dimers. Thymine-thymine, thymine-cytosine, cytosine-thymine, and cytosine-
cytosine dimers are formed, and each exists in four stereo isomers. These
lesions are normally repaired in humans and other species described below. In
addition to cyclobutane-coupled pyrimidine dimers, ultraviolet induces other
photoproducts in DNA. These include other dimers (single-bond-coupled-
dipyrimidines, thyminyldihydrothymidine) and nondimer products including
133
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thymine glycol, cytosine hydrate, DMA-DMA cross-links, and DMA-protein cross-
links. Cells are usually able to repair at least some of these lesions, with
important exceptions.
The repair of cyclobutane-coupled pyrimidine dimers in DMA has been given
substantial attention in recent years. This repair seems to have biologic
significance since the reversal of pyrimidine dimers at least partially
restores colony-forming ability; transcriptional capacity; semiconservative
DNA synthesis; and normal, low, mutagenesis rates in irradiated cells. Three
types of repair have been defined: Excision repair, postreplication repair,
and photoreactivation; other repair systems may exist.
In excision repair, a battery of enzymes act in a sequential manner to
remove the dimer and subsequently to resynthesize undamaged DNA. This repair
system is well developed in humans and is clearly deficient in the rare
genetic disease xeroderma pigmentosum (XP), which is characterized by extreme
sensitivity to the effects of ultraviolet, including an extraordinary sensi-
tivity to ultraviolet-induced cancers.
The sequence of events in this repair has been shown to include the
following: (a) pyrimidine dimer produced by ultraviolet distorts DNA
molecule; (b) the backbone of the damaged DNA chain is broken by an enzyme,
endonuclease; (c) a small region containing the thymine dimer is excised by
another enzyme, exonuclease; (d) synthesis of new DNA strand, with correct
bases corresponding to those on the remaining intact DNA strand; and (e) the
two ends of the new strand are joined by a further set of enzymes designated
as polynucleotide ligase.
Less is known about the other forms of DNA repair. Postreplication
repair allows restoration of DNA synthesis without dimer removal. Gaps left
in daughter DNA strands are filled in by de novo synthesis. Although this
form of repair is not well understood, it does occur in humans (Lehmann
1975). Photoreactivation is a light-dependent process that requires a single
enzyme and either UV-A or visible radiation. The original pyrimidines are
reconstituted in situ without DNA strand breakage or resynthesis. Photo-
reactivation appears to occur in humans (Sutherland 1978), although its impor-
tance is not clear.
Recently scientists have found that not all genes are repaired with
uniform ease (Bohr et al. 1985) and that certain chemical lesions (i.e., some
forms of pyrimidine dimers) may be more resistant to repair than others
(Lippke et al. 1981). As we understand these processes better, we will
probably learn much about how cancer is actually induced by ultraviolet.
Humans with XP have a deficiency in DNA repair, clinical sun sensitivity,
and excessive ultraviolet-induced skin cancers (Kraemer 1983). Cultured cells
from patients with XP are unable to repair ultraviolet-damaged DNA. Cell
fusion studies have demonstrated the existence of at least nine types of DNA
repair defects, any of which may lead to the disease. Despite these studies,
the specific responsible enzyme defect has not yet been identified for any
form of XP. Most XP patients develop freckles very early in life and on
continued exposure to sunlight develop abnormally 'aged' skin, eye abnor-
malities, and changes on the tip of the tongue. These changes are generally
quite marked before the age of 10. Patients with XP have a greater than one
134
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thousand increase in frequency of skin cancers including basal cell
carcinomas, squamous cell carcinomas and melanomas. The predilection of XP
patients to sun-induced diseases is so great that if a disease condition is
seen in great excess in XP, it is taken as prima facie evidence that sun
exposure causes the condition.
ACTION SPECTRUM AND BIOLOGICAL EFFECTIVENESS SPECTRA
For any biological response to ultraviolet radiation, there is an action
spectrum which is defined as the relationship between the intensity of the
response and the spectrum of wavelengths that incite the reaction. In
practice, an action spectrum is most easily defined for acute and early
effects of ultraviolet and is more difficult to determine for chronic and
complex effects.
Figure 2 shows the action spectra curve developed by Cogan and Kinsey
(19^6) for keratitis (inflammation of the cornea of the eye) in the rabbit.
The maximum sensitivity is at about 290 nm. The action spectrum for erythema
of the skin has peaks at two wavelengths which are longer and shorter than
those that produce keratitis. Neither of these spectra correspond exactly to
the absorption spectra of either nucleic acids or proteins which are also
shown in the figure.
100-
80-
«H
0)
(A
40-
20-
0-
Nuclear
Protein
Serum
Protein
Erythema
Curve
Keratitic
Curve
I I II T T
220 240 260
I I I I T
280 300 320
Wavelength (nm)
Figure 2. Action Spectra for Experimental Photokeratitis in the
Rabbit Cornea and Erythema of the Skin. The absorption spectra for
nuclear and serum proteins are also shown (from Cogan and Kinsey
1946).
135
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One might think the action spectrum to be identical to the absorption
spectrum for the chromophore which initiates the reaction; determination of
the action spectrum has enabled us in some instances to identify the respon-
sible chromophore for photobiologic reactions. However, the action spectrum
for a response in vivo and the in vitro absorption spectrum of the chromophore
may differ for many reasons, including that the absorption spectrum of the
chromophore in vivo differs from that in vitro because of variations in pH,
binding on other phenomena, or that the effective radiation received by the
target chromophore in vivo is modified by the optical properties of the over-
lying tissue.
In addition to action spectra we can also describe biologic effectiveness
spectra. These may be used to address possible changes in the magnitude of
health effects of ultraviolet, such as those that might occur with solar
radiation if the stratospheric ozone layer is altered. A biological effec-
tiveness spectrum is the relationship between the photobiologic response and
the wavelengths present in a specific source. It is obtained by multiplying
the relevant points on the action spectrum curve (expressed as reciprocal
dose) by the energy of the radiation of each wavelength present in the light
source used. The integral of the area under the curve represents the
biologically effective energy of that particular light source.
Action spectra are generally determined using monochromators to study the
effects of narrow ultraviolet wavebands (approaching single wavelengths).
However, interactions between different wavebands also may occur in producing
biological effects. Interactions have been identified between UV-A and UV-B
in the production of erythema and may occur between UV-A and UV-B in carcino-
genesis. Such interactions are not normally addressed in the classical
available action spectra but should be considered in determining likely
responses to any particular source of ultraviolet radiation.
EFFECTS OF ULTRAVIOLET ON THE SKIN
We now summarize the effects of ultraviolet radiation on the skin, which
are listed in Table 3-
Mon-Neoplastic Effects
The role ultraviolet radiation plays in Vitamin D metabolism is a bene-
ficial effect of ultraviolet radiation (Haussler and McCain 1977). Solar
ultraviolet converts epidermal 7-dehydrocholesterol to previtamin D which
undergoes a nonphotochemical, temperature-dependent, isomerization to Vitamin
D3 which is transported from the epidermis by plasma Vitamin D binding
protein. The bone disease rickets, which is caused by Vitamin D deficiency,
was common in recent generations, particularly in those with heavily pigmented
skin who lived in urban surroundings and were not exposed to sufficient solar
radiation. However, now that Vitamin D is added to milk, this is no longer a
significant problem in the United States.
Sunburn or solar erythema (Hawk and Parrish 1982) is associated with
vasodilatation and inflammation of the skin. A variety of chemical mediators
that appear to be responsible for erythema are released from the skin
following ultraviolet exposure; the actual sequence of events seems to be
quite complex. Among the changes is an alteration and depletion of Langerhans
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cells, the major epidermal cell concerned with antigen presentation and the
development of allergic and immune responses in the skin.
Ultraviolet radiation produces two types of tanning reactions (Quevedo,
Fitzpatrick, and Jimbow 1985) in those genetically able to tan: immediate
tanning due to darkening and redistribution of existing pigment; and the more
important process of delayed tanning, one or more days after irradiation, in
which there is production of new melanin pigment and proliferation of
melanocytes.
Table 3. Effects of Ultraviolet Radiation on Human Skin
Acute
Sunburn
Thickening of the Epidermis
Pigmentation
Vitamin D Production
Chronic
Actinic Elastosis and Photoageing
Carcinogenic
Monmelanoma skin cancer
Actinic keratosis (precancerous)
Squamous cell cancer
Melanoma (?)
Diseases Triggered by Ultraviolet, or Characterized by
Photosensitivity
Genetic
Xeroderma Pigmentosum
Albinism, etc.
Nutritional
Kwashiorkor
Pellagra, etc.
Infectious
Herpes Simplex, Lymphogranuloma venereum, etc.
Immunologic
Lupus erythematosus
Pemphigus, etc.
Metabolic
Porphyria cutanea tarda, etc.
Immediately after sufficient exposure to UV-B reductions in DNA, RNA, and
protein synthesis occur. Later, beginning within one day, increased synthesis
of these substances with thickening and hyperplasia of the epidermis occurs.
Both this thickening and the production of new melanin pigment give a measure
of protection against further ultraviolet damage.
Ultraviolet radiation is the major cause of aging changes in the skin,
particularly in those with fairer-skin colorations. These occur as a chronic
effect and presumably reflect cumulative sun exposure and individual suscepti-
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bility. These changes include patchy alterations in pigmentation, loss of the
surface architecture, epidermal atrophy, telangiectasia (widening of small
blood vessels), and the premalignant change of actinic keratoses. The elastic
fibers of the dermis are damaged so that they become thick and coarse and lose
their elasticity resulting in coarse, furrowed skin, a condition known as
actinic elastosis. The action spectrum for actinic elastosis is undetermined
but it is believed to include at least ultraviolet.
Apart from skin cancers, a number of skin diseases are either triggered
by ultraviolet exposure or are manifested, at least in part, by excessive
sensitivity to ultraviolet (photosensitivity) so that sun exposure makes their
symptoms worse. Examples are listed in Table 3, including hereditary genetic
diseases such as XP or albinism; nutritional deficiency states such as
Kwashiorkor (protein-calorie deficiency) or pellagra (niacin deficiency);
infectious diseases such as herpes simplex; immunologically mediated diseases
such as lupus erythematosus; altered metabolic states including porphyrias;
and others (Fitzpatrick et al. 1979). Although these diseases are common to
various degrees, when skin cancers are included, sun-induced skin diseases
account for more than half of all skin diseases seen by dermatologists among
fair-skinned persons in areas with high sun exposure, such as rural Australia.
Nonmelanoma Skin Cancer
The skin neoplasms unequivocably associated with sun exposure include the
premalignant actinic keratosis, basal cell carcinomas, and squamous cell
carcinomas (Emmett 1973; Epstein 1983; Van der Leun 1984). The evidence that
such tumors might be associated with solar radiation includes their increased
prevalence on parts of the body habitually exposed to sunlight; in lightly
pigmented and thereby less protected individuals; in areas of the world which
have the greatest insolation; in individuals who spend more time outdoors; and
especially in those who suffer from xeroderma pigmentosum. The highest inci-
dences of such tumors are seen amongst those of Anglo-Saxon and Celtic descent
in such areas as Queensland, Australia, and Arizona and Mew Mexico in the
United States. Complete statistics are not available, but there is clearly a
relationship between latitude and incidence of nonmelanoma skin cancers in
Caucasians in the United States.
Although basal cell and squamous cell carcinomas are often grouped under
the designation nonmelanoma skin cancer, they represent biologically distinct
diseases that should be considered separately and indeed have different
relationships to ultraviolet radiation. There are at least three reasons for
this distinction. First, basal cell carcinoma and squamous cell carcinoma
differ in their microscopic and histologic appearance as well as in their
biologic behavior, pattern of growth, and tendency to metastasize. Second,
comparisons between the sites of occurrence of squamous cell and basal cell
carcinomas on the skin and the amounts of ultraviolet radiation these sites
receive indicate that while squamous cell carcinomas almost all occur in
heavily exposed skin, about one third of basal cell carcinomas in lightly
pigmented individuals occur on customarily shaded sites of the face. The
third indication of differences between basal cell and squamous cell
carcinomas arises out of recent attempts to construct mathematical models
relating the occurrence of various types of skin cancer to the amount of solar
ultraviolet radiation received by the individual. This is a difficult area,
partly because we do not have sufficient details about exposure to make good
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models. However, the studies to date suggest that the basal and squamous cell
tumors have different quantitative relationships to sun exposure (Scotto,
Fears, and Fraumeni 1981). Data from various centers around the world also
indicate that the ratio of squamous cell to basal cell carcinomas becomes
higher as one approaches the equator.
Some individuals are much more prone than others to sun-induced skin
cancers of all types. Phenotypic characteristics that are risk factors for
skin cancer in controlled studies include fair complexion, light eye color,
light original hair color, poor ability to tan, and easy and repeated sun-
burns. Persons of Celtic (Scottish, Irish, Welsh) descent may be particularly
vulnerable, possibly even in the absence of these phenotypic character-
istics. The risk is extreme in those with XP. Limited studies also suggest
that subjects with actinic keratoses have less capacity to repair damaged DMA
than controlled populations. In contrast to light-skinned people, skin cancer
is relatively rare in deeply pigmented groups in whom basal cell epitheliomas
are uncommon while squamous cell carcinomas generally occur on the lower
extremities and do not appear related to ultraviolet radiation.
Much information concerning ultraviolet carcinogenesis and the factors
that affect the process has been gained from studies in animals. It is easy
to produce fibrosarcomas in many species from repeated ultraviolet irradia-
tion. The hairless mouse has proven a particularly useful experimental model
since, like humans, it develops squamous cell tumors. Basal cell tumors have
been produced experimentally in rats using chemical carcinogens, but not to
date in any species using ultraviolet.
Experimental factors shown to be important in causing squamous cell
cancer include pigmentation, presence or absence of hair, stratum corneum
thickness, wavelength of the irradiation, ambient temperature, wind, total
ultraviolet dose, and the way the ultraviolet dose is fractionated. Experi-
ments by Forbes, Davies, and Urbach (1978) suggest that delivery of the same
amount of ultraviolet in divided doses, i.e., five exposures a week, was more
effective at producing tumors than when delivered once a week. UV-B is the
most efficient in producing cancers; UV-C is also effective. Although UV-A
markedly accentuates acute skin damage from UV-B, conflicting results exist
about whether UV-A augments UV-B carcinogenesis.
A number of different types of chemicals can augment the carcinogenic
properties of UV-B. These include skin exposure to chemical carcinogens (such
as polycyclic aromatic hydrocarbons, certain nitrosureas, and N mustard),
promoting agents (such as croton oil, dodecane, and possibly all-trans
retinoic acid), some but not all phototoxic agents (for example, 8
methoxypsoralen but not anthracene), skin irritants, and immunosuppressives.
Certain agents have been shown to inhibit experimental ultraviolet carcino-
genesis including caffeine, theophylline, certain antioxidants and some sun-
screen agents. Some of these observations appear to relate directly to human
experience. For example, an increase in squamous cell carcinomas has been
observed in patients having immunosuppressive treatment following renal
transplantation and in those who have been treated for psoriasis
with 8-methoxypsoralen and UV-A (Stern, Zierler, and Parrish 1980).
Immunosuppression may play an important role in the development of ultra-
violet-induced tumors. Kripke and her colleagues (Kripke 1981, 1982) have
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shown that ultraviolet irradiation of mice results in specific susceptibility
to transplantation with highly antigenic ultraviolet-induced cancers. This
effect does not result from general loss of immune competence but rather from
the production of supppressor T cells with antigen specificities directed
toward ultraviolet-induced tumor antigens. The action spectrum for this
effect is primarily in the UV-B.
Ultraviolet and Malignant Melanoma
Melanomas (Lee 1982) are malignant neoplasms that arise from melanocytes,
the melanin producing cells found both within the skin and some other sites.
Melanomas of the skin are much less common than basal cell and squamous cell
carcinomas but are important because of their tendency to metastasize easily
and kill the patient. In contrast to all other cancers except lung cancer,
both the incidence and to a lesser extent death rates from melanoma appear to
have been rising steadily over the last several decades in fair-skinned popu-
lations worldwide. This effect has been seen in England, Wales, the United
States, Australia, New Zealand, Scandinavia, Israel, and elsewhere. A similar
trend has been seen in Japan, but no clear trend exists in the mortality from
melanoma of the skin among U.S. nonwhites. In the United States, the mean
annual increase in death rates from malignant melanoma over the last 20 years
has been about 3 percent for males and 2 percent for females. This increase
is not due to changes in diagnostic proficiency; it has occurred despite an
improvement in survival rates for those who develop melanomas. If age-
specific death rates over a number of years are examined in terms of birth
cohorts, we see that the trends are dominated by year of birth. This
indicates steadily increasing risk. Interestingly, no such trends have yet
been detected with regard to melanoma of the eye.
Although there is evidence that sunlight plays some role in melanoma
genesis in white-skinned individuals, this relationship remains problematic
and far from definitely proven. We lack an accepted animal model in which
ultraviolet or sunlight reproducibly causes melanoma. Available epidemiologic
studies are almost all ecologic and associate melanomas with some potential
surrogate of sun exposure such as latitude of residence. Although it is often
presumed that UV-B is the region of solar radiation responsible for causing
melanoma (because it damages DNA), this supposition lacks proof, even if we
accept a relationship to sun exposure.
Perhaps the single most convincing piece of evidence for a role for UV-B
in the induction of melanoma is the high frequency of melanoma in XP. But
even in this condition the repair defect is not confined to UV-B induced
photoproducts, so that agents other than UV-B could conceivably account for
this predisposition.
Melanomas occur in at least three distinguishable histologic forms which
appear to have differing relationships to solar radiation. Lentigo maligna
melanoma, which accounts for about 14 percent of melanomas, is slow growing
and occurs characteristically on the heavily sun-damaged skin of the face of
older, light-skinned, individuals. Modular melanoma (32 percent) and super-
ficial spreading melanoma (54 percent) occur mostly on the trunk and limbs and
are less clearly related to sun exposure.
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There are several observations that possibly link melanomas to sun
exposure, but the evidence is not consistent. Melanoma is much more frequent
in those who are light-skinned and those who sunburn easily. It is even more
frequent in those who have certain types of pigmented moles called dysplastic
nevi (Kraemer and Greene 1985). These moles tend to run in families and to a
large extent, but perhaps not entirely, the familial tendency of melanomas is
determined by the presence of these lesions. Melanomas are more frequent in
those who sunburn easily and who have had severe or repeated sunburns in
childhood; however, in contrast to most nonmelanoma skin cancers, melanomas
are not usually on exposed parts of the body. Latitude studies have shown a
broad relationship between melanoma in Caucasians and insolation, but studies
are inconsistent. Migrant studies strongly support a childhood spent in a
sunny location as an important factor in the later development of melanoma.
Melanoma is a disease of higher socioeconomic classes and is not seen as much
in those with the highest outdoor exposure. It has, therefore, been suggested
that a causal factor for melanoma might be intermittent (i.e., weekend or
vacation) high sun exposure, but this hypothesis awaits proof. Indeed the
risk of melanomas in individuals seems to be less in those with increasing sun
exposure, suggesting that individuals continually exposed to the sun have less
risk either because of tanning or because susceptibles purposely avoid sun
exposure, or both (Graham et al. 1985).
In any case, if solar radiation is a factor in causing human melanomas
the relationship appears complex, and the distribution of the disease popula-
tions is probably not directly determined simply by total cumulative sun
exposure.
ULTRAVIOLET EFFECTS ON THE EYE
The effects of ultraviolet radiation on the eye (Lerman 1980) are
affected both by the amount of ambient radiation incident on the surface of
the eye and by differential transmission through the ocular tissues. We have
been studying the amount of radiation that may impact the corneal surface in
outdoor workers. Only a small proportion of the ambient solar ultraviolet
impinges on the eye; the amount varies with season, activity, reflecting
surfaces in the vicinity, and whether or not the subject wears a hat or
glasses. Plastic lenses are particularly effective in reducing the flux of
UV-B at the surface of the eye. Although direct effects of ultraviolet on the
retina are not generally expected in normal individuals because the radiation
is absorbed in the lens, substantial ultraviolet reaches the retina in aphakic
individuals.
The known effects of ultraviolet on eye are indicated in Table 4. The
best known effect on the conjunctiva and cornea is acute photokeratitis, most
effectively caused by radiation in the 288- to 290-nm wavelength region in
which necrosis and death of corneal cells occur. The condition, known by such
names as "welders flash burns" or "snow blindness," is characterized by a
gritty sensation in the eyes, tearing, photophobia (sensitivity to light) and
blepharospasm (spasm and closure of the eyelids). The eyelids are also often
red. The symptoms occur after a latent period of from 30 minutes to 24 hours,
which varies inversely with the dose. Symptoms are usually self-limited and
heal within 48 hours. Permanent injury is rare.
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Table 4. Effects of Ultraviolet Radiation on the Eye
Conjunctiva and Cornea
Photokeratoconjunctivitis
Chronic Actinic Keratopathy
Corneal Tumors
Benign Pterygia
Carcinoma of the Cornea (very rare)
Diseases Triggered by Ultraviolet
Herpes Simplex Keratitis
Recurrent Corneal Erosions, etc.
Lens
Nuclear Cataract
Retina
Retinal Damage (aphakics, others?)
Ocular Melanoma (?)
In chronic actinic keratopathy there are white or yellow-brown nodular
opacities confined to the sites of the cornea covered by the lids. These have
a restricted geographic location and are confined to areas of the world with
high ultraviolet exposure in the eye (e.g., "Labrador keratopathy").
Ultraviolet radiation appears to be a major factor in developing pterygia
and pingueculae, benign tumors of the conjunctivae and cornea, respectively.
It can also trigger the development of certain corneal diseases including
herpes simplex and recurrent corneal erosions.
The effect of ultraviolet on the human lens is of great interest.
Cataracts can be experimentally produced in rabbits by ultraviolet radiation,
which appears to exert an effect on the lens, at least in part, by acting on
protein-bound tryptophan residues. Nuclear cataracts appear to be more
frequent in human populations where increased ultraviolet exposure occurs,
although studies that relate this exposure to individual ultraviolet exposure
are very few (Pitts et al. 1986). With age there is an increase in pigments
formed in the lens which may both contribute to nuclear cataracts and serve a
photoprotective function in screening deeper tissues in the eye from
radiation.
The retina is particularly sensitive to damage from shorter wavelengths
of ultraviolet. There is no uniform agreement regarding the significance of
this observation for normal people, but in aphakic individuals substantial
opportunity for retinal damage seems to exist. Two recent studies have raised
the possibility that ocular melanoma, a relatively rare but serious neoplasm,
might be related to sun exposure (Tucker et al. 1985). If this finding is
correct, it remains speculative whether the ultraviolet portion of solar
radiation is responsible.
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ROLE OF PHOTOSENSITIZING SUBSTANCES
A number of foreign substances act as photosensitizers in that they
absorb ultraviolet (or visible) radiation and augment or change the tissue
response to this radiation (Emmett 1979). Well-known photosensitizers include
several components of coal tars and pitches; chemicals produced by plants
including psoralens; a variety of dyes, drugs, and antibacterials in common
use; and photoinitiators used for industrial photochemical processes.
Potential photosensitizers are increasingly common components of products used
in modern life.
The most common reactions are designated as "phototoxic" and occur as
direct toxic effect from the chemical and ultraviolet radiation without
mediation of the immunologic system. A -variety of reactions are produced on
the skin, including severe reactions resembling sunburn and severe blister-
ing. In the eyes, photokeratoconjunctivitis and cataracts may result. As
mentioned previously, some photosensitizers, notably 8-methoxypsoralen in
combination with UV-A, have been shown to be carcinogenic both in experimental
animals and humans.
More rarely, individuals can develop photoallergy, an allergy of the skin
dependent on exposure to both the chemical and ultraviolet radiation. Photo-
allergic reactions are not known to result in cancer but a so-called persis-
tent light reaction can ensue which will persist for years with trivial
amounts of sun exposure, even in the absence of further contact with the
inciting chemical.
CONCLUSION
We have reviewed the various effects of ultraviolet on human health. In
considering the health effects of ozone modification, we are particularly
concerned with the chronic effects of ultraviolet radiation. These are not
determined solely by the amount of ultraviolet radiation but also by other
factors. The three major factors involved are exposure to ambient solar
radiation, individual susceptibility, and personal behavior. From the point
of view of human health we cannot sensibly address the issues involved without
considering all three factors.
Future studies of chronic effects will advance the field to the extent
that they gather information on individual susceptibility and behavior, and in
the case of studies of tumors, by relating to or distinguishing individual
tumor types. Future risk assessments will only make medical or biologic sense
to the extent that they take these factors into account.
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Ozone Depletion and Ocular Risks From
Ultraviolet Radiation
Morris Waxier
Center for Devices and Radiological Health
Food and Drug Administration
Rockville, Maryland USA
INTRODUCTION
Because depletion of the ozone layer (Watson et al. 1986) increases
ultraviolet (UV) radiation, and since ambient outdoor levels of UV radiation
have been implicated as a risk factor for retinal damage and cataract
formation (Waxier, In press), expected atmospheric changes may increase the
risk of eye damage.
Ultraviolet (UV) radiation can damage the cornea (Pitts 1973), the
crystalline lens (Pitts et al. In press), the ocular photoreceptors (Massof et
al. In press), and the retinal pigment epithelium (Ham et al. In press). This
damage may contribute to long-term problems such as retinal degeneration
(Newsome et al. In press), visual aging (Owsley et al. In press), impaired
visual development (Fulton et al. In press), and cataracts (Pitts et al. In
press). These analyses were made to determine whether optical radiation has
the potential to produce long-term visual health problems and, if so, under
what conditions they might occur. A risk assessment was conducted (Waxier, In
press) to focus attention on estimating the risks that optical radiation poses
for long-term visual health problems, the conditions under which they might
occur, and the ways by which we can minimize the occurrence of such problems
on the basis of what we know. This risk assessment will provide the basis for
judging the extent to which depletion of the ozone layer increases these
problems.
VISUAL HEALTH PROBLEMS
To provide some informed guesses about the likelihood that long-term
visual health problems could result from exposure to optical radiation, we
need to specify the visual health problems about which we are concerned, and
then to analyze the evidence of involvement of optical radiation in these
problems. First, the potential health problems already have been identi-
fied. They are cataracts, stable retinal disorders, retinal degeneration,
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visual aging, and developmental disorders. Second, because these long-term
problems stem from similar photobiological and visual science principles, the
following series of questions were devised to help in this risk assessment:
• Does the ocular tissue involved in the disorder absorb optical radia-
tion?
• Does the absorbed radiation induce bioeffects in this tissue?
• Are these radiation bioeffects a hazard to this tissue?
• Can the disorder be deduced from the damage induced in the ocular
tissue by the radiation?
• Is there evidence confirming that the disorder is caused, wholly or in
part, by optical radiation?
• Can the probability that optical radiation induces this disorder be
estimated?
Cataracts
First, we know that the crystalline lens absorbs ultraviolet radiation
(Boettner and Wolter 1962; Kinsey 1948; Cooper and Robson 1969). Moreover, UV
radiation can induce biochemical and histological effects in the crystalline
lens of various animals (Pitts et al. 1977; Zigler and Goosey 1981). In
addition, some of these bioeffects are related to UV-induced opacities in
human and animal lenses in vitro (Lerman 1983; Varma et al. 1983). Although
there are a number of limitations to extrapolating these data to the In situ
lens of the human eye (Pitts et al. In press), the deleterious bioeffects do
provide a basis for identifying cataracts as a hazard of ultraviolet radia-
tion. Various studies have determined the wavelengths and radiant exposures
needed to induce cataracts (Pitts 1973; Pitts and Cullen 1981; Schmidt and
Zuclich 1980; Zuclich and Connolly 1976). Several photochemical pathways have
been described whereby cataracts could be induced in humans (Jose 1978; Zigman
1981). Moreover, there are similarities between UV-induced cataracts and
human cataracts of unknown etiology that provide an added basis for postu-
lating a risk of UV cataracts in humans (Lerman and Borkman 1976). Finally,
there are clinical reports of photosensitized cataracts in humans (Lerman et
al. 1983) and, more importantly, epidemiological evidence that demonstrates an
association between exposure to ultraviolet radiation and cataracts (Hollows
and Moran 1981; Hiller, Giacometti, and Yuan 1977; Taylor 1980; Hiller,
Sperduto, and Ederer, 1983; Ederer, In press). Thus, there is sufficient data
to identify cataracts as a risk of ultraviolet radiation. However, the
uncertainties associated with this evidence limit the utility of this
epidemiological data for estimating the risk of human cataracts from UV
radiation.
Stable Retinal Disorders
Studies have been conducted that provide a chain of evidence on which to
postulate that optical radiation can contribute to human retinal disorders
that are not progressive, i.e., stable retinal problems. This chain starts
with the knowledge that UV-B, UV-A, and light are absorbed by various retinal
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tissues (Wolbarsht 1976; McGuinness and Proctor 1973)- Moreover, the amount
of radiant energy incident on the retina depends on the transparency of the
cornea and lens, and on pupil diameter. Next, a large number of bioeffects of
these wavelengths have been identified as being hazardous to the retina
(Massof et al. In press; Ham 1984). Further, empirical estimates have been
made of the domain of time, intensity, and wavelength that can induce damage
to the pigment epithelium, the photoreceptors, and the inner retina. These
estimates provide sufficient quantitative evidence to establish safety
standards to protect people from the short-term retinal damage which could be
induced by lasers and other intense sources of optical radiation (Ham 1984;
Sliney and Wolbarsht 1980). There is, moreover, sufficient evidence of
additive and persistent changes in the monkey and human retina to hypothesize
that some stable long-term visual impairments in humans may be related to
optical radiation. There are reports that optical radiation produces retinal
damage hours, days, months, and years after irradiation. Although it is
sparse, this evidence is instructive. For example, sungazing by humans has
been reported to produce persistent, evolving, and delayed alterations in the
visual system. Craik reported that aniseikonia may persist for years
(Cavonius, Elgin, and Robbins 1974). Pigmentary patches and blind spots have
been reported to evolve in a complicated fashion over many months after solar
retinopathy (Loewenstein and Steel 1941). In addition, late complications
resulting in reduced visual acuity have been described (McFaul 19&9).
Furthermore, there are several reports in humans of prolonged and even
cumulative impairments in dark adaptation following extended viewing by humans
of skylight (Hecht et al. 1948; Clark, Johnson, and Dreher 1946) or bright
blue, violet (Brindley 1953), and ultraviolet (Wolf 1949) radiation. Also,
there is at least one report of persistent visual impairment resulting from
accidental exposure to ultraviolet radiation from a welding arc (Naidoff and
Sliney 1974). Even more important is the description by Tso and Woodford
(1983) of sub-RPE neovascularization and late impairment in fluid transport
after several years of evolving changes in retinal pathology following
excessive exposure to optical radiation. Although long-term observations of
the monkey retina damaged by UV have not been conducted, some of the
fluorescein leakage that has occurred within days or weeks following irradia-
tion suggest longer term sequelae.
Some of these effects are the result of injury to the retina, which was
ophthalmoscopically visible; others resulted from exposures to optical radi-
ation that did not produce ophthalmoscopically visible damage. Most important
are two demonstrations that the addition of subthreshold exposures separated
by several days induces retinal damage (Griess and Blankenstein 1981; Kuwabara
and Okisake 1976). The data strongly suggest that retinal damage induced by
optical radiation can accumulate over days. This is especially important
since the concern about long-term visual health problems necessarily involves
consideration of the intermittent nature of exposure to emissions from
multiple sources over an extended period of time. Split-dose experiments
using UV-A radiation of the monkey retina are in progress and strongly suggest
that the damage accumulates over days to produce pathological changes that
persist for months. Photobiological principles suggest that a similar
cumulative effect would occur in the UV-B region.
Retinal Degeneration. There are some reasons to suspect that retinal damage
induced by ultraviolet radiation can be unstable, that is, it can produce
progressive damage. The retina of monkeys can be damaged by ultraviolet
149
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radiation (Ham 1984; Peyman, Sloan, and Lira 1983). This damage to the retinal
pigment epithelium, to the photoreceptors, and to the neurons is dose-
dependent, photochemically mediated, and cumulative over hours and days.
Although very few long-term observations have been made on the primate retina
following excessive exposure to optical radiation, there are theoretical
reasons to suspect that a retina compromised by disease or age would be more
vulnerable to any degenerative changes that could be induced by optical
radiation (Young 1981). The combination of short-wavelength optical
radiation, oxygen, chromophores, and photosensitizers in the retina is potent
with possibilities for producing retinal degeneration, although direct
evidence of the exacerbation of retinal degeneration by optical radiation has
been obtained only in rodents (LaVail and Battelle 1975). In addition, the
higher retinal doses of UV received by aphakes and pseudophakes make these
individuals especially vulnerable to cystoid macular edema (Kraff et al.
1985). Fluorescein leakage occurs following exposure of the retina of the
aphakic monkey eye to UV-A radiation (Peyman, Sloan, and Lira 1983; Tso et
al. Work in progress), but comparable studies using UV-B radiation have not
been conducted. Therefore, retinal degeneration should be considered a risk
of excessive exposure to ultraviolet radiation.
Very little research has been conducted on primates, on diurnal animal
models of human retinal degenerations, or on retinas compromised by chemicals,
age, or other agents. The striking evidence of long-delayed and persistent
changes in the monkey retina following optical radiation, coupled with some
clinical evidence in humans, suggests that research on primates needs to be a
priority.
Aging Disorders. Deterioration of the visual system as individuals age is a
fact (Owsley et al. In press). The likelihood that optical radiation
contributes to this deterioration is high for several reasons. First, the
cellular pathology observed in older individuals is similar in appearance to
radiation-induced damage (Kuwabara 1979). Second, the ophthalmoscopic
appearance of the aged retina is sometimes similar to a retina exposed to
optical radiation (Guyer et al. 1986). Third, some of the kinds of vision
loss described in the aged are consistent with the losses that could be
produced by optical radiation damage (Klein 1958; Jaffe, de Monestario, and
Podgor 1982). Fourth, the accumulation of lipofuschin material in the RPE and
other changes in the retina suggest that the aged retina has less capability
of repair (Feeney-Burns, Berman, and Rothman 1980). The retina of the human
aphakic eye has three times more macular drusen and pigmentary changes than
the retina of the phakic eye, suggesting that UV plays a role in aging the
human retina (Guyer et al. 1986).
Optical radiation may have quite different visual health consequences for
eyes with and without ocular disease. Optical radiation may accelerate the
deterioration of central vision in older individuals with central retinal
disease, whereas, in those free of ocular disease, optical radiation may
impair paramacular and peripheral vision more than foveal vision. This inter-
pretation is offered to reconcile the facts of visual loss outside the macula
in disease-free aged eyes (Owsley et al. In press) with Young's prediction
that the central retina will exhibit the major effects of lifetime retinal
exposure to optical radiation (Young 1981). This ad hoc explanation is not
very satisfactory but it does indicate the need to temporize theory with
data. Other interpretations also are possible, e.g., those individuals with
150
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central retinal disease may have had a different exposure history or some
genetic vulnerability.
Given these facts and theoretical considerations, exposure of the aged
retina to more ultraviolet radiation than permitted by the phakic eye probably
is hazardous. The retina of the aged individual is exposed to more radiation
than phakics receive when the crystalline lens is extracted without placing a
comparable filter in front of the retina, even when ordinary sunglasses are
used.
Research is needed to determine the extent to which optical radiation is
a factor in the deterioration of the vision of the elderly. In the meantime,
we should take practical steps to protect our eyes from excessive optical
radiation, and thus prolong our visual lifetime.
Development Disorders. While there are several reasons to suspect hazardous
effects of optical radiation on visual development, almost no research has
been conducted on the developing primate retina. In fact, there is very
little experimental data on the exposure of the developing retina of any
species.
Glass et al. (1976) have reported that the probability of retinopathy of
prematurity (ROP) is highest in infants exposed to more light during their
hospital stay. This evidence is consistent with the evidence for the
interaction of oxygen and light in retinal damage (Lerman 1980). The action
spectrum for this effect is unknown but UV-B and UV-A probably play a role.
Furthermore, there is a large variety of sources of optical radiation and
situations in which infants are exposed to optical radiation. Some of the
same evidence that gave rise to suspicions about the role of optical radiation
in retinal degeneration and visual aging is relevant to the potential hazards
to visual development, i.e., short-wavelength radiant energy incident on the
retina, short-wavelength chromophores in the retina, dose-dependence of
retinal damage, cumulative effects, long-duration effects, and delayed
effects. In addition, special properties of the developing visual system
might decrease injury threshold, such as more transparent ocular media and
different densities of chromophores and screening pigments, or might increase
the vulnerability of infants, such as long periods of post-natal retinal
development (especially foveal) and early dependence on nonfoveal visual
fields. Thus, the long periods required for many visual processes to mature
suggest a window-of-vulnerability during which time optical radiation might
alter later visual performance, especially if optical radiation alters the
spatial and temporal summation properties of the neural retina.
Even though there is little experimental data on the effects of optical
radiation on the developing retina, photobiological and visual science
evidence is sufficient to postulate that exposure to optical radiation may
cause disorders of visual development.
151
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CONDITIONS AFFECTING RISKS
Exposure Variables
Several exposure conditions affect the likelihood of long-term visual
impairment. The fundamental parameters are wavelength, level of radiant
exposure, and duration of radiant exposure. Ocular damage occurs at lower
radiant exposures and shorter exposure durations for shorter wavelengths.
More intense repetitive exposures at various wavelengths can cause eye damage,
as can exposures of longer duration at intermediate levels of radiation.
Depletion of the ozone layer increases the ambient level of UV-B radiation and
therefore also increases the risk of eye damage.
Biological Variables
A number of biological factors influence the potential for visual
impairment from exposure to optical radiation. Pupil size and the absorption
characteristics of ocular tissues are quite important. Lens transparency and
yellowing, aphakia, and pseudophakia are important factors in estimating how
much retinal damage will occur. Lens yellowing may promote additional
opacification of the lens by increasing the absorption of UV and blue light;
on the other hand, the retinal damage threshold will be increased. An
increase in oxygenation and temperature in ocular tissues will greatly
increase the potential for visual impairment. Also, the developing infant eye
and the aging eye may be especially vulnerable to the damaging effects of
radiation. The retina may be more vulnerable to radiation effects when it is
degenerating because of genetic or other toxic effects. The cumulative effect
of photochemical events and tissue repair rates are crucial biological
variables influencing the likelihood of long-term visual health problems.
Long-Term Risk—An Exercise in Its Estimation
This section attempts to estimate the domain of optical radiation risk to
long-term visual health. This domain refers to a subset of the wavelength and
radiant exposure parameters. This is an effort to establish a boundary
between those exposure conditions that are likely to produce visual health
problems and those that are not.
Determine Radiant Exposure Associated With Disorders. First, to establish
such a boundary, the radiant exposures of each particular ocular disorder must
be determined.
The Possible Effect of UV Exposure on Cataracts. Some of the epidemiologic
data on sunlight and cataracts can be used to estimate the radiant exposure at
UV-B wavelengths (Hollows and Moran 1981; Hiller, Giacomett, and Yuan 1977;
Taylor 1980). Each of these studies found that cataracts were positively
associated with sunlight exposure when the latter exceeded an annual level of
2500 Minimal Erythemal Doses (MEDs). Luckiesh et al. (1930) reported the MED
in the UV-B to be about 0.004 joules per square centimeter. Therefore, 2500
MED equals 10 joules per square centimeter annually. The daily radiant
exposure would be the annual dose divided by 365 days, 0.027 joules per square
centimeter and a three-hour daily exposure would be 0.0068 joules per square
centimeter. On the other hand, if we use 3^8 joules per square centimeter as
the value (Parrish, Jaenicke, and Anderson 1982) for the MED at 300 nm, the
152
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three-hour estimated dose becomes 0.06 joules per square centimeter. Another
estimate can be derived by using the local ambient level at 310 nm at 15°N
reported by Johnson et al. (1976) and the epidemiologic data reported by
Zigman et al. (1979). This estimate is 0.9 joules per square centimeter.
Several estimates of the UV-A radiant exposure needed to induce cataracts
can be derived or have been reported. If only the UV-A wavelengths emitted by
the sun are responsible for the cataracts associated with 2500 MEDs insola-
tion, then the annual radiant exposure associated with cataracts would be
140,000 joules per square centimeter, approximately 395 joules per square
centimeter daily and 98.8 joules per square centimeter for a three-hour daily
exposure; this assumes (Johnson, Mo, and Green 1976) that one MED at 365 nm
equals 57.7 joules per square centimeter. Another estimate can be obtained
from Lerman (1980). He estimated that accidental exposure of the the human
eye to a UV-A photopolymerization device produced cataracts at 21.6 joules per
square centimeter. Finally, the Zigman et al. (1979) epidemiologic data
suggest an estimate of 0.44 joules per square centimeter, using the local
ambient level (Pitts, Bergmanson, and Chu 1983) at 340 nm at 15°N.
Experimental levels of radiant exposure needed for UV cataractogenesis
are summarized by Pitts et al. (In press). Several values were selected for
comparison to the above epidemiologic estimates. These estimates are
summarized in Table 1. The lowest radiant exposure for UV cataractogenesis is
at 300 nm as estimated from the epidemiologic data. Moreover, even when the
joule equivalent for the MED used is 348 joules per square centimeter rather
than 4.0 joules per square centimeter, the three-hour radiant exposure
estimate of the former is only one log unit higher than the latter. The
Zigman et al. (1979) estimate is only 0.3 log units higher than this high
estimate. Experimental estimates are in this intensity range. These
comparisons strongly suggest that decades of exposure to UV-B induces
cataracts in humans at doses comparable to that suggested by the experimental
evidence. On the other hand, comparison of these UV-B estimates with the UV-A
epidemiologic estimates clearly demonstrates that higher doses of UV-A than
UV-B are needed to induce cataracts. However, how much higher is not clear.
The estimates based on the Hollows and Moran (1981); Hiller, Giacometti, and
Yuan (1977); and Taylor (1980) data correspond closely to the experimental
data, suggesting that 4.0 log units more radiant exposure are needed at UV-A
than at UV-B wavelengths. On the other hand, the UV-A estimate based on
either the Zigman or the Lerman data suggest that only 1.5 log units higher
doses are needed.
The Possible Effect of UV Exposure on Retinal Problems. The following
estimates of the level of radiant exposure needed to induce long-term retinal
problems assume a three-hour daily exposure additivity over days and
additivity over wavelength. When the data used for the estimation were based
on an exposure of less than three hours, the level of radiant exposure was
calculated based on the particular duration used in that study (i.e., 1000
seconds). Evidence that the damaging effect would accumulate over a period of
time at least as long as three hours provides a critical bridge between these
shorter durations of exposure (higher dose rate). On the other hand, when the
data were based on exposures longer than three hours, dose was prorated to a
three-hour duration. For broad-band sources of optical radiation, wavelength
additivity was assumed and the estimate was based on the total integrated dose
reported.
153
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Table 1a. Radiant Exposure for Cataractogenesis: Experimental
Wavelength
Band
UV-B
Radiant
Exposure
(Jem'2)
1.2 x 10~1r3
4.5r3
1.26 x 101r3
Exposure
Duration
(s)
191. 5r
6374r
4749r
Corneal
Irradiance
(WcnT2)
6.27 x 10~4r
7.06 x 10~4r
2.65 x 1(T3r
UV-A
5.06 x 101r3 3.6 x 104r
1.0 x 102r3
1.405 x 10~3r
Table 1b. Radiant Exposure for Cataractogenesis: Epidemiologic
Wavelength
Band
UV-B
Radiant
Exposure
(Jem'2)
6.8 x 10~3d
6.0 x 10~2d
9.0 x 10"2d
3.24 x 10~1d
Exposure
Duration
(s)
1.08 x 10^a
1.08 x 10^a
1.08 x 104a
1 .08 x 10^a
Corneal
Irradiance
( Jem )
2500MED1r23'24'25
2500MED2r23'24'25
1.3 x 102r,a70'71
3.0 x 10~5Wcm-2r*
UV-A
4.5 x 10-1d 1.08 x 104a 6.56 x 102r70'71
9.88 x 10~1d 1.08 x 104a 2500MED3r23'24'25
r - reported
d - derived
a - assumed .
1 - 1.0 MED = 4.0 x 10~3Jcm-2 r,a°jj
2 - 1.0 MED = 3.48 x 102JcnT2 r,a°9
3 - 1.0 MED = 5.77 x 101JcnT2 r,ab9
* - Dose rate reported to be associated with cataracts induced by dental
photopolymerizer (Cole et al. 1985)
154
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The only human data from which one could derive an estimate of the
radiant exposure of UV that could damage the retina were in Hecht et al.
(1948) and Clark et al. (1946). These data showed that staring at skylight
for several hours induced an abnormal retardation of dark adaptation. Since
rhodopsin has an absorption ban in the UV-A (Kurzel, Wolbarsht, and Yamanashi
1977), this deficit could have been due to the ambient outdoor UV-A. If the
ambient level of UV-A at the cornea was about 0.09 joules per square
centimeter as suggested by Ham and Mueller (1982), then the retinal radiant
exposure might have been about 0.009 joules per square centimeter in the Hecht
and Clark studies. Experimental estimates of UV retinal damage in monkeys
have been few. Schmidt and Zuclich (1980) found the threshold at 325 nm to be
10 joules per square centimeter. Recent evidence in phakic rabbits (Pitts,
Bergmanson, and Chu 1983) and rats (Rapp, Jose, and Pitts 1985) suggests that
the radiant exposure necessary to damage the retina is even lower at 300 nm.
The current threshold for 300 nm damage to the monkey retina is approximately
0.6 joules per square centimeter. Ham and Mueller (1982) found that the
aphakic monkey has thresholds of 5.0 joules per square centimeter at 325 nm,
5.4 joules per square centimeter at 350 nm, and 8.1 joules per square
centimeter at 380 nm. These estimates are summarized in Table 2. Estimates
are provided for wavelengths longer than 400 nm to compare the effectiveness
of various spectral regions.
Griess and Blankenstein (1981) have shown that the damage at 441 nm is
cumulative over days, thus, not only verifying the radiant exposure needed to
produce the damage, but also demonstrating that one-half the energy can be
delivered 24 hours later and still damage the retina! Preliminary data (Tso
et al. Work in progress) show that a similar effect occurs with UV-A radia-
tion. UV-B probably produces a comparable effect, although this is an
extrapolation based on photobiological principles, not on direct split-dose
evidence.
Identify Ambient Levels and Compare to Radiant Exposure Estimates. Ambient
levels of optical radiation have been measured at many geographical locations
around the world. Johnson, Mo, and Green (1976) have measured solar radiation
as a function of latitude from 305 to 340 nm. These data are adjusted for
three-hour daily exposures. Since their data included only wavelengths up to
340 nm, the solar spectral radiance reported by Sliney and Wolbarsht (1982)
was used for wavelengths longer than 340 nm. Their spectrum for the "summer
sun near zenith" was multiplied by a solar disc size of 0.00006 sr to obtain
the solar spectral irradiance and then multiplied again by the number of
seconds in a three-hour exposure to obtain the solar radiant exposure.
Several other sources are available for more detailed analytical research on
ambient levels of solar radiation (Green, Sawada, and Shettle 1974; Green,
Cross, and Smith 1980).
The relationship of these outdoor ambient levels to the radiant exposure
estimates for cataracts and retinal disorders should be noted. Cataracts can
result from outdoor ambient levels of UV-B and UV-A; however, UV-B is much
more effective. Ozone depletion would increase ambient levels of UV-B
radiation much more than UV-A radiation. Within the UV-A region there is
considerable variability in the estimates. The possible bases for these
differences will be discussed later. Ambient UV-A levels outdoors seem to be
sufficiently intense to damage the retina. Most damage thresholds between 400
and 760 nm are one or two log units above ambient light levels outdoors with
155
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Table 2. Radiant Exposure for Retinal Damage
Wavelength Radiant
(nm) Exposure
( Jem )
1
5
5
5
9
9
9
1
2
3
5
2
2
1
6
8
9
1
3
3
3
3
1
1
1
6
3
5
1
1
7
1
9
9
.0 x
.Or
.4r
.5r
. ir
.0 x
.0 x
.5 x
3V
A
.0 x
.0 x
.2 x
.57 x
'.4r
.52 x
.0 x
.2 x
.0 x
.0 x
.0 x
.0 x
.1 x
.08 x
.0 x
.0 x
.Od
.Od
• 3d
.0 x
.5 x
.08 x
.0 x
.5 x
101d
10~2d
10~3d
10 r
10 r
10 r
10 r
101r
10V
10'r
10~^d
10 V
102d
10 r
10Jr
102r
102r
10"3r
10~2r
102r
1Q r
102r
10 r
Exposure Retinal
Duration Irradiance
(s) (Wcm~2)
8
1
1
1
1
1
1
1
1
1
r 4
1
3
6
9
1
1
1
1
1
1
1
1
1
1
1
.0 x
.08 x
.08 x
.0 x
.0 x
.0 x
.0 x
.08 x
.0 x
.0 x
.8 x
.0 x
.2 x
.0 x
.0 x
.02 x
.2 x
.0 x
.08 x
.0 x
.0 x
.08 x
.0 x
.08 x
.0 x
.0 x
10"1r
104a
1Q4a
102r
103r
103r
1Q a
102r
102r
103r
2
101r
102r
102r
103r
103r
1°3U
10 r
104r
104a
in
10 r
10;>r
10 r
1
1
1
1
1
8
8
1
2
3
5
2
2
1
1
2
9
3
5
3
2
2
1
1
1
6
1
1
1
9
7
1
9
9
.3 x
.0 x
.0 x
.0 x
8x
x
.0 x
.5 x
.5 x
.5 x
.3 x
.0 x
.0 x
.0 x
.57 x
.3 x
.0 x
.0 x
.0 x_
.75d8
.0 x
.3 x
.9 x
.5 x
.1 X
.0 x
.0 x
.0 x
.08 x
.08 x
.08 x
.3 x
.5 x
.0 x
.0 x
.5 x
101d
102r
102r
|j)lr
1°-g
1 O
10~7
10~2
io-2
io-2
io-2
1
^
d
r
r
r
r
10~3r
10~1r
102r
10
io:2
1,82
10"?
io-2
io-2
io-2
10
1°-5
w~l
1|
104
10
10~7
10~1
10~2
10~J
10~'
d
r
r
r
r
r
r
r
r
r
7 »
39
*
77
77
80
80
44
4'
57
58
80
c* f^
83
83
83
83
80
44
85
85
a. 2
a. 4
a
d
r
r
O r*i
80
r» A-.
77
5 0 x 10~2r77
. . j .\j iw i
5.1 x 10~^r''
5.4 x 10~2r77
8 I x 1 0 r
.«.973 x 10~3r77
,7
7, **
**
»
4x 10" r'
,
8 x 10~4r49»121
•6 x 10-^9-121
1 2 x 10~4r84
|39,40
rQn
r
UU
r - reported
d - derived
a - assumed
* - assumes 10% corneal exposure
# - R.G. Allen, personal communication
additivity over days at 1.0, 0.5 and 0.25 times threshold dose
** _
- R.G. Allen, personal communication
156
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the sun at zenith. However, several estimates are within 0.5 log units of
outdoor ambient levels.
Determine Proportion of Ambient Likely to Be Incident on the Cornea. So far
we have assumed that all of the ambient radiation in a three-hour period was
incident on the cornea. However, Cole et al. (1985) have demonstrated that
only 25 percent of ambient radiation reaches the skin of the face of a human
standing upright and looking forward. Furthermore, in a standing position,
the corneal dose may be only 10 percent of ambient due to shielding from the
brow ridge and the corneal grazing angle in the ultraviolet (Wolbarsht
1982). However, an individual prone on his back with eyes open could receive
a 100 percent corneal dose of ambient. On the other hand, Sliney (1986) and
Rosenthal (1985) report higher ocular irradiances of UV-B from reflective
surfaces on the earth's surface than from skylight.
These considerations suggest that cataracts associated with UV ambient
levels may be due to corneal doses 1.0 log unit lower than the ambient
level. Since the Hecht et al. (1945) and Clark, Johnson, and Dreher (1946)
data are based on staring at the sky, 100 percent of ambient level is an
appropriate value for their data. However, for those individuals who do not
stare at the sky, the corneal dose may be 1.0 log unit lower than the ambient
radiation.
Determine Proportion of Ambient Level to Which anIndividual Is Likely to Be
Exposed and _Number of Days Exposed Per Annum. The variety of physical,
cultural, and occupational environments in which people live is enormous. The
previous discussions assumed that everyone is exposed to ambient outdoor
levels 365 days per annum, three hours per day. Situations exist where people
may be exposed to much more or much less than this amount.
Setting Risk Boundaries. Most of the estimates of radiant exposure that can
damage the eyes are within 1.0 log unit of outdoor ambient levels. Therefore,
one risk boundary can be established as 1.0 unit below the average outdoor
ambient levels to establish a safety factor. This boundary should be moved
lower to take into account increases in UV-B radiation that are caused by
ozone depletion. The implication is that radiant exposure of the eye for
three hours at levels above this boundary (the pink area) is probably a long-
term visual health risk, i.e., the "probable risk" area.
Since there are some estimates that fall below this region of probable
risk, a lower boundary was constructed to take these estimates into account,
as well as certain worst-case conditions. For example, the epidemiologic
estimates for cataracts were derived as if the effects occurred independently
at only two wavelengths, 300 and 365 nm, an unlikely possibility;
cataractogenesis due to broad-band UV exposure is probably additive across
wavelengths. (Note: As a matter of fact, there isn't even any experimental
evidence that UV at 365 nm can induce cataracts in vivo at doses below 100
joules per square centimeter.) As a consequence, the lower boundary could be
set two log units below the upper boundary. In addition, these epidemiologic
studies are not very precise, so that perhaps cataracts are associated with a
lower number of annual MEDs.
If certain worst-case assumptions are made, such as subthreshold effects,
genetic susceptibility, exogenous photosensitivity, poor nutrition, and
157
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frequent exposure to ultraviolet radiation, then perhaps the lowest radiant
energy at which cataracts might be induced is an order of magnitude lower than
the lower boundary. However, the empirical estimates already may represent
worst-case conditions; for example, cumulative effects over time and
wavelength were assumed in establishing the estimates. If worst-case
assumptions are accepted, then perhaps the reported estimates should be
lowered by an order of magnitude at wavelengths shorter than 460 nm. Some of
the worst-case assumptions are aphakia and pseudophakia without blue and
ultraviolet blocking filters, transmittance of infant lenses close to 1.0,
genetic and disease susceptibilities, exogenous photosensitization, and addi-
tivity of damage over days. Each of these is a special case requiring
clinical management.
Although some of these estimates are based on sparse data and assume
worst-case conditions, they provide some prediction of the wavelength-radiant
exposure domain within which optical radiation can be expected to produce
long-term visual health problems in the primate eye. Therefore, to conduct
critical tests of long-term visual health problems, wavelengths in the blue
and ultraviolet regions should be used at radiant exposures from as low as
approximately 0.1 joules per square centimeter to 0.000001 joules per square
centimeter, respectively.
Reduce Invisible Radiation of the Eye. People in outdoor occupations should
protect their eyes. Reducing the amount of ocular irradiation by using hats,
umbrellas, or sunglasses is a simple precaution that can be taken to avoid
potential long-term visual impairment. Shielding the eyes from sunlight is
especially valuable on bright sunny days on a sandy beach or snow field.
Sunglasses that absorb the proper wavelengths certainly should be worn when
staring into skylight. One should never gaze directly at the sun or an
eclipse, even when wearing sunglasses.
While sunglasses have been available for many years, questions have been
raised about their effectiveness in protecting the eyes from ultraviolet
radiation (Sterne 1984). Although voluntary standards (ANSI Z 80.3) exist for
nonprescription sunglasses (American National Standards Institute 1977), there
are no standards for prescription sunglasses. Therefore, there is no
assurance that there is sufficient filtration of ultraviolet radiation in
prescription sunglasses. While the Sunglass Association of America claims
that those nonprescription sunglasses made in compliance with the voluntary
standard provide adequate protection from UV radiation (Loomis, personal
communication), the consumer has no way of knowing whether any particular
brand conforms to this standard. Furthermore, there is disagreement about
whether this standard is sufficiently stringent, especially in the UV-A
region. In addition, there may be sunglasses on the market that are so dense
in the visible region that the pupil can be dilated sufficiently so that the
partial UV filtration is negated by the increased pupil diameter. Various
proposals have been made to solve these problems and they are under vigorous
discussion within the ANSI Z-80 Committee and within the Food and Drug
Administration. Some of these proposals are as follows:
• Require each pair of sunglasses to have a tag with the spectral
transmittance on it.
158
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• Require a "sunscreen" eye protection rating with each pair of
sunglasses.
• Require certification that the sunglasses are made in conformance with
the voluntary standard.
• Increase the voluntary density requirement in the UV.
• Require that prescription sunglasses conform to a standard comparable
to the voluntary nonprescription standard.
Some manufacturers urge consumers to purchase expensive sunglasses which may
not provide much more protection than much less expensive sunglasses. Clearly
some kind of sunglass standard is needed to ensure that both prescription and
nonprescription sunglasses reduce the corneal level of radiant exposure below
the levels associated with cataracts and retinal damage.
UNCERTAINTY
Until there is a more precise understanding about the role of optical
radiation in visual development, visual aging, retinal degeneration, photo-
sensitized reaction, and cataracts, there will be uncertainty about whether
particular protective measures provide too much or too little protection.
People are exposed to optical radiation from a large number of sources over
varying periods of time for an entire lifetime. In addition, depletion of
ozone over time and in certain geographical regions lends more uncertainty.
No matter where the maximum permissible exposure limit is established for
immediate ocular damage, ambient outdoor levels of UV may approach this limit
under some conditions. Until these limits are related to specific long-term
visual health problems, protective measures should be based on some worst-case
estimates. This may mean that "overprotection" will be established, but
people will be better served by using too much protection than by using
borderline or insufficient protection.
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164
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Overview of Our Current State of Knowledge
of UV Effects on Plants
Alan H. Teramura
University of Maryland
College Park, Maryland USA
Fifteen years ago, we virtually knew nothing about the effects of UV
radiation on plants (Nachtwey, Caldwell, and Biggs 1975). Therefore, one of
our first needs was to estimate the degree of UV sensitivity that occurs in
plants. To date, over 200 different plant species and varieties have been
screened for their responsiveness to increased UV (Teramura 1983; Van and
Garrard 1975; Van, Garrard, and West 1976; Tevini and Iwanzik 1982; Biggs and
Kossuth 1978). Most of this work was done on crop plants but also a fair
number of native plants and trees have been examined. Although this initial
work was performed by numerous independent investigators under a wide array of
experimental techniques, an alarming trend emerged: nearly two out of every
three plants tested showed some degree of UV sensitivity (Teramura 1983;
National Academy of Sciences 1982). Members of the pea and bean, squash and
melon, and cabbage families are especially sensitive to UV damage (Teramura et
al. 1983; Biggs and Kossuth 1978; Sisson 1981; Steinmuller 1986). A diverse
array of UV responses can be seen in plants, including physiological and
biochemical responses, as well as morphological and anatomical ones (Teramura
1983; Klein, Edsall, and Gentile 1965; Caldwell 1981; Tevini, Duansik, and
Thomas 1981). In general UV radiation deleteriously affects plant growth
reducing leaf size, limiting the area available for energy capture (Table 1).
Plant stunting and a reduction in total dry weight are also typically seen in
UV-irradiated plants. Of course this large degree of sensitivity elicited
considerable concern; however, during the last five years it has been found
that at least some of this sensitivity was directly attributable to the
experimental growth conditions (Teramura 1982; Teramura, Biggs, and Kossuth
1980). In general, plants grown in growth chambers and greenhouses are much
more susceptible to UV than plants grown outdoors. Although not fully
understood, at least part of this is due to the incomplete development of some
of the natural plant protective mechanisms against UV damage (Mirecki and
Teramura 1984). Therefore it is necessary to examine whole plant responses in
the field whenever possible. Unfortunately, due to the greater costs and
complexities of field experiments, less than a dozen or so studies have been
165
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Table 1. A Summary of the Effects of UV-B Radiation
on Crop Growth
A. Physiological/biochemical effects
1. Photosynthesis
Hill reaction
Electron transport
RuBP carboxylase
PEP carboxylase
Dark respiration
Stomata
Photosynthetic pigments
2. Soluble proteins
3. Lipids
4. Carbohydrates
5. Non-photosynthetic pigments
6. Plant hormones
B. Morphological/anatomical effects
1. Leaf area
2. Specific leaf weight
3. Epidermal transmission
4. Bronzing/glazing/chlorosis
5. Seedling growth/stunting
6. Dry matter production/allocation
7. Yield
C. Response differences
1. Interspecific (species differences)
2. Intraspecific (cultivar differences)
D. Environmental interactions
1. Visible radiation (photoprotection)
2. Water stress
Source: Teramura (1983)
166
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attempted (Teramura 1983). Currently there are only three ongoing field
studies: two sponsored by the United States Environmental Protection Agency
(EPA), and one European study is being sponsored by the West German Ministry
for Research and Technology (BMFT).
While there is a need for field validations to examine whole plant
responses, it is also essential to perform some key growth chamber studies to
understand the underlying causes and mechanisms of UV damage. Otherwise we
will have to blindly screen plants in the field. Controlled environment
studies have provided us with insights into natural mechanisms that protect
plants from UV (Beggs, Schneider-Ziebert, and Wellman 1986; Wellmann 1975).
These protective mechanisms include a wide assortment of diverse biochemical
and morphological adaptations that collectively suggest that UV radiation has
been a strong selective force during the evolution of plants. For example,
many plants produce UV-absorbing pigments in their upper leaf surfaces,
preventing UV from penetrating into the leaf (Robberecht and Caldwell 1978;
Robberecht, Caldwell, and Billings 1980; Wellmann 1982). This is somewhat
analogous to suntanning in human skin. Yet despite these and other mechanisms
against UV damage, some plants still appear to be sensitive to even current
outdoor levels of UV radiation (Sisson and Caldwell 1976; Bogenrieder and
Klein 1978).
Experimental evidence indicates that the effectiveness of UV radiation on
plants is not necessarily linear and there is not always a one-to-one
relationship between UV dose and damage. It is especially clear in field
studies that UV effectiveness is modified by other environmental factors,
including the pattern of precipitation, temperature during the growing season,
soil fertility, and others (Murali and Teramura 1986). For example, under
water stress or mineral deficiency, plants are less susceptible to UV injury
(Murali and Teramura 1985). Therefore, the greatest UV damage is anticipated
under well-fertilized, irrigated situations.
Although it is probably the most important issue concerning the general
public, the effects of UV radiation on crop yield has only been examined in a
handful of studies (Teramura 1983). In fact, detailed information only exists
for one or two crops. Field studies at the University of Maryland (U.S.A.)
have found that a 25% ozone depletion can result in up to a 2Q%-25% reduction
in total soybean crop yield (Table 2). Additionally, UV radiation reduces
seed quality, in terms of reduced seed protein and oils (Teramura unpublished
data). This UV-induced reduction in yield is in addition to current losses
from weeds, pests and diseases, insect attack, etc. Some preliminary evidence
suggests that UV might also heighten losses in these other categories (Esser
1980), effectively producing even greater yield reductions. If these data for
soybean are also generally applicable for other key crops, such as rice,
wheat, or corn, then there is no doubt that we should be greatly concerned
with the potential consequences of ozone depletion upon global food
production.
In addition to direct effects on plants, UV radiation may also play a
more subtle role by indirectly affecting the manner or degree by which plants
interact with one another (Fox and Caldwell 1978; Gold and Caldwell 1983). A
simple example of this might be seen in the competitive interaction between a
crop plant and its associated weedy species. UV radiation may produce a
167
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Table 2. Summary of UV Effects on Soybean Yield and Quality
Year % change in yield % change in seed quality
protein oils
1981
1982
1983
1984
1985
-25
-23
+6
-7
-20
-5
-4
0
0
-2
+ 1
-2
0
Source: Teramura (unpublished)
subtle change, perhaps an increase in rooting depth of the weed, which may
then allow the weed to outcompete the crop plant for water or nutrients. The
net effect of such a change would be an increase in weediness and the
associated problems. In a natural ecosystem, this weediness would lead to a
proliferation of UV-tolerant organisms at the expense of UV-sensitive ones,
which potentially means that the distribution of species may be quite
different in a UV-enriched future.
Despite our increased knowledge of the biological effects of UV
radiation, there is still an enormous amount of uncertainty concerning the
consequences of ozone depletion (Table 3). For example, we,, know that there
exists a tremendous diversity of responses among different plant species to UV
radiation. Yet we still do not have a good understanding why these differences
occur. Although over 200 species and varieties of plants have been screened
for UV sensitivity, 90% of these were crop plants. Therefore, very little
information exists on the impacts of UV on native terrestrial plant
communities, which account for over 90% of the total productivity in the world
(Table 4). Therefore, to address the larger question of the potential
consequences of enhanced levels of UV-B radiation on global communities and
ecosystems, we must currently make the unlikely assumption that perennial
woody trees, such as oaks, respond in an analogous fashion as herbaceous
annual agricultural species, such as spinach.
Although we recently have obtained some information on the effects of UV
in combination with some other commonly experienced stresses, such as water
stress and mineral deficiency, we have virtually no information on the effects
of UV in combination with other atmospheric change, such as increased con-
centrations of ozone, sulfur dioxide, or carbon dioxide. Although UV radia-
tion generally produces deleterious effects on plants, increased ambient
levels of C02 have beneficial effects (Table 5); the combination of the two
may not necessarily be compensatory. One alternative possibility is larger
plants resulting from CC>2 enrichment, which in turn would still be
deleteriously affected by UV radiation. Without experimental evidence,
critical uncertainties such as this cannot presently be resolved.
168
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Table 3. Current Uncertainties of UV Effects on Plants
• Action spectra
• Reasons for tolerance and sensitivity
• Effects on natural communities and ecosystems
• Combined effects with pollutants
• Effects in high ambient CC>2 environment
Table 4. Survey of UV Studies by Major Terrestrial Plant
Ecosystems (after Whittaker 1975)
Ecosystem
Tropical forest
Temperate forest
Savanna
Boreal forest
Agricultural
Woodland and scrubland
Temperate grassland
Swamp and marsh
Desert and semidesert
Tundra and alpine
Global NPP
(109 ton/yr)
49.4
14.9
13.5
9.6
9.1
6.0
5.4
4.0
1.7
1.1
Total Area
(10b knT)
24.5
12.0
15.0
12.0
14.0
8.5
9.0
2.0
42.0
8.0
Included in
UV Study ]_/
no
yes
no
no
yes
no
yes
no
no
yes
]_/ Only studies examining some aspect of growth.
169
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Table 5. Summary of UV-B and C02 Effects on Plants
Plant Characteristic
Enhanced UV-B
Doubling of C02
Photosynthesis
Leaf conductance
Water use efficiency
Dry matter produc-
tion and yield
Leaf area
Specific leaf weight
Crop maturity
Flowering
Interspecific
differences
Intraspecific
differences
Drought stress
Decreases in many
Co and C|| plants
No effect in many
plants
Decreases in most
plants
Decreases in many
plants
Decreases in many
plants
Increases in many
plants
Mo effect
In Co plants in-
crease up to 100% but
in C4 plant only a
small increase
Decreases both in Co
and Cjj plants
Increases in both Co
and Ch plants
In Co plants almost
doubles but in Cjj
plants only a small
increase
Increases more in Co
than in Cjj plants
Increases
Accelerated
May inhibit or stimu- Flowers produced
late flowering in some earlier
plants
Species may vary in
degree of response
Response varies among
cultivars
Major differences
occur between Co
and Cjj plants
Response may vary
among cultivars
Plants become less Plants become more
sensitive to UV-B but drought tolerant
not tolerant to drought
Source: Lemon (1983); Teramura (1983)
170
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In summary, we know that large differences exist among species and these
are manifested in a diverse array of physiological, biochemical, and
morphological responses. We know that for whole plant responses, field
validation experiments are essential because plants are more sensitive to UV
when grown indoors. Key growth chamber studies are necessary to provide an
understanding of the mechanisms of UV sensitivity in plants. UV effectiveness
can be modified by the prevailing microenvironment. For example, water stress
can completely mask any UV effects seen in the field. Moderately large ozone
depletions can reduce crop yields in the field. UV can produce subtle shifts
that alter the competitive balance among'plants.
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ultraviolet-radiation induced injury. Oecologia. 32:277-287.
Robberecht, R., M.M. Caldwell, and W.D. Billings, 1980. Leaf ultraviolet
optical properties along a latitudinal gradient in the artic-alpine life
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Sisson, W.B. 1981. Photosynthesis, growth, and ultraviolet irradiance
absorbance of Cucurbita pepo L. leaves exposed to ultraviolet-B radiation
(280-315 nm). Plant Physiol. 67:120-124.
Sisson, W.B. and M.M. Caldwell. 1976. Photosynthesis, dark respiration, and
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Steinmuller, D. 1986. Zur Wirkung ultravioletter Strahlung (UV-B) auf die
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Akkumulation und Biosynthese der Kutikularlipide einiger Nutzpflanzer.
Ph.D. Dissertation. Botanisches Institut II, Universitat Karlsruhe, F.R.G.
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Teramura, A.H. 1983. Effects of ultraviolet-B radiation on the growth and
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Teramura, A.H., R.H. Biggs, and S. Kossuth. 1980. Effects of ultraviolet-B
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The Effect of Solar UV-B Radiation on
Aquatic Systems: An Overview
R. C. Worrest
Oregon State University
Corvallis, Oregon USA
ABSTRACT
Various experiments have demonstrated that UV-B radiation causes damage
to fish larvae and juveniles, shrimp larvae, crab larvae, copepods, and plants
essential to the aquatic food web. These damaging effects include decreases
in fecundity, growth, survival, and other functions of these organisms. In
natural marine plant communities a change in species composition rather than a
decrease in net production would probably result of enhanced UV-B exposure.
The change in community composition could result in a more unstable ecosystem
and would be likely to have an influence on higher trophic levels. A decrease
in column ozone would diminish the near-surface season of invertebrate
zooplankton populations. Whether the population could endure a significant
shortening of the surface season is unknown.
The direct effect of UV-B radiation on food-fish larvae closely parallels
the effect on invertebrate zooplankton. Information is required on seasonal
abundances and vertical distributions of fish larvae, vertical mixing, and
penetration of UV-B radiation into appropriate water columns before effects of
incident or increased levels of exposure to UV-B radiation can be predicted.
However, in one study involving anchovy larvae a 20 percent increase in
incident biologically damaging UV-B radiation (a result of about a 9 percent
decrease in the atmospheric ozone column) would result in all the larvae
within a ten-meter mixed layer in April and August being killed after fifteen
days. It was calculated that about 8 percent of the annual larval population
throughout the entire water column would be directly killed by a 9 percent
decrease in column ozone.
INTRODUCTION
Aquatic environments include shallow freshwater ponds, lakes and streams,
fresh and saline inland seas, brackish-water marshes, swamps and estuaries,
and a wide variety of marine habitats. The marine habitats extend from
175
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inshore coastal regions, surf zones, and fringing reefs to the wide spaces of
the open sea and the abyssal deeps. Inland waters cover less than 1 percent
of the earth's surface, while the oceans extend over more than 70 percent of
the earth's surface.
Because of the relatively small volume of inland waters, freshwater plant
production contributes only a few percent to the total global productivity
(Table 1). Marine systems, covering a vast area, contribute significantly to
global productivity—an amount equivalent to half the terrestrial plant
production. The coastal kelp forests have productivities said to rival those
of tropical rain forests, generally considered the world's most productive
plant ecosystems (Mann 1973; Lieth 1975). Of the five major marine habitats
considered in Table 1, the microscopic plants of the open sea are the most
productive, contributing 75 percent of the marine primary production, 24
percent of the global total.
Photosynthesis, the conversion of radiant energy from the sun into
chemical energy (food), is the basis of almost all life on the earth.
Photosynthesis requires light, but adequate sunlight seldom penetrates to the
bottom of natural waters; thus, aquatic photosynthesis is largely confined to
a relatively thin layer at the water surface termed the euphotic zone, the
surface layer where plants create more chemical energy by photosynthesis than
they use for their own metabolism.
Organisms in fresh water or the oceans are either swimmers (nekton),
bottom-dwellers (benthos), or drifters (plankton). Plankton can be either
plants (phytoplankton) or animals (zooplankton). An important zooplankton
group, the icthyoplankton, is comprised of the drifting eggs and larvae of
many species of fish. Zooplankton in general contain nearly all groups of
aquatic animals, at least for some phase in their life history, such as the
egg and/or larval stage. Zooplankton are found at all depths, depending on
species and season, but are most abundant in the upper 100 m sunlit where the
bulk of their food, including phytoplankton, is found. As feeding progresses
from the phytoplankton through the zooplankton to fish and other higher
organisms (the food web), the chemical energy generated by aquatic
photosynthesis becomes more and more concentrated into organisms of larger
size, reaching organisms suitable for harvesting for human use.
Marine ecosystems are highly dynamic and of bewildering complexity. Many
of the fundamental processes affecting the abundance of marine resource stocks
are poorly understood. For example, the complexity of food webs in the ocean
appears to be much greater than for terrestrial populations (Larkin 1978).
Little is known in a quantitative sense about marine ecosystems, although some
geographical areas are currently under intensive investigations.
Many other sources of complexity in marine population dynamics exist.
Simple density-dependence mechanisms, for example, can theoretically result in
so-called "chaotic" oscillations in population abundance (Levin and Goodyear
1980). Most fish stocks undergo significant irregular fluctuations, the
underlying causes of which are not well understood. In most cases both
density-dependent and density-independent effects are probably involved.
For any given level of fish mortality, the productivity or equilibrium
yield of a stock depends upon growth, recruitment, and natural mortality.
176
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Table 1. Representative Primary Production and Plant Biomass Summaries of the
Earth (adapted from Whittaker and Likens 1975)
Ecosystem Type
Area
(millions of
square
kilometers)
Net Primary
Productivity
(grams per square
meter per year)
Mean Plant
Biomass
(kilograms per
square meter)
17.0
7.5
.0
.0
5.
7.
TERRESTRIAL
Tropical rainforest
Tropical seasonal forest
Temperate evergreen
Temperate deciduous
Boreal forest
Woodland and shrubland
Savannah
Temperate grassland
Tundra and alpine
Desert and semi-desert scrub
Extreme desert, rock,
sand and ice
Cultivated land
Swamp and marsh
Lake and stream
Total/Average
Percent of Worldwide
MARINE
Open ocean 332.0
Upswelling zones 0.4
Continental shelf 26.6
Algal beds and reefs 0.6
Estuaries (excluding marsh) 1.4
Total/Average 361
Percent of Worldwide 71$
WORLD TOTALS/AVERAGES 510
12.0
8.5
15.0
9.0
8.0
18.0
24.0
14.0
2.0
2.0
149
297*
2200
1600
1300
1200
800
700
900
600
140
90
3
650
2000
250
773
68$
125
500
360
2500
1500
152
32$
333
45.0
35.0
35.0
30.0
20.0
6.0
4.0
1.6
0.6
0.7
0.02
1.0
15.0
0.02
12.3
99-8$
0.003
0.02
0.01
2.0
1.0
0.01
0.2$
3.6
Growth is relatively easy to measure and understand; recruitment is relatively
easy to measure but difficult to understand; and natural mortality is both
difficult to measure and difficult to understand. The phenomena that are
difficult to measure or understand are usually masked by the standard
productivity analysis.
As early as 1925, scientists were aware of the damaging effects from the
ultraviolet component of sunlight even oq aquatic organisms (Huntsman 1925;
Klugh 1929, 1930; Harvey 1930; ZoBell and McEwen 1935; Giese 1938; Bell and
Hoar 1950; Dunbar 1959; Marinaro and Bernard 1966). It was shown at these
early dates that different species have various sensitivities to UV radiation,
and that this differential sensitivity might relate to the depth at which the
species were found.
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There have been several more recent studies on the effects of UV-B
radiation on a variety of marine organisms (WAS 1979; MAS 1984). Regardless
of species investigated, each study has potential importance through the role
of the particular organism in its environmental or food web context. Some
studies, in addition, have considered economically important zooplankton
species, such as larval stages of certain shrimp, crab, and fish. Recent
literature reviews (Calkins 1982; Worrest 1982, 1983a,b) have summarized the
results of most of these studies.
Physical Effects on Organisms
UV-B radiation is readily absorbed by proteins and nucleic acids, and is
effective in inducing photochemical reactions in plants and animals (Caldwell
1971; Murphy 1975; Giese 1976). Even though proteins and nucleic acids are
commonly involved in biological responses to UV-B radiation, the action
spectra for tissue damage in many organisms may differ because of wavelength-
dependent refraction, reflection, or absorption, and hence protection, by
outer tissues (Cheng, Douek, and Goring 1978).
The usual effects of environmental stress (e.g., pollution) are changes
in overall productivity and reduction in species diversity. Diversity is
associated with stability in ecosystems, allowing alternate routes and choices
within food webs. In field situations under slight stress one often cannot
measure changes in productivity or size of specific populations, but sometimes
changes in species diversity can indicate that adverse effects are
occurring. With loss of species an ecosystem loses some of its natural
resiliency and flexibility. In aquatic ecosystems we must consider a great
number of species with different life stages and different trophic levels.
With increased knowledge of ecosystems and the physical and chemical
environments, the effects of enhanced solar UV radiation on single species
could be placed in perspective.
As already noted, the biological response to ultraviolet radiation can be
very wavelength-dependent. This wavelength specificity makes it necessary to
develop weighting functions to express ultraviolet radiation in biologically
meaningful terms. Biological action spectra normally serve as the basis for
these weighting functions. The weighting function is normally taken as an
action spectrum for a particular response. Several action spectra have been
developed describing the response of biological systems to UV-B radiation
(Caldwell et al. 1986). Examples are a representation of DMA response (Set-
low 1974), and a generalized plant response (Caldwell 1968).
Based on an analytic characterization of ultraviolet sun- and skylight, a
10 percent ozone reduction at 45°N latitude would result in only a 1 percent
increase in total solar ultraviolet (290-360 nanometers) daily exposure at the
surface of the earth. This would be of minimal consequence if radiation
throughout the solar spectrum were of equal biological effectiveness.
However, when the biological weighting functions based on the action spectra
are employed, a very different picture emerges. Based on DNA damage, a 10
percent ozone reduction would result iq a 28 percent increase in biologically
effective radiation (Table 2). The generalized plant response (damage) would
increase by 21 percent.
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Table 2. Relationship Between Ozone Depletion and Biological
Effectiveness of Increased UV-B Radiation.
Ozone
Decrease
10$
20%
30%
40$
Increase in
290-320 nm
8%
17$
27%
38%
UV Radiation
290-320 nm
1.1$
2.4$
3.1%
5.2%
Increase in
DNA
28$
67$
125$
213$
Effectiveness3
Plant
21$
49$
85$
132$
aAction spectra are referenced to 300 nm - 1.00.
The increased exposure to biologically effective (DNA, plant) ultraviolet
radiation resulting from a 10 percent decrease in stratospheric ozone would
correspond to migrating over 30° toward the equator—a change of ecological
significance. Levels of UV-B irradiance vary latitudinally, with the highest
exposures in the tropics. The current difference between the extremes of
exposures is about three- to sixfold but biota are presently adapted to the
levels that are normally experienced at their current locations.
There is increasing evidence that marine ecosystems change as a result of
natural as well as events induced by human activities. Many of these changes
occur on time scales of tens of years. The past changes may be associated, in
some general context, with gradual climatic trends, but ecological changes
seem to occur quite rapidly, with relatively persistent communities existing
in the intervening periods. In any region, rather than having one ecosystem,
there are two, or possibly several, alternatives—each resilient to some range
of variability but capable of being replaced if some factors in the
environment pass a threshold. To this natural episodic response we must now
add the effects of anthropogenic perturbations. The evidence suggests that we
will continue to have such changes but will have additional questions of
attributing cause to natural stresses or to stresses resulting from human
activities. Although we may not be able to predict when, or possibly why,
such changes occur, they can be regarded as alternative ecological
solutions. Once again, whether we consider these changes deleterious or
beneficial is a matter of human values, but we must keep in mind that these
problems are occurring on a global scale.
Phytoplankton
The amount of UV-B radiation reaching the ocean's surface has long been
suspected as a factor influencing primary production. Research shows
convincingly that ultraviolet radiation, at levels currently incident at the
surface of natural bodies of water, has such an influence (Steemann Nielsen
1964; Jitts, Morel, and Saijo 1976; Hobson and Hartley 1983). It has been
calculated that near the surface of the ocean, enhanced UV-B radiation
simulating a 25 percent reduction in ozone concentration would cause a
decrease in primary productivity of about 35 percent (Smith et al. 1980); the
estimated reduction in production for the whole euphotic zone would be about
These calculations are based on attenuation lengths, i.e., the product
179
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of depth in the water column and the diffuse attenuation coefficient of the
water. Therefore, waters of various turbidities and absorption character-
istics can be compared.
Effects induced by solar UV-B radiation have been measured to depths of
more than twenty meters in clear waters and more than five meters in unclear
waters. The euphotic zone (i.e., those depths with light levels sufficient
for net photosynthesis to be positive) is frequently taken as the water column
down to the depth to which 1 percent of the surface photosynthetically active
radiation penetrates (Figure 1). In marine ecosystems, UV-B radiation
penetrates approximately 10 percent of the upper marine euphotic zone before
it is reduced to 1 percent of its surface irradiance (Figure 2). Penetration
of UV-B radiation into natural waters is a key variable in assessing the
potential impact of this radiation on any aquatic ecosystem.
If one assumes that present phytoplankton populations sense and control
their average vertical position in such a way as to limit UV-B exposure to a
tolerable level, then a 10 percent increase in solar UV-B radiation would
necessitate a downward movement of the average position sufficient to reduce
the average UV-B exposure by 10 percent. There would be a corresponding
reduction of light for photosynthesis; the loss of photosynthetically active
radiation is the primary limiting factor for marine productivity (Russell-
Hunter 1970). The loss of photosynthetically active radiation from optical
measurements has been estimated to be in the range of 2.5 to 5 percent for a
10 percent increase in UV-B radiation (Calkins, Volume 2). If the
photosynthetic base of aquatic ecosystems were perturbed one would expect
ramifications to extend up through the food web through predator-prey
relationships.
Experiments with marine diatoms have shown significant reductions in
biomass, protein, and chlorophyll at UV-B irradiances equivalent to ozone
reductions ranging from 5 to 15 percent In addition, studies on chain-forming
diatoms and other phytoplankton in the laboratory showed that increased growth
occurs when the UV-B radiation is filtered out of the incident solar radia-
tion, indicating that existing levels of UV-B radiation depress productivity
(Thomson, Worrest, and Van Dyke 1980; Worrest 1982). Furthermore, indirect
effects of ambient levels of UV-B radiation endanger the survival of
microorganisms (Euglena, slime mold, some blue-green algae) by decreasing
their motility and by inhibiting phototactic and photophobic response (Haeder,
see Volume 2). This reduces the ability of a population to move into
favorable environments, which would result in damage that may impair develop-
ment.
Direct measurements of photosynthesis that span a single day could
underestimate the overall action of solar UV exposure by failing to account
for the next day's population level. Growth delay or direct killing may cause
the subsequent population to fall below the numbers that an unexposed
population would attain. Prolonged delays (about two days) in growth of the
survivors have been observed when two strains of the diatom Thalassiosira were
irradiated with simulated solar ,UV-B radiation at doses below lethal levels.
If unicellular organisms are in a rapid growth phase, a growth delay equaling
the time of one growth cycle produces the same effect on the subsequent
population as would be produced by 50 percent killing (without growth delay).
180
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0.5 L
— Dc, Compensation depth (PC=RC)
Ic, Compensation light intensity
a Dcr, Critical depth
Dm, Depth of mixing
Figure 1. The Relationship Between the Compensation Depth or Euphotic
Depth, the Critical Depth, and the Depth of Mixing
600 r
UJ
o 500
9 400
<
a:
cc
- 300
LL)
jZ 200
<
_J
PERCENTAGE OF ENERGY
2 4 6810 20 4060100,
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4
WAVELENGTH
Figure 2. Solar spectral irradiance at the surface of the ocean and at
four depths (adapted from Sverdrup et al. 1942). Insert illustrates per-
centage of energy transmitted at depth in oceanic waters.
181
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In Hawaii, long-term photoinhibition of growth of six algal species under
natural sunlight was measured by Jokiel and York (1984). Two strains could
not grow at all at the levels of irradiance for full natural surface
sunlight. Of the species tested, those collected from tropical surface water
showed the greatest adaptive power, but it is reasonable to conclude that
resistance to solar UV radiation is achieved through expenditure of resources
that can be better applied to other needs in less-exposed species.
In simulated marine ecosystems, enhanced UV-B radiation levels,
simulating 15 percent decreases in ozone, result in shifts of the species
diversity and community composition of phytoplankton communities (Worrest,
Thomson, and Van Dyke 1981). It appears that in natural communities a change
in species composition rather than a decrease in net production might be a
more likely result of an enhanced UV-B exposure. The decreased species
diversity observed in simulated field studies is usually not accompanied by
deleterious effects on biomass and chlorophyll accumulation or by deleterious
effects on total community primary productivity. However, a change in
community composition might result in a more unstable ecosystem and might have
influence on higher trophic levels (Kelly, Volume 2). One effect of enhanced
levels of UV-B radiation would be to alter the size distribution of the
component producers in a marine ecosystem. Increasing or decreasing the size
of the representative primary producers upon which consumers graze can
significantly increase the energy allotment required for consumption, thereby
reducing the feeding efficiency of the consumer. In addition, the food
quality of the producers is altered by exposure to UV-B radiation. It has
been demonstrated that the protein content, dry weight, and pigment
concentration are all depressed by enhanced levels of UV-B radiation.
Zooplankton
Zooplankton are critical components in typical aquatic food webs
(nutrient pathways) that lead to larger animals, including those comprising
commercial fisheries (finfish and shellfish) and therefore humanity itself.
With respect to potential impacts of enhanced solar UV-B radiation, only the
zooplankton living in daylight in the upper several meters would be directly
affected. Many zooplankton species normally live very close to the surface,
even in daylight, while others occupy the near-surface layer during only part
of their life cycle.
The near-surface layer is a very important zone in the interactions of
the physical, chemical, and biological components of aquatic systems.
Zooplankton have apparently evolved mechanisms and behavior by which they have
adjusted to current levels of UV radiation (Damkaer 1982), but they may not be
able to adjust to relatively rapid increases. If there were changes in the
abundance of zooplankton species, those changes would have an impact far
beyond any direct effects because of the critical role of zooplankton in
energy transfer within the ecosystem.
Karanas, Van Dyke, and Worrest (1979, 1981) presented evidence that acute
exposure of a marine invertebrate zooplankton resulted in reduced survival of
the organisms. They also showed that exposure of this species to sublethal
exposures of UV-B radiation could also reduce the fecundity of the parents.
Thomson (Volume 2) demonstrates that current levels of UV-B radiation are of
significance in the developmental life of several species of shellfish. For
182
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some species, a 10 percent decrease in column ozone could lead to as much as
an 18 percent increase in the number of abnormal larvae produced.
Spawning of zooplankton (and fish) is usually timed so that survival at
hatching is optimized. Compared to birds and mammals, the lack of internal
temperature control, such as prevails in most aquatic animals, makes ambient
temperature exert overriding and continuous accelerating or decelerating
influences on metabolic functions and, hence, on the growth of aquatic animals
at whatever stage.
Before feeding by zooplankton can begin, variations in exposure to UV-B
radiation may cause stresses at various stages of egg and very early larval
development, causing mass mortalities or an alteration in time of occurrence
at the surface. The matching in time of the onset of larval feeding and the
spring phytoplankton bloom—which, in turn, depends on climatic events for its
timely occurrence—will, in fact, determine the sizes of year classes of
grazers (Gushing 1972).
Fish stocks suffer most from the vagaries of climate through the effects
that changes in ambient conditions have on the larvae. The biological
dynamics at the larval stages in the life cycles of fishes and aquatic
invertebrates have a short time horizon and are highly variable. Instant
mortality coefficients during the larval stages range between 300 and 400,
while they are 0.2 to 1.5 in the juvenile and adult stages (Rothschild
1981). The most catastrophic and frequent event that can befall larvae is a
mismatch in time between their food needs and the prevalence of their food
(Gushing 1972). Larval stages last only a few days. Small as the biomass of
fishes is during very early life, their future numbers are largely determined
then and not later in life, when the biomass is large and when the commercial
fishery takes its toll.
Regardless of the cellular-level responses to UV irradiation, it is
usually noted that up to some level of UV exposure there is no apparent effect
on the organism (Damkaer et al. 1980; Damkaer and Dey 1982). At greater doses
either the repair systems themselves may become inactivated by the radiation
or the damage to the general tissues goes beyond the capacity of the repair
systems (Damkaer and Dey 1983). For such impacts to occur these threshold
levels probably must be exceeded during several consecutive days. The
apparent thresholds are near current levels. The thresholds for all groups in
one test appeared to be above the present median solar incident UV levels at
the test location, at least until late in the time span of natural occurrence
near the surface (Damkaer, personal communication). This season could be
significantly shortened by a 20 percent ozone reduction. Whether or not the
populations could endure with a drastically reduced time of near-surface
occurrence is not known. Success of any year-class depends on the timing of a
great number of other events in addition to levels of exposure to UV-B
radiation (Hunter, Kaupp, and Taylor 1982).
It has been thought that the superabundance of eggs spawned by most
marine organisms make. egg production an irrelevant factor in population
control. The superabundance of marine eggs, however, is of clear evolutionary
significance and must interrelate with the variability of population size.
183
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The superabundance of eggs could have any number of purposes. First, it
could satiate predators, thus enabling a certain fraction of eggs and larvae
to slip through the predatory network. It could also maintain ecosystem
integrity and metabolism by directly serving as food for other organisms or by
being degraded into various essential nutrients, sustain cannibalistic
species, or contribute to a patchy distribution of organisms, which is
apparently essential to marine ecosystem structure.
As fish stocks decline in size, the biomass of eggs decreases at a faster
rate than recruitment; the ordinary functions of the superabundance of eggs
become stressed and modified. But stocks compensate to some extent for
biomass decline by growing faster, tending toward an earlier maturity, and
increasing in fecundity.
Hunter, Kaupp, and Taylor (1982) exposed anchovy eggs and larvae and
mackeral larvae to high doses of UV-B radiation in small closed containers.
These authors provided data that indicated that anchovy larvae off southern
California are typically centered in moderately productive ocean water.
Baker, Smith and Green (1981) calculated surface DNA-effective UV-B irradiance
levels expected for this area, and Smith and Baker (1979) calculated the
penetration of UV-B radiation into the moderately productive ocean water. An
analysis of Damkaer (personal communication) indicates that 14.7 percent of
the anchovy larvae would die in four to ten days if there were no vertical
mixing of the larvae. These static situations no doubt approach "worst case"
scenarios. However, static situations are not likely because of physical
vertical mixing of water (through the action of wind, density currents, and
tides) and the active and passive movement of fish larvae. If some vertical
mixing did not offer relief from the effects of UV-B radiation, it is likely
that even today there would be no anchovy larvae above a few meters depth,
which is clearly not the case. The surface mixed layer probably extends to a
depth of at least twenty-five meters from December to February (Sverdrup,
Johnson, and Fleming 1942). A mixed layer of at least ten meters can be
assumed for the rest of the year.
For the mixed situation in February, the larvae would spend less than one
hour each day in the upper one meter, resulting in exposures where the
threshold doses would never be reached in the larval stage. In the February
model, with mixing to twenty meters, there would have to be a sixfold increase
in incident UV-B radiation before threshold doses would be reached. For the
months from March to October, with mixing to ten meters, the threshold doses
are also not reached within the twenty days available before the larvae become
vertically migrating. Only with the highest surface irradiances of April and
August are these doses approached within this available time (about twenty-two
days).
From March to October, with ten-meter mixing and a 20 percent increase in
incident UV-B radiation (a result of about a 9 percent decrease in the
atmospheric ozone column) the depth of the threshold dose-rate is increased.
With the 20% increase in incident irradiance for the dose/dose-rate threshold
model, all of the anphovy larvae within the ten-meter mixed layer in April and
August would be killed, the threshold doses being achieved after fifteen days.
Apparently at all months about 36 percent of the larval anchovy
population is less than ten meters deep (Hunter, Kaupp, and Taylor 1981). The
184
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greatest numbers of anchovy larvae are found below the surface in April. (20
percent of annual population), so that 7.2 percent of the annual population
would be eliminated with a 9 percent ozone decrease. Only 1.9 percent of the
annual population is present in August, so the loss of those less than ten
meters deep would amount to 0.7 percent of the annual population. The total
predicted loss, then, due to a 9 percent decrease in total ozone column, would
be about 8 percent of the larval anchovy population (Figure 3).
Because of complex interactions between mixing depths, vertical
distribution of larval anchovy, seasonal changes in solar irradiance and the
penetration of UV radiation into seawater, and seasonal changes in anchovy
abundance, there is no linear relationship between mixing depth and predicted
annual loss of anchovy larvae.
In addition to the direct effects upon the fisheries, it is possible that
with less primary production of organic biomass there would also be an
increased mortality in larval fish due to food limitation. And perhaps there
would be a synergistic effect on mortality in that some animals could die from
direct exposure, some from lack of food, and some from the combination of a
reduction in food and the weakening from exposure (or could be weakened and be
out-competed by other fauna for limited food reserves).
The impact on marine fisheries as a food supply to humans would be
significant if the species of phyto- and zooplankton that adapted to enhanced
levels of UV-B radiation were of different nutritional value (if they altered
growth and fecundity of the consumers). If the indirect impact of suppression
upon consumers were linear, a 5 percent reduction of primary production would
result in a 5 percent reduction in fish production. A question still under
investigation is whether these relationships might be nonlinear. For example,
there may be an amplification factor involved that results in a relatively
greater impact at higher trophic levels than at the primary producer level.
As illustrated in Table 3, a 5 percent reduction in primary production (P1)
would give an annual yield of 115 million metric tons of fish flesh (a 5
percent reduction), whereas a 5% reduction in the ecological efficiency of
energy transfer (e) would yield 103 million tons of fish flesh (a 14 percent
reduction).
Potential Consequences to World Fisheries
Well over 95 percent of the sea's living resources occur within belts of
ocean two hundred miles wide, surrounding the coastal nations of the world.
By international agreement each nation exercises economic jurisdiction over
these Extended Economic Zones (EEZs). With the establishment of the two
hundred-mile EEZs, the coastal nations of the world have acquired an area of
sea surface amounting to about 25 percent of the globe. More than 99 percent
of the global catch of marine fisheries is currently taken within the EEZs.
These fish are of crucial importance in world nutrition, making up about 18
percent of the average world animal protein intake. That figure rises to
nearly 40 percent in Asia where more than half of the world's population
lives. The people of Japan, for instance, derive about 60 percent of their
intake of animal protein from the ocean (Clark 1981). The annual income to
the world's fishermen from marine catches is roughly US$10 billion, with a
world fish catch of about seventy million metric tons.
185
-------
30
Larval Northern Anchovy
0 10 20 30 40 50 60 70
INCREASED UV-B RADIATION (%)
Figure 3,. Effect of increased levels of solar UV-B radiation on the
predicted loss of larval Northern Anchovy from annual populations, considering
the dose/dose-rate threshold and the vertical mixing models (based on data of
Hunter, Kaupp, and Taylor 1981, 1982).
186
-------
Table 3. Annual fish production in coastal waters and impacts of 5
percent reductions in primary production and ecological efficiency of energy
transfer. Baseline data for coastal waters adapted from Ryther (1960).
Baseline -5% P1 -5% e
Primary production, kJ/m2yr 4200 4000 4200
Ecological efficiency per trophic
level, (e) 0.15 0.15 0.14
Number of trophic levels from plant
production to fish production, (n) 3 33
Fish production, kJ m2yr 14 13 12
Total fish production, millions of
metric tons per year (using
Winberg's transformation,
4.2 kJ = 1 g fish flesh) 121 115 103
Percentage of baseline fish production (100$) (95%) (86$)
To address the economic impact of enhanced levels of UV-B radiation on
global fisheries the principal concepts that need to be considered are supply,
demand, and the economic marketplace. Supply is the relationship between the
quantity of a commodity that will be produced and the price of the output.
For fish, the supply curve is heavily dependent on the biological productivity
of the stock as well as economic factors, because supply is derived from the
average cost required to produce a pound of fish. Supply is also affected by
the fish or uncertainty associated with the various costs or availability of
the raw material or other economic components of the supply curve. Demand is
the relationship between the price consumers are willing to pay for a
commodity and the quantity of the commodity that is available. Global
production of fish has been predicted to be 92.5 million tons in the year 2000
(Robinson 1979). Based on per capita consumption of fish and population
growth, the projected global demand for fish in the year 2000 will be 97.1
million tons. The economic marketplace is the abstract setting where producer
interests in the form of the supply curve are brought together with consumer
interests in the form of the demand curve.
The Peruvian anchoveta fishery is an example of the economic impact
resulting from a stress on a fishery. The fishery developed in the 1960s into
the world's largest single fishery. Since the export of anchoveta fishmeal
constituted Peru's second largest source of foreign exchange, the loss of the
fishery had a major influence on the Peruvian economy.
In 1970, Peru's anchovy harvest amounted to 12.3 million metric tons,
more than 20 percent of the total world marine finfish catch for that year.
These fish rely on phytoplankton blooms that result from the surfacing of
colder nutrient-rich water. In 1972, the Peruvian catch plummeted to 4
187
-------
million metric tons and fell further in 1973 to 1.8 million metric tons. The
primary cause of this drastic collapse was the occurrence of an El Nino,
although heavy fishing aggravated the condition (Bardach and Santerre 1981).
The economic consequences to the fishery were catastrophic. The major use of
the anchoveta harvest was for the production of fishmeal, which was used as a
major source of bulk protein in livestock feed. A shortfall of the fishmeal
in the world's markets had severe ripple effects on other animal feeds and on
livestock prices. The price of fishmeal rose 127 percent, the price of
soybean meal rose 99 percent, and the cost of pork, for example, rose 96
percent, adjusted for inflation.
The recovery of a depleted fishery population may require many years,
even if catches are prohibited. Economic survival of the existing resource
industry may, however, depend upon continuing catches, even though these will
delay rebuilding of the stock and perhaps increase the probability of the
population's collapse. In the language of the mathematical theory of games,
common-property resource exploitation has the characteristics of the
prisoner's dilemma.
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191
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OBSERVED RATE OF TEMPERATURE CHANGE (°C/CENTUHY)
-9Q
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TEMPERATURE (FIVE YEAR RUNNING MEAN)
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Plate 2. Observed rate of temperature change in the past century, estimated from meteorological station data. The geographical
temperature trends in part (a) include estimates for remote regions with station records as short as 25 years. The zonal mean trends in part
(b) refer to the average for all longitudes with available records. A nonlinear scale is used in part (b) so that there is a similar area for each
color.
Source: Hansen et al. (this volume)
194
-------
Plate 3. Annual mean temperature changes
computed with the Goddard Institute for
Space Studies global climate model, which
has a sensitivity of about 4°C for doubled CO2.
Parts a and b, for the decades 1990-1999 and
2010-2019, respectively, were obtained from
the transient experiment with CO2 and trace
gases increasing according to Scenario A; the
indicated temperatures are the difference
between the transient run and a control run
with 1958 atmospheric composition. Part c is
the equilibrium warming in the model for
doubled CO2.
Source: Hansen et al. (this volume)
195
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Legend:
Black - rivers
Red - forest cover; transplanted
aman/fallow
Orange - deepwater aman rice/boro rice
Blue - water
White - aman rice/fallow
Grey - deepwater rice/urban area (Dacca)
Scale 1: 250,000
6 10
it V1..'-.' * " »*.** •
Plate 4. The high scenario represents the shoreline retreat from a 2 to 2.5 meter global rise in sea level if dams built on
the Ganges prevent sediment from reaching the delta. The low scenario represents the impact of a 50 centimeter global
rise with only a partial disruption of the sedimentation process.
196
Source: Broadus et al. Volume 4
-------
CLIMATE CHANGE
-------
The Greenhouse Effect: Projections of Global
Climate Change
J. Hansen1, A. Lacis1, D. Rind1, G. Russell1,1. Fung1, P. Ashcraft2
S. Lebedeff3, R. Ruedy3, and P. Stone4
SUMMARY
We present projections of global climate during the next several decades,
based principally on climate model simulations in which atmospheric CC^ and
trace gases increase steadily at rates estimated from observations. This is
the first time that a global climate model has been used for simulating the
climate effects of the transient growth of greenhouse gases, and as such it
permits an estimate of when the greenhouse effect should begin to be evident
above the level of natural climate variability. We emphasize that a number of
caveats must be attached to the climate model results. But we also stress
that the climate sensitivity of our model has been extensively compared to the
sensitivity of other models and is consistent with available empirical evi-
dence from past climate changes.
Our presentation is organized as a response to a letter from Chairman
John Chafee of the United States Senate Subcommittee on Environmental Pollu-
tion of the Committee on Environment and Public Works who requested testimony
at a hearing on the greenhouse effect on June 10, 1986. Specifically, his
letter asked that the following topics be addressed:
• The nature of our work in modeling greenhouse climate effects
• How we test the models to determine their validity
2 NASA Goddard Space, Flight Center, New York, NY
2 State University of New York, Albany, NY
•j M/A COM Sigma Data Inc., New York, NY
Center for Meterology and Physical Oceanographies, Massachusetts
Institute of Technology, Cambridge, MA
199
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• The relative contribution of different greenhouse gases to possible
future climate change
• The temperature changes predicted for the next few decades and the
next century, assuming some reasonable growth in trace gases
• How the predicted temperatures compare to past temperatures experi-
enced on the earth
• How temperature changes of the magnitude predicted might alter the
number of days with temperatures above a given limit for Washington,
D.C. and other U.S. cities
• Further evidence needed to confirm and quantify the greenhouse theory.
GLOBAL CLIMATE MODELING
In principle, global climate models are quite simple. For example, in
our model (Hansen et al. 1983, hereafter referred to as paper 1) the earth is
divided into 'gridboxes' as shown in Figure 1, and each gridbox is divided
vertically into a number of layers, typically nine, in the atmosphere. Simi-
larly, the ground or ocean in each gridbox is divided into several vertical
layers. The mathematical equations describing the fundamental conservation
laws of physics are solved numerically for each gridbox by a computer program,
which calculates the transfer of mass, energy, and momentum from one box to
another and also simulates physical processes within the boxes which represent
sources and sinks of these substances.
Such global climate models, or GCMs, are able to reproduce the general
features of the earth's climate. Climate variables such as temperature,
winds, and storm tracks, and their variations from season to season, from
latitude to latitude, and from continent to ocean, are represented realist-
ically, at least in a qualitative sense. But the models are not sufficiently
realistic to portray accurately regional patterns of precipitation, ocean
currents, and other processes that are important for determining the practical
consequences of climate trends because of greenhouse warming. Recent evidence
that the large-scale ocean circulation may have undergone dramatic changes in
the past (Broecker, Peteet, and Rind 1985) is of special concern; the repre-
sentations of oceans in current GCMs are not sufficiently realistic to predict
such phenomena.
Improvement of the climate models will depend especially upon better
knowledge of physical processes occurring within the climate model gridboxes.
These processes are represented by submodels or "parameterizations." For
example, Figure Ib schematically illustrates convective clouds associated with
convective transport of moisture, heat, and momentum between model layers.
Although there have been major field experiments to study convection clouds,
substantial work is needed to provide more realistic submodels for use in
GCMs. Another example, one which is beginning to receive greater attention,
concerns the role of vegetation and soil processes in the transfer of
moisture, heat, and momentum between the earth's surface and the atmosphere.
As a final example, we must have a better understanding of small-scale ocean
200
-------
-60 -
-90
-ISO
-120
TABLE 1 Fundamental equations
180
Longitude (degrees)
Conservation of momentum dV _
(Newton's second law of ~ft = ~2U X V ~ p p
motion) + g -I- F (Tl)
Conservation of mass dp
(continuity equation) 4, ~ 0"'V + C D (T2)
Conservation of energy dl dp'
(first law- of J, = -P ~^~ + Q (T3)
thermodynamics)
Ideal gas law p = PRT (T4)
(approximate equation of
state)
hotalion
V velocity relative to rotating earth
/ time
— total time derivative = — + V- V
dl L dl J
fl planet's angular rotation vector
p atmospheric density
g apparent gravity [=true gravity - Q X (Q X r)]
r position relative to planet's center
F force per unit mass
C rate of creation of (gaseous) atmosphere
D rate of destruction of atmosphere
/ internal energy per unit mass 1=^7"]
Q heating rate per unit mass
K gas content
c, specific heat at constant volume.
•' . -. :. stratospheric
aerosols • .' y ••.••'••:•
.y^^- .** 1.T -^VZt— r~— . - -,
I large-scale supersaturation cloud >
convective cloud .
c ~y~
~"[_)'
latent and
sensible
heat fluxes .
i t It
OCEAN OCEAN ICE
heat and .
moisture
storage
radiative
constituents:
H20,C02,0S,
— trace gases,
clouds,
aerosols
* »
run-off _,tt )CE
LAND T*~-Z.( diurnal)
^^±?+^
s^ -*• Z 2 (seasonal 1
(b)
Figure 1.
201
-------
mixing before we can develop an accurate model of global ocean circulation and
currents.
A principal conclusion is that decades of research are likely to be
required to improve climate models to the point that they can be used to
predict local and regional climate changes with a high degree of confidence.
Such improvements will be possible only if appropriate observations of the
climate system and climate processes are carried out. In the meantime,
climate models can provide a useful indication of the possible magnitude of
future climate trends, although the results must be accompanied by appropriate
explanations and caveats, especially the results at smaller scales.
Finally, we would like to stress one key characteristic of both climate
model results and real-world climate, i.e., natural climate variability.
Figure 2 illustrates the global mean temperature in a 100-year control run of
our 3-D GCM. It can be seen that the temperature fluctuates, both from year
to year and with decadal trends, even though the amount of atmospheric C02 and
other climate "forcings" are unchanging in the model. Such variability or
"noise" is a natural characteristic of the climate system. Although this
phenomenon is captured by the governing fundamental equations in the climate
model, individual fluctuations are not predictable. Thus, for any climate
trend to be detected, it must exceed the level of natural climate variability.
o
o
0.5
0.4
0.3
0.2
oo.i
0
-O.I
-0.2
-0.3
I I I I I I T
Global Annual-Mtan Surface Air Temptraturt
IOO Year GCM Control Run
10 20 30 40 50 60
Time (years)
70
80
90
100
Figure. 2. Global-mean annual-mean surface air temperature in
the 100-year control run with the GISS global climate model with
predicted ocean temperature. Atmospheric CC>2, trace gases, and
aerqsols are unchanging during this run. The ocean-mixed layer
has the observed seasonal and geographical depth variations and
no exchange of heat with the deeper ocean.
202
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TESTS OF CLIMATE MODELS
A good overall test of the greenhouse effect is provided by examining the
climates of several planets—Mars, Earth, and Venus—which have a wide range
of abundances of atmospheric greenhouse gases. These planets are warmer than
they would be if they were simply in blackbody equilibrium with the energy
absorbed from the sun. The observed greenhouse warmings are a few degrees on
Mars, about 35 degrees on Earth, and several hundred degrees .on Venus. The
magnitude of these warmings is in excellent agreement with the greenhouse
theory and simple climate models.
Another test, of more direct relevance, is provided by prehistoric
climate variations on Earth. This test is only recently beginning to be
exploited. The climate of the Earth has fluctuated between ice ages and
interglacial warm periods several times during the past few hundred thousand
years. It has been realized for more than a decade that small variations in
the earth's orbital characteristics about the sun were the 'pacemakers' of the
10,000- to 100,000-year climate changes (Hays et al. 1976), but the mechanisms
by which global temperature changes were produced remain uncertain. Recently
it has been discovered that the atmospheric C02 abundance fluctuated along
with ancient climate, and was thus a probable agent producing the global
temperature changes. This inference of past C02 warming allows an empirical
evaluation of climate sensitivity to a C02 change.
In particular, the paleoclimate record indicates that a C02 change of 50-
100 parts per million (ppm) (Oeschger et al. 1984) is associated with a global
mean temperature change of 4°-5°C (CLIMAP Project 1981). The global radiative
forcing ( ATQ) due to this C02 change, i.e., the surface temperature change
which would occur if there were no climate "feedback" processes, can be
accurately computed and is
ATQ ~ 0.5°C. (1)
Thus, under the assumption that the C02 change is the dominant forcing for the
global temperature change, the total climate feedback factor f, defined by
AT = fAT , (2)
is f ~ 10 for the recent glacial-to-interglacial climate changes. Physical
processes contributing to f have been analyzed (Hansen et al. 1984, hereafter
referred to as paper 2) and it has been shown that a substantial part of the
total feedback factor is due to the growth and decay of large continental ice
sheets, a process which is not significant on the time scale of the next few
decades. The feedback factor inferred from the paleoclimate data for
processes that are relevant to a climate change on decadal time scales is
f ~ 2-4.
The paleoclimate evidence thus indicates that if atmospheric C02 were
doubled from, say, 300 ppm to 600 ppm, and the climate system were allowed to
come to a new equilibrium, the earth would warm by
AT(2*C02) ~ (2°-4°C) * ATQ ~ 2.5°-5°C, (3)
203
-------
where ATO ~ 1.25 is the no-feedback radiative forcing due to doubling
atmospheric COg.
The climate sensitivity inferred from paleoclimate evidence is reasonably
consistent with the climate sensitivity estimated by several National Academy
of Science studies (Charney et al. 1979; Smagorinsky et al. 1982),
AT(2*C02) = 3° ± 1.5°C, (4)
which was based mainly on inter comparison and analysis of several different
climate model studies. Thus there is general agreement about the magnitude of
global climate sensitivity, but the uncertainty in its value is at least a
factor of two.
Despite all the above evidence, the one truly convincing test of the
models must be a comparison of the models' predictions with the observed
response of the earth's climate to the present anthropogenically induced
growth of atmospheric CC^ and trace gases. Thus, we illustrate in Plate 2 the
temperature changes that have occurred during the past century, a time during
which CC>2 has increased from about 280 ppm to 340 ppm and several other trace
gases have also increased.
The geographical patterns of temperature change (Plate 2a) contain a
large amount of natural variability, as well as errors in regions where there
are few stations and short records. The influence of the climate 'noise' and
incomplete station coverage is reduced by averaging results over all longi-
tudes. Plate 2b shows the resulting temperature trends for the period 1880-
1984 as a function of latitude.
Several conclusions follow from the data illustrated in Plate 2. Most of
the earth has warmed in the past 100 years, but there is a great amount of
local variability. The global mean warming since 1880 is about 0.6°C (1°F),
with both hemispheres warming by about that amount. Although the earth was
about as warm in the 1930s and 1940s as it is in the 1980s, the earlier
warming was more concentrated in the high latitudes of the Northern Hemi-
sphere, while the recent warming is more global.
The global warming of 0.6°C in the past century is of the magnitude
expected as a result of increasing CC>2 an<^ trace gases. It is difficult to
make a more definitive statement than that, in part because the greenhouse
forcing is time dependent (most of the growth coming in the past 25 years) and
the climate system has a finite response time, probably several decades (paper
2 and Hansen et al. 1985), so that only a part of the eventual warming due to
these added gases has occurred as yet. Also, a warming of 0.6°C is not parti-
cularly large compared to climate fluctuations that have occurred in the past
millenium, as illustrated below.
We show below that the expected greenhouse climate signal is rising
rapidly and should soon rise well above the level of natural variability.
This would provide strong empirical verification of the greenhouse effect.
204
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PREDICTED TEMPERATURE CHANGES
The estimated contributions of different greenhouse gases to climate
forcing is illustrated in Figure 3 for different periods. The C02 contri-
bution is known accurately, within about 10 percent. The contributions of
chlorofluorocarbons CCloF (F^) and CC12F2 (F^' comPounds which are entirely
man made, are also known accurately. The CHjj greenhouse contribution is less
certain; there is some recent evidence suggesting that the CH^ growth rate we
assumed (0.6 percent per year in the 1960s, 1 percent per year in the 1970s,
and 1.5 percent year in the 1980s) may be too high for the 1980s and perhaps
too low for the 1960s (Rasmusson and Khalil 1986; Rinsland et al. 1985; Blake
and Rowland 1986). The Oo and stratospheric H20 changes, based on a chemical
model, are very uncertain and are best described as hypothetical; indeed,
recent spotty observations of Oo profiles do not support a positive greenhouse
forcing due to changing 0^ (Lacis et al. 1986). Despite uncertainties about
the trends of some of the gases, two firm conclusions can be made:
• In the past few decades the rate of increase of greenhouse forcing of
the climate system has increased rapidly; it is now three to ten times
greater than during the previous century, 1850-1960.
• Non-C02 greenhouse gases now add to the greenhouse effect at a rate
comparable to that of C02.
We have carried out the first GCM simulations of climate trends due to
the current changes of atmospheric C02 and trace gases. One disadvantage of
presenting recent research results is that we cannot claim that the results
have been confirmed by other climate modeling groups. However, the sensiti-
vity of our global climate model has been compared and found to be similar to
that of other climate models at the NSF National Center for Atmospheric
Research (Washington and Meehl 1984) and the NOAA Geophysical Fluid Dynamics
Laboratory (Manabe and Broccoli 1985; Wetherald and Manabe 1986). Thus we
expect that the general conclusions discussed below would not be changed if
the models of these other laboratories were used, provided that similar basic
assumptions were made, for example, with regard to trace gas growth rates and
ocean heat uptake.
The global climate model employed for these simulations is our model II
documented in paper 1, which has an equilibrium global mean sensitivity of
4.2°C for doubled C02 as documented in paper 2. For these transient experi-
ments the ocean mixed layer depth is based on climatology, including geogra-
phical and seasonal variations. Heat capacity of the ocean beneath the mixed
layer is included by treating a heat perturbation as a passive tracer which
can diffuse into the deeper ocean; the diffusion coefficient varies geographi-
cally as a function of the climatological local stability beneath the mixed
layer, according to the empirical relation given in paper 2. Horizontal ocean
heat transports are fixed as described in paper 2.
205
-------
0.10
0.08
^0.06
o
o
0.04
0.02
Decadal Increments of Greenhouse Forcing
C02
4.2
ppm
slr.H20
C02
8.2
ppm
str.
TiT
12
CH,
1850 -I960
(per decade)
1960's
"CFCs
CO,
12.8
ppm
str.
£••••»*•*• u n
;CFCsSH2°
N,0
CH.
1970's
CO,
15.6
ppm
CFCs:
12
N20
CH4
I980's
Decadal additions to global mean greenhouse forcing of the
ATO is the computed temperature change at equilibrium for
Figure 3.
climate system.
the estimated decadal increase in trace gas abundances, with no climate
feedbacks included. Multiply AT0 by the feedback factor f to get the
equilibrium surface temperature change including feedback effects. Most of
the estimated trace gas increases are based on measurements. However, the Oo
and stratospheric f^O trends (dotted bars) are based principally on 1-D model
calculations of Wuebbles et al. (1983).
206
-------
Our GCM simulations begin in 1958, when CC^ began to be monitored accu-
rately by C.D. Keeling, and extend through the present into the future. We
consider two scenarios, A and B, to allow for uncertainties about past trace
gas changes and future CC^ and trace gas changes. Scenario B includes only
five greenhouse gases that have been measured reasonably well (C^, FH» ^12'
CHjj, N20) and it assumes that their growth rates will decrease rapidly during
the next few decades. Scenario A includes an allowance to approximate the
greenhouse forcing of the several other hypothesized gases in Figure 3, and it
allows presently estimated growth rates to continue. We do not contend that
Scenarios A and B represent extreme possibilities; however, they do help us to
estimate how sensitive the conclusions are to assumptions about the climate
forcings.
Scenario A achieves a radiative forcing equivalent to that for doubled
C02 about 40 years from now, in the late 2020s. Scenario B achieves this
level of forcing in about 2060. The more detailed trace gas scenario of
Ramanathan et al. (1985) is close to Scenario A (see Figure 4). Finally, we
note that both scenarios include some additional radiative forcing due to
volcanic aerosols, a forcing that tends to cool the surface. The aerosol
forcing is the same in the two scenarios for the period 1958-1986, with two
significant coolings: 1963-66 (Mt. Agung) and 1982-85 (El Chichon). Scenario
B assumes that the mean aerosol forcing in the future will be similar to that
in the period 1958-1966, a period of active volcanism, while Scenario A
assumes a negligible future volcanic forcing, as was the case for the period
1910-1960.
Global maps of temperature changes obtained in the GCM climate experi-
ments are shown in Plate 3. The detailed geographical patterns of these
changes are not to be taken seriously in view of the limitations of current
GCMs mentioned above and the gross assumption about ocean heat transports.
However, some of the large-scale features are more likely to be meaningful.
The warming in Scenario A at most midlatitude Northern Hemisphere land
areas such as the United States is typically 0.5°-1.0°C (1°-2°F) by the decade
1990-2000 (Plate 3a) and 1°-2°C (2°-4°F) by the decade 2010-2020 (Plate 3b).
Even in the latter decade the warming is much less than the equilibrium
response to doubled C02 (Plate 3c) which has a warming of about 5°C in the
United States. At all future times the largest temperature changes are in
regions of sea ice and the smallest are at low and middle latitude ocean
areas.
The global mean temperatures computed by the model are compared to obser-
vations in Figure 5 for the period 1958 to the present. In this period the
greenhouse forcing of Scenarios A and B differ only by about 10 percent. It
is apparent that the observed temperatures and the model results are consis-
tent during this period. But the natural variability of temperature in both
the real world and the model are sufficiently large that we can neither
confirm nor refute the modeled greenhouse effect on the basis of current
temperature trends.
207
-------
o
o
I '
Greenhouse Forcing
for two trace gas scenarios
Scenario
Current
Growth
Rates
doubled .
CO, V
Scenario B,
Reduced
Growth
Ramanathan etol. (1985)
1980 2000
2020 2040
Date
2060 2080 2100
Figure 4. Greenhouse forcing for two trace gas scenarios. ATO is the
equilibrium warming with no climate feedbacks. Scenario B includes only COp,
CHh, NpO,
and F*, and it assumes that their growth rates will decrease
^ ^*,
rapidly in the next 2.5 years. Scenario A includes an allowance for other
trace gasses hypothesized in Figure 3 and it allows current growth rates to
continue indefinitely.
In Scenario A CO^ increases as observed by Keeling for the interval 1958-
1984 and subsequently with a 1.5 percent growth of the annual increment.
CCloF and CCl2Fp emissions are from reported rates to date and assume 3
percent per year increased emission in the future, with atmospheric lifetimes
for the gases of 75 and 150 years, respectively. CH^ increases from 1.4 parts
per billion in 1958 at a rate of 0.6 percent per year until 1970, 1 percent
per year in the 1970s and 1.5 percent per year thereafter. N^O increases
according to the semi-empirical formula of Weiss (1981), the race being 0.1
percent per year" in 1958, 0.2 percent per year in 1980, 0.4 percent per
year in 2000 and 0.9 percent per year' in 2030. Potential effects of several
other trace gases (such as Oo, stratospheric HpO, and chlorine and fluorine
compounds other than F,, and F«p) are approximated by multiplying the CFC
amount by the factor 2.
In Scenario B the growth of the annual increment in COp is reduced from
1.5 percent today to 1 percent in 1990, 0.5 percent in 2000 and zero in
2010. The growth in annual emissions of CCloF and CClpFp is reduced from 3
percent today to 2 percent in 1990, 1 percent in 2000 and 0.5 percent in
2000. N20 increases are based on Weiss' (1981) formula, but the parameter
specifying annual growth in anthropogenic emissions decreases from 3.5 percent
today to 2.5 percent in 1990, 1.5 percent in 2000 and 0.5 percent in 2010. No
increases are included for other chlorofluorocarbons, ozone, stratospheric
water or any other gases.
208
-------
On the other hand, it is also apparent from Figure 5 that the predicted
greenhouse warming for Scenario A rises above the level of natural variability
by the 1990s. The standard deviation of the five year smoothed global
temperature during the past century is o ~ 0.2°C. Thus a global warming of
0.6°C, compared to, say, the 1958-1980 mean temperature, would be a 3o effect,
significant at the 99 percent confidence level. The model predicts that such
a warming will be achieved in the 1990s.
Indeed, the model predicts a temperature level in the next 15 years that
has not existed on earth in the past 100,000 years, as illustrated below. In
view of the significance of such conclusions, we stress here the principal
caveats which must accompany the result:
• The model sensitivity is 4.2°C for doubled C^. Emergence of the
warming signal above the level of natural climate variability will be
delayed if the true sensitivity is less than that.
• The projection is based on Scenario A. If Scenario B is more
realistic, emergence of the warming signal will be delayed. We esti-
mate that Scenario B would delay the emergence of the signal by
several years, but a more quantitative statement requires extension of
the Scenario B simulation.
• Other major climate forcings that tend to counteract the greenhouse
warming may occur during the next several years. As one example,
satellite measurements indicate that solar irradiance decreased in the
period 1980-1984 (cf. references in Kerr 1986) at a rate that would
approximately cancel the increase in greenhouse forcing during the
same period. Although decreases in solar irradiance are probably
cyclical and must be balanced by comparable increases over a time
scale of several decades, it is possible that a decreasing trend could
continue for several more years. As a second example, an unusual
increase in volcanic activity could conceivably counteract the green-
house warming for as long as a decade or so: Scenario B contains a
substantial amount of volcanic aerosols, similar to the amount in the
volcanically active period 1958-1985, but it is possible to have a
still greater level of volcanic activity.
• There may be crucial climate mechanisms that are omitted or poorly
simulated in current climate models. An example is changes in ocean
circulation, such as the formation of deep water (Bennett et al.
1985). If the rate of deep water formation is reduced, it is even
possible that the North Atlantic and Europe may cool while most of the
world is warming. A change in ocean circulation would also raise the
possibility of a more rapid transition to a warmer climate, if it
reduced the effective thermal inertia of the ocean and thus reduced
the climate response time (paper 2; Hansen et al. 1985).
COMPARISON WITH PAST TEMPERATURES
Global temperature changes are illustrated in Figure 6 for the past
century, millenium, and 25,000 years and in Figure 7 for the past 150,000
years. The global mean temperature has varied by about 0.5°C in the past
century and 5°C in the past several hundred thousand years (National Academy
209
-------
0.8
(a) Seasonal Mean Global Temperature Trends
OBSERVATIONS
SCENARIO A
SCENARIO B
I I
V V
1958 I960
Date
l.b
1,4
1.2
1.0
0.8
o
^ 0.6
<
0.4
0.2
0
-0.2
-0.4
1
1
OBS
SCE
SCE
y*
1 1 1 1
b) 5
ERVAT
MARIO
NARIO
*J-'
1 1 1
-Yea
r Smc
1
>othed Glo
nwr
A
•J~~^
1 1 1
,./.
i i
1 y— •>
•-.,-'"
1 1 1 1
1
1 1 1 1
bal Temperature Trends
i i
1 1 i i
i i i
i i i i
MM
I I I
V V V V V V V
I960 1970 1980 1990 2000 2010 201
Date
Figure 5. Global temperature trends from observations (solid line) and
from calculations with the GISS global climate model. Part (a) shows the
temperature anomalies plotted each season (December-January-February, March-
April-May, etc.). Part (b) shows the 5-year smoothed results. Simulations
have only been carried out into the future for Scenario A.
210
-------
Q.4
p °
<
-0.4
o
ID
(o) past cintury
annual mean
5-year running mean
I
1
I
1900 1920 1940
Date
(b) past millenium
I960
I960
I i I i I
I
I
1000 1200 1400 1600 1800
Date
(c) past 25,000 years
I
I
I
30 25 20 15 10
Thousands of Years Ago
Figure 6. Global temperature trend for the past century (a), millenium
(b), and 25,000 years (c). (a) is based on Hansen et al. 1981, updated
through 1981. (b) is based on temperatures in central England, the tree limit
in the White Mountains of California, and oxygen isotope measurements in the
Greenland ice (W. Dansgaard, private communication), with the temperature
scale set by the variations in the last 100 years, (c) is based on changes in
tree lines, fluctuations of alpine and continental glaciers and shifts in
vegetation patterns recorded in pollen spectra (National Academy of Sciences
1975), with the temperature scale set by the 3°-4°C cooling obtained in a 3-D
climate model (Hansen et al. 1984) with the boundary conditions for 18,000
years ago. Thus the shapes of curves (b) and (c) are based on only Northern
Hemisphere data.
211
-------
of Sciences 1975). During the peak of the current interglacial (Altithermal
period 5,000 to 10,000 years ago) the mean temperature is estimated to have
been 0.5°-1.0°C warmer than today (Figure 6).
A comparison of the temperature changes projected for the next few
decades with estimated temperatures for the past 150,000 years is shown in
Figure 7. By the early twenty-first century the global temperature should
have risen well above any level experienced in the past 100,000 years.
o
o
Global Mton Ttmperaturc
I
I
I
I
f«—2025
I (Dal«)
•4-ZOOO
Model
( Sctnario A)
150 125 100 75 50
Thousands of Years Ago
25
Figure 7. Global temperature trend for the past 150,000 years and
as projected for the next few decades on the basis of the global
climate model simulation with Scenario A trace gas trends.
TEMPERATURE CHANGES IN THE UNITED STATES
How might temperature changes of the magnitude predicted alter the number
of days with temperatures above a given limit for Washington, D.C. and other
U.S. cities? We estimate this by compiling climatological data for a given
city from a long series of daily observations (including maximum and minimum
temperatures for each day) and adding to this record the mean (monthly)
increase in daily maximum temperature and in daily minimum temperature as
predicted by the climate model for the gridbox that includes that city. This
procedure tends to minimize the effects of any errors in the model's control
run climatology. Although we should, in principle, also examine the effect of
changes in higher moments of the temperature distribution, Mearns et al.
(1984) have shown that changes in the higher moments have relatively little
effect on the total number of days above a temperature extreme.
We have carried out this procedure for several U.S. cities for the equi-
librium change in climate for doubled CQ^- Because of the climate system's
finite response time, the results may be most applicable to some time in the
middle of the twenty-first century, if the trace gas growth rate of Scenario A
is approximately correct.
212
-------
The results of this exercise for several cities in the United States are
shown in Figure 8. The number of days per year in which the maximum daily
temperature exceeds 38°C (100°F) increases from about one to twelve in
Washington and from three to twenty in Omaha. The number of days with maximum
temperature exceeding 32°C (90°F) increases from about thirty-five days to
eighty-five days in both cities. The number of days per year in which the
nighttime temperature does not fall below 27°C (80°F) increases from less than
one day in both cities to nine days in Omaha and nineteen in Washington,
D.C. Analogous results for six other U.S. cities are included in Figure 8.
There are a number of reasons why these estimates may differ from the
real world response. Principal among these are the following. First, the
estimates are based on a model with a sensitivity of 4°C for doubled CC^; the
real world sensitivity is uncertain by about a factor of two. Second, the
model assumes that the ocean will continue to operate essentially as it does
today; if North Atlantic deep water formation and the Gulf Stream should be
substantially modified, for example, that could change the results for a
location such as Washington, D.C. And third, there are many small-scale
processes that are not resolved by the model, which could cause local
responses to vary.
A number of expected effects of the greenhouse warming in the United
States are summarized in Table 1. The summer cooling requirements in some
United States cities will increase several times. On the other hand, heating
degree days in the winter decrease on the order of 50 percent. The winter
warming, expected to exceed that in summer, may also affect such things as the
ability of indigenous forests to survive (Shantz and Hoffman 1986), and the
amount, type, and distribution of precipitation. Table 1 also indicates that
the growing season will increase in the United States, typically by fifty
days, and it is expected that increasing atmospheric C02 will enhance plant
growth (Lemon 1983). Nevertheless, the high midsummer temperatures could
conceivably result in lower agricultural productivity, as occurred in
(regional) midsummer heat waves in the United States in 1980 and 1986.
Quantitative evaluation of beneficial and detrimental effects will require
greatly improved climate forecast capabilities as well as research in societal
impact.
We conclude that the magnitude of temperature changes predicted by
current climate models is sufficiently great that, on the average, the warming
will be very noticeable to the populations at middle latitudes. Other discus-
sions of the practical impacts of greenhouse warming have focused on possible
indirect effects such as changes of sea level, storm frequency, and drought.
We believe, however, that the temperature changes themselves will
substantially modify the environment and have a major impact on the quality of
life in some regions.
EVIDENCE NEEDED TO CONFIRM AND QUANTIFY THE GREENHOUSE THEORY
From a scientific point of view, evidence confirming the essence of the
greenhouse theory is already overwhelming. However, the greenhouse issue is
not likely to receive the full attention it deserves until the global tempera-
ture rises above the level of natural climate variability. This will not
occur at some sharp point in time, but rather gradually over a period of
time. If our model is approximately correct, that time may be soon, within
the next decade.
213
-------
Days per Year with Temperature Exceeding 100°F
••(950-1963 Climate
I 1 Doubled C02
12
-L a
Washington D.C.
21
Omaha
16
0
New York
78
19
Denver Los Angeles Dallas
(a)
_6
Chicago
42
4
^m
Memphis
Days per Year with Temperature Exceeding 90°F
87
36
I
66
37
I
Washington D.C. Omaha
33
27
Denver
••(950-1983 Climate
I I Doubled C02
48
56
15
16
New York Chicago
162
145
100
65
Los Angeles Dallas
Memphis
(b)
Days with Minimum Temperature Exceeding 80°F
1950-1983 Climate
Doubled COz
19
Washington D.C. Omaha
I 3
New York
68
(c)
0
Chicago
00 01 4
Denver Los Angeles Dallas
2
Memp
51
his
214
Figure 8. Annual
number of days in
several U.S. cities with
(a) maximum temperature
greater than 100°F, (b)
maximum temperature
greater than 90°F, and
(c) minimum temperature
greater than 80°F. The
results for doubled CC>2
were generated by adding
the warming in a doubled
CO-
climate
model
experiment to recorded
temperatures for 1950-
1983.
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When that point in time is reached people will begin to ask practical
questions and want quantitative answers. We are now totally unprepared to
provide information of the specificity that will be required. Our under-
standing of the climate system and our ability to model climate must be vastly
improved. Some of the tasks, such as the development of a realistic ocean
model appropriately interactive with atmospheric climate changes, will require
major long-term efforts.
The greatest need, in our opinion, is for global observations of the
climate system over a period of at least a decade. Observations are needed to
document and quantify climate trends, to allow testing and calibration of
global climate models, and to permit analysis of many small-scale climate
processes which must be parameterized in the global models. The data needs
will require both monitoring from satellites and in situ studies of climate
processes. Prestigious scientific groups, such as the Earth System Sciences
Committee appointed by the NASA Advisory Council, have defined the required
observations in detail.
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218
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The Causes and Effects of Sea Level Rise
James G. Titus
U.S. Environmental Protection Agency
Washington, DC USA
INTRODUCTION
For the last several thousand years, sea level has risen so slowly that
for most practical purposes it has been constant. As a result, people and
other maritime species have had the opportunity to extensively develop the
shorelines of the world. Whether one is talking about a vacation spot in Rio
de Janeiro, swamps in Bangladesh, farmland in the Nile Delta, marshes along
the Chesapeake Bay, or the merchants of Venice, life along the coast is in a
sensitive balance with the level of the sea.
This balance would be upset by the rise in sea level that could result
from the global warming projected by Hansen et al. (this volume). Such a
warming could raise sea level one meter or more in the next century by
expanding ocean water, melting mountain glaciers, and perhaps eventually
causing polar ice sheets to melt or slide into the oceans. Sea level rise
would inundate low-lying areas, drown coastal marshes and swamps, erode
beaches, exacerbate flooding, and increase the salinity of rivers, bays, and
aquifers throughout the world.
This paper provides an overview of the causes and effects of sea level
rise.
CAUSES OF SEA LEVEL RISE
Past Trends in Sea Level
The worldwide average sea level depends primarily on (a) the shape and
size of ocean basins, (b) the amount of water in the oceans, and (c) the
average density of seawater. Subsidence, emergence, and other local factors
can cause trends in "relative sea level" at particular locations to differ
from trends in "global sea level."
219
-------
Hays and Pitman (1973) analyzed fossil records and concluded that over
the last 100 million years, changes in mid-ocean ridge systems have caused sea
level to rise and fall over 300 meters. However, Clark, Farrell, and Peltier
(1978) have pointed out that these changes have accounted for sea level
changes of less than one millimeter per century. No published study has
indicated that this determinant of sea level is likely to have a significant
impact in the next century.
The impact of climate on sea level has been more pronounced. Geologists
generally recognize that during ice ages the glaciation of substantial por-
tions of the northern hemisphere has removed enough water from the oceans to
lower sea level one hundred meters below present levels during the last
(18,000 years ago) and previous ice ages (Don, Farrand, and Ewing 1962;
Kennett 1982; Oldale 1985).
Although the glaciers that once covered much of the northern hemisphere
have retreated, the world's remaining ice cover contains enough water to raise
sea level over seventy-five meters (Hollin and Barry 1979). Table 1 shows
estimates by Hollin and Barry (1979) and Flint (1971) that existing alpine
glaciers contain enough water to raise sea level 30 or 60 centimeters, respec-
tively. The Greenland and West Antarctic Ice Sheets each contain enough water
to raise sea level about seven meters, while East Antarctica has enough ice to
raise sea level over 60 meters.
There is no evidence that either the Greenland or East Antarctic Ice
Sheets have completely disintegrated in the last two million years. However,
it is generally recognized that sea level was about seven meters higher than
today during the last interglacial period, which was one to two degrees warmer
(Moore 1982; Mercer 1968). Because the West Antarctic Ice Sheet is marine-
based and thought to be vulnerable to climatic warming, attention has focused
on this source for the higher sea level. Mercer (1968) found that lake sedi-
ments and other evidence suggested that summer temperatures in Antarctica have
been 7° to 10°C higher than today at some point in the last two million years,
probably during the last interglacial period 125,000 years ago, and that such
temperatures could have caused a disintegration of the West Antarctic Ice
Sheet.
Tidal gauges have been available to measure the change in sea level at
particular locations over the last century. Studies combining these measure-
ments to estimate global trends have concluded that sea level has risen 1.0 to
1.5 mm/yr during the last century (Barnett 1983; Gornitz, Lebedeff, and Hansen
1982; Fairbridge and Krebs 1962). Barnett (1983) found the rate of sea level
rise for the last fifty years to be between 2.0 and 2.5 mm/yr, while in the
previous fifty years there was little change; however, the acceleration of the
rate of sea level rise was not statistically significant. Emery and Aubrey
(1985, n.d.) have filtered out estimated land surface movements in their
analyses of tidal gauge records in northern Europe and western North
America, and have found an acceleration in the of sea level rise over the
last century.' Braatz and Aubrey (n.d.) have found that the rate of
This result was reported in the North America study. The data also shows
it to be true in the northern Europe study, but the result was not re-
ported. David Aubrey, Woods Hole Oceanographic institute, Woods Hole,
Massachusetts, personal communication.
220
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Table 1. Snow and Ice Components (Modified from Hollin and Barry 1979)
Area
(105
km2)
Ice
Volume
(10b km3)
Sea-Level
Equivalent3
(m)
Land ice: East Antarctica13 9.86 25.92 64.8
West Antarctica0 2.34 3.40 8.5
Greenland 1.7 3.0 7.6
Small ice caps and mountain
glaciers (Hollin and Barry 1979; 0.54 0.12 0.3
Flint 1971) 0.6
Permafrost (excluding Antarctica): 0.6
Continuous 7.6 0.03 0.08
to to
Discontinuous 17.3 0.7 0.17
Sea ice: Arctic
Late February 14.0 0.05
Late August 7.0 0.02
Antarctic6
September 18.4 0.06
February 3.6 0.01
f
Land Snow Cover
N. Hemisphere
Early February 46.3 0.002
Late August 3.7
S. Hemisphere
Late July 0.85
Early May 0.07
3 400,000 km3 of ice is equivalent to 1 m global sea level.
Grounded ice sheet, excluding peripheral, floating ice shelves (which do
not affect sea level). The shelves have a total area of 1.62 x 10 km
and a volume of 0.79 x 10° knH (Drewry and Heim 1983).
° Including the Antarctic Peninsula.
Excluding the Sea of Okhotsk, the Baltic Sea, and the Gulf of St. Lawrence
(Walsh and Johnson 1979). Maximum ice extents in these areas are 0.7
million, 0.4 million, and 0.2 million km , respectively.
e Actual ice area excluding open water (ZwaJJy et al. 1983). Ice extent
ranges between 4 million and 20 million km .
Snow cover includes that on land ice but excludes snow-covered sea ice
(Dewey and Heim 1981).
Source: Glaciers, Ice Sheets, and Sea Level, National Academy Press, p. 272.
221
-------
relative sea level rise on the east coasts of North America accelerated after
1934.
Several researchers have attempted to explain the source of current
trends in sea level. Barnett (1984) and Gornitz, Lebedeff, and Hansen (1982)
estimate that thermal expansion of the upper layers of the oceans resulting
from the observed global warming of 0.4°C in the last century could be respon-
sible for a rise of 0.4 to 0.5 millimeter per year. Roemmich and Wunsch
(1984) examined temperature and salinity measurements at Bermuda, found that
the 4°C isotherm had migrated 100 meters downward, and concluded that the
resulting expansion of ocean water could be responsible for some or all of the
observed rise in relative sea level. Roemmich (1985) showed that the warming
trend 700 meters below the surface was statistically significant. However,
Barnett (1983) found no significant trend based on an examination of the upper
layers of the ocean. Nevertheless, Braatz and Aubrey (n.d.) note that long-
term steric changes in the ocean are not confined to the upper layers of the
oceans, which implies that the Barnett analysis does not necessarily contra-
dict the Roemmich and Wunsch conclusion.
Meier (1984) estimates that retreat of alpine glaciers and small ice caps
could be responsible for a current contribution to sea level of between 0.2
and 0.72 millimeters per year. The National Academy of Sciences (NAS) Polar
Research Board (Meier 1985) concluded that existing information is insuffi-
cient to determine whether the impacts of Greenland and Antarctica are posi-
tive, negative, or zero. Although the estimated global warming of the last
century appears at least partly responsible for the last century's rise in sea
level, no study has demonstrated that global warming might be responsible for
an accelerated rate of sea level rise.
Impact of Future Global Warming on Sea Level
Concern about a substantial rise in sea level as a result of the
projected global warming stemmed originally from Mercer (1968), who suggested
that the Ross and Filchner-Ronne ice shelves might disintegrate, causing a
deglaciation of the the West Antarctic Ice Sheet and a resulting six to seven
meter rise in sea level, possibly within 40 years.
Subsequent investigations have concluded that such a rapid rise is
unlikely. Hughes (1983) estimated that such a disintegration would take at
least two hundred years, and Bentley (1983), five hundred. Other researchers
have estimated that this process could take considerably longer (Fastook 1985;
Lingle 1985).
Researchers have turned their attention to the magnitude of sea level
rise that might occur in the next century. The best understood factors are
the thermal expansion of ocean water and the melting of alpine glaciers. In
the National Academy of Sciences report Changing Climate, Revelle (1983) used
the model of Cess and Goldenberg (1981) to estimate temperature increases at
various depths and latitudes resulting from a 4.2°C warming by 2050-2060
(Figure 1). While noting that his assumed time constant of 33 years probably
resulted in a conservatively low estimate, he estimated that temperature
increases would result in an expansion of the upper ocean sufficient to raise
sea level thirty centimeters.
222
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60° N 40° N 20° N
LATITUDE
0 20°S 40°S 60°S 80°S
2OO
t
UJ
400-
600
800
1000
5.S
I
1
4.0
1
J
1.8
r
r5"
4.2
2.6
1.3
1
-sJ
4.2
2.3
1.3
3.5
2.7
1.6
0.5
rai
1-6 I
0.9
0.3
2.5
2.0
1.1
0.4
1
| 3.5
2.7
1.6
0.5
5
3.9
2.2
0.7
4.5
3.5 :
-"1 '
0.6
4
i.4
1.3
1.0
t
3
2
1
J
.4
•3
.0
3.5
2.9
[•"I
0.9
3 2
2.5 1.7
1.7 1.1
0.8 0.5
Figure 1. Computed near-equilibrium changes in ocean temperature
for a doubling of atmospheric carbon dioxide and probable increase
in other greenhouse gases, about 2080. The surface temperature
increase is based on Flohn's (1982) prognosis.
Using a model of the oceans developed by Lacis et al. (1981), Hoffman,
Wells, and Titus (1985) examined a variety of possible scenarios of future
emissions of greenhouse gases and global warming. They estimated that a
warming of between 1° and 2.6°C could result in a thermal expansion contribu-
tion to sea level of between 12 and 26 cm by 2050. They also estimated that a
global warming of 2.3° to 7.0°C by 2100 would result in thermal expansion of
28-83 cm by that year.
Revelle (1983) suggested that while he could not estimate the future
contribution of alpine glaciers to sea level rise, a contribution of 12 centi-
meters through 2080 would be reasonable. Meier (1984) used glacier balance
and volume change data for twenty-five glaciers where the available record
exceeded fifty years to estimate the relationship between historic temperature
increases and the resulting negative mass balances of the glaciers. He esti-
mated that a 28-mm rise had resulted from a warming of 0.5°C, and concluded
that a 1.5° to 4.5°C warming would result in a rise of 8-25 cm in the next
century. Using these results, the WAS Polar Board concluded that the contri-
bution of glaciers and small ice caps through 2100 is likely to be 10 to 30 cm
(Meier et al. 1985). They noted that the gradual depletion of remaining ice
cover might reduce the contribution of sea level rise somewhat. However, the
contribution might also be greater, given that the historic rise took place
over a sixty-year period, while the forecast period is over one hundred
years. Using Meier's estimated relationship between global warming and the
alpine contribution, Hoffman, Wells, and Titus (1986) estimated alpine contri-
butions through 2100 at 12-38 cm for a global warming of 2.3° to 7.0°C.
223
-------
The first published estimate of the contribution of Greenland glacier
meltwater to sea level was Revelle's (1983) estimate of 12 cm through the year
2080. Using estimates by Ambach (1980, 1982) that the equilibrium line
(between snowfall accumulation and melting) rises one hundred meters for each
0.6°C rise in air temperatures, he concluded that the projected 6°C warming of
Greenland would be likely to raise the equilibrium line 1,000 meters. He
estimated that such a change in the equilibrium line would result in a 12-cm
contribution to sea level rise for the next century.
The MAS Polar Board (Meier et al. 1985) noted that the large ablation
area makes Greenland a "significant potential contributor of meltwater to the
ocean if climatic warming causes an increase in the rate of ablation and an
upward shift of the equilibrium line." They found that a 1,000-m rise in the
equilibrium line would result in a contribution of 30 cm through 2100.
However, because Ambach (1985) found the relationship between the equilibrium
line and temperature to be 77 meters per degree (C), the panel concluded that
a 500-m shift in the equilibrium line would be more likely. Based on the
assumption of a 6.5°C warming by 2050 and constant temperatures thereafter,
the panel estimated that such a change would contribute about 10 cm to sea
level through 2100, but also noted that "for an extreme but highly unlikely
case, with the equilibrium line raised 1,000 m, the total rise would be 26
centimeters." Although Bindschadler (1985), had treated the two cases as
equally plausible, his analysis was conducted before the results of Ambach
(1985) were known; he has since indicated agreement with the findings of Meier
et al. (1985).
Available estimates of the Greenland contribution assume that all melt-
water flows into the oceans and that the ice dynamics of the glaciers do not
change. The NAS Polar Board suggested that some of the water would refreeze,
decreasing the contribution to sea level rise. Although a change in ice
dynamics might imply additional deglaciation and increase the rate of sea
level rise, the panel assumed that such changes were unlikely to occur in the
next century.
The potential impact of a global warming on Antarctica in the next
century is the least certain of all the factors by which a global warming
might contribute to sea level rise. Meltwater from East Antarctica might make
a significant contribution by the year 2100, but no one has estimated it.
The contribution of ice sliding into the oceans, known as "deglaciation," has
been the subject of several studies.
Bentley (1983) examined the processes by which a deglaciation of
Antarctica might occur. First an accelerated melting of the undersides of the
Ross and Filchner-Ronne ice shelves would occur due to warmer water circu-
lating underneath them. The thinning of these ice shelves could cause them to
become unpinned and their grounding lines to retreat. Revelle (1983) suggests
that the ice shelves might disappear in 100 years, after which time the
Antarctic ice streams would flow directly into the oceans, without the back
Robert Bindschadler, Goddard Space Flight Center, Greenbelt, Maryland,
personal communication.
James Hansen, Goddard Institute for Space Studies, New York, personal
communication to J.S. Hoffman.
224
-------
pressure of the ice shelves. Bentley suggests that all the ice could be
discharged over a period of 500 years.
Although a West Antarctic deglaciation would occur over a period of
centuries, it is possible that an irreversible deglaciation could commence
before 2050. If the ice shelves thinned more than about one meter per year,
Thomas, Sanderson, and Rose (1979) suggested that the ice would move into the
sea at a sufficient speed that even a cooling back to the temperatures of
today would not be sufficient to result in a reformation of the ice shelf.
To estimate the likely Antarctic contribution for the next century,
Thomas (1985) developed four scenarios measuring the impact of a 3°C global
warming by 2050:
• A shelf melting rate of 1 m/yr with seaward ice fronts remaining at
present locations—implies a rise of 28 cm by the year 2100.
• A shelf melting rate of 1 m/yr with ice fronts calving back to a line
linking the areas where the shelf is grounded, during the 2050s—
implies a rise of 1.6 m by 2100.
• Same as case 1 but with a melt rate of 3 m/yr—implies a rise of 1 m
by 2100.
• Same as case 2 but with a melt rate of 3 m/yr—implies a rise of 2.2 m
by 2100.
Thomas concluded that the 28-cm rise implied by case 1 would be most
likely. He also stated that even if enhanced calving did occur, it would be
likely to occur after 2050, "suggesting that probably associated sea level
rise would be closer to the 1 m of case 3 than the 2.2 m of case 4."
The MAS Polar Board (Meier et al. 1985) evaluated the Thomas study and
papers by Lingle (1985) and Fastook (1985). Although Lingle estimated that
the contribution of West Antarctica through 2100 would be 3 to 5 cm, he did
not evaluate the contribution from East Antarctica, while Fastook made no
estimate for the year 2100. Thus, the panel concluded that "imposing
reasonable limits" on Thomas' model yields a range of 20 to 80 cm by 2100 for
the Antarctic contribution. However, they also noted several factors that
could reduce the amount of ice discharged into the sea: the removal of the
warmest ice from the ice shelves, the retreat of grounding lines, and
increased lateral shear stress. They also concluded that increased precipi-
tation over Antarctica might increase the size of the polar ice sheets
there. Thus, the panel concluded that Antarctica could cause a rise in sea
level up to 1 m, or a drop of 10 cm, with a rise between 0 and 30 cm most
likely.
Table 2 summarizes the various estimates of global sea level rise. The
report Projecting Sea Level Rise (Hoffman, Keyes, and Titus 1983) estimated
that the rise would be between 56 and 345 cm, with a probable rise between 144
and 217 cm. Revelle (1983) estimated that the rise was likely to be 70 cm,
ignoring the impact of a global warming on Antarctica; Revelle also noted that
the latter contribution was likely to be 1 to 2 m per century after 2050, but
declined to add that to his estimate. The NAS Polar Board (Meier et al. 1985)
225
-------
Table 2. Estimates of Future Sea Level Rise (centimeters)
Year 2100 by
NAS (1983)
EPA (1983)
NAS (1985)1*
Thomas (1985)
Hoffman et al
Total Rise in
NAS (1983)
EPA (1983)
low
mid-range
mid-range
high
Hoffman et al
low
high
Cause (2085 in the
Thermal
Expansion
30
28-115
-
-
. 1986 28-83
Specific Years:**
2000
-
4.8
low 8.8
high 13.2
17.1
. 1986
3.5
5.5
case of NAS
Alpine
Glaciers
12
#
10-30
-
12-37
2025
-
13
26
39
55
10
21
1983):
Greenland Antarctica
12 * 70
# # 56-345
10-30 -10-+100
0-200
6-27 12-220
2050 2075 2085
-70
23 38
53 91
79 137
117 212
20 36 44
55 191 258
Total
50-200
-
57-368
2100
56.0
144.4
216.6
345.0
57
368
NOTES:
* Revelle (1983) attributes 16 cm to other factors.
** Only EPA reports made year-by-year projections for the next century.
# Hoffman et al. (1983) assumed that the glacial contribution would be one
to two times the contribution of thermal expansion.
## NAS (1985) estimate includes extrapolation of thermal expansion from
Revelle (1983).
Sources: Hoffman et al. (1986); Meier et al. (1985);
Hoffman et al. (1983); Revelle (1983); Thomas (1985).
226
-------
projected that the contribution of glaciers would be sufficient to raise sea
level 20 to 160 cm, with a rise of "several tenths of a meter" most likely.
Thus, if one extrapolates the earlier MAS estimate of thermal expansion
through the year 2100, the 1985 NAS report implies a rise between 50 and 200
cm. The estimates of Hoffman, Wells, and Titus (1985) were similar to the
estimates of Hoffman Keyes, and Titus (1983) for the year 2100, but for the
year 2025, they lowered their estimate from 26-39 cm to 10-21 cm.
Future Trends in Local Sea Level
Although most attention has focused on projections of global sea level,
impacts on particular areas would depend on local relative sea level. Tidal
gauge measurements suggest that relative sea level has risen 10 to 20 cm per
century more rapidly than the worldwide average along much of the U.S. coast
(Hicks, DeBaugh, and Hickman 1983). However, Louisiana is subsiding close to 1
m per century, while parts of Alaska are emerging 10 or more cm per century.
Bruun argues that throughout most of the world, sea level has been rising.
However, Bird (Volume 4) argues that sea level appears to be stable in
Australia, which may imply that future rates of sea level rise will also be 10
to 15 cm per century less than the worldwide average.
Local subsidence and emergence are caused by a variety of factors.
Rebound from the retreat of glaciers after the last ice age has resulted in
the emergence of Alaska and parts of Scandinavia. The emergence in polar
latitudes has resulted in subsidence in other areas. Groundwater pumping has
caused rapid subsidence around Houston, Texas; Taipai, Taiwan; and Bangkok,
Thailand, among other areas (Leatherman 1984; Kuo, Volume 4). River deltas
and other newly created land subside as the unconsolidated materials compact.
Although subsidence and emergence trends may change in the future,
particularly where anthropogenic causes are curtailed, no one has linked these
causes to future climate change in the next century. However, the removal of
ice from Greenland and Antarctica would deform the ocean floor. Clark and
Lingle have (1977) calculated the impact of a uniform 1-m contribution from
West Antarctica. They concluded that relative sea level at Hawaii would
increase by an additional 25 cm, and that along much of the U.S. Atlantic and
Gulf Coasts there would be an additional 15 cm. On the other hand, sea level
would drop at Cape Horn by nearly 10 cm, and the rise along the southern half
of the Argentine and Chilean coasts would be less than 75 cm.
Other influences on local sea level that might change as a result of a
global warming include currents, winds, and freshwater flow into estuaries.
None of these impacts, however, has been estimated.
EFFECTS OF SEA LEVEL RISE
A rise in sea level of one or two meters would permanently inundate
wetlands and lowlands, accelerate coastal erosion, exacerbate coastal
flooding, threaten coastal structures, and increase the salinity of estuaries
and aquifers. Substantial research has been done on the, implications of sea
level rise for coastal erosion and wetlands, while relatively little work has
been done in the other areas.
227
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Submergence of Coastal Wetlands
The most direct impact of a rise in sea level is the inundation of areas
that had been just above the water level before the sea rose, also described
by Park, Armentano, and Cloohan in Volume 4. Coastal wetlands are generally
found at elevations below the highest tide of the year and above mean sea
level. Thus, wetlands account for most of the land less than 1 m above sea
level.
Because a common means of estimating past sea level rise has been the
analysis of marsh peats, the impacts of sea level rise on wetlands are fairly
well understood. For the rates of sea level rise of the last several thousand
years, marshes have generally kept pace with sea level through sedimentation
and peat formation (Emery and Uchupi 1972; Redfield 1972, 1967; Davis 1985).
As sea level rose, new wetlands formed inland while the seaward boundary was
maintained (Figure 2a, 2b). Because the wetland area has expanded, Titus,
Henderson, and Teal (1984) hypothesized that one would expect a concave marsh
profile, i.e., that there is more marsh area than the area found immediately
above the marsh. Thus, if sea level rose more rapidly than the marsh's
ability to keep pace, there would be a net loss of wetlands (Figure 2c).
Moreover, a complete loss might occur if protection of developed areas
prevented the inland formation of new wetlands (Figure 2d).
Kana, Baca, and Williams (1986) and Kana et al. (n.d.) surveyed marsh
transects in the areas of Charleston, South Carolina, and two sites near Long
Beach Island, New Jersey, to evaluate the concavity of wetland profiles and
the vulnerability of wetlands to a rise in sea level. Their data from the
Charleston area showed all the marsh to be between 30 and 110 cm above current
sea level, an elevation range of 80 cm. The area with a similar elevation
range just above the marsh was only 20 percent as large. Thus, a rise in sea
level exceeding vertical marsh accretion by 80 cm would result in an 80
percent loss of wetlands. In the New Jersey sites, the marsh was also found
within an elevation range of 80 cm; a rise in sea level 80 cm in excess of
marsh accretion would result in 67 to 90 percent losses.
The future ability of marshes to accrete vertically is uncertain. Based
on field studies by Ward and Domeracki (1978), Hatton et al. (1983), Meyerson
(1972), and Stearns and MacCreary (1957), Kana et al. (n.d.) concluded that
current vertical accretion rates are approximately 4 to 6 mm/yr in the two
case study areas, greater than the current rate of sea level rise but less
than the rates of rise projected for the next century. If current accretion
trends continue, then 87 and 160 cm rises by 2075 would imply 50 and 80
percent losses of wetlands in the Charleston area. Kana et al. (n.d.) also
estimated 80 percent losses in the New Jersey sites for a 160-cm rise through
2075. However, because the high marsh dominates in that area, they concluded
that the principal impact of an 87-cm rise by 2075 would be the conversion of
high marsh to low marsh.
In both cases, the losses of marsh could be greater if inland areas are
developed and protected with bulkheads or levees. Because there is a buffer
zone between developed areas and the marsh in South Carolina protecting
development from a 160-cm rise would increase the loss from 80-90 percent.
Without the buffer, the loss would be close to 100 percent.
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A. 5000 Years Ago
-z— Sea Level
B. Today
Sedimentation and
Peat Formation
Current
Sea Level
Past
Sea Level
C. Future
Substantial Wetland Loss Where There is Vacant Upland
Future
-Z- Sea Level
Current
Sea Level
D. Future
Complete Wetland Loss Where House is Protected
In Response to Rise In Sea Level
Future
. Sea Level
Current
Sea Level
Figure 2. Evolution of Marsh as Sea Level Rises
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. Louisiana, whose marshes and swamps account for 40 percent of the coastal
wetlands in the United States (excluding Alaska), would be particularly
vulnerable to an accelerated rise in sea level. The majority of the Louisiana
wetlands are less than one meter above sea level, and are generally subsiding
approximately one meter per century as its deltaic sediments compact (Boesch
1982). Until the last century, the wetlands kept pace with this rate of
relative sea level rise, because of the sediment the Mississippi River
conveyed to the wetlands.
Human activities, however, have largely disabled the natural processes by
which coastal Louisiana might keep pace with sea level rise. Dams, navigation
channels, canals, and flood protection levees have interrupted the flow of
sediment, fresh water, and nutrients to the wetlands. As a result, over 100
square kilometers of wetlands convert to open water every year (Gagliano et
al. 1983). A substantial rise in sea level would further accelerate the
process of wetland loss in Louisiana.
To develop an understanding of the potential nationwide impact of sea
level rise on coastal wetlands in the United States, Park, Armentano, and
Cloonan (Volume 4) use topographic maps to characterize wetland elevations at
fifty-two sites comprising 4800 square kilometers (1.2 million acres) of
wetlands, over 17 percent of all U.S. coastal wetlands (see also Armentano,
Park, and Cloonan n.d.). Using published vertical accretion rates, they
estimate the impact of 1.4 and 2.1 m rises in sea level through the year 2100
for each of the sites. Park, Armentano, and Cloonan (Volume 4) estimate that
these scenarios imply losses of 40 and 76 percent of the existing coastal
wetlands in their sample, which could be reduced to 22 and 58 percent if new
wetlands are allowed to form inland. However, Titus (n.d.) found that if the
Park et al. sample is weighted according to an inventory of wetlands in parti-
cular areas (Alexander, Broutman, and Field 1986), the resulting estimates of
U.S. wetland loss are somewhat higher, 47-82 percent of existing wetlands,
with a potential for reducing those losses to 31 to 70 percent.
Throughout the world, people have dammed, leveed, and channelized major
rivers, curtailing the amount of sediment that reaches river deltas. Even at
today's rate of sea level rise, substantial amounts of land are converting to
open water in Egypt and Mexico (Milliman and Meade 1983). Other deltas, such
as the Ganges in Bangladesh and India, are currently expanding seaward. These
areas would require increased sediment, however, to keep pace with an acceler-
ated rise in sea level. Additional projects to divert the natural flow of
river water would increase the vulnerability of these areas to a rise in sea
level. Broadus et al. (Volume 4) examine this issue in detail for Egypt and
Bangladesh.
Plate 4 (appearing immediately before this section) shows the projected
land loss for Bangladesh for two scenarios:
• Low—a 50-cm global rise in sea level with current rates of subsidence
and sedimentation
• High—a 200- to 250-cm rise with alterred sedimentation due to
additional dams.
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Several options have been identified for reducing wetland loss due to sea
level rise. Abandonment of developed areas inland of today's wetlands could
permit new wetlands to form inland. In some cases, it might be possible to
enhance the ability of wetlands to accrete vertically by spraying sediment on
them or—in the case of Louisiana and other deltas—restoring the natural
processes that would provide sediment to the wetlands. Finally, some local
governments in Louisiana have proposed to artificially control water levels
through the use of levees and pumping stations (Edmonson and Jones 1985).
The need for anticipating sea level rise would vary. Artificial means to
accelerate wetland accretion need not be implemented until the rise takes
place (although a lead time would be necessary to develop the required tech-
nologies). Similarly, levees and pumping stations could be delayed. On the
other hand, a planned retreat would require several decades of lead time to
permit the design of new mobile structures and the depreciation of the old
immobile structures.
Inundation
Although coastal wetlands are found at the lowest elevations, inundation
of lowland could also be important in some areas, particularly if sea level
rises at least one meter. Unfortunately, the convention of ten-foot contours
in the mapping of most coastal areas has prevented a general assessment of
land loss. Although a few case studies have been conducted in the United
States, very few studies have been undertaken to quantify the potential
impacts on other countries, other than the paper by Broadus et al. (Volume 4).
Kana et al. (1984) used data from aerial photographs to assess eleva-
tions in the area around Charleston. They concluded that 160- and 230-cm
rises would result in 30 and 46 percent losses of the area's dry land, respec-
tively. Leatherman (1984) estimated that such rises would result in 9 and 12
percent losses of the land in the area of Galveston and Texas City, Texas,
assuming that the elaborate network of seawalls and levees were maintained.
(Many of the summary results from Leatherman 1984; Kana et al. 1984; and
Gibbs 1984 appear in the appendix of Titus et al. 1984.)
Schneider and Chen (1980) conducted the first nationwide assessment of
the inundation from projected sea level rise. Unfortunately, the smallest
rise in sea level they considered was a 4.5-m (15-ft) rise, in part because
smaller contours are not generally available in topographic maps. Neverthe-
less, their findings suggest which coastal states would be most vulnerable:
Louisiana (which would lose 28 percent of its land and 51 percent of its
wealth), Florida (24 and 52 percent), Delaware (16 and 18 percent),
Washington, D.C. (15 and 15 percent), Maryland (12 and 5 percent), and New
Jersey (10 and 9 percent).
As with wetland loss, the responses to inundation fall broadly into the
categories of retreat and holding back the sea. Levees are used extensively
in the Netherlands and New Orleans to prevent the flooding of areas below sea
level and could be similarly constructed .around other major cities. In
sparsely developed areas, however, the cost of a levee might be greater than
the value of the property being protected. Moreover, even where levees prove
to be cost-effective, the environmental implications of replacing natural
shorelines with manmade structures would need to be considered.
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Coastal Erosion
Sea level rise can also result in the loss of land above sea level
through erosion. Bruun (1962) showed that the erosion resulting from a rise
in sea level would depend upon the average slope of the entire beach profile
extending from the dunes out to the point where the water is too deep for
waves to have a significant impact on the bottom (generally a depth of about
10 meters). By comparison, inundation depends only on the slope immediately
above the original sea level. Because beach profiles are generally flatter
than the portion of the beach just above sea level, the "Bruun Rule" generally
implies that the erosion from a rise in sea level is several times greater
than the amount of land directly inundated. (See Figure 3.)
As Bird (Volume 4) emphasizes, processes other than sea level rise also
contribute to erosion, including storms, structures, currents, and alongshore
transport. Because sea level has risen slowly in recent centuries, verifi-
cation of the Bruun Rule on the open coast has been difficult. However, water
levels along the Great Lakes can fluctuate over one meter in a decade. Hands
(1976, 1979, and 1980) and Weishar and Wood (1983) have demonstrated that the
Bruun Rule generally predicts the erosion resulting from rises in water levels
there.
The Bruun Rule has been applied to project erosion due to sea level rise
for several areas of the United States where it is believed to adequately
project future erosion. Bruun (1962) found that a 1-cm rise in sea level
would generally result in a 1-m shoreline retreat, but that the retreat could
be as great as 10 m along some parts of the Florida coast. Everts (1985) and
Kyper and Sorensen (1985), however, found that along the coasts of Ocean City,
Maryland, and Sandy Hook, New Jersey, respectively, the shoreline retreat
implied by the Bruun Rule would be only about 75 cm. Kana et al. (1984) found
that along the coast of South Carolina, the retreat could be 2 m. The U.S.
Army Corps of Engineers (1979) indicated that along the coast of San
Francisco, where waves are generally larger than along the Atlantic Coast, the
shore might retreat 2-4 m for a 1-cm rise in sea level.
Dean and Maurmeyer (1983) generalized the "Bruun Rule" approach to
consider the "overwash" of barrier islands. Geologists basically believe that
coastal barriers can maintain themselves in the face of slowly rising sea
level through the landward transport of sand, which washes over the island
during storms, building the island upward and landward. Because this formu-
lation of the Bruun Rule extends the beach profile horizontally to include the
entire islands as well as the active surf zone, it always predicts greater
erosion than the Bruun Rule. However, the formulation may not be applicable
to developed barrier islands, where the common practice of public officials is
to bulldoze sand back onto the beach after a major storm.
The potential erosion from a rise in sea level could be particularly
important to recreational beach resorts, which include some of the world's
most economically valuable and intensively used land. Relatively few of the
most densely developed resorts have beaches wider than about 30 m at high
tide. Thus, the rise in relative sea level of 30 centimeters projected in the
next 40 to 50 years could erode most recreational beaches in developed areas,
unless additional erosion response measures are taken.
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Initial
Condition
Immediate
Inundation When
Sea Level Rises
Subsequent
Erosion Due to
Sea Level Rise
Figure 3. The Bruun Rule
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Bruun (Volume 4) examines potential responses to erosion in considerable
detail (see also Magness 1984; U.S. Army Corps of Engineers 1977). The
responses fall generally into three categories: construction of walls and
other structures, the addition of sand to the beach, and abandonment.
Although seawalls have been used in the past, they are becoming increasingly
unpopular among shore communities because erosion can proceed up to the wall,
resulting in a complete loss of beach, which has happened in many areas (Kyper
and Sorensen 1985; Howard, Pilkey, and Kaufman 1985). A number of other
structures have been used to decrease the ability of waves to cause erosion,
including groins (jetties) and breakwaters. Bulkheads are often used where
waves are small (Sorensen, Weisman, and Lennon 1984).
A more popular form of erosion control has been the placement of sand
onto the beach. Although costs can exceed one million dollars per kilometer
(U.S. Army Corps of Engineers 1980; Howard, Pilkey, and Kaufman 1985), it is
often justified by the economic and recreational value of beaches. A recent
study of Ocean City, Maryland, for example, concluded that the cost of holding
back the sea for a 30-cm rise in sea level would be about 25 cents per
visitor, less than 1 percent of the cost of a trip to the beach (Titus
1985). That community also provides an example of the practical consequences
of sea level rise. Until 1985, the State of Maryland's policy for erosion
control was the construction of groins, which curtail erosion caused by sand
moving along the shore, but not erosion caused by sea level rise. Sea level
rise was cited as the motivating concern for the state to abandon the groin
plan and use beach replenishment, which can effectively control erosion caused
by both types of erosion (Associated Press 1985).
Although shore protection is often cost-effective today, the favorable
economics might change in the future. A more rapid rise in sea level would
increase the costs of shore protection. A number of states have adopted
erosion policies that assume a retreat from the shore. North Carolina
requires homes that can be moved to be set back from the shore by a distance
equal to shoreline recession from 30 years of erosion, while high-rises must
be set back 60 years. Maine requires people to demonstrate that new
structures will not erode for 100 years. Other jurisdictions discourage the
construction of bulkheads and seawalls (Howard, Pilkey, and Kaufman 1985). As
Bird (Volume 4) discusses, in many undeveloped countries, small, relatively
inexpensive houses are found very close to the shore. Because the value of
these houses is less than the cost of protecting them, they must be moved as
the shore erodes. An accelerated rise in sea level would speed this process
of shoreline retreat.
The need for anticipating erosion caused by sea level rise varies. Where
communities are likely to adapt to erosion, anticipation can be important.
The cost and feasibility of moving a house back depends on design decisions
made when the house is built. The willingness of people to abandon properties
depends in part on whether they bought land on the assumption that it would
eventually erode away or had assumed that the government would protect it
North Carolina Administrative Code, Chapter 7H, 1983. Raleigh, North
Carolina: Office of Coastal Management.
Fred Michaud, Office of Floodplain Management, State of Maine, personal
communications.
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indefinitely. Less anticipation is necessary if the shore will be protected;
sand can be added to the beach as necessary. Nevertheless, some advanced
planning may be necessary for communities to know whether retreat or defending
the shore would be most cost effective.
FLOODING AND STORM DAMAGE
A rise in sea level could increase flooding and storm damages in coastal
areas for three reasons: erosion caused by sea level rise would increase the
vulnerability of communities; higher water levels would provide storm surges
with a higher base to build upon; and higher water levels would decrease
natural and artificial drainage.
The impact of erosion on vulnerability to storms is generally a major
consideration in projects proposed to control erosion, most of which have
historically been funded through the Army Corps of Engineers in the United
States. The impact of sea level rise, however, has not generally been
considered separately from other causes of erosion.
The impact of higher base water levels on flooding has been investigated
for the areas around Charleston, South Carolina, and Galveston, Texas (Earth
and Titus 1984). Kana et al. (1984) found that around Charleston, the area
within the 10-year flood plain would increase from 33 percent in 1980, to 48,
62, and 74 percent for rises in sea level of 88, 160, and 230 cm, respec-
tively, and that the area within the 100-year flood plain would increase from
63 percent to 76, 84, and 90 percent for the three scenarios. Gibbs (1984)
estimated that even an 88-cm rise would double the average annual flood
damages in the Charleston area (but that flood losses would not increase
substantially for higher rises in sea level because shoreline retreat would
result in a large part of the community being completely abandoned).
Leatherman (1984) conducted a similar analysis of Galveston Island,
Texas. He estimated that the area within the 100-year flood plain would
increase from 58 percent to 94 percent for an 88-cm rise in sea level, and
that for a rise greater than one meter, the Galveston seawall would be over-
topped during a 100-year storm. Gibbs estimated that the damage from a 100-
year storm would be tripled for a rise of 88 cm.
A wide variety of shore protection measures would be available for
communities to protect themselves from increased storm surge and wave damage
due to sea level rise (Sorensen, Weisman, and Lennon 1984). Many of the
measures used to address erosion and inundation, including seawalls, break-
waters, levees, and beach restoration, also provide protection against
storms. In the case of Galveston, which is already protected on the ocean
side by the seawall, Gibbs hypothesized that it might be necessary to
completely encircle the developed areas with a levee to prevent flooding from
the bay side; upgrading the existing seawall might also be necessary.
Kyper and Sorensen (1985 and n.d.) examined the implications of sea level
rise for the design of coastal .protection works at Sea Bright, New Jersey, a
coastal community that currently is protected by a seawall and has no beach.
Because the seawall is vulnerable to even a 10-year storm, the U.S. Army Corps
of Engineers and the State of New Jersey have been considering a possible
upgrade. Kyper and Sorensen estimated that the cost of upgrading the seawall
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for current conditions would be $3-5 to $6 million per kilometer of shoreline,
noting that if designed properly, the seawall would be useful throughout the
next century. However, they estimated that a rise in relative sea level of
30-40 cm would be likely to result in serious damage to the seawall during a
major storm, due to higher water levels and the increased wave heights
resulting from the erosion of submerged sand in front of the seawall. To
upgrade the seawall to withstand a 1-m rise in relative sea level would cost
$5.7 to $9 million per kilometer (50 percent more). They concluded that
policy makers would have to weigh the tradeoff between the cost of designing
the wall to withstand projected sea level rise and the cost of subsequent
repairs and a second overhaul.
In addition to community-wide engineering approaches, measures can also
be taken by individual property owners to prevent increased flooding. In
1968, the U.S. Congress created the National Flood Insurance Program to
encourage communities to avoid risky construction in flood-prone areas. In
return for requiring new construction to be elevated above expected flood
levels, the federal government provides flood insurance, which is not
available from the private sector. If sea level rises, flood risks will
increase. In response, local ordinances will automatically require new
construction to be further elevated, and insurance rates on existing
properties will rise unless those properties are further elevated. As
currently organized, the National Flood Insurance Program would react to sea
level rise as it occurred. Various measures to enable the program to anti-
cipate sea level rise have been proposed, including warning policy holders
that rates may increase in the future if sea level rises; denying coverage to
new construction in areas that are expected to be lost to erosion within the
next 30 years; and setting premiums according to the average risk expected
over the lifetime of the mortgage (Howard, Pilkey, and Kaufman 1985; Titus
1984).
Kuo (Volume 4) describes case studies in Charleston, South Carolina, and
Fort Walton Beach, Florida, which examined the implications of sea level rise
for rainwater flooding and the design of coastal drainage systems. Waddell
and Blaylock (n.d.) estimated that a 25-year rainstorm (with no storm surge)
would result in no damages for the Gap Creek watershed in Fort Walton Beach.
However, a rise in sea level of 30-45 cm would result in damages of $1.1 to
$1.3 million in this community of 4,000 residents during a 25-year storm. An
upgrade costing $550,000, however, would prevent such damages.
LaRoche and Webb (n.d.), who had previously developed the master drainage
plan for Charleston, South Carolina, evaluated the implications of sea level
rise for the Grove Street watershed in that community. They estimated that
the costs of upgrading the system for current conditions would be $4.8
million, while the cost of upgrading the system for a 30-cm rise would be $5.1
million. If the system is designed for current conditions and sea level rises,
the system would be deficient and the city would face retrofit costs of $2.4
million. Thus, for the additional $300,000 necessary to upgrade for a 30-cm
rise, the city could ensure that it would not have to spend an additional $2.4
million later. Noting that the decision whether to design now for a rise in
sea level depends on the probability that sea level will rise, they concluded
that a 3 percent real social discount rate would imply that designing for sea
level rise is worthwhile if the probability of a 30-cm rise by 2025 is greater
than 30 percent. At a discount rate of 10 percent, they concluded, designing
for future conditions is not worthwhile.
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Increased Salinity in Estuaries and Aquifers
Although most researchers and the general public have focused on the
increased flooding and shoreline retreat associated with a rise in sea level,
the inland penetration of salt water could be important in some areas.
As de Sylva (Volume 4) describes, a rise in sea level increases the
salinity of an estuary by altering the balance between freshwater and salt-
water forces. The salinity of an estuary represents the outcome of (1) the
tendency for the ocean salt water to completely mix with the estuarine water
and (2) the tendency of freshwater flowing into the estuary to dilute the
saline water and push it back toward the ocean. During droughts, the salt
water penetrates upstream, while during the rainy season, low salinity levels
prevail. A rise in sea level has an impact similar to decreasing the fresh-
water inflow. By widening and deepening the estuary, sea level rise increases
the ability of salt water to penetrate upstream.
The implications of sea level rise for increased salinity have only been
examined in detail for Louisiana and the Delaware estuary. In Louisiana and
other river deltas, saltwater intrusion is causing the conversion of cypress
swamps (which cannot tolerate salt water) to openwater lakes, and increasing
the salinity levels of fresh and intermediate marshes. Accelerated sea level
rise would speed up this process.
The impact of current sea level trends on salinity has been considered in
the long range plan of the Delaware River Basin Commission since 1981 (DRBC
1981). The drought of the 1960s resulted in salinity levels that almost
contaminated the water supply of Philadelphia and surrounding areas. Hull and
Tortoriello (1979) found that the 13-cm rise projected between 1965 and 2000
would result in the "salt front" migrating two to four kilometers farther
upstream during a similar drought. They found that a moderately sized reser-
voir (57 million cubic meters) to augment river flows would be needed to
offset the resulting salinity increases.
Hull, Thatcher, and Tortoriello (1986) examined the potential impacts of
an accelerated rise in sea level due to the greenhouse warming. They esti-
mated that 73-cm and 250-cm rises would result in the salt front migrating an
additional 15 and 40 kilometers, respectively, during a repeat of the 1960s
drought. They also found that the health-based 50-ppm sodium standard (equi-
valent to 73 ppm chloride) adopted by New Jersey would be exceeded 15 and 50
percent of the time, respectively, and that the EPA drinking water 250-ppm
chloride standard would be exceeded over 35 percent of the time in the latter
case.
Lennon, Wisniewski, and Yoshioka (1986) examined the implications of
increased estuarine salinity for the Potomac-Earitan-Magothy aquifer system,
which is recharged by the (currently fresh) Delaware River and serves the New
Jersey suburbs of Philadelphia. During the 1960s drought, river water with
chloride concentrations as high as 150 ppm recharged these aquifers. Lennon
et al. estimated that a repeat of the 1960s drought with a 73-cm rise in sea
level would result in river water with concentrations as high as 350 ppm
recharging the aquifer, and that during the worst month of the drought, over
one-half of the water recharging the aquifer system would have concentrations
greater than 250 ppm. With a 250-cm rise, 98 percent of the recharge during
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the worst month of the drought would exceed 250 ppm, and 75 percent of the
recharge would be greater than 1000 ppm.
Hull and Titus (1986) examined the options by which various agencies
might respond to increased salinity in the Delaware estuary. They concluded
that planned but unscheduled reservoirs would be more than enough to offset
the salinity increased from a one-foot (30-cm) rise in sea level, although
those reservoirs had originally been intended to meet increased consumption.
They noted that construction of the reservoirs would not be necessary until
the rise became more imminent. However, they also suggested that, given the
uncertainties, it might be advisable today to identify additional reservoir
sites, to ensure that future generations retained the option of building
additional reservoirs, if necessary.
A rise in sea level could increase salinities in other areas, although
the importance of those impacts has not been investigated. Kana et al.
(1984) and Leatherman (1984) made preliminary inquiries into the potential
impacts on coastal aquifers around Charleston and Galveston, respectively.
However, they concluded that in-depth assessments were not worthwhile because
the aquifers around Charleston are already salt-contaminated because of over-
pumping, and pumping of ground water has been prohibited in the Galveston area
as it causes land subsidence. The potential impacts on Florida's Everglades
and the shallow aquifers around Miami might be significant, but these have not
been investigated.
Economic Significance of Sea Level Rise
Only two studies have estimated a dollar value of the likely impacts of
sea level rise for particular nations. Broadhus et al. (Volume 4) examine the
impacts on Egypt and Bangladesh. Schneider and Chen (1980) estimated the
economic impact on the United States of what was once (but is no longer)
thought to be a plausible scenario: rises of 4.6 to 7.6 meters (15 to 25
feet) occurring with little or no warning during the early part of the twenty-
first century. They estimated that these scenarios would result in real
property losses of $100 to $150 billion, representing 6.2 to 8.4 percent of
all real property in the nation.
The only comprehensive attempt to place a dollar value on the impacts of
sea level rise for particular communities was the study by Gibbs (1984) of the
Charleston and Galveston areas, summarized in Volume 4. Gibbs' analysis,
which considers scenarios ranging from 0.9- to 2.4-meter rises through 2075,
estimates what the economic impact would be if actions are taken in antici-
pation of sea level rise versus the cost of responding to sea level rise as it
occurs. Gibbs also modeled how investment decisions might respond to floods
and erosion, and explicitly considered community-wide strategies to limit
losses, including shore protection and abandonment.
In the Charleston study, Gibbs assumed that in anticipation of sea level
rise, efforts would be made to avoid developing some vacant suburban areas
likely to be flooded in the future; that a partial abandonment would take
place; and that the existing seawalls protecting Charleston would be elevated
to provide additional protection. For a rise of 28-64 cm through 2025, Gibbs
estimated that the present value of the cumulative impact would be $280-1065
million (5-19 percent of economic activity in the area for the period), which
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could be reduced to $160-420 million if sea level rise was anticipated. Most
of this impact would result from a 10-100 percent increase in expected storm
damages, although Gibbs also estimated $7-$35 million in losses as a result of
erosion. For the period 1980-2075, Gibbs estimated that the economic impacts
would be $1250 - $2510 million (17-35 percent) and could be reduced to $440
- $1100 million through anticipatory measures. Gibbs performed a similar
analysis of the Galveston area, concluding that the impacts of sea level rise
through 2025 would represent $115 - $360 million (1.1 - 3.6 percent) if not
anticipated, and $80 - $140 million if anticipated.
Other studies can be used to understand the economic significance of
particular classes of impacts. As discussed above, a thirty-centimeter (one
foot) rise in sea level would erode most recreational beaches back to the
first row of houses. The studies cited in our section on erosion indicate
that the typical beach profile extends out about 1000 meters, implying that
300,000 cubic meters of sand per kilometer of shoreline are required to raise
the beach profile 30 cm. If sand costs are typically $3-$10 per cubic meter,
the beach rebuilding costs of a 30-cm rise in sea level would be $1 - $3
million per kilometer. If the United States has a few thousand kilometers of
recreational beaches, then it would cost billions and perhaps tens of billions
of dollars to rebuild these beaches in response to a 30-cm rise in sea
level. This estimate considers only the beaches themselves; raising people's
lots to avoid inundation would further increase the costs. The U.S. Army
Corps of Engineers (1971) estimated that in 1971, 25,000 kilometers of shore-
line (exclusive of Alaska, the Great Lakes, and Hawaii) were eroding, of which
17 percent were "critically eroding," and would require engineering
solutions. If 17 percent of all shorelines require erosion control, that
would imply protection of close to 10,000 kilometers of shoreline. Sorensen
(1986) describes dozens of engineering options for preventing erosion, the
least expensive of which costs $300,000 per kilometer, implying a cost of at
least $3 billion for protecting shorelines.
Other Impacts of the Greenhouse Warming
The impacts of sea level rise on coastal areas, as well as their
importance, are likely to depend in part on other impacts of the greenhouse
warming. Although future sea level is uncertain, there is a general consensus
that a global warming would cause sea level to rise; by contrast, the direc-
tion of most other changes is unknown, as Manabe and Wetherald describe in the
next paper.
One of the more certain impacts is that most areas will be warmer. For
coastal resorts in mid latitudes, the beach season would be extended by a
number of weeks. For densely developed communities like Ocean City with a
three-month peak season, such an extension might increase revenues 10 to 25
percent, far more than the estimated cost of controlling erosion. Some areas
where the ocean is too cold to swim today might have more tolerable water
temperatures in the future. Warmer temperatures in general might encourage
more people to visit beaches in the summer.
Warmer temperatures might change the ability of wetlands to keep pace
with sea level rise. Mangrove swamps, which are the tropical equivalent of
salt marshes, generally accrete differently than salt marshes. If warmer
temperatures enable mangroves to grow at higher latitudes, the loss of wet-
239
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lands to sea level rise may be altered. On the other hand, marsh peat
formation is generally greater in cooler climates; warmer temperatures might
reduce the rate of vertical accretion for these wetlands.
De Sylva (Volume 4) suggests that changing climate could alter the
frequency and tracks of storms. Because hurricane formation requires water
temperatures of 27°C or higher (Wendland 1977), a global warming might result
in an extension of the hurricane season and in hurricanes forming at higher
latitudes. Besides increasing the amount of storm damage, increased frequency
of severe storms would tend to flatten the typical beach profile, causing
substantial shoreline retreat unless additional sand was placed on the
beach. A decreased frequency of severe winter storms might have the opposite
impact at higher latitudes.
Because warmer temperatures would intensify the hydrologic cycle, it is
generally recognized that a global warming would result in increased rainfall
worldwide. Thus, rainwater flooding might be increased because of both
decreased drainage and increased precipitation. The impact of sea level rise
on saltwater intrusion could be offset by decreased drought frequency or
exacerbated by increased drought frequency (Rind and Lebedeff 1984).
CONCLUSIONS
The studies reviewed in this paper appear to support the following
conclusions regarding the causes and effects of sea level rise:
Causes
• The projected global warming would accelerate the current rate of sea level
rise by expanding ocean water, melting alpine glaciers, and eventually,
causing polar ice sheets to melt or slide into the oceans.
• Global average sea level has risen 10 to 15 cm over the last century.
Ocean and glacial studies suggest that the rise is consistent with what
models would project, given the 0.4°C warming of the past century.
However, no cause and effect relationship has been conclusively demon-
strated.
* Projected global warming could cause global average sea level to rise 10 to
20 cm by 2025 and 50 to 200 cm by 2100. Thermal expansion could cause a
rise of 25 to 80 cm by 2100; Greenland and alpine glaciers could each
contribute 10 to 30 cm through 2100. The contribution of Antarctic
deglaciation is likely to be between 0 and 100 cm; however, the possi-
bilities cannot be ruled out that (a) increased snowfall could increase the
size of the Antarctic ice sheet, thereby offsetting part of the sea level
rise from other sources; or (b) meltwater and enhanced calving of the ice
sheet could increase the contribution of Antarctica to as much as two
meters.
• Disintegration of the West Antarctic Ice Sheet might raise sea level an
additional six meters over the next few centuries. Glaciologists generally
believe that such a disintegration would take at least three hundred years,
and probably as long as five hundred years. However, a global warming
240
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might result in sufficient thinning of the Ross and Filcher-Ronne ice
shelves in the next century to make the process irreversible.
Local trends in subsidence and emergence must be added or subtracted to
estimate the rise at particular locations.
Effects
A substantial rise in sea level would permanently inundate wetlands and
lowlands, accelerate coastal erosion, exacerbate coastal flooding, and
increase the salinity of estuaries and aquifers.
Bangladesh and Egypt appear to be among the nations most vulnerable to the
rise in sea level projected for the next century. Up to 20 percent of the
land in Bangladesh could be flooded with a two meter rise in sea level.
Although less than 1 percent of Egypt's land would be threatened, over 20
percent of the Nile Delta, which contains most of the nation's people,
would be threatened.
A large fraction of the world's coastal wetlands may be lost, threatening
some fisheries. A rise in sea level of one to two meters by 2100 could
destroy 50-80 percent of U.S. coastal wetlands. Although no study has
been taken to estimate the worldwide impact, this result is probably
representative.
Erosion caused by sea level rise could threaten recreational beaches
throughout the world. Case studies have concluded that a thirty-centimeter
rise in sea level would result in beaches eroding twenty to sixty meters or
more. Because the first row of houses or hotels is often generally less
than twenty meters from the shore at high tide, if available studies are
representative, then recreational beaches throughout the world would be
threatened by a thirty-centimeter rise unless major beach preservation
efforts are undertaken.
Sea level rise would increase the costs of flooding, flood protection, and
flood insurance in coastal areas. Flood damages would increase because
higher water levels would provide a higher base for storm surges; erosion
would increase the vulnerability to storm waves; and decreased natural and
artificial drainage would increase flooding during rainstorms.
Future sea level rise may already be an appropriate factor to consider in
the designing coastal drainage and flood protection structures.
Increased salinity from sea level rise would convert cypress swamps to open
water and threaten drinking water supplies.
The adverse impacts of sea level rise could be ameliorated through antici-
patory land use planning and structural design changes.
Other impacts of global warming might offset or exacerbate the impacts of
sea level rise. Increased droughts might amplify the salinity impacts of
sea level rise. Increased hurricanes and increased rainfall in coastal
areas could amplify flooding from sea level rise. Warmer temperatures
241
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might enable mangrove swamps—which accrete differently than salt marshes—
to advance further north, perhaps changing wetland loss caused by sea level
rise.
River deltas throughout the world would be vulnerable to a rise in sea
level, particularly those whose rivers are dammed or leveed.
Economic studies of Bangladesh, Egypt, and the United States suggest that
sea level rise would be economically important to coastal areas.
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Reduction in Summer Soil Wetness Induced by an
Increase in Atmospheric Carbon Dioxide1
S. Manabe and R. T. Wetherald
Geophysical Fluid Dynamic Laboratory/NOAA
Princeton University
Princeton, New Jersey USA
ABSTRACT. The geographical distribution of the change in soil wetness in
response to an increase in atmospheric carbon dioxide was investigated by
using a mathematical model of climate. Responding to the increase in carbon
dioxide, soil moisture in the model would be reduced in summer over extensive
regions of the middle and high latitudes, such as the North American Great
Plains, western Europe, northern Canada, and Siberia. These results were
obtained from the model with predicted cloud cover and are qualitatively
similar to the results from several numerical experiments conducted earlier
with prescribed cloud cover.
In assessments of the possible change in climate caused by the increasing
CC^ in the atmosphere, major emphasis has been placed on estimating the change
in atmospheric temperature. However, for agricultural planning, the change in
soil wetness may be just as important. In this study, which is a continuation
of earlier studies (Manabe, Wetherald, and Stouffer 1981; Manabe and Wetherald
1985), CC^-induced changes in soil wetness were investigated using a
mathematical model of climate in which cloud amount is a predicted variable.
Because of the large temporal variability of the model hydrology, it has been
difficult to distinguish the CC^-induced change from the natural variability
of soil wetness. Therefore, the earlier reports discussed mainly the zonal
mean rather than the geographical distribution of soil wetness. To overcome
this difficulty, it is necessary to determine soil wetness of the model
averaged over a very long period. The present study represents an attempt to
extract the geographical distribution of soil wetness by substantially
extending the average period.
1 Reprinted from Science 232:626-27, May 2, 1986, Copyright 1986 AAAS.
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The mathematical model of climate used for this research is an
atmospheric general circulation model coupled with a static mixed-layer ocean
model . The model has a' global computational domain, realistic geography, and
seasonally varying isolation.
Precipitation is computed whenever supersaturation is indicated by the
prognostic equation for water vapor (Manabe, Smagorinsky, and Stickler 1965).
It is identified as snowfall when the air temperature near the surface falls
below freezing; otherwise it is identified as rain. The moist convective
processes are parameterized by a moist convective adjustment scheme (Manabe,
Smagorinsky, and Strickler 1965). Cloud cover is predicted whenever the
relative humidity exceeds a certain critical value, which is 99$ in this
case. The distribution of cloud cover thus determined is used for the
computation of solar and terrestrial radiation (Wetherald and Manabe 1980).
A change in snow depth is computed as a net contribution from snowfall,
sublimation, and snowmelt that is determined from the requirement of surface
heat balance (Manabe 1969). The budget of soil moisture is computed by the
so-called bucket method (Manabe 1969). For simplicity it is assumed that soil
can hold 15 cm of liquid water. When soil is not saturated with water, the
change in soil moisture is predicted as a net contribution of rainfall,
evaporation, and snowmelt. If the bucket is full, the excess water is
regarded as runoff. The rate of evaporation from the soil surface is
determined as a function of the water content of the bucket and potential
evaporation.
The mixed-layer model of the ocean is idealized as a 50-m thick,
vertically isothermal layer of water with predicted sea ice (Manabe and
Stouffer 1980). The effects of horizontal heat transport by ocean currents
and heat exchange between the mixed layer and the deeper layer of the ocean
are neglected.
Two separate experiments were performed, one with the normal atmospheric
concentration of CO^ (300 ppm), and the other with twice the normal value (600
ppm). By comparing the results from the two experiments, the CC^-induced
change in hydrology could be determined. In each experiment a numerical
40-year integration of the model was conducted starting from an isothermal
The thickness of the mixed-layer model of the oceans was chosen so that
the amplitude of the observed seasonal variation of sea-surface
temperature was approximately reproduced by the model (Manabe and
Stouffer 1980).
The moisture-holding capacity of soil is assumed to be constant
everywhere in view of our ignorance of its geographical distribution.
According to unpublished results from a recent numerical experiment, the
simulated distribution of soil moisture expressed as a fraction of the
moisture-holding capacity of soil is not very sensitive to the magnitude
of the field capacity.
Potential evaporation is the evaporation that would occur were there an
adequate soil moisture supply at all times. According to M. Budyko
(1974) potential evaporation is approximately equal to the total
radiative energy absorbed by continental surfaces.
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initial condition. Toward the end of this period, the temporal variation of
the global mean sea-surface temperature of the model no longer had a
systematic trend, indicating that the model had attained an equilibrium
climate. To distinguish the CC^-induced change from the natural variability
of the model hydrology, the results were averaged over a sufficiently long
period, i.e., the last 10 years of the 40-year integration. It is encouraging
that, in the experiment with the normal C02 concentration, the model
successfully reproduced the broad-scale features in the geographical
distributions of precipitative and annual mean runoff.
The geographical distribution of the CC^-induced change in soil moisture
during June to August is illustrated in Figure 1A. In summer the soil becomes
drier in the mid-continental region of North America, western Europe, and
Siberia in response to the doubling of atmospheric CC^.
The reduction in soil moisture in North America, western Europe, and
Siberia is statistically significant at the 10$ level (Figure 1B). In other
words, the probability of falsely rejecting the null hypothesis of no change
in soil moisture is 10/5 or less in these regions.
To demonstrate the practical implication of the CC^-induced summer
dryness identified above, the change in soil moisture was expressed as a
percentage of the soil moisture from the normal CC>2 experiment (Figure 1C).
This result suggests that the CC^-induced reduction in soil moisture in the
mid-continental regions of North America, Siberia, and western Europe amounts
to a substantial fraction of the soil moisture present in the standard CC^
case.
In general, the soil moisture in the model continents in middle and high
latitudes is reduced from the peak level in spring to the minimum level in
summer. In high latitudes, this spring-to-summer reduction in moisture is
caused by intense evaporation in late spring, when the continental surface
absorbs a large amount of solar energy because of strong insolation and the
disappearance of snow cover with high albedo. In middle latitudes a similar
mechanism also operates over the model continents. In addition, the reduction
in soil moisture from spring to summer in middle latitudes is caused by the
termination of the rainy period in spring that results from the poleward shift
of the rain belt.
According to the comparison of the surface water budget between the
normal and high CC>2 experiments, the CC^-induced reduction in soil moisture in
summer in Siberia and northern Canada is a result of the earlier disappearance
of snow cover in the warmer climate. Since the snow cover has a high surface
albedo, its disappearance increases the surface absorption of solar energy
and accordingly increases the rate of potential evaporation (Budyko 1974).
Thus, the earlier termination of the snowmelt season results in the earlier
Student's t test was used. For this test, ten samples of summer soil
moisture were obtained from the last 10-year periods of normal and above-
normal CC>2 experiments conducted in this study. Because each sample
represents an average of ninety daily soil moistures, it is likely that
these samples are distributed approximately as Gaussian (as inferred from
the central limit theorem), justifying application the of this test.
251
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I I I I I I I I
30 -
60 -
90
0 30 60 90 120 150 180 ISO 120 90 60 30 0
Figure 1. (A) Geographical distribution of the change in soil moisture
(centimeters) in response to a doubling of C02 for the period from June to
August. Shading indicates regions where the C02-induced change is negative.
(B) Statistical significance of the C02-induced change in soil moisture shown
in (A). Areas shaded with lines are regions where the negative soil moisture
change is statistically significant at the 10$ level. (C) C02-induced change
in soil moisture expressed as a percentage of soil mositure obtained from the
normal C02 experiment.
252
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commencement of the spring-to-summer reduction in soil moisture, causing the
COp-induced reduction in soil moisture in summer.
In the Great Plains the earlier termination of the snowmelt season also
contributes to the summer CC^-induced reduction in soil moisture. Another
factor responsible for the summer reduction is the change in the rate of
precipitation in middle latitudes. The, CC^-induced warming in the lower
troposphere in the model increases with increasing latitude. Therefore, in
the high COp atmosphere the warm, moisture-rich air penetrates into higher
latitudes than in the normal CC>2 atmosphere. Thus the rate of precipitation
increases markedly in the northern half of the middle latitude rain belt of
the Northern Hemisphere, whereas it decreases in the southern half of the rain
belt. Because of the poleward shift of the rain belt from winter to summer, a
location in middle latitudes which is situated at the northern half of the
rain belt during winter enters the southern half in summer. Therefore, the
COp-induced increase in rate of precipitation at this location is rapidly
reduced from spring to early summer, contributing to the reduction in soil
moisture during this period.
In western Europe the CC^-induced reduction in soil moisture occurs in
summer in a manner qualitatively similar to that in North America. However,
the contribution of snowmelt is much smaller.
The summer dryness in North America and western Europe is further
enhanced by the positive feedback process involving the change in cloud
cover. When soil moisture is reduced, a larger fraction of radiative energy
absorbed by the continental surface is ventilated through the upward flux of
sensible heat rather than through evaporation. As a result, the temperature
of the continental surface and the overlying layer increases, causing the
general reduction in relative humidity and precipitation in the lower
troposphere of the model. Accompanying the reduction in relative humidity is
a reduction in total cloud amount, causing an increase in solar energy
reaching the continental surface. Thus, the radiation energy absorbed by the
continental surface also increases, raising the rate of potential evaporation
(Budyko 197^). Both the decrease in precipitation and the increase in
potential evaporation further reduce soil moisture during early summer and
help to maintain it at a low level throughout the summer.
During summer over the Great Plains total cloud cover is reduced and
surface air temperature increases substantially in response to the doubling of
the CC>2 concentration in the model atmosphere (Figure 2). Qualitatively
similar but smaller changes in cloud cover and temperature also occur over
western Europe. In summary, the positive feedback process involving cloud
cover enhances the CC^-induced summer dryness in the Great Plains and western
Europe.
The seasonal variation of the change in zonal mean soil moisture caused
by the COg doubling is illustrated in Figure 3. In middle and high latitudes,
zonal mean soil moisture over the continents declines substantially during
summer months and is consistent with the geographical distribution of soil
moisture change discussed above.
253
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76«N
46
150»W
120*
eo«
Figure 2. Geographical distributions of the changes in (A) total cloud
amount (%) and (B) surface air temperature (°C) in response to a doubling of
CC>2 content for June to August. Only the distributions in the neighborhood of
the North American continent are illustrated.
Figure 3. Latitude-time distribution of the change in zonal mean soil
moisture (centimeters) over the continents of the model in response to a
doubling of CC^. Results are not shown for latitudes where open ocean
dominates.
254
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In winter, when the middle latitude rain belt is displaced toward the
equator, soil wetness increases not only in high latitudes but also in middle
latitudes. However, it is reduced at about 25°N, that is, in the southern
half of the rain belt. Qualitatively similar changes of zonal mean soil
moisture have been obtained previously (Manabe, Wetherald, and Stouffer 1981;
Manabe and Wetherald 1985; Manabe and Stouffer 1980; Wetherald and Manabe
1981).
The results described above were obtained by using the model with
predicted cloud cover. Similar experiments are also conducted by using
another model with fixed cloud cover. A detailed analysis of these
experiments also indicates the CC^-induced reduction of soil moisture in
summer, although the magnitude of the reduction is considerably smaller than
that suggested here. These results suggest that the summer dryness in the
mid-continental regions occurs despite the absence of the cloud feedback
process. However, the cloud feedback process enhances the dryness.
In the subtropical portion of the continents in the Northern Hemisphere
(such as the northern coast of Africa, central Asia, India, and Southeast
Asia) the geographical distribution of the CC^-induced change in soil moisture
varies greatly from one experiment to another. Furthermore, these changes are
not always statistically significant, partly because of the large natural
variability of the model hydrology. Therefore, one should not take the
changes in these regions too literally, pending further investigation. A
similar caution applies to the geographical distribution of the CC^-induced
change in the soil moisture in the continents of the model in the tropics and
the Southern Hemisphere.
It is tempting to speculate that the Dust Bowl drought of the 1930s may
have been induced by a warm-climate anomaly. As noted by Vinnikov and
Groismann (1982) the seasonal and latitudinal profiles of the positive anomaly
of surface air temperature during the 1930s resemble the CC^-induced warming
obtained from the present experiments.
In the model the CC^-induced global mean increase in surface air
temperature with predicted cloud cover is about 4°C and is 1.5 to 2 times
larger than the corresponding warming with prescribed cloud cover (Manabe and
Stouffer 1980). This indicates that the cloud feedback process can enhance
C02~induced increase in global mean surface air temperature, as suggested by
Hansen et al. (1984). However, a recent study by Somerville and Remer (1984)
suggests that the increase in the liquid water content of clouds in response
to the warming of air may act as a negative feedback between temperature and
cloud cover by increasing the planetary albedo, thereby reducing the
sensitivity of climate. This effect is not considered in the model. In view
of the primitive state of the art for the parameterization of cloud formation
and other processes, the quantitative aspect of the present study should be
interpreted with caution.
Despite these uncertainties, it seems significant that all the
experiments discussed in this report indicate C02-induced summer reduction and
winter enhancement of soil wetness over extensive, mid-continental regions in
middle and high latitudes. Furthermore, the analysis of the soil moisture
budget suggests that these large-scale changes in soil wetness are determined
by the latitudinal and seasonal profiles of the CC^-induced warming and do not
255
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critically depend on the details of the warming. Therefore, it is likely that
the basic conclusion is valid despite imperfections of the model.
ACKNOWLEDGEMENTS
We thank A.J. Broccoli and R.J. Stouffer, who gave excellent advice for the
interpretation of the results from the numerical experiments conducted in the
present study, and T. Delworth, N.C. Lau, and H. Levy II for valuable comments
on the manuscript.
REFERENCES
Budyko, M. 1974. Climate and Life. New York: Academic Press.
Hansen, J.E., A. Lacis, D. Rind, and G. Russell, 1984. Climate Processes and
Climate Sensitivity. Washington, D.C.: American Geophysical Union.
Manabe, S. 1969. Mon. Weather Rev. 97:739.
Manabe, S., and R.J. Stouffer. 1980. J. Geophys. Res. 85 (C10):5529.
Manabe, S., and R.T. Wetherald, 1985. Adv. Geophys. XXVIII (part A):131.
Manabe, S., J. Smagorinsky, R.F. Strickler. 1965. Mon. Weather Rev. 93:769.
Manabe, S., R.T. Wetherald, R.J. Stouffer. 1981. Clim. Change. Ill 347.
Somerville, R.C.J., and L.A. Remer. 1984. J. Geophys. Res. 89:9668.
Vinnikov, K.Ya., and P.Ya. Groisman. 1982. Izv. A.S. USSR Atmos. Ocean. Phys.
18:1159.
Wetherald, R.T., and S. Manabe. 1980. J. Atmos. Sci. 37:1485.
Wetherald, R.T., and S. Manabe. 1981. J. Geophys. Res. 86 (C2):1194.
256
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Effects of Climatic Changes on Agriculture and
Forestry: An Overview
Martin L Parry
Atmospheric Impact Research Group
University of Birmingham, UK
Timothy R. Carter
International Institute for Applied Systems Analysis
Laxenburg, Austria
INTRODUCTION
The purpose of this paper is to give an overview of the potential effects
of climatic change on agriculture and forestry. We focus largely on long-term
climate changes, particularly those likely to result from changes in the
composition of the atmosphere. We do not distinguish climate change caused by
natural factors from that caused by greenhouse gases; but we are concerned
with evaluating the potential effects of the resultant climatic change,
whatever its causes. We note at the outset that our concern here is with
climatic change, not with the "direct" effects of changes in composition of
the atmosphere (e.g., the enhancing effects of increased atmospheric carbon
dioxide (CC^) on plant growth). A strong case can be made that effective
assessment of the potential effects of increased CC>2 requires both direct and
indirect (climatic) effects be considered, but that case will not be further
developed here.
In this paper, we first consider briefly the types of climate change that
may affect agriculture and forestry. This discussion is followed by an
outline of the impact that climatic changes are known to have had in the past
and what we can learn from this experience. We then examine the methods that
have been developed, quite recently in most cases, to assess the effects of
climatic change. There is then some discussion of the results of a few recent
assessments, particularly of the potential effects of (X^-induced climatic
changes on agriculture and forestry. The paper concludes with an indication
of the present gaps in our knowledge and our future research priorities.
TYPES OF CLIMATIC CHANGE
Because different types of climatic change can have markedly different
ecological and economic effects, it is important to distinguish them. First,
we should distinguish between climatic noise, climatic variability, and
climatic change [see Hare (1985) for further details]. We may use the term
257
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climatic noise to refer to that part of the variance of the climate resulting
from short-term weather changes. It includes, for example, anomalous weather
extremes (such as floods and droughts) that can have a serious impact on
agriculture. Climatic variability represents the manner of variation of the
climatic parameters (e.g., their standard deviation, frequency, etc.) within
the typical averaging period (normally 30 years). Climatic change refers to
those differences between successive averaging periods that cannot be
accounted for by noise.
Secondly, we should distinguish three types of climatic change [see Parry
(1986) for further details]:
• Short-term, frequent changes to which social and economic systems are
generally adjusted
• Medium-term climatic changes to which society probably needs to adapt
to avoid undesirable impact
• Long-term climatic changes that occur on time scales too large to be
considered significant for the planning horizons of most societies.
This classification may seem somewhat unusual because it is based not on
the nature of the climatic changes, but on their impact. It may, however, be
appropriate since our task is to assess impacts, not to explain them. We may
pursue this line of argument further by identifying two additional
perspectives on climatic changes, once again distinguished by their impact
rather than by their nature. The first, termed by Warrich, Gifford, and Parry
(1986) as the "slow change" view, emphasizes the significance of gradual
increases in mean surface temperatures likely to result from increases in
atmospheric CC>2. These can be expected to lead to gradual, long-term, and
cumulative changes in average regional climates. Following this view, we
might conclude that so long as we can predict the long-term climate trend,
there need be no surprises in store for the farmer or forester who should have
time to modify their practices accordingly.
The alternative view emphasizes the changes in the frequencies of
unusually disruptive (or beneficial) events that may result from changes in
climate. This view assumes that impact from climatic change comes not only
from the average but also from the extreme event, a point that has been
developed at some length elsewhere (Parry 1978, 1985). To illustrate, few
farmers plan activities on their expectation of the average return. They
gamble on good years and insure against bad ones (Edwards 1978). In general,
we might expect subsistence farmers to tune their activities to bad years,
attempting to minimize the impact of those years, while commercial farmers
(such as those on the Canadian prairies) may tune them to good years [which is
why the prairie farmer is periodically stressed when bad years prevail (McKay
and Williams 1981)].
The impact from extremes can alter in a number of ways. To illustrate,
let us assume that annual rainfall or temperature has a Gaussian (normal)
distribution about the mean x and variance k . We also assume that
agriculture is only seriously affected if rainfall or temperature is outside
the range ( x ± k) (Figure 1a). In the first type of change, x changes but
258
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Impulsive change of
central tendency
increasing variability
Change in centra! tendency
and increasing variability
Figure 1. Changes in probability distributions and stochastic outcomes
for shifts in mean, variance, or both. After Fukui (1979) and Hare (1985).
259
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remains unchanged (Figure 1b). The frequency of negative extremes (as
originally defined by the agricultural system which we assume to be slow to
adapt to the new climate regime) is increased, and positive extremes are
reduced. If this change occurred for rainfall on the Canadian prairies, we
might expect the bad years to far exceed the good years. In the second type
of climatic change, k changes but x does not (Figure 1c). There is
increased risk of both deficient and excessive temperatures and/or rainfall.
Both x and k change in the third type (Figure 1d).
HOW HAS THE CLIMATE CHANGED IN THE PAST?
Our intention here is to present a very brief summary of some of the
changes in climate which we know to have occurred in the past [for more
information, see Wigley, Ingram, and Farmer (1981)] to provide a backdrop for
a later discussion of the effect of these changes on agriculture and forestry.
Changes on a Millenial Scale
If we take as our starting point the last glacial maximum (around
eighteen thousand years ago), we may note that a rapid global warming began
around thirteen thousand years ago, was interrupted around eleven thousand
years ago by a sharp and severe cooling episode around 11,000 BP, and was then
resumed (Wigley, Jones, and Kelly 1986) (Figure 2a). By about ten thousand
years ago (the beginning of the so-called Holocene), global temperatures had
roughly reached their present-day mean.
Changes on a Secular Time Scale
During the past two thousand years, the major changes that have occurred
include the medieval warm epoch (800 to 1200 A.D.) and the Little Ice Age (ca.
1500 to 1800 A.D.) (Figure 2b). In western Europe mean annual temperatures at
the nadir of the Little Ice Age were about 2°C lower than in the early
medieval period. These estimates are based on a wide array of proxy data,
including oxygen isotopes, harvest size and harvest dates, and dates of
freezing and thawing of navigable rivers and lakes.
Decadal Changes
The instrumental record enables us to be more precise for periods after
1850. A long-term warming trend appears to have occurred, interrupted by cool
episodes around 1900 and during the 1960s. Present-day mean surface
temperatures have been broadly restored to their medieval levels. Figure 2c
shows observed temperatures and the moving average from 1850 to the present.
HOW WILL THE CLIMATE CHANGE?
The following section is a brief summary of a recent synthesis of our
present knowledge [for further detail, see Dickinson (1986)]. Our aim here is
simply to indicate the direction and approximate scale of the changes that may
occur and how these compare with changes experienced in the past. These may
be summarized as follows (WHO 1986):
260
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_ 45
(J
| 40
(0
fij
| 35
u
K
30
900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900
04°C
-0.4°C- •
1850
1900
1950
1980
Figure 2. (a) schematic representation of temperature changes during the
past 20,000 years (Wigley 1982); (b) 50-year averages of winter temperature
for England. The continuous line gives unadjusted values based soley on
regression analysis and Winter Severity index values prior to 1700. Ninety-
five percent confidence limits based on the regression equations and using the
t-distribution are shown. Values shown after 1700 (temperature) are observed
instrumental data from Manley's central England temperature series (Manley
1974). The long dashed lines project the unadjusted estimates back in time,
but only 100- to 200-year means are given based on sparse data. The short
dashed line in the temperature curve gives adjusted values, accounting for
botanical evidence. The dotted curve is the analyst's opinion based on a wide
variety of evidence (Lamb 1981); (c) Northern Hemisphere annual mean surface
temperatures from land-based record (Wigley et al. 1986).
261
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• The change in global equilibrium temperature from increases of C02 and
other trace gases equivalent to a doubling of COp is expected to be in
range of 1.5 to 5.5°C (Dickinson 1986). This change would be of the
same order as that which occurred between the last glacial maximum and
the Hypsithermal (Figure 2a). A doubling of C02 concentrations is
expected to be reached between 2050 and 2100.
• The global warming up to the present suggested by models to result
from previous increases of COp and other trace gases is in the range
of 0.3° to 1.1°C (WHO 1986). The observed increases in mean
temperature during the last century "cannot be ascribed in a
statistically rigorous manner to the increasing concentration of C02
and other greenhouse gases, although the magnitude is within the range
of predictions" (WMO 1986).
• There are indications that warming will be enhanced in high latitudes
and that summer dryness may become more frequent over the continents
at middle latitudes in the Northern Hemisphere (WMO 1986).
EFFECTS OF CLIMATIC CHANGES IN THE PAST
In this section we review some of the effects that climatic changes have
had on agriculture and forestry in the past. Our aim is to indicate some of
the types of effects that have occurred and some of the adjustments that have
proven successful, which provides a basis for considering potential impacts in
the future and for identifying appropriate responses to them. We take a
number of examples to illustrate the different kinds of climatic changes
outlined in the section on types of climatic change, from single extreme
events to long-term trends. The examples are arranged in research
chronological order, moving from recent isolated extreme events to prehistoric
long-term climatic changes.
The Effect of Isolated Extreme Events
Drought in the U.S. Corn Belt, August 1983. Midsummer 1983 saw a pronounced
drought in the U.S. corn belt and the southeastern United States. U.S. maize
yields fell by about a third, from over seven thousand kilograms per hectare
to about five thousand kilograms per hectare (Figure 3). In the same year,
however, the Payment-in-Kind Program (PIK) had encouraged large numbers of
corn (maize) farmers not to plant in 1983 (as part of an effort by the USDA to
reduce the national grain surplus). As a result, the U.S. area planted to
maize also fell by about a third, from thirty to twenty-one million hectares
(Figure 3). The combined effect of decreased yield and reduced area was a
fall in U.S. maize production by almost one half (from 210 million metric tons
in 1982 to 110 million metric tons in 1983) (Figure 3).
The effects were felt not only nationally, but also globally, because
U.S. maize accounts for about one-eighth of the world's total marketed cereal
production. World total cereals production in 1983 fell by 3 percent,
harvested area by 1.4 percent, and yield by 2 percent, these reductions being
almost fully accounted for by the U.S. figures alone (Figure 4).
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USA MAIZE PRODUCTION, AREA HARVESTED AND GRAIN YIELD 1972-1983
200
MILLION
METRIC TONS;
USA MAIZE PRODUCTION
USA MAIZE AREA
HARVESTED
HECTARES
USA MAIZE GRAIN YIELD
21
7000
KILOGRAMMSPER
HECTARE I
1972
1975
1980
1983
Figure 3.
(FAO).
USA Maize Production, Area Harvested and Grain Yield 1972-83
263
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WORLD TOTAL CEREALS: PRODUCTION. HARVESTED
AREA AND GRAIN YIELD 1972-1983 (FAO)
1750
1700
MILLIONSOF
METRIC TONSi
1500
1300 +
1250
755
750
MILLIONS OF|
HECTARES'
2350
2300
KILOGRAMMSl
PER HECTARE
20004
1900
18501
ANNUAL PRODUCTION OF WORLD
TOTAL CEREALS
WORLD AREA
HARVESTED
WORLD TOTAL CEREALS YIELD
1972
1975
1980
1983
Figure 4.
1972-83 (FAO).
World Total Cereal Production, Harvested Area, and Grain Yield
264
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Drought in the United Kingdom, 1976. From May 1975 to August 1976 rainfall in
the southeast of England was about 60 percent of normal (Doornkamp, Gregory,
and Burn 1980). (Mo drier spell of comparable length appears on the 300-year
instrumental record.) Almost all crops were affected. Nationally, potato
yields were down 25 percent of the 1970-74 average and cereal yields 10 to 15
percent. Since planted area had not been substantially affected, falls in
production were broadly commensurate: Potato production down 2.25 million
tons and wheat down 2 million tons. The shortfall in cereal production
required the import of around 1 million tons of cereal worth 80 million
(British) pounds.
But prices responded accordingly. U.K. potato prices increased threefold
over 1975-76 and wheat increased one third over 1976-77 from the previous
year. As a result, aggregate net income of the agricultural industry rose in
real terms by 7 percent from 1975 to 1976, with little change from 1976 to
1977. Certainly some farmers suffered (such as those engaged in livestock
fattening in lowland areas where higher feed prices were not fully balanced by
increased livestock prices), but the general message of the 1976 drought is
that market reactions combined with sensitive government response in raising
guaranteed prices can effectively buffer even the severest of climatic
events. The problem really arises when government policy is insensitive to
climate change, such as the U.S. Department of Agriculture's Payment-in-Kind
program, which could not foresee that a massive yield downturn as a result of
drought, in combination with reduced planting induced by government policy,
could lead to reductions in production that were almost twice as large as
those intended. Fortunately, U.S. corn yields were back up in the benevolent
weather-year of 1984. But if 1984 had also been a drought year, the outcome
could well have been a severe drop in national and global cereal food
stocks. This leads us naturally to consider the dramatic effects that a
series of climatic anomalies can have on agricultural production.
The Effect of Recurrent or "Back-to-Back" Climatic Events
Runs or sequences of anomalous weather-types tend to have a cumulative
and compounding impact, the net effect being greater than the sum of the
single extreme-year effects. Over 1932-37, for example, persistent drought in
the U.S. Great Plains helped bring about approximately two-hundred thousand
farm bankruptcies or involuntary transfers and the migration of more than
three-hundred thousand people from the region. If the same weather were to
occur today, assuming 1975 technology and a 1976 crop area, the impact would
still be considerable. For a recurrence of the worst weather-year, 1936,
simulated production shows a drop of 25 percent, reducing national wheat
production by about 15 percent (assuming average production elsewhere in the
USA) (Figure 5). The cumulative effect could be substantial: yearly yields
simulated for the weather over the period 1932 to 1940 average about 9 to 14
percent below normal and amount to a cumulative loss over the decade equal to
about a full year's production in the Great Plains (Warrich 1984).
The Effect of Secular Fluctuations of Climate
To assess the past effects of long-term changes of climate our subject
matter becomes historical, and one problem confronting us is that there are
few proofs in history: connections between climatic changes and economic
265
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60%
BISMARK
80%
'/o
OMAHA
100%
100%
• PREDICTED YIELDS
IN
(BUSHELS/
PLANTED ACRE)
•PERCENT OF
EXPECTED YIELDS
80%
Figure 5. Simulated Wheat Yields on the Great Plains;
1975 Technology (Warrick 1984).
1936 Weather,
266
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changes in the past depend on skilled but essentially qualitative interpreta-
tion. However, to illustrate the potential effects of secular climatic
changes, we refer to one or two episodes during which the two events have been
plausibly connected by historical scholarship.
The Little Ice Age in Western Europe 1500-1800. Between about 1500 and 1800
mean annual temperatures were about 1.5°C below that of the present norm and
also that of the preceding warm epoch of A.D. 800 to 1200. At the nadir of
this cold episode, the accumulated temperature of the growing season in
southern Scotland was 10 percent less than at present (Parry 1978). There was
a permanent snowfield in the Scottish highlands. Icebergs were reported to
have drifted ashore carrying polar bears from the Arctic (Lamb 1982). There
was widespread desertion of the more marginal upland settlements in
Scotland. In Norway about half of the farms were abandoned in the late
Middle Ages (Parry 1978). In Iceland the cultivation of cereals died out
before 1600 AD. The period was clearly one of considerable difficulty for
those farming near the northern limit of agriculture, but few historians would
deny that even under these unusual climatic conditions there existed a range
of adjustments that farmers could employ to respond and survive. Deserting
settlements and moving somewhere else more attractive were simply some of the
more radical forms of one response.
Late Medieval Cooling, 1250-1500. On the issue of adaptation the experience
of Morse settlers in Greenland can be instructive. The Norse had gained a
foothold along the Greenland coast in around 985, but their settlements had
been completely abandoned at least by 1500, probably between 1350 and 1450.
In the 13th century the population, which then totaled about six thousand in
two settlements, was subjected to a synergistic interaction of stresses from
hostile Eskimos (Inuit), the decline of the European market for walrus ivory,
and challenging spells of cool summers and stormy winters, particularly around
1270-1300, 1320-1360, and 1430-1460. The failure to adapt to the changing
circumstances is believed to explain much of the Norse decline (McGovern
1981). The Norse continued to emphasize stock raising in the face of reduced
capacity of the already limited pastures. The option of exploiting the rich
seas around them, as the Inuit successfully did, was not taken up, perhaps
because of the inflexible attitude of priest-rulers in a highly stratified
religious society:
"Baldly put, a society whose administrators (as well as its peasants)
believe that lighting more candles to St. Nicholas will have as much (or
more) impact on the spring seal hunt as more or better boats is a society
in serious trouble" (McGovern 1981).
According to McGovern, the Norsemen had lost some of the adaptiveness and
resourcefulness that they displayed some three hundred years earlier at the
time of the settlement. It is an extreme example of how governments can fail
to identify and implement appropriate policies of response, not only to
climatic change but to the synergistic effects of a number of concurrent
events, and it serves to emphasize the value of designing policies that are
responsive to the "package" of environmental issues currently facing us
today—of increasing concentrations of greenhouse gases, acid deposition,
desertification, groundwater pollution, salinization, deforestation, etc.—a
package that requires an integrated set of policies.
267
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METHODS IN CLIMATE IMPACT ASSESSMENT
One particularly promising way of studying the interactions between
climate and society is to trace the effects of a climatic event as they
cascade through physical and social systems, and are disguised and modified by
various sets of intervening factors. An example of this approach is offered
by Warrich and Bowden (1981), tracking the impacts of drought occurrence in
the U.S. Great Plains (Figure 6). These authors traced a variety of pathways
that drought impacts could take, spanning a variety of spatial scales (from
local to global) and a variety of systems (from agricultural to social). The
cascade of effects of an anomalous climatic event work their way through a
hierarchy of responses (e.g., climatic anomaly, crop yield, farm production,
farm income, regional agricultural sector, regional economy, national economy,
society). To understand and evaluate each level of response, we need to
develop a hierarchy of models that can simulate these impacts. In particular,
we can identify three sets of models: climatic changes, climate impacts on
potential and actual yield, and the downstream economic and social effects of
these (Figure 7). Scenarios using outputs from climate models (e.g., atmo-
spheric general circulation models) or data from instrumental climatic records
are used as inputs to agroclimatic models to predict potential or actual yield
responses to climatic change. To trace the downstream effects of yield
changes, outputs from the agroclimatic models are used as inputs to economic
models (farm simulations, regional input-output models, etc.). It is then
possible to consider what policies best mitigate certain impacts at specified
points in the system. This research strategy has been adopted in a number of
recent climate impact assessments, the results of which are summarized in the
next section.
System affected
Scale AGRICULTURAL ECONOMIC SOCIAL
/ 7 ' 7
, , GRAIN PRICES. ___/ STRESS ,
/ GLOBAL / Jf DISTRIBUTION S ' "" eq ,
GLOBAL / FOOD / f / ! lam.rw. /
/ SUPPLY / V FOREIGN / / social /
ECONOMIES / conflict /
/ . / ECONOMIES ; conflict /
/ A I i i I
i -f- / -f -/ r
/ / / ..FOODPRICES. - y STRESS /
i / US FOOD ' S DISTRIBUTION S '"~ «9 • /
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/
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____/____._/.__^L/
^. FARM ' STRESS /
/' health effects. /
Farm bankruptcy /
Gov't policy vulnerability /
RESOURCE
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perception
DROUGHT
Figure 6. The Hypothetical Pathways of Drought Impacts on Society
(Warrick and Bowden 1981).
268
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Recent Assessments 1: Effects on Crop Yields
In this section we draw heavily from a recent review by Warrich, Gifford,
and Parry (1986) who have summarized results from a number of studies. We
reduce here part of their summary, updated to include recent results from the
Soviet Union (Figure 8). In essence, Warrich's conclusion is that, despite
the diversity of modeling methods and scenarios adopted in these different
studies, there is a remarkable degree of unanimity regarding the expected
direction of effects of climatic changes on crop yields. Warming appears
detrimental to cereals in the core wheat-growing areas of North America and
Europe. With no change in precipitation (or radiation), slight warming (+1°C)
might decrease average yields by about 1 to 9 percent while a 2°C increase
might reduce average yields by about 3 to 17 percent. To place this in
perspective Warrick notes that a 10 percent decrease in wheat and maize yields
in North America is equivalent to about 20.5 million metric tons, or 10
percent of global trade in cereals. Reduced precipitation also tends to
decrease yields, implying that both higher precipitation and temperature could
have offsetting effects on yields, as reflected in the negative slope to the
plots in Figure 8. To these conclusions we add first, that quite different
effects on the same crop may occur in different regions (note the differences
for the same wheat cultivar in Perm, 58°N latitude, and Volgograd, 48°N
latitude) and that different cultivars may respond quite differently. We
shall see later that these variations can be important in suggesting the kinds
of technological adjustments that may be most appropriate for responding to a
given climate change.
If, for the present, we ignore the adjustment in agriculture, such as a
switch of crops, that is likely to accompany or follow a long-term climate
change, we may conclude that given the kind of changes in climate most likely
to result from increased C02 and other greenhouse gases, particularly enhanced
warming in higher latitudes, with summer dryness becoming more frequent over
the continents at middle latitudes in the Northern Hemisphere, then decreases
in yields on the order of 10 percent might occur in the core wheat production
areas of North America and the USSR. We should emphasize, however, that such
estimates are unrealistic in that they fail to acknowledge that adjustments in
agriculture will occur.
Recent Assessments 2: Spatial Effects on Crop Location
One of the major adjustments most likely to occur is the spatial shift of
cropping areas, which is somewhat akin to the shift of biomes that has
occurred as a response to long-term climatic changes in the past (see section
on forestry below). We can map this effect through a sequence of steps that
has been summarized by Parry (1985) as follows:
• Identification of the climatic variables that constrain crop growth in
the region and limit its spatial extent
• Identification of critical levels of those that limit the spatial
extent of the crop
• Characterization of climatic changes as changes of the critical levels
• Mapping these as a shift of extent of the crop.
270
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CANADIAN WHEAT LIMIT BASED ON CLIMATE AND TERRAIN
I I 1C colder
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Figure 9. Estimated shift of the Canadian Spring Wheat Belt and the U.S.
Corn Belt in response to a 1 degree reduction in annual temperature (after
Williams and Oakes 1978; Newman 1980).
This approach has been used to estimate the effects of climate change on
wheat- and maize-growing areas in North America. In Canada the isopleth
bounding the wheat-maturing zone is based on photothermal time scale equations
which consider the date of first fall freeze, growing season temperature, and
radiation conditions (Williams and Oakes 1978). For the U.S. corn belt the
limits have been expressed in terms of minimum frost-free period for maturity,
minimum and maximum thermal requirements, and moisture requirements. Both
crop zones are shown as shaded areas in Figure 9. In this example, an
arbitrary decrease of 1°C has been used to perturb the crop zones. In Canada
the area of spring wheat is reduced by about one-third. In the corn belt, a
1°C cooling with no change in precipitation would shift the belt in a south-
westerly direction by about 175 kilometers since moisture stress would be
reduced at the drier SW margin while the growing season would be reduced at
the cool NW margin. A logical development of this approach is to consider the
shift of wheat-growing regions for climatic scenarios predicted by general
circulation models for doubled concentrations of CC^ experiments. The model
projects a great extension of the winter wheat belt into Canada, a switch from
hard to soft wheat in the Pacific Northwest due to increased precipitation,
and an expansion of areas in fall-sown spring wheat in the southern latitudes
due to higher winter temperatures. In Mexico, wheat-growing regions would
remain the same but greater high-temperature stress may occur (Figure 10).
272
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Recent Assessments 3: Potential Effects on the Regional Agricultural
Economy
Hierarchies of linked models, similar to those discussed above, have been
used to assess the potential effects of climatic changes on the regional
economy. In the International Institute for Applied Systems Analysis/UNEP
project (Parry 1986) climatic scenarios using outputs from climate models
(e.g., model experiments for doubled CC^ climate) provide inputs to
agroclimatic models to estimate potential or actual yield responses to
climatic change. Output from the agroclimatic models provide inputs to the
economic models (e.g., farm simulations, regional input-output models,
etc.). While each set of models attempts to simulate a limited number of
feedback effects within its own subsystem, the form of analysis is essentially
sequential, allowing estimates to be made of a series of effects based on an
assumed and essentially static set of agronomic and economic responses. We
may call calculations "impact experiments"; they record the impacts that would
occur if there were no changes in the farming system. However, as we have
seen, farming systems have been remarkably adaptive to climatic changes in the
past and we can reasonably expect them to be in the future. The major task we
face is to make the adaptations in an optimal manner, that is, with the
minimum of social and economic cost. It is possible to evaluate the various
options that are available for either mitigating the negative effects or
exploiting the positive ones by altering some of the assumptions in our
agroclimatic and economic models, for example, by experimenting with a switch
to a different crop, different amounts of fertilizer, or different amounts of
irrigation. For each set of these "adjustment experiments" we can generate a
new set of impact estimates that can be compared with the initial impact
estimates (on the unadjusted system), and thus begin to identify the more
appropriate types of adjustment to various types of climatic change.
In the summary that follows we outline results selected from a wide range
of experiments for both impacts and adjustments. Only a few are presented
here. These are drawn from studies conducted in Canada, the Soviet Union and
Japan. Other studies in the IIASA/UNEP project were conducted in Iceland,
Finland, Ecuador, Brazil, Kenya, India, and Australia (Parry 1986). In each
case study region a series of three or four impact experiments were conducted
along the lines outlined above and in a broadly compatible manner. These were
then followed by a series of adjustment experiments to evaluate the
appropriateness of various responses. In the example summarized here the
emphasis was on the potential effects of climatic changes due to increased
atmospheric CC>2. Scenarios of these changes were based on outputs from the
doubled-COo experiment for the GISS GCM. To compare these effects with the
effects of short-term climatic variations, the results were compared with
those for an extreme decade and extreme year scenario. Because different
crop-weather models require different data (ten-day, monthly, annual, etc.),
this array of scenarios varied somewhat between the case studies. The Soviet
study, for example, includes synthetic scenarios that vary temperature and
precipitation by arbitrary increments. In general, however, the results
permit comparison of the potential effects of a doubled CC^ climate both
between different regions and between the effects of a long-term climate
change and short-term climatic variability. The results are, of course, not
predictions. A high level of uncertainty is attached both to model
predictions of regional climatic change and to the estimations of their
effects on agriculture.
274
-------
Regional Variations in Effects on Crop Yields. As indicated above, the higher
temperatures that may be expected to prevail under conditions of increased
atmospheric C02 tend to favor higher yields of cereal crops now grown in
regions where temperature limits the growing season. In the central European
region of the Soviet Union, for example, wheat yields under the doubled CC^
climate projected by GISS increase by about one third (Table 1). If we assume
that these warmer conditions do not create problems of water supply and that,
for example, Japanese rice production will remain fully irrigated, we may
expect average rice yields in central Japan (To Kohu) to increase by perhaps 5
percent (Table 2). However, where cereal production is already drought-
prone, increased rates of evapotranspiration may well place a brake on
output. Simulations of wheat yield in Saskatchewan point to quite severe
early-summer moisture stress on ground spring-sown wheat plants with
consequent yield reductions of between one-fifth and a third, depending on
soil type (Table 3). As we discuss below, one way of mitigating these
negative effects is to switch from spring- to winter-sown wheat. However, the
regional pattern of crop yield responses will probably be extremely varied for
a number of reasons.
* Spatial Complexity of the Climate Change. This is not simply the
result of the varying degrees of absolute change in temperature,
precipitation, cloudiness, etc., and other factors that could be
expected to occur in different places, but also stems from the ratio
of this change to the existing climate. Thus, while effective
temperature sums (ETS) in central Japan (To Kohu) increase by 27
percent in the GISS doubled C02 experiment, in the north at Hokkaido
(where they are already one quarter lower than in the center) the
increase is 37 percent. Thus much of the variation in yield response
estimated for irrigated rice in Japan is a function of the geography
of existing agroclimatic potential. This factor, as much as greater
increases in temperature expected in Hokkaido, explains why average
rice yields in Hokkaido increase by 8 percent and in To Kohu by 5
percent.
* Spatial Complexity Introduced by Non-climatic Factors. In the
estimates presented above we have assumed the same terrain, soil,
management, etc. When regional variations in these are introduced
there can result quite localized variations in responses to climatic
change. To illustrate, while spring wheat yields in Saskatchewan are
reduced by one-fifth under the GISS projection for doubled CO^ climate
on brown soils, on black soils they are reduced by one-third.
Overlaid on these variations are differences in infrastructure (farm
size, etc.) and management (levels of fertilizer applications,
pesticides, etc.). Even if we assume the same management for all farm
sizes, the effects of similar yield changes on farm income vary
according to farm size partly because of varying yield-income
functions and partly because different sized farms are found on
different soil types (Table 3).
275
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NOTES TO TABLE 1.
1. Unless otherwise stated (lakimets, Pitovranov and Sirotenko).
2. Technology trend, 1980-2035, unless otherwise stated (lakimets and
Pitovranov).
3. Up to the year 2000 (lakimets et al).
4. Goodard Institute for Space Studies (GISS) General Circulation model 2 x
COp experiment; output processed for impact experiments (Bach), unless
otherwise stated.
5. GISS model climate, fertilizer, drainage or crop varieties adjusted.
21. May-September mean air temperature at Perm (station adjacent to Cherdyn),
period undetermined.
22. May-September mean precipitation at Perm, period undetermined.
23. Arbitrary warming relative to 1951-80 baseline (May-September mean)
(Sirotenko).
24. GISS model climate; May-September mean, interpolated from grid points to
Cherdyn (Sirotenko).
25. Arbitrary variations in precipitation (May-September) (Sirotenko).
26. GISS model climate; calculated as 2 x COo - 1 x C02 precipitation;
interpolated from grid point data (SirotenkoJ.
21. Simulated yield relative to modeled 1951-80 mean yield (Sirotenko).
28. Precipitation 29 mm below baseline (Sirotenko).
29. Baseline precipitation (Sirotenko).
30. Precipitation 20 mm above baseline (Sirotenko).
31. Present crop variety and farming efficiency (Sirotenko).
32. Simulation incorporating direct effects of C02 on plant photosynthesis
and water use (Sirotenko).
33- New middle-maturing variety requiring an extra 50 GDD temperature during
the growing season (Sirotenko).
34. New late-maturing variety requiring 100 GDD higher temperature during the
growing season (Sirotenko).
35. Annual mean air temperature at Moscow (assumed representative of the
Central Region), period undetermined.
277
-------
36. Annual mean precipitation at Moscow, period undetermined.
37. Arbitrary temperature change relative to baseline (annual mean);
precipitation unchanged, assumed to occur in 1995 (Kiselev).
38. As in Note 37, this is not the GISS scenario (Kiselev).
39. Based on 1970-80 technology trend (Kiselev).
40. Area of crop required to minimize total expenditure (Kiselev).
41. The product of area and crop yield (Kiselev).
42. Expenditure per hectare and resource supply function (Kiselev).
43. Trend yield for 1980, quintals per hectare (Kiselev).
44. Trend yield extrapolated to 1995, relative to 1980 trend yield (Kiselev).
45. Estimates relative to 1980 trend yield using crop production simulation
model (Kiselev)
46. Cropped area in 1980 (Kiselev).
47. Cropped area under improved technology, assumed the same as in 1980
(Kiselev).
48. Optimization model for minimizing expenditure: values relative to 1980
(Kiselev).
49. Area of perennial grassland for hay production fixed at 1980 value
(Kiselev).
50. Mix of crops chosen primarily to meet human demand for vegetable products
(Kiselev).
51. Trend production (matching yield trend) (Kiselev).
52. Cost based on trend data (rouble/quintal), 1980 values (Kiselev).
53. Costs assumed the same, under improved technology, as in 1980 (Kiselev).
278
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NOTES TO TABLE 2
1. Unless otherwise stated.
2. 1980, unless otherwise stated.
3. 1974-83, unless otherwise stated.
4. 1957-66, unless otherwise stated.
5. 1978, unless otherwise stated.
6. Goddard Institute for Space Studies (GISS) General Circulation Model 2 x
CC>2 experiment; output processed for impact experiments (Bach). Air
temperature change only; precipitation change not considered important
for irrigated rice crops in impact experiments.
7. District average; July-August air temperature (T. Uchijima).
8. District average; July-August air temperature (Horie).
9. Calculated as 2 x CC^ - 1 x CC^ temperature; spatial average (T.
Uchijima).
10. Effective temperature sum (ETS) above 10°C base; values based on
relationship between July-August air temperature and ETS over all Japan
(150 station) (Uchijima and Seino).
11. Present altitudinal limit (meters) (T. Uchijima).
12. Using temperature lapse rate and ETS threshold for rice cultivation of
2600 GDD (above 10°C base). Values relate to a baseline temperature of
20.4°C (T. Uchijima).
13. Rice yield regression index developed for 1888-1983 detrended yields.
Values relative to baseline index value of 100 (T. Uchijima).
25. Integrated Economic and Climatic Model; Simulation period 1966-82
(Tsujii).
26. Approximate value relative to 1966-82 baseline (Tsujii).
27. July-August temperature change of 3.4°C (Tsujii).
28. Using temperature lapse rate and ETS threshold for rice cultivation of
2600 GDD (above 10°C base). Values relate to a baseline temperature of
22.5°C (T. Uchijima).
280
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281
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NOTES TO TABLE 3
1. Calculations for a northern station, Uranium City, are footnoted where
appropriate.
2. Unless otherwise noted.
3. Unless otherwise noted.
4. Goddard Institute for Space Studies (GISS) General Circulation Model 2 x
C02 experiment; output processed for impact experiments (Bach). Air
temperature and precipitation changes included in scenario.
5. GISS model outputs: air temperature changes only. Precipitation fixed
at 1951-80 baseline.
6. May-August: all crop districts: precipitation values rounded to nearest
5 mm (Stewart)
Uranium City values: 12.8°C, 149 mm.
7. Calculated as 2 x C02 - 1 x C02 temperature; spatial average (Stewart).
21. Estimates from farm level simulation models (Fautley).
22. 1980 value (Fautley).
23. Aggregated for all crop districts based on yield simulations (Stewart).
24. Income aggregated by farm size, whole province; 1980 values; all cereals
(Fautley).
25. Aggregated for all farms, whole province; 1980 values; all cereals
(Fautley).
26. Employment model (Fautley).
27. 1980 data; whole province (Fautley).
28. Input-out model (Fautley).
282
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Differential Crop Responses. Because different crops have different
growing requirements, they frequently respond quite differently to
changes in their environment. In the central-European part of the
Soviet Union, for example, a moderate warming would increase winter
wheat yields (which are at present limited by a short, relatively cool
growing season in the region) but decrease barley yields (since
spring-sown barley is suited to the cool conditions but is susceptible
to the early summer moisture stress that might accompany increased
temperatures). Under a warming experiment ( AT = +1.5°C) winter wheat
yields in this region increased by 30 percent and barley yields
decreased by 4 percent (Table 1). As might be expected, cool
temperate crops such as oats and potatoes also decrease, while corn
(maize) increases.
Resultant Changes in Crops' Potential. Two consequences flow from the
geographic complexity described above: there are spatial shifts of
crop potential and spatial shifts of comparative advantage. Areas
that, under present climatic conditions, are judged to be most suited
to a given crop, combination of crops, or a specified level of
management will change location. This means that a change will occur
in the range of crops that can be profitably grown at a particular
place, as a result of the shift of the physiological limits for growth
of different crops. For example, we might expect that under a warmer
climate both winter and spring wheat will expand northward, assuming
that terrain and soils permit. This is well-illustrated in Hokkaido,
where the limits of the "safely cultivable" area for irrigated rice
(defined as a return period of critically low growing season
temperatures that can cause failure of the rice crop) fluctuate quite
markedly between warm and cool periods and could be expected to expand
under a climatic warming induced by increased atmospheric CC^ or other
greenhouse gases (Figure 11).
Spatial Shifts of ComparativeAdvantage. More important are the
changes in area under different crops resulting from differential
changes in yield that, in turn, result in changes either in their
relative profitability at a particular place or in the comparative
advantage that one crop may hold over another. For example, under a
market system, it is probable that, if other factors remain unchanged,
crops that exhibit a substantial decrease in yield would be displaced
by those that show an increase in yield. An important assumption here
is that alternative areas are available for production of this
displaced crop. The relative availability of potential production
areas would affect their comparative advantage. If alternative areas
were not available, the crop might not be displaced and there would be
no radical change in the pattern of land use. The operation of these
forces of supply and demand in determining how much change occurs in
the pattern of land use can be more clearly seen in a centrally
planned economy such as that of the Soviet Union. To illustrate this
point Table 1 includes results from experiments with an optimization
model that allocates land to various crops to minimize expenditure on
inputs (e.g., fertilizers and machinery) while meeting certain
regional production targets. Under the +1.5°C experiment this
approach increases the allocation of land to winter wheat by 26
percent while reducing that under barley by 20 percent reflecting the
283
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284
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fact the wheat yields increased by 30 percent and barley yields fell
by 4 percent.
• Inter-regional Differences in Crop Yield Sensitivity. The picture is
further complicated by the fact that the same crop grown in different
regions will respond differently to the same change in climate. In
northern Finland under the GISS scenario, for example, barley would
relish a higher ETS without moisture shortage, whereas in southern
Finland yields could actually decrease because of early summer
moisture stress (for details see Parry 1986). Comparable sensitivity
analyses of spring wheat yields in the northern and southern parts of
the European USSR indicate similarly contrasting responses. In Perm
(west of the Ural Mountains) yields increase with increasing
temperature, while in Volgograd (some 1,000 km further south) they
decrease (Table 1). These differing regional responses will, in turn,
affect the pattern of comparative advantage in cropping and thus
influence the shift of cropping patterns that may result from changes
in climate.
• Effects on Crop Responses to Management. One of the difficulties of
estimating effects of climatic change on agriculture is that the
sensitivity of yield to inputs, such as fertilizers and pesticides,
also varies with climate. Generally speaking, the more ideal the
climatic conditions are for plant growth, the greater the plant
response to fertilzer applications, which means that adjusting levels
of fertilization can be an effective means of stabilizing yield
variability resulting from short-term climatic changes.
• Effects on Variability of Production. Even if we disregard those
changes in interannual variability of temperature and rainfall that
may occur as part of a transition to a warmer climate and assume that
climatic variability remains unchanged, the effect of a change in mean
climate on mean yield can be different from its effect on the above-
or below-average yields. Figure 12, for example, shows that in
southern Finland quite different increases occur in the 5-percent,
mean, and 95-percent spring wheat yields simulated for the recent warm
period 1966-73, and that similar (though perhaps less pronounced)
differences are likely to occur with different wheat varieties in a
the doubled C02 climate projected by GISS.
Recent Assessments 4: Downstream Economic Effects
From experiments with farm simulation models and input-ouput models, we
can estimate the effects of climatic changes, via crop yields, on farm
incomes, employment, and levels of economic activity in nonagricultural
sectors. The critical parameters here are the relationships between yield and
farm income, farm income and on-farm employment, and farm income and
expenditures by farmers of nonagricultural goods. These relationships are
described by regression equations that pertain to a particular data set (for
example, the models for Saskatchewan-are based upon data for 1974 and 1980).
They allow an estimation of the effects of a specific climatic event, such as
an extreme dry year or dry decade, if that event were to occur now. But these
background factors are constantly changing and, indeed, would almost certainly
change in response to a longer term transient change in climate resulting
from, for example, increases in atmospheric CO^ or other greenhouse gases.
285
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a) Warm period (1966-73) scenario
MEAN
95%
5%
Helsinki
MEAN
b) GISS 2 x C02 scenario
95%
5%
Figure 12. Effect of climate on mean, lowest (95 percentile) and highest
(5 percentile) spring wheat yields in Finland a) for warm period 1974-82, with
present-day variety; b) for GISS "2 x CC>2" climate with adapted variety having
thermal requirement 120 GDD greater than present varieties. Isolines indicate
percentage of yield simulated for the period 1959-83. From 0. Rantanen, in
Parry et al. 1986.
286
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With these caveats in mind, we report that experiments in Saskatchewan
indicate that under the changes in temperature and precipitation indicated by
the GISS projections, total provincial farm income decreases by 26 percent,
on-farm employment by 3 percent, and provincial gross domestic product by 12
percent. Considerable margins of error embrace these estimates. For details,
see Fautley in Parry (1986). In this experiment the change in climate is
treated as a sudden, step-like event in which no adjustment is allowed for
changes in technology, management, prices, harvested area, etc. In reality we
can be sure that these would change substantially between now and the time at
which levels of atmospheric COp are doubled. Current estimates for the COo
doubling time lie between 2050 and 2100 (Bolin et al. 1986).
Because of the uncertainties surrounding future changes in prices,
management, and technology, the results from these experiments present an
extremely unreal picture of the effect of long-term climatic changes. They
do, however, provide a means of testing a number of adjustments to climate
change by comparing the results of the adjusted experiments with those of the
initial, unadjusted ones. The analysis can thus take on an interactive form
which more closely resembles the dynamics of the real world. These
adjustments are discussed in the following section.
Recent Assessments 5: Some Technological Responses to Climatic Changes
In this section we refer only to adjustments that could be put in place
now, since this enables us to parameterize and input them to the linked
models. Vague assumptions about future changes in technology, demand, and
prices are much less easy to specify. The adjustments are of four types:
crop variety, soil management, land allocation, and purchases to supplement
production.
Changes in Crop Variety. Changes in crop variety can be made to respond to
climatic changes. Such problems include changing from spring to winter
varieties, changing to varieties with higher thermal requirements, and
changing to varieties that give less varied yields.
• Change from Spring to Winter Varieties. Our investigations in Canada,
Finland, and the northern USSR indicated that spring-sown crops (e.g.,
wheat, barley and oats) experienced reduced yields under the GISS
projections of future climate because the increased frequency of
moisture stress early in the growing period (see Tables 1 and 3). A
switch to winter wheat or, in some areas, winter rye might reduce the
effects of high evaporotranspiration in the early summer a well as
taking advantage of the longer potential growing season (assuming that
snow cover remained sufficient to protect the crop against winter
kill). In Saskatchewan, the Prairie Farm Rehabilitation
Administration (PRFA) has experimented by switching 5 percent of the
cropped area from spring wheat to winter wheat to assess the effect on
average yield and yield security. The initial work has focused only
on dark brown soils and for a single extreme year (the 1961-type
drought). This indicates that while overall wheat production would be
less than at present in a normal year as a result of this change, it
would be greater in a drought year. The next step is to evaluate the
effects over five or ten years of variable weather to see which mix of
varieties offers the longest aggregate production or, alternatively,
287
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the most stable income over a given period. The PFRA could then
recommend various planting strategies for various farming goals.
* Change to Varieties with Higher Thermal Requirements. A logical way
of exploiting longer and warmer growing seasons at high latitudes is
to use later maturing varieties with higher thermal requirements. In
some cases the yields of present-day varieties such as spring wheat in
northern USSR and early-maturing rice in Northern Japan tend to be
reduced under the GISS climate projections for doubled C02 (see Table
2). However, spring wheat varieties with thermal requirements 50 to
100 GDD greater than present-day varieties exhibit increased yields.
Allowing both for the direct effects of atmospheric COp on plant
photosynthesis and water use and the change in varieties, spring wheat
yields in the Perm regions are a third to a half greater than at
present (Table 1). In Hokkaido, late-maturing varieties of rice (at
present grown in central not northern, Japan) gave yields about 30
percent greater under the GISS scenario than the present early variety
grown in Hokkaido.
• Change to Varieties Giving Less Variable Yields. We know little about
what changes could occur in the interannual variability of temperature
and precipitation. But, even if we assume the same degree of
variability under an altered climate, the effects on crop yields would
be significant; it is possible to test a number of varieties for
stability of yield. Figure 13 illustrates graphically the effects of
the climate projected by GISS on two different varieties (for further
details see T. Horie in Parry 1986).
Changes in Fertilizing and Drainage. Also can be made to respond to climatic
change.
• Altered Fertilizer Applications. The IIASA/UNEP project includes two
types of fertilizer experiments. The first increases levels of
fertilizer application to optimize yields under the climate for
doubled COp projected by GISS. The second varies applications to
maintain, for example, 1980 production levels. Variable applications
of fertilizer to stabilize yields by offsetting the effects of
anomalously cool or warm summers are at present being tested for
feasibility by the Icelandic government (for details, see lakimets et
al. and Bergthorsoon et al. in Parry 1986).
• Improvements in Soil Drainage. Increased precipitation predicted in
the GISS experiment for doubled COp might be expected to cause
increased soil erosion, which might offset the beneficial effects of a
warmer climate and technological improvements. It should be noted
that precipitation may well be considerably exaggerated by the GISS
model. Improvements in soil drainage are therefore tested in the
11 ASA study of the Leningrad region of northern USSR, which indicated
slightly reduced yields, presumably a result of the leaching of soil
nutrients. This effect would have to be weighed against reduced
erosion and more efficient disposal of nitrate pollutants in the
regions to fully assess the consequence of such a measure (see
lakimets et al. in Parry 1986).
288
-------
GISS "2 x C02" climate:
late-maturing variety
en
.*
3
u
GISS "2 x C02" climate:
present variety
Observed climate:
present variety
I I I i I I I
1974
1976
1978
YEAR
1980
1982
Figure 13. Simulated rice yield under present (observed) and GISS "2 x
COp" climate applied to 1974-83 in Hokkaido, N. Japan. Responses to the
doubled CC^ climate of two varieties of rice are shown. From T. Horie in
Parry et al. 1986.
Changes in Land Allocation. Finally, land allocation can be changed to
respond to the effects of climatic change.
• Changes of Land Use to Optimize Production. Because different crops
respond differently to changes of climate and to various levels of
fertilizer application under those climates, any attempt to maximize
output of each crop while minimizing production costs is likely to
identify quite different allocations of land to alternative crops
under different climates. In the central region, European USSR,
experiments for arbitrary increases in mean annual temperature, for
example a 1°C increase, indicate an optimal land use, which increases
the area under winter wheat, corn, and vegetables while decreasing the
allocation to spring-sown barley, oats, and potatoes (Table 1.) This
pattern of land use begins to resemble that at present found further
south in the USSR and points to the value of using regional analogs to
289
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identify possible responses to climate changes, a point we shall
return to later. Broadly similar experiments in Iceland have
investigated the increase in carrying capacity of both improved
grassland and unimproved rangeland, assuming unaltered technology
(carrying capacity increases by two thirds or more under the GISS
projections). Given that inputs are unchanged, estimates show that
increases in carcass weight of sheep could be obtained at the 1980
stocking levels, or alternatively the 1980 capacity levels could be
maintained with reduced inputs (Bergthorsoon et al. in Parry 1986).
• Changes of Land Use to Stabilize Production. Experiments by the PFRA
in Saskatchewan have tested the efficacy of removing marginal cropland
from production as a means of drought mitigation. Wheat crops on this
land tend to be profitable in years of normal or above-normal rainfall
but can cause major losses in dry years. The present work has
identified previously unimproved land brought into wheat production
over 1951-81. This amounts to about 14 percent of all present
cropland. In the experiments this is converted back from wheat to
pasture for beef cattle, and total provincial output from the new mix
of land uses is compared with that from the present land use for a
variety of drought and nondrought years (Williams and Oakes 1986).
EFFECTS ON FOREST ECOSYSTEMS AND TIMBER PRODUCTION
A spatial shift of climatic zones resulting from a change of climate
would, all other things being equal, lead to a spatial shift of vegetation
types. But the rate of response would depend on the rates of migration of the
species. These vary from ten to one hundred meters per year for many cool-
temperate forest species in Europe (Shugart et al. 1986). There is evidence
that considerable changes in the distribution of forests have occurred as a
result of climatic changes in the past. Shugart et al. cite the transforma-
tion from spruce-dominated to jack pine-dominated forests in eastern Minnesota
about 10,000 years ago occurring over at most a few hundred, and perhaps in
less than one hundred years. They also note the effect of smaller climatic
episodes such as that of the Little Ice Age in the prairie-forest border
region of Minnesota where an increase in precipitation caused a reduction in
the frequency of fires, thus encouraging a forest with more large hardwood
trees than the oak forest it replaced. More recently, we may note the effect
of even a small fluctuation such as that of a series of warm summers in
northern Scandinavia in the 1930s inducing a regeneration of the boreal forest
at its northern limit and a measureable advance of the timber line (Shugart et
al. 1986). If we ignore for the present our uncertainties surrounding the
rates of climatic change that might occur as a result of increasing
atmospheric C02 and also the rates of migration of forest species in response
to an altered climate, we can consider the equilibrium locations of forests
that can be predicted for a given scenario of climatic conditions. Emanuel,
Shugart, and Stevenson (1985) have mapped the changes in vegetation as
classified by Holdridge Lifezones that would result from altered temperature
and precipitation values for the Manabe and Stouffer (1980) 2 x C02 climatic
changes scenario. Values from the Manabe and Stouffer experiment, which was
for quadrupled C02, were halved to approximate values for doubled C02.
Comparison of the base climate and doubled C02 maps shows a 37 percent
decrease in the areal extent of the boreal forest, which is replaced at its
southern edge by cool temperate step and to a lesser degree by cool boreal
forest (Figure 14).
290
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•Ill TROPICAL WET FOREST
•MB SUBTROPICAL WET FOREST
SUBTROPICAL MOIST FOREST
TROPICAL DRY FOREST
WARM TEMPERATE FOREST
DRY WARM TEMPERATE FOREST
COOL TEMPERATE FOREST
MOIST BOREAL FOREST
WET BOREAL FOREST
TROPICAL THORN WOODLAND
TEMPERATE THORN STEPPE
COOL TEMPERATE STEPPE
TEMPERATE DESERT BUSH
TROPICAL DESERT BUSH
BOREAL DESERT
TUNDRA
TROPICAL WET FOREST
SUBTROPICAL WET FOREST
TROPICAL MOIST FOREST
TROPICAL DRY FOREST
WARM TEMPERATURE FOREST
T- »•>
DRY WARM TEMPERATE FOREST V*
COOL TEMPERATE FOREST
MOIST BOREAL FOREST
WET BOREAL FOREST
TROPICAL THORN WOODLAND
TEMPERATE THORN STEPPE
COOL TEMPERATE STEPPE
TEMPERATE DESERT BUSH
TROPICAL DESERT BUSH
BOREAL DESERT
TUNDRA
Figure 14. Holdridge Classification of N. America: a) base case b) with
biotemperature increased to reflect climate simulated under elevated
atmospheric C02 concentration. (Emanuel et al. 1985)
291
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More insight into how forests might respond to changes of climate can
probably be achieved by running computer simulations of forest growth,
appropriately validated against independent data, under altered climates. The
general results of the study have been summarized by Shugart et al. (1986) as
follows:
* Slower growth of most deciduous tree species throughout much of their
geographical range;
• A dieback of many dominant trees particularly in the transition
between boreal and deciduous forest;
• An invasion of the southern boreal forest by temperate deciduous trees
that is delayed by the presence of the boreal species; and
• A shift in the overall pattern of forest vegetation that resembled the
pattern obtained from the Holdridge experiments by Emanuel, Shugart,
and Stevenson (1985) and with a time lag of up to 300 years.
Some preliminary studies have recently been undertaken to consider the
economic implications of these kinds of large-scale spatial shifts of forest
types. As in the case of assessing economic impacts in agriculture, the task
is one of using outputs from a general circulation model for doubled C02
experiment with a simple growth model and then using the estimates of changes
in growth and forest area as inputs to an economic model. In the first part
of the study, Kauppi and Posch (1985) correlated the location of the boreal
forest with minimum and maximum effective temperature sum (ETS) require-
ments. They remapped the ETS boundaries for the projected climate and
inferred the northward displacement of the boreal forest. From these maps
Binkley (in Parry et al. 1986) has calculated, country by country, the change
in productive areas as taiga areas become warm enough to support forest
ecosystems and also the increase in growth on extant forest lands (Table 4).
Using these new data, the IIASA global forest sector model, which projects
production, consumption, prices, and trade of sixteen forest products in
eighteen countries on the basis of forest growth, timber supply, processing
facilities, and final demand was solved for a fifty-year projection horizon to
provide estimates of changes in price, harvest, and income from timber
sales. In general, timber producers in northern regions benefit by the warmed
climate, although the size of the benefit is small except in Finland. Income
from timber sales declines for all producing countries except Finland and
Canada, as a result of substantial price falls. To illustrate, while the
quantity of coniferous sawlogs harvested in Sweden increased by 24.5 percent,
prices fell by 14.9 percent and income by 7.6 percent. For Finland the
figures were +63.2, -8.6, and +22.4 percent, respectively. Full details are
reported in Binkley.
292
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Table 4. Impact of 2 x CCU on forest growth and area.
| Growth
Finland
Sweden
Norway
USSR
Canada
East
West
Increase in
forest area (%}
25.0
16.7
0.0
85.0
22.2
36.8
Current3
3.15
(3'l8)b
3.90
(3-01 )
2.51
(2.40)
1 .82
'
1.89
(1 .60)
2.21
(2.13)
2xC02a
5.45
5.90
5.63
3.20
4.47
3-53
% increase
73.0
51.3
124.3
75.8
136.5
59.7
m-vha/yr, based on the Kauppi
temperature data interpolated on
Shutz and Gabes (1971 ).
and
a 4°
Posch
x 5°
(1986) growth model and
latitude/longitude grid by
b: (), Estimates of current growth, m'/ha/yr (Binkley and Dykstra 1985, Table
23.5).
RESEARCH PRIORITIES
We summarize in Figure 15 and its accompanying notes the direction that
future research should take. Four main needs emerge. First, we require more
specific and user-oriented information regarding climatic change (its
likelihood, nature, magnitude, areal extent, duration, and most important,
rate of onset). This information needs to be expressed in terms readily
applicable to the user (and often as derived parameters such as date of first
and last frost, days of heat stress, etc.), which would enable agroclimatic
measures, such as length of growing season, to be more readily assessed. It
is also important that information on variability be available to provide
estimates of possible changes in those extreme conditions that we have seen to
be important in agricultural decision-making.
Second, an important path of climatic impact on the most climate-
sensitive sectors of our society (farming, fishing, and forestry) is an
indirect one, i.e., they occur through changes in other physical systems (soil
chemistry, and ocean currents, agricultural pests and diseases, and their
vectors). Although we have barely begun to grasp these interactions, they
clearly have a major influence on some production systems. The collapse of
the Peruvian anchovy fishery as a result of the 1972 El Nino is one example.
Probably more widespread is the effect of climatic conditions on disease.
Outbreaks of many plant diseases (such as potato blight, wheat rust, etc.)
are triggered by specific weather conditions. Climatic changes that affect
the frequency of these conditions could alter the incidence of such outbreaks.
293
-------
c >
O W
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a
6)
CK
L.
a
c.
10
o
a
w
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Natural
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. 1
tnergy/
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T .
[First-order impacts)
1
Agriculture
en
c
a
o
Impacts at enterprise level
(e.g. firms, farms etc..
Downstream effects at
regional & national level
Figure 15. Some Research Priorities for Climate Impact Assessment:
1) More appropriate data
2) Better understanding of relationships between climate and changes
in other physical systems
3) Better understanding of first-order impact
4) Greater precision in tracing downstream effects
5),6) Greater precision in simulating impacts at enterprise and regional
levels. Better understanding of
7) Perception of effects,
8) Adaptive responses at enterprise level
9) Strategy formulation at regional, national, and international
levels (Parry 1986).
294
-------
Furthermore, we need to specify with greater precision the interaction
between climate and other resources in the primary sector, by modeling
empirically or by simulation crop-climate and timber-climate relationships.
It should then be possible to trace, with greater confidence, the downstream
effects of these first-other impacts on other sectors of economy and society,
by reference to a hierarchy of the three types of models we have considered:
climatic, impact, and economic.
Finally and, perhaps most important, we need to explore in greater detail
the range of technological and policy adjustments available in agriculture in
order to evaluate their efficiency in mitigating negative impacts or
exploiting new options offered by changes of climate.
REFERENCES
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ecosystems: synthesis of present knowledge. Chichester: Wiley.
Dickinson, R.W. 1986. The climate system and modeling of future climate. In
The greenhouse effect, climatic changes and ecosystems: synthesis of
present knowledge, eds. Bolin, et al. Chichester: Wiley.
Doornkamp, J.C., K.J. Gregory, and A.S. Burns. 1980. Atlas of drought in
Britain, 1975-76. London: Institute of British Geographers.
Edwards, C. 1978. Gambling, insuring and the production function.
Agricultural Economics Research. 30:25-28.
Emanuel, W.R., H.H. Shugart, and M.P. Stevenson. 1985. Climatic changes and
the broad-scale distribution of terrestrial ecosystem complexes.
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Fukui, H. 1979. Climatic variability and agriculture in tropical moist re-
gions. In WMOProceedings of the World Climate Conference. Geneva, 12-
13 February 1979. Geneva:WMO.
Hare, F.K. 1985. Climatic variability and change. In Kates et al.
Kauppi, P., and M. Posch. 1985. Sensitivity of boreal forest to possible
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Lamb, H.H. 1981. An approach to the study of the development of climate and
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M.J. Ingram, and G. Farmers. Cambridge: Cambridge University Press.
Lamb, H.H. 1982. Climate, history and the mordern world. London: Methuen.
Manabe, S. and R.J. Stouffer 1980. Sensitivity of a global climate model to
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McGovern, T.H. 1981. The economics of extinction in Norse Greenland. In
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McKay, G.A., and G.D.V. Williams. 1981. Canadian climate and food production.
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Parry, M.L.
Archon.
1978. Climatic change, agriculture and settelment. Dover:
Parry, M.L. 1985. The impact of climatic variations on agricultural margins,
In Climate impact assessment, eds. R.W., Kates, et al. Chichester:
Wiley.
Parry, M.L. 1986. Some implications of climatic change for human
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Parry, M.L. 1985. Potential CC^-induced climate effects on North American
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Shugart, H.H., M.J. Antonovsky, P.G. Jarvis, and A.P. Sandford. Assessing the
response of global forests to climatic change and direct effect of
increasing C02. In The greenhouse effect, climatic changes and
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Chichester: Wiley.
Solomon, A.M., and H.H. Shugart. 1984. Integrating forest stand simulations
with paleoecological records to examine the long-term forest dynamics.
In State and change of forest ecosystems. Indictors of current research,
ed. G.I. Agren. Report 13, Uppsala, Sweden: Swed. Univ. Agricu. Scie.,
Dept. of Ecology and Environmental Research.
Wigley, T.M.L. 1982. Personal communication, quoted by Jager, J. (1983)
Climate and energy systems. Chichester: Wiley.
Wigley, T.M.L., M.J. Ingram, and G. Farmer, eds.
Cambridge: Cambridge University Press.
1981. Climate and history.
Wigley, T.M.L., P.D. Jones, and P.J. Kelly. 1986. Warm world scenarios and
the detection of a CO^ induced climatic change. In The greenhouse effect.
climatic changes and ecosystems, synthesis of present knowledge, eds. B.
Bolin et al. Chichester: Wiley.
WMO. 1986. Report of the International Conference on the Assessment of the
Role of COp and of Other Greenhouse Gases in Climate Variations and
Knowledge, Associated Impacts, WMO, No. 661. Geneva: WMO.
Warrick, R.A. 1984. Possible impacts on wheat production of a recurrence of
the 1930s drought on the U.S. Great Plains. Climatic Change. 6:27-37.
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Warrick, R.A., and M. Bowden. 1981, Changing impacts of drought in the Great
Plains. In The Great Plains: perspectives and prospects, eds. M. Lawson
and M. Baker. Lincoln, Nebraska: Nebraska University Press.
Warrick, R.A., R.M. Gifford with M.L. Parry. 1986. C02, climatic change and
agriculture. In The greenhouse effect, climatic changes and
ecosystems: synthesis of present knowledge, eds. Bolin et al.
Chichester: Wiley.
Williams, G.D.V., and W.T. Oakes 1978. Climatic resources for measuring
barley and wheat in Canada. In Essays on meteorology and climatology,
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3. Alberta, Canada: University of Alberta, Studies in Geography.
297
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The Water Resource Impact of Future Climate
Change and Variability
Max Be ran
Institute for Hydrology
Wallingford, Oxfordshire, United Kingdom
ABSTRACT
An altered availability of water will be one of the more obvious impacts
of climatic change. This paper describes methods and models that have been
used by hydrologists to try to forecast the effect of climatic change on the
availability of water for human consumption, irrigation, power production,
effluent dilution, and navigation. This assessment requires two steps; the
first concerns impact on hydrological variables such as annual runoff; the
second is required to assess the impact in human terms and expresses the
hydrological variables in terms that quantify the exploitable fraction of the
runoff.
This paper surveys the literature on both parts of this process. Causal,
conceptual, and empirical models have been used to translate GCM and analogue
climate scenarios into hydrological terms. Conceptual and empirical models
have been applied to the further task of modeling the consequences to water
resource outputs, particularly the performance of storage reservoirs. In an
alternative approach an empirical model based upon the storage yield diagram
is used to quantify the impact on reservoir reliability of given changes to
the mean and variability of reservoir inflows. To extend this approach to
accommodate climatic rather than hydrological change, the use of comparative
hydrology techniques is advocated in which a future climate at a point is
likened to the current climate elsewhere.
The advantages and shortcomings of the various approaches are enumerated,
and these give rise to a list of research suggestions and strategies for
future impact studies. The few papers and reports devoted to the subject
clearly, indicate that too little attention has been given to the problem in
the past. Interest has begun to increase since the scientific consensus on
climatic change appears to have centered on a global warming induced by
radiatively active gases. International organizations have an important role
in coordinating the necessary effort.
299
-------
HYDROLOGY, WATER RESOURCES AND CLIMATE
Scope of Paper
This paper consists primarily of a survey of the literature on
hydrological and water resource impacts of climatic change. The paper
comments on the status of the methods and suggests further necessary
research. Water resource impacts are clearly a relatively unworked area:
only twenty-one papers and reports have been uncovered that concern themselves
with future changes.
However, hydrologists have not ignored the climatic change issue and
considerable literature exists on paleohydrology in which actual and surrogate
hydrological records are used to detect past climatic fluctuations.
Hydrologists also contribute to the general study of climatic change through
their mathematical descriptions of hydrological process in global atmospheric
circulation models (GCMs). These two topics are not covered in any detail in
this survey.
The following subsections distinguish hydrology from water resources and
describe hydrological measures that may be used to quantify water resource
problems. The section on hydrological modeling for impact studies is
concerned with the types of climate-hydrology transfer functions that have
been used in studies of impacts on catchment response. Readers unaccustomed
to hydrological modeling may wish to limit their reading to introductory and
closing paragraphs, i.e., postscripts. The section on sensitivity of
reservoir reliability to climate change deals with those few papers that focus
directly on water resource impacts, in each case through its effect on
reservoir performance. The section on research requirements lists
requirements revealed by this survey and describes the role of international
organizations in coordinating climate impact research.
The Distinction Between Hydrology and Water Resources
The subject areas of meteorology occupy neighboring segments of the
familiar water cycle diagram. Hydrology is concerned with the near-land phase
of the cycle and follows the progress of moisture from vegetation canopy
level, through the soil, into aquifers and watercourses, while losing sight of
it as it enters the sea. Analytical techniques span a range of complexities
reminiscent of the zero to three dimensional atmospheric models of
meteorology. There is also a branch of the science equivalent to climatology
in which the hydrological regime is characterized statistically through
measures of the mean and variability of such elements as flood, drought,
aquifer state, or soil moisture deficit.
This climatological treatment rather than the description of processes is
of most interest to the water resource planner. Until recently the planner
and the hydrologist have not been distinct but increasingly the two have
diverged as water resource science has introduced techniques drawn from other
disciplines such as economics and administration. The planner's attention is
focused strictly on the fraction of the water that is capable of
exploitation—most critically for human consumption, but also for hydropower,
cooling, effluent disposal, irrigation, navigation, and amenity. Thus while
all natural water is of hydrological interest, only water that is available at
300
-------
the time and place required, and in suitable quantity and quality, is of water
resources interest.
It is helpful to imagine the hydrological system as a transfer function
whose outputs are forced by input meteorological variables. Similarly it is
useful to think of water resources as a system in which hydrological inputs
are transformed to water resource outputs. Since water resource projects tend
to be site-specific, formulating general relationships between the inputs and
outputs that encompass all projects is not possible. However, a limited
number of characteristic hydrological relationships tend to be influential in
determining the properties and performances of water resource schemes. By
substituting such relationships for output from climate-hydrology-water
resource models quantifying the water resources impact of climatic change
becomes possible. The following subsection describes the most important of
these characteristic hydrological relationships and considers three classic
water resource problems.
Examples of Water Resource Variables
Water Storage. A very common instance is urban water supply from a local
catchment. Often an incomplete match between availability and need occurs in
that, although in annual average terms the attachment runoff may exceed the
demand seasons and occasionally entire years occur during which the river
cannot meet the demand. A reservoir stores excess water from periods when
runoff exceeds demand in order to meet the town's requirements during such
periods of deficit. The relationship characteristic of this problem is the
storage yield diagram Figure 1 which shows the reservoir volume needed to
supply a given continuous yield with a given level of security, here expressed
as percentage failure rate.
Flood Risk. A second case concerns flood-prone land alongside a river. An
upstream detention reservoir can contain excess water or the river's carrying
capacity can be increased. The objective in either case is to increase the
value of the land by reducing flood incidence. Peak discharges and hydrograph
volumes are analyzed statistically as an initial step in the design process of
devising a scheme that maximizes the margin of benefit over construction
costs. Figure 2 shows the flood frequency curve which is the characteristic
relationship for this class of problem.
River Abstraction. Many rivers receive and convey waste, so knowledge of
their diluting capabilities is important. Interest here focuses on the
proportion of time that the river flow drops below some threshold level
representing the limiting condition for self-purification. The flow duration
curve Figure 3 is the characteristic relationship for this problem. The same
relationship applies to many other problems where water is abstracted directly
from rivers such as run-of-river hydropower, and small irrigation and water
supply projects.
In all three cases the high and low flows, i.e., hydrological extremes,
determine the water resource decision. These examples are deliberately
simplified—real cases mix elements from each. They may span more than single
sources and demand points, and decisions often must take account of factors
outside the domain of scientific hydrology. Nevertheless, for purposes of
climatic change impact studies these examples and their characteristic
relationships can substitute adequately for water resource decision variables.
301
-------
100.0
10.0
Eh
o
'o
1.0
0. 1
95
90
85
80
70
60
50
40
30
20
99.9 98 90 70 50 30 10 2 1.00.5
PERCENTAGE OF YEARS REQUIRING ANNUAL MAXIMUM GREATER THAN Y
Figure 1. Storage yield diagram. The reservoir storage corresponding to
a given constant demand and risk of failure can be read from i;he diagram.
Alternative representations show failure risk as parameter (McMahon and Mein
1978).
302
-------
• 58/2 Wy* it Bclmont
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o
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2
, ,
0
,
5
,
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,
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i i i
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Figure 2. Flood frequency curve. The graph shows the average recurrence
interval between exceedances of the given peak discharge. It can be drawn for
flood volume as well as peak.
1000
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i DAr
10 10 30 40 50 80 70 80 9} 98 MM
PERCENTAGE OF TIME DISCHARGE EXCEEDED
Flow duration curve. The graph shows the proportion of time
Figure 3.
the flow in the river exceeds the given level.
distribution function of flows.
It is the complement of the
303
-------
START
INPUT Program control parameters
INITIALIZATIONS
Micrometeorological characteristics of control site
Characteristics of canopy to be modeled
Characteristics of soil moisture storage
INPUT
Standard meteorological data at control site for hour
METEOROLOGICAL MODEL (Control Site)
Computes balance of momentum, energy, and water; profiles of wind,
temperature, and humidity, and resistances to turbulent transfers
Computes Geostrophic Wind
Computes wind speed, temperature, and humidity at reference height
MULTILAYER CROP MODEL
Computes momentum balance below-canopy profiles of wind,
temperature, and humidity; above canopy turbulent resistances; within-
canopy profiles of wind, temperature, and humidity, soil heat flux, and
thence complete energy balance of crop
Computes water balances of crop and soil moisture
giving interception, transpiration, throughfall stemflow, etc.
ADVANCE
ONE TIME STEP
ACCORDING TO STATE
OF CANOPY WETNESS
ENDOF
SIMULATION
PERIOD
HYDROLOGICAL MODEL
Updates soil moisture storage
Figure 4. Illustration of water balance of small vegetated catchment
(Lockwood 1985) physical model tends to concentrate attention on the crop
and/or soil system.
304
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HYDROLOGICAL MODELING FOR IMPACT STUDIES
Types of Hydrological Model
Models of the land phase of the water cycle vary considerably in their
complexity and in their approximation to physical reality. Although
categorization boundaries may be blurred, four types of model are recognized:
• At the leading edge are causal models which closely replicate physical
processes within small segments of the cycle such as moisture flux at
vegetated surfaces, below ground level, and in river channels.
• Models that operate at the catchment or aquifer unit scale—the rele-
vant one for water resource studies—tend to lump processes into
conceptual relations (the hydrological analogue of parameterizing
sub-grid processes in GCMs).
• The third level of process simplification includes empirical models
that exhibit little direct dependence on physical principles. Often
they consist of statistical associations, e.g., regression equations,
or of convolution relationships between input and output variables.
• The simplest type of model is the water balance. Although apparently
based upon a physical principle—the conservation of mass—dynamical
aspects of the processes which can be important at the annual time
scale are neglected.
All four types of model have been used to assess the influence on runoff
of climatic change and examples from the literature follow. In addition,
models of the second and third type have been applied to water resource
sensitivity studies and their application is described below. Although not
directly related to the problem of impacts, there is considerable current
interest in incorporating causal models, especially of soil moisture
processes, within the structure of modern GCMs (Bauer et al. 1984; Brandyk,
Dooge, and O'Kane 1985; Carson 1981; Hansen et al. 1983; Hunt 1985; Mintz
1981, 1984).
Causal Models
It is helpful here to consider the hydrological phase of the water cycle
as a system whose inputs are precipitation and evaporation and whose output is
river runoff. The inputs to this system therefore interface with state
variables of climate models. The physics of the processes in the immediate
vicinity of this interface are reasonably well understood. However, with very
few exceptions, "downstream" processes are not readily expressible in physics
terms; consider for example the complexities of the passage of a particle of
water through vegetation toward a watercourse. As a consequence, models that
adopt the more physical route describe processes on the plot, or even leaf,
scale. Figure 4 shows one example, the MANTA model (Sellers and Lockwood
1981; Lockwood 1985), which closely replicates energy and moisture fluxes
between ground and canopy level but devotes much less attention to the details
of moisture movement within the "Hydrological Model" box.
305
-------
Nemec (1983) following Lettau and Baradas (1973) has termed the output
from this type of model as "climatonic runoff," and contrasts it with measured
runoff which is the integration of the output of many differing spatial and
temporal units through a complex of hillslope, subsurface, and channel
processes.
The Briggs Model. An estimate of the impact of COp doubling on runoff was
made for the European Community area by Schnell (1984). His approach was to
adapt the rain and evaporation component of the Briggs biomass potential model
in which runoff is computed as the rainfall remaining after evapotranspiration
and soil moisture replenishment. The British Meteorological Office GCM
(BMO-GCM) provided the precipitation and temperate change inputs. Schnell
recognizes the distinction between measured catchment runoff and the value
generated from the model which is labeled "runoff potential." Figure 5, which
maps the predicted change in average runoff due to COp doubling, reveals an
overall north to south trend in runoff reduction.
Evaporation Impact. Shuttleworth (1983) contemplates the use of causal models
to describe the response of evaporation to changes in climate variables. He
sounds a warning note to atmospheric modelers who incorporate land-surface
interactions but neglect the certainty that vegetation will change in response
to changes in precipitation and temperature. A quantitative basis for
describing transitions between biomes that occupy adjacent climatic niches is
needed and this limits predictions to small-scale or short-term climate
change.
Conceptual Models
Conceptual models combine features of physics-based and empirical models
of the land phase of the hydrological cycle. They are the workhorses of many
water resource investigations because they incorporate sufficient physics to
answer "what if" questions about change of land use, and they are flexible
enough to link to mathematical models of water resource schemes.
Meteorological time series are input to the models which yield hydrological
time series, usually catchment runoff, as output. When the hydrological
output is in turn put into the project description, then water resource
decision variables, for example, a cash flow, can be generated from climatic
inputs. Schaake and Kaczmarek (1979) suggested the use of models of this type
to investigate climate impacts and two examples of their use in hydrological
sensitivity tests are described below.
Sacramento Model. Figure 6 shows the algorithmic arrangement of the
Sacramento model used by Nemec and Schaake (1982) in their studies of climate
change impact. Instead of the detailed treatment of moisture and energy
fluxes of causal models, the "boxes" of conceptual models contain relatively
simple "step, branch, and ramp" formulations. The Sacramento model has been
refined by the U.S. National Weather Service to serve nationally as a river
flow forecasting tool. As a consequence it is structured to emphasize
processes that control hydrograph geometry. Most of its parameters are
determined from field experience and the model is calibrated to match recorded
flows by adjusting the values of a few dominant parameters controlling the
runoff response.
306
-------
Q
BIO 8MO
Aunol t « mm /a
ISO BM01
Figure 5. Generalized change in the runoff potential (mm)
of western Europe following CC^ doubling.
Figure 6. Flow chart for Sacramento model.
307
-------
Results concerning runoff sensitivity only are discussed here: water
resource sensitivity is included in the next major section. The Sacramento
model was calibrated on the records of three rivers, two in the United States
and an influent stream to Lake Victoria in the Upper Nile basin. Baseline
statistics, primarily long-term mean runoff, were extracted from the model's
output time series (see Table 1). The authors then considered a range of
altered climate scenarios ranging from a 25 percent decrease to a 25 percent
increase in rainfall, and from a 4 percent decrease to a 12 percent increase
in potential evaporation (supposed equivalent to a 1°C decrease to a 3°C
increase in surface air temperature). These adjustments were affected by
scaling the input series, for example, by multiplying each rainfall value by
1.25.
Table 1. Percentage Change in Runoff from Base Due to Climatic Forcing
River
Pease
Leaf
Nzoia
Precip.
Base
(mm)
540
1314
1233
Runoff
Base
(mm)
11
409
169
Runoff Ratio for Scenarios
+25, +12
+ 154$
+ 49T«
+ 170$
-25. -4
-67%
-53%
-15%
Taken from Figures 4 and 5 of Klemes and Nemec (1985) or inter-
polated from the original paper. First figures of scenario headings
relate to the precipitation change from base, the second to
evapotranspiration change.
The authors conclude that the changes in runoff fall outside the range of
modeling error of the rainfall runoff process. The experiment is said to
reveal the dominance of changes to precipitation and the extreme sensitivity
of arid area catchments.
Klemes and Nemec (1985) subjected Nemec and Schaake's results to detailed
statistical scrutiny. The principal concern appeared to be the statistical
significance of the change, that is, whether or not the forecast runoffs lie
outside the range of fluctuations that occur naturally under the current
climate. By random sampling from a log-normal parent it was determined that
changes in runoff due to precipitation changes of less than about 15 percent
to 20 percent could not be distinguished from random fluctuations in the base
record. This result is of course dependent on the record length used.
SHOLSIM Model. Aston (1984) considered the effect of C02 doubling on the
hydrology of the study area in New South Wales, Australia. Although GCM
predictions indicated no change in precipitation for the area, Aston
anticipated an important impact due to the direct effect of C02 enrichment on
vegetation—an increase in stomatal resistance with consequent reduction in
transportation. Evidence presented in the paper shows that in many plants a
308
-------
doubling of COo concentration can lead to more than a two-fold increase in
resistance. The scenario studied is for a doubling in resistance. An initial
estimate based upon a combination equation for evaporation pointed to an
increase in (climatonic) runoff of 85 percent.
Aston then pursued this finding through a conceptual model, SHOLSIM, of a
417 km catchment. This model uses a much-simplified description of the
evaporation process in which the overall effect of the resistance change was
represented by doubling the gradient of the ratio of actual to potential
evapotranspiration (AE to PE) with soil moisture content, and also by reducing
the limiting rate at which transportation can occur. The result of the second
influence amounted to a nearly 60 percent increase in runoff in an average
year; the two influences together cause the modeled catchment runoff to
increase by 90 percent, very much in accord with the causal model result.
Postscript on Conceptual Models. At first sight, the two studies are not easy
to compare as the first is strictly an exercise in model sensitivity, while
the second traces the effect of a specific climatic scenario. Aston
considered the changes due to the direct effect of CC^ enrichment to equate to
an approximate halving of PE, well outside the nominal range considered in the
Sacramento model simulations. However, Klemes and Nemec (1985) in their
analysis of Nemec and Schaake's results revealed very strong linearities
within the simulated series. Extrapolating (perhaps unreasonably) from these
one finds a 1 percent increase in runoff for a 1 percent decrease in ETP for
the Leaf river model, and by about twice this amount for the Pease and Nzoia
river cases. This suggests that SHOLSIM and Sacramento model predictions are
in reasonable accord.
It is important to remember that these results relate to model, not
prototype, sensitivities. A good fit to the output series within the
calibration period is no guarantee of a continued close match beyond it, nor
of the correctness of the physical principles embodied in the model. Likewise
statistical significance of the difference between the runoff records from two
climate scenarios do not prove the truth of either.
However, the writer is unclear on the relevance of Klemes' and Nemec's
(1985) requirement for establishing significance. When searching for
discontinuities in past records it is clearly essential for statistical
significance to be established. But in a prognostic study, it is beyond
contention that changes in input create changes in output and changes, no
matter how small, must be regard as real effects. In this context, lack of
significance provides an interesting sidelight on the limitations imposed on
an imaginary analyst searching for evidence of change in the past data by
short records but serves no useful function in prognosis studies. Here the
contentious issue is whether the model continues to replicate runoff correctly
through a climatic change.
Neither Nemec's nor Aston's studies considered the compatibility of the
precipitation with the hypothesized evaporation pattern, nor was it allowed
that under the altered climate the rainfall may occur in different seasonal or
storm patterns. Catchment response to intense periods of rainfall tends to a
proportional rather than the subtractive response pattern implicit in the
"bucket" model approach (see the section on water balance models).
309
-------
Aston's study is more immediately helpful to planners in that it follows
the logic of the specific climate change as far as current knowledge permits,
although by substituting "resistance doubling" for "C0? doubling" some
important issues are sidestepped. Contrary, or at least moderating, views on
the direct CC^ effect have appeared in the literature (e.g., Kramer 1981,
quoted in Woodwell 1985) with the following implications and caveats:
• Plant species vary greatly in their reaction to CC>2 concentrations and
it is reasonable to suppose that a plant mix would eventually develop
that would exploit available resources
• The impact reduces as the plant matures
• Catchments are not fully vegetated
• Published experience relates to ideal conditions, e.g., greenhouses,
where other stresses do not impinge
• "Greenhouse gases" other than CC>2 that may be responsible for climatic
warming are not beneficial to plant development
• Nutrient availability and light conditions also control growth, and
stomatal resistance is but one dependent state variable within a
complex physiological process (Jones 1984).
Empirical Modeling
This class of model includes some that can operate in the time domain
such as regression versions of conceptual models and others that consist of
associations between average values but imitate in an empirical fashion the
causal models discussed above.
Time Series Regression Approach. Nemec and Schaake (1982) reported that in
1979, two researchers named Beard and Maristany calibrated a regression
relationship between seasonal runoff and climate data. They then scaled the
precipitation and temperature input data to study the influence on runoff.
The conclusions they reached are stated to be comparable with those quoted by
Nemec and Schaake for their conceptual modeling approach. This can be
explained by Klemes'and Nemec's (1985) observation of strong linearities in
the monthly simulated runoff such that, although ostensibly nonlinear
(Figure 6), the Sacramento model behaves as a regression equation with respect
to its primary inputs.
Analysis of Historic Records. Palutikof, Wigley, and Lough (1984) used
observed temperature, pressure, and precipitation data to investigate possible
spatial and seasonal distributions of climatic change. Noting that the effect
of the CC>2 increase is hemispherical warming, they argue that some
appreciation of its effect could be gained from the contrast between the
coldest (1901-20) and the warmest 20-year period (1934-53) in this century.
This type of analysis has been extended by this writer to consider runoff
from major European basins. Table 2 shows the difference, warm-cold, between
catchment rainfall and runoff.
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Table 2. Seasonal Rainfall and Runoff Differences for Some European Basins
(Difference - Standard Deviation Units)
Season
Winter P
Q
Spring P
Q
Summer P
Q
Autumn P
Q
Thames
-0.3
+0.1
-0.2
-0.2
-0.6
-0.6
+0.8
+0.1
Loire
+0/2
0.0
-0.7
-0.4
-0.2
-0.2
-0.2
-0.1
Rhone
+0.3
+0.1
-0.7
-0.8
0.0
-0.5
+0.5
+0.2
Danube
0.0
-0.1
-0.5
+0.1
-0.1
-0.3
-0.1
-0.2
Elbe
+0.3
-0.4
0.0
0.0
+0.1
+0.1
+0.4
+0.1
Oder
-0.4
-0.2
0.0
0.0
+0.2
0.0
+0.3
+0.1
Vistula
0.4
-0.2
+0.1
-0.2
0.0
-0.5
+0.3
0.0
The rainfall values (P) were obtained by eye interpolation from
maps presented in Palutikof, Wigley, and Lough (1984). The runoff
(Q) data were prepared by the writer. The differences are
expressed as a multiple of the seasonal standard deviation.
Total agreement between rainfall and river flow should not be expected
because the latter is influenced by antecedent climatic conditions. However,
agreement in terms of the sign of the change is good; only four of the twenty-
eight show a reversal, and this is reduced further if a half-season lag is
incorporated into the comparison. Apart from a small autumn increase, runoff
appears to have reduced during this historical hemispherical warming; in the
standardized units shown on Table 1, this was most marked in the spring and
summer, but in absolute units the winter reduction was more important.
This approach does not by itself provide quantitative estimates of
climate impacts. The most immediate question concerns the extent to which
non-CX^-induced warming can be represented, even in muted form, by contrasts
between historic sequences in which COp warming presumably played little
part. Some support comes from the GCM findings of mid-latitude cooling and
precipitation reduction (see Section 6.3.4 of Wigley, Jones, and Kelly, in
press).
Another question of interest not directly answered by the approach is
what fraction of the total C^-induced movement is represented by this
historic change? In terms of the hemispherical temperature change the
historical warming represented no more than 20 percent of the lower bound
estimates of the C^- induced movement. The runoff reductions are very
variable—11 mm in the Thames and 48 mm in the Rhone—overall of the order of
10 percent of the values shown in Figure 5.
Empirical Evaporation Model Approach. Cohen (1986) computes net runoff from
the 766,000 km catchment area of the Great Lakes for current and double (X>2
conditions. The heart of the model is an empirical formula, a modified form
of the Thornthwaite model, from which monthly mean evaporation may be obtained
from temperature and latitude. A soil model is also included from which
311
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"climatonic" runoff is computed and then calibrated to accord with measured
runoff.
Temperature patterns from two distinct GCMs (GISS and GFDL) were used to
provide alternative sets of inputs for the Thornthwaite model. Some 32
percent of the catchment area consists of lakes, so open water evaporation is
of great importance. Alternative wind scenarios had to be superimposed on the
GCM results. The effect of C02 doubling varied between a 15 percent and 21
percent reduction in runoff with current or GCM generated winds for the
different models. If a reduced wind speed was allowed, the runoff reduction
was diminished to only 4 percent.
Cohen notes the seasonal differences but annual similarity between the
results from the two models. Uncertainties regarding the future windfield
over the lakes and lack of information on annual variability preclude any but
very generalized conclusions about consequential water resource impacts.
Postscript on Empirical Models. Close inspection of the empirical procedures
may leave an impression of "clutching at straws" by the authors. However, an
analysis of their weaknesses reveals few that do not equally afflict the
ostensibly more "respectable" causal and conceptual approaches. Those that
can yield a time series, the regression, and Cohen's approaches have the
advantage that they can provide inputs to water resource studies although in
the regression case the series will differ from the base series in a purely
linear fashion, a very unlikely eventuality.
Water Balance Models
The basic water balance equation is:
Q = P - E
where Q is runoff, P is precipitation, and E incorporates evaporation and
other "losses." A few authors have used this relation to either directly or
in modified form quantify the impact on Q of climatic change acting through P
and E.
Average Rainfall Runoff Relations. Stockton and Boggess (1979) made use of
relationships for predicting annual average losses from temperature and
precipitation that had been derived by the U.S. Geological Survey (USGS).
They investigated the effect on runoff of a GCM predicted 2°C temperature
increase and 10 percent precipitation decrease across the United States. The
implied sensitivities were checked by Revelle and Waggoner (1983) using an
interannual regression based estimator of the sensitivity of the Colorado
River annual runoff at Lea Ferry to those same changes. The agreement between
the approaches was quite good; 40 percent reduction by regression compared
with 44 percent by the earlier method. Over the entire study area with
average precipitation of 30 cm and 4°C average temperature, the expected
diminution in runoff is 35 percent. The most severely affected areas are
those with lower rainfall and higher temperatures (see Waggoner, Volume 3).
Transpiration Effect. The conclusions of Revelle and Waggoner were questioned
by Iso and Brazel (1984), who disputed the applicability of the USGS empirical
relationships in a CC^-enriched environment. When the effect of reduced
312
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transpiration (conceptual models section) was allowed for the average 41
percent runoff reduction on five study basins predicted by the original method
became a 42 percent increase. The authors list shortcomings in their
analysis, though for the most part shared by the original analysis, and
conclude with a salutory phrase that "plausible additions to state-of-the-art
model studies of the COo problem can dramatically alter current perceptions of
future consequences."
Simple Water Balances. Wigley and Jones (1985) used equation 1 to investigate
the representativeness of the apparently differing results quoted above as
well as those of Rind and Lebedeff (1984) and Aston (1984). This approach
invokes differential calculus to derive the proportional change in runoff,
AQ/Q, due to a given proportional change in precipitation, AP/P, and
evaporation, AE/E. The large proportional increases quoted by Idso and Aston
were shown to occur only in regions where P-E is small; in more temperate
situations the rainfall change dominates and runoff can be expected to
reduce. The approach has been extended by Glantz and Wigley (in press) who
separate the contribution of deep infiltration loss from the evaporation
terms. In the case where precipitation change dominates, the amplification
factor between runoff and rainfall change is given as the reciprocal of the
runoff coefficient, i.e., P/Q. In general the results indicate greater
sensitivity than those predicted by Stockton and Boggess (1979).
Non-subtractive Models. The present writer has investigated the source of the
difference between Wigley's and Stockton's conclusions. It was suspected that
the main cause must be the imposition of a purely subtractive formulation for
runoff formation in equation 1. Examination of observed catchment precipita-
tion and loss values reveals tendencies such as those shown on Figure 7 for
Cypriot rivers. The reduction in P-Q as Q increases can be interpreted as a
transition from a proportional response to rainfall—runoff coefficient—to a
subtractive response—constant losses.
The United States Soil Conservation Service (USSCS) model provides a
suitable functional form for this type of response as it permits the runoff
coefficient to vary according to the state of a notional storage. Although
originally intended for "event" analysis the USSCS model can be modified for
use with annual rainfall and runoff data.
Q = (P-I)2/(P+S-I)
Parameter I represents initial abstraction and parameter S can be thought of
as a maximum evaporation loss such as would occur if water supply were not
limiting. A good fit to the Cypriot data of Figure 7 is achieved with S = 51
= 1350 mm.
Consider first the case of the simple water balance model of equation 1
with P = 600, E = 535, and Q = 65 mm. The runoff ratio is therefore 0.11,
which, as explained above, gives rise to a nine-to-one amplification in runoff
over rainfall change. Because equation 2 is nonlinear, no simple or general
relationship exists between the sensitivity of an individual year to a given
climatic adjustment and the average over all years. For illustrative
purposes, however, it is sufficiently accurate to assume that the effect on an
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1000 ••
E
8OO-
flt
o
600-
3
e
•£ 400-
o
|
u
"3
o
200-
Xeropotamos
~ Kouri9
~ Zyghos
~ Dhiarizos
200 4OO 6OO 800 1OOO
Catchment Annual Rainfall mm
1200
14OO
Figure 7. Rainfall/catchment loss diagram for rivers draining the
Troodos mountains, Cyprus. This pattern is typical of semi-arid regions where
annual rainfall is seasonal and varies from 300 to 1000 mm.
314
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individual year experiencing average rainfall will represent the average over
all years. Taking increments of equation 1 gives
AQ 2P(1-yei/ep) P(1+Uyei/ep)
Q " (P-I) + (P-f-41)
where y is the ratio of I to P and ei and ep are relative changes in I
and P. With P = 600 as before equation 3 yields an amplification factor
between runoff and precipitation change of 3.3, very much smaller than that
given by the purely subtractive model of equation 1. Under the runoff
relation of equation 2 the amplification is controlled by \i rather than by
the runoff coefficient.
Postscript on Water Balance Models. The use of time averages and simple
formula have the advantages that they can be easily calibrated against
observed data. Nevertheless, little agreement exists between the results
obtained by the various approaches. The disparities are as much due to
differences in mathematical structure as to the uncertainties that accompany
extrapolation to a different climatic regime. This was demonstrated by
contrasting a subtractive and a partially proportionate model. It is
significant that as well as equation 1 many other models, implicitly or
explicitly, employ a formulation in which runoff appears as a residual from
rainfall. This property is shared also by the structure of the Sacramento
model (Figure 6) which may therefore also be expected to exaggerate the impact
on low-runoff catchments. This writer also cannot agree with Glantz and
Wigley's structure that extra caution is required "in accepting
results ... if these results appear to be at odds with simple water budget
calculations." Equation 1 does not express a dynamical truth and the
year-on-year interaction between P and E needs to be considered in climatic
impact studies.
SENSITIVITY OF RESERVOIR RELIABILITY TO CLIMATE CHANGE
Introduction
Despite its popularity as a paper or report title, very few authors
consider impacts to water resource variables in the sense that the section on
the distinction between hydrology and water resources describes. Impacts may
be divided into the altered requirement for water due to climatic change and
the altered availability of water to meet those demands. Those authors who
have attempted to quantify water resource impact have used the reliability of
reservoir supply (Figure 1) so it is that measure that is discussed here.
Effect on Demand
The projection of future demand for water is an art practiced at various
levels of sophistication by water supply authorities. Single purpose projects
such as irrigation or power supply pose a relatively simple problem in demand
forecasting. However, most planning problems are multidimensional and fraught
with uncertainties even within the existing climatic regime. The imposition
of trend on an already fluctuating climate was considered by Schwartz (1977)
as "additional fuel for the 'let's wait and see' style of facilities
planning."
315
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In the same report Lofting and Davis (1977) considered the definition of
demand as it relates to water supply noting that it is led by supply and not
subject to the same checks and balances encountered with conventional
industrial products and services. In their paper, they analyze the demands of
various users separately and make projections to the year 2020 for the United
States. They consider the impact of climatic change through demand pattern in
the agricultural sector alone.
Hargreaves (1981) considered irrigation project planning specifically.
He reduces the problem to one of estimating the change in potential
evapotranspiration (PE), this being regarded as the sole determining influence
on water demand. His analysis of GCM results leads to a latitude related
increase in PE of 16 percent to 63 percent, which is to be fed into U.S.
standard procedures for computing irrigation need. As admitted, this
assessment makes no allowance for changes in clouds (affecting radiation),
precipitation, or photosynthesis.
Cohen (1986) presents in a flowchart the many interconnected components
of climate impact assessment in his Great Lakes study. As well as the direct
effects on consumption of an altered temperature, many indirect effects are
listed. For power production these may take the form of a switch from water
resources for hydropower to cooling water for coal, oil, or nuclear power
stations. Crops may require less water in a COp-enriched world, and if the
study area occupies a zone where warming occurs then enhanced biological
activity requires a lesser dilution of effluents.
Glantz and Wigley (in press) report briefly on demand impact and refer to
recent more comprehensive work by Callaway and Currie (1986) who divide the
impact sector by sector.
Effect on Availability
Schwartz* Methods. Schwartz (1977) offers three approaches to the task of
evaluating the water supply impact:
• Case studies of particular schemes with special reference to their
reaction to past anomalies
• Speculation about impact on broad classes of system attributes to
types of change in runoff pattern
• Behavior analysis of water supply facilities with synthetically
generated inflow sequences.
The first approach, also used by Glantz and Wigley (in press), reveals
important issues to be treated in the second and third approaches, but does
not provide any quantitative estimate of impacts.
The result from the second approach was an "impact matrix" showing the
direction of change in run-of-river, reservoir, and groundwater yield due to a
decrease in mean streamflow, and increase in variance, skewness, and
persistence. Other attributes which were considered included water quality,
system reliability, operation costs, and flexibility to change.
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In the third approach Monte Carlo simulation was used to generate 1000
year synthetic traces. Eight scenarios were considered with two levels of
decrease in the mean, and increase in variance, skewness, and persistence.
The flow sequences were input to a reservoir whose capacity had been
determined to give 5 percent probability of failure under present-day
conditions. The most severe effect of the eight was the case of a reduction
in the log-mean of 20 percent but even this reduced the reliability only to 91
percent. Restoring the reliability to the original 95 percent reduced the
yield by 20 percent.
Sacramento Model. Nemec and Schaake (1982) used their adjusted data series
(empirical modeling section) as recommended by Schaake and Kaczmarek (1979) by
treating them as inflows to a storage reservoir. They investigated the change
in yield from a given storage and the change in storage to maintain a given
yield. In both cases the reliability was held constant. Klemes and Nemec
(1985) extended the results to consider how the reliability of supply from an
existing reservoir was affected by the same range of changes.
Figure 8a shows some amplification in the yield change over precipitation
change but the more dramatic effect occurred with the storage change for a
given yield. Figure 8b shows highly nonlinear results with up to 20:1
amplification over rainfall change. As with the runoff experiments the
precipitation change was more critical than the evaporation change. For a
drier climate, the drop in reliability may be more significant than the drop
in precipitation; this effect is greatest on river systems with a high level
of development. In one of the experiments, a yield equivalent to over
three-quarters of the mean flow was assumed. To provide 95 percent supply
reliability this requires a 600 million nr storage. Under the drier climatic
regime this reliability drops to below 25 percent, i.e., in three out of every
four months the desired yield would be unavailable.
Empirical Approach. The United Kingdom Low Flow Studies (Institute of
Hydrology 1980) demonstrated that the storage yield diagram within a region
can be stabilized if the yield is expressed as a point on the flow duration
curve (FDC). Figure 9 shows such curves for Britain, Malawi, and Southeast
Germany. Despite considerable differences among the three regions it is
notable that the curves are not entirely dissimilar.
Beran (1984) considered that such diagrams permit a preliminary
estimation of the impact of climatic change on reservoir performance. Like
Schwartz (1977) he assumed that climatic change would be effected through
changes in the mean and variability of discharge. Mo change in the
standardized storage yield diagram was thought necessary.
Consider a reservoir in Malawi designed for a yield equivalent to the 80
percentile point on the FDC and supplied with 90 percent reliability, i.e., 10
percent failure rate. The effect of a change in mean runoff is
straightforward—a decrease of 20 percent leads to an equal decrease in
yield. The effect on failure rate is more complex as it depends on the
gradient of the FDC. Figure 9 indicates a storage requirement equal to 2
percent of the annual runoff. If the average runoff were to decrease by 20
percent then this reservoir would appear to hold 2.5 percent of the revised
annual runoff. For most influent streams to Lake Malawi the yield would now
correspond to between the 70 and 75 percentile points on the revised FDC.
317
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6OO
200
2 .a
o
-o
!; 100
sa
w
% changes In ETP
• -4%
A +4%
• +12%
——— Leaf River
— —Pease River
500-
o
N 400H
o
a
9
a
S 3OO
15
*
•
^
•o
200-
o
35
1OO-
lncr*M*in ETP
4% lncr««*« In ETP
4% d»cr««»« in ETP
-25-20 -10 0 +10 +2O+25
% change in precipitation
+35 +25 +1O 0 -K)
% change in precipitation
-25
-35
Figure 8. Effect of changes in precipitation and evaporation on (a)
reservoir yield for a fixed storage equivalent to 10? of annual runoff and
fixed reliability of 90?; and (b) reservoir storage for a fixed yield
equivalent to 20? of mean discharge and fixed reliability.
318
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20 H
o
c
3
CD
CO
CO
CD
CO
15
c
co
CD
CD
CO
•+•*
C
CD
O
h»
CD
a
co
CO
CD
O)
CO
5-
2-
1-
o 0-5-
CD
_3
o
> 0-2
Yield = 60 percentile flow
Yield » 80 percentile flow
Yield = 90 percentile flow
United Kingdom
— — — Malawi
_ . mm South-east Germany
50 40 30 20 10 5 21
Percentage of years in which given reservoir would
be inadequate to supply the stated yield.
Figure 9. Standardized storage yield diagrams for United Kingdom and
Malawi. This differs from Figure 1 only in that the yield is expressed as a
percentile on the flow duration curve.
319
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Reentering Figure 9 with the revised yield and storage values results in a
postchange reliability of 70 percent equivalent to a drop from a 10-year to a
three-year return period of failure.
The effect of increased variability can be more dramatic. If the same
reservoir were subjected to a 20 percent increase in the coefficient of
variation (proportional to the gradient of the FDC on lognormal paper) the
percentile corresponding to the given yield reduces from 80 percent to 70
percent, which without the compensating effect of an apparent storage increase
gives rise to a four-fold diminution in reliability.
The impact in the United Kingdom and Germany is more complex as the range
of FDC types is much wider. The largest impact is on rivers with steep FDCs
corresponding to catchments of impermeable geology and low base flow
support. Most upland reservoirs in the United Kingdom occupy catchments of
this type. The impact is aggravated by the relative steepness of the storage
yield lines.
Figure 9 applies principally to smaller reservoirs where over-year
storage is seldom required. McMahon and Mein have derived simple
relationships expressing reservoir volumes as a function of the interannual
variability of the inflow series for use in more variable climatic regimes
where over-year storage is common. These indicate amplifications between 1.5
and 2 between inflow variability and storage requirements; in other words a 10
percent increase in variability leads to a 15 to 20 percent increase in
reservoir volume requirement (Beran 1984).
Use of Comparative Hydrology Approach. Of the three quantitative procedures,
only the Sacramento model currently uses climatic inputs; even so, no specific
climate model-based scenario was considered. The other quoted procedures,
Schwartz' and Beran's, did not employ climatic inputs but were based upon
predefined changes in the runoff regime. This could have been remedied by
directly relating the salient statistics used in those approaches—storage
yield, skewness, and persistence—to controlling climatic statistics.
The technique of "comparative hydrology" is one means for deriving such
connections in which hydrological characteristics such as those listed above
are computed from the available hydrological data and then compared with
corresponding quantities from different climatic regions. This step will
introduce further uncertainty and in this respect is inferior to a model that
operates in the time domain and that uses climatic inputs directly.
All the examples described in the previous section assumed that the
inputs would change but the internal model structure and relationships would
be preserved over the climatic change. While such a standpoint may serve for
a preliminary assessment any fuller impact evaluation should assume that the
transfer function itself may change with the climate.
Again the comparative hydrology approach may be useful. If it is
possible to express climatic change scenarios in terms such as "the future
climate of Britain may be similar to the current climate of (for example)
southeast Germany" then the current data for that region (Figure 9) will
provide the necessary answers. This approach cannot readily be applied to the
320
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conceptual model approach and in this respect the empirical approach is
superior.
This is an approach that has already been employed in impact studies of
food production by comparing climates within the North American midwest (Parry
1984). Quantitative methods of climate typology such as Litynski's (1983)
procedure will be valuable in recognizing climatic analogs.
RESEARCH REQUIREMENTS
Introductory Remarks
A vast literature has accumulated on the topic of climatic change in
general and impact studies in particular. The reference list at the end of
this paper confirms that surprisingly little of this activity has concerned
hydrological and water resource futures. Only twenty-one relevant papers have
been discovered, the majority of which treat hydrological aspects only, mean
annual runoff being the most commonly treated variable. Fewer than five
papers consider water resource oriented variables in a quantitative way.
Moreover, no consensus on preferred methods of attack is apparent from these
few papers.
An obvious need therefore exists for more research, particularly impact
studies of water resources, and the following subsection makes suggestions
based upon this survey. An international framework exists through the World
Meteorological Organization (WMO) and the United Nations Environment Programme
(UNEP) for impact studies and relevant aspects of their programs are described
below.
Research Topics
In the past, the main contribution by hydrologists to the climatic change
issue has been to paleoclimate studies and land-phase process descriptions for
GCMs. Engineering hydrology had tended to distance itself from the issue in
the period when even the sign and time scale of projected change remained
uncertain. Reaction was typified by one correspondent to Rodda, Sheckley, and
Tan (1977): "water management policy could not be based on models with low
explained variance." Since climate projections have centered on radiatively
active gas-induced warming a little more attention has been given to water
resource impact studies. The listed topics have been suggested primarily by
shortcomings and uncertainties in the models that have been used so far.
Climate-Hydrology Transfer Function. This has been a long-term preoccupation
of hydrological science for which climatic change studies provide yet further
impetus. Models of all types need continued development particularly to
inject increased physical content in conceptual models. To date models have
tended to concentrate attention either on hydrograph generation or on soil
processes. Such models need "balancing" to achieve a greater uniformity of
process description.
Hydrology-Water Resource Transfer Function. There is a need for "type
projects" on which to base experiments and test sensitivities. The three
suggestions of this report retain their hydrological heritage but others are
desirable that encompass more complex schemes. It is important that chosen
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project descriptions be realistic and capable of transfer to a range of
climatic and geographical regions.
Relationship Between Climatonic and Measured Runoff. Many of the more
physically based models equate runoff with the drainage term in a crop
model. Were general relations available that explained the spatial and
temporal scale on which the two runoff types could be equated, or how one may
be translated into the other, then greater practical use could be made of the
causal model predictions. An extra benefit from this knowledge would be the
ability to make direct use of GCM hydrological outputs.
Other Hydrology Variables. There has been a tendency to concentrate on runoff
as the variable of prime interest. However, in certain circumstances other
variables are of equal or greater importance and some may be more amenable to
climate impact investigation. Actual and potential evaporation, soil moisture
deficit, and groundwater recharge have a good claim for investigation. Other
physical and chemical properties of water should also be studied, for example
temperature and buffering capacity.
Effect of COp Enrichment on Transpiration Rate. Although more properly a
topic for plant physiologists rather than hydrologists, recent research has
demonstrated the importance of this phenomenon on water resources impact.
Statements are required about the likely vegetation response, and these
(possibly alternative) views should be incorporated in impact models. One
crucial issue is the transpiration response to increased (X^ of different
vegetation classes growing in an outdoor competitive environment. Another
concerns the likelihood and time scale of biome adjustment to the
opportunities presented by a new regime.
Historical Data. Scenarios based upon past periods of warming and cooling
will remain for some time to come the most believable indicator of the likely
regional and seasonal (i.e., sub-grid) pattern of climatic change. Further
research is needed to extend the approach to water resource variables in
different localities. It would be useful for standard regional sets to be
made available based upon known contrasting periods in order to provide the
test bed for sensitivity experiments and intercomparisons.
Model Intercomparisons. At a later time it will be important to set up
controlled experiments along the lines of previous WHO intercomparisons of
forecasting and snowmelt models to compare the capabilities of various models
to forecast impacts on standard water resource schemes.
Empirical Approach and Comparative Hydrology. Diagrams such as the
standardized storage yield diagram will probably retain their basic form over
a climatic change. Further work is needed to produce such diagrams (as well
as other diagrams and statistics representing different water resource
problems) for climatic regions, to identify the major controls, and to
quantify likely changes to stated climatic variation. Historic data from
recent past warm and cool periods can provide temporal validation of the
approach. There exists already a program within Unesco's "International
Hydrology Pogramme" on comparative hydrology.
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Water Budget Models. Useful insight has been obtained from simple
formulations concerning mean values and annual, totals. This paper presents
ideas for generalizing their form to accommodate more closely the statistical
dynamics of runoff on the annual scale. Further development is needed to
apply them to temperate regions and to incorporate possible reduced
transpiration and model inaccuracy.
Demand Forecasting. A more analytical approach is needed to demand
forecasting through a period of climatic change. Direct and indirect effects
should be enumerated and a judgment made about the direction of response.
Probabilistic Impact Forecasting. Even though the scientific community has
now arrived at a consensus about the likely direction for the climate, much
will remain uncertain about spatial and temporal details. By attaching
weights to alternative scenarios and models, probabilistic statements could be
made about the range of water resource impacts. Alternative design strategies
could be tested in this way. For example, an important practical issue
concerns the period of record that should be used for project evaluation—is
it better to use the entire period of record, is it better to use a short but
recent run of data, or should designers project forward in time to try to
account for possible climatic changes? Data requirements for recognizing
various levels of change should also flow from such an analysis.
Coupling of Water Resource and Other Impact Variables. Agricultural and
energy impacts have a similar socioeconomic importance to water resource
impacts and are also, to some extent, water dependent. Impact studies which
could simultaneously encompass all three would be of value in assessing their
relative importance in particular changed circumstances, and in ensuring
mutual compatibility in policy determination.
International Programs
The international community has recognized the crucial importance of the
climate issue. Perhaps the clearest statement yet to emerge was that issued
by the UNEP/WMO/ICSU meeting at Villach in October 1985 (WHO 1986). This
meeting asserted that the combined concentrations of "greenhouse" gases will
be radiatively equivalent to a doubling of CC^ concentration by as early as
2030 and this will lead to a global warming of between 1.50 and 4.5°C. There
was little residual doubt that there would be profound effects on global
ecosystems, agriculture, water resources, and sea ice, so governments were
urged to support programs to improve knowledge and ameliorate effects.
The World Climate Programme instituted in 1979 following the World
Climate Conference is the main agency for coordinating the international
effort. This has four components: research, data, applications, and impact.
This last component is being supervised by UNEP but is also strongly
represented within WMO's Commission for Hydrology (CHy) through the World
Climate Programme (Water).
The WCP is not solely concerned with the climatic change issue although
this has become increasingly central to its activities, especially those of
the WCRP. UNEP's programs so far have concentrated on food and climate
variations, and more recently on ecosystem and societal impacts of climatic
change. WCP (Water), largely organized within the WHO Commission for
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Hydrology, has components corresponding to the main divisions of WCP.
Research topics concern the use of long term hydrological data in the
detection of past changes as well as contributions to the HAPEX and other WCRP
experiments. Nemec's, Klemes', and Beran's studies cited here have all been
conducted under WCP (Water) auspices.
SUMMARY AND CONCLUSIONS
Now that consensus has been reached on the likely direction of climate,
at least in global terms, more effort must be given to projecting the likely
hydrological and water resource impacts. In this paper, hydrological
variables have been described which may substitute for water resource
problems. Models of varying levels of complexity have been presented which
allow climatic information to be translated into hydrological terms. Examples
from the literature illustrate this process and have allowed a number of
conclusions to be reached about fruitful avenues of future research.
Scale and process shortcomings in climate modeling still may radically
alter forecasts insofar as they affect individual regions. For this reason it
is considered that historical data from the study region should provide the
base data for extrapolation in impact studies. In this approach salient
hydrological properties are extracted from recently relatively cool and warm
periods. The contrast between the two sets of statistics can be scaled up to
conform to the projected climatic change.
No preference is expressed between models as all have strengths and
drawbacks. Conceptual models are inevitably deficient in their physical
description and offer no greater certainty of correct performance than much
cruder water budget or empirical formulations. However, it is easier
operationally to allow for a climatic change through adjustments to the inputs
to a conceptual or regression model than empirical models such as the storage
yield diagram or water budget which work with time average quantities.
Nevertheless, because the latter can make use of climate scenarios based upon
analog regions they also offer, through comparative hydrology, a powerful
approach to answering impact questions.
Research suggestions that promote all approaches have been made together
with a framework for intercomparisons. Researchers must remain vigilant to
research elsewhere in climate science as surprises that may upturn forecasts
are still possible. An example from the recent past is the possibility that
water use by vegetation may be much inhibited in a CC^-rich environment.
Future surprises may emanate from sea-level changes, and from new knowledge on
gas uptake by oceans and the effect of improved treatment of oceans, clouds,
and soil moisture within GCMs.
Research findings from paleoclimatology and hydrology should also be
studied closely for information on past analogs. One obstacle that still
remains to acceptance of the CO-, issue is that, despite an already
considerable increase in the atmospheric concentration of radiatively active
gases (possibly 20 percent, since preindustrial times), there has been no
unequivocal and identifiable hydrological impact that cannot be explained in
terms of random fluctuations.
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This desirability for water impact studies to be part of the community of
climatic change research gives it the character of "big science" in terms of
the intellectual, experimental, and computational requirements. While scope
exists for individual effort the greater dividends will come from concerted
research by networks of laboratories operating within the general framework of
the WCP.
ACKNOWLEDGEMENTS
Thanks are due to colleagues at the Institute of Hydrology, especially to
Dr. Jim Shuttleworth for detailed comments on an early draft and to Dr. John
Roberts for advice regarding the possible effect of CC^ enrichment on
vegetation. Dr. Tom Wigley of the Climatic Research Unit kindly provided
preprints and advance information on related studies.
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REVIEW AND ASSESSMENT
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Determining the Options—The Role of UNEP in
Addressing Global Issues
Peter Usher
United Nations Environment Programme
Nairobi, Kenya
UNEP is the environmental consciousness of the United Nations System. It
is not an implementing agency. Research and application of knowledge is the
responsibility of the specialized agencies and for governments. UNEP's role
is to identify environmental concerns, assess the nature and scale of the
problem, and as necessary, to develop and recommend methods or guidelines for
the sound environmental management of the issue concerned. It does so by
means of coordination and catalysis:
0 Coordination of global activities and research to ensure the accurate
analysis and efficient management of the issues
0 Catalysis in the sense of encouraging and supporting relevant
activities necessary to achieve the goal of managing the issue through
avoidance, prevention, or mitigation of the problem.
UNEP draws the attention of the world to environmental issues and may
make suggestions that specific issues be addressed. The decisions regarding
what will be done are those of the UNEP Governing Council, a representation
of member states of the United Nations. The Executive Director of UNEP has
the responsibility to satisfy these decisions, and my task, as UNEP's
atmospheric specialist, is to ensure that the appropriate assessment of rele-
vant atmospheric issues is made in a timely and efficient manner upon which
managerial decisions can be based. Thus the classic role of UNEP is problem
recognition, assessment, and then identification of policy alternatives. UNEP
is currently applying this policy to two major global issues - the risks to
the ozone layer and the greenhouse gas/climate change issue.
Some may view this report as a collection of research results and infor-
mation on the impacts of modification of climate or the ozone shield. I am
obliged to look at it in the broader context of future global response to
environmental concerns and in particular how this report and the conference
aid me in making available to governments the best assessment of ozone-layer
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modification, its impacts, and the implications of climate change, in order
that the most appropriate response can be formulated and applied. This report
is to me a single link, yet an absolutely essential one in the protection of
the ozone layer and in dealing with a future climate never before experienced
by mankind.
To illustrate this, I would like to describe the events, these other
links in the chain, that have led us to this point and to speculate what we
can hope to achieve.
The hypothesis of Rowland and Molena of stratospheric ozone layer made in
1974 led to worldwide speculation and the categorization of the issue by UNEP
as an emerging environmental issue. The UNEP Governing Council asked the
Executive Director to convene an international conference to review the matter
and my association with the Programme began when I was seconded from the
national meteorological service for whom I worked to organize the conference,
which took place at the State Department building in Washington, D.C. in March
1977. The outcome, as discussed by Golubev (this volume), was a World Plan of
Action on the Ozone Layer requiring research carried out or coordinated by the
appropriate specialized agencies and government and nongovernment institutions
under the overall coordination of UNEP. The initial task was to assess the
issue and quantify the risk preliminary to determining the response.
A Coordinating Committee (about twenty active members, mostly government
representatives) meets regularly to consider recent research results and
assess ozone layer modification and its impact. Under the plan of action,
this assessment should consider the results of monitoring and modelling
changes of the atmosphere, and should estimate the consequences for humanity
and the environment of predicted ozone layer change, including UV-B radiation
effects on human health, on aquatic and terrestrial ecosystems, on plants and
agriculture, on climate and on the socioeconomic implications of such changes
or of mitigation strategies, a menu similar to this report's table of
contents.
The Committee first met in Geneva in November 1977 and has met eight
times through June 1986. Each year its assessment has grown physically larger
as knowledge improves; this year it incorporates the results of the NASA
assessment made by an international team over the previous year. As a conse-
quence of having to digest this voluminous product, it was not possible to
make an assessment of effects of ozone layer change and, also as a result of
the NASA effort in addressing the physical and chemical science of the ozone
layer, an imbalance in the quality of the respective parts of the assessment
became apparent. Effects science needed a boost and I decided on the need for
a scientific conference on effects to inject momentum into the process to
estimation of effects. By happy coincidence, EPA was travelling the same
road, and we have combined forces to produce this report and the associated
conference. My next job is to use the information presented here and with the
help of the Coordinating Committee on the Ozone Layer (CCOL), make an assess-
ment of effects to complement the already available physical assessment.
UWEP, in response to governments' requests, also organized workshops that
will, among other matters, assess the costs of some of the possible measures
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suggested to protect the ozone layer. Thus the World Plan of Action on the
Ozone Layer is being implemented and the assessments made are the best
possible under the circumstances.
Nevertheless, the issue is not one that can yet be confirmed by monitor-
ing nor quantified with certainty by research. Unfortunately, it is not
possible to await these clarifications and still have time to avoid the conse-
quences of inaction. UNEP has been obliged at its Council's request to begin
the process of identifying management options for the issue.
The Vienna Convention is now a reality and will soon enter into force.
Soon an ad hoc legal and technical working group will be convened to decide on
a very significant document, a protocol to the Convention on Chlorofluorocar-
bons, which will require its signatories to restrict their emissions of CFCs
to agreed limits. Observance of these limits is likely to exact economic
penalties and should not be overly conservative. UNEP's Environmental Law
Unit will convene and service these meetings. My responsibility will be to
provide the best available scientific and technical information, a globally
accepted assessment of ozone layer modification, impacts of such modification,
and a socioeconomic analysis of the consequences of changes and control. The
program that I have outlined hopefully provides the lawyers and administrators
sufficient factual data and realistic projections on which they can make
realistic policy recommendations. The report and the "Effects Conference"
have been essential to that process.
The option under consideration limits production and emission of CFC 11
and 12 as an initial step. Control of other CFCs and additional potential
ozone-depleting substances are options available in the future, and will
depend on progress in developing safer substitutes or technological improve-
ments in manufacture and use of these chemicals to prevent emissions. UNEP
will have a continuing role as assessment coordinator and will act, at least
temporarily, as secretariat to the Convention.
The environment should not be manipulated beyond its capacity to return
to its former state. Unhappily, the limit has been exceeded beyond recall in
many instances, and economic demands oblige acceptance of change for the
greater good.
Climate change is also under consideration by UNEP as a result of tropos-
pheric trace gas increases, particularly carbon dioxide, and the discussions
on potential impacts have been most useful. The UNEP program in this area
mirrors that addressing the ozone layer problem: identification, assessment,
and analysis of policy options.
Two assessments have been made and a consensus has been reached on the
probable physical response. However, the problem of response is far more
complex than for ozone. Prohibition of nonessential uses of relatively small
amounts of some chemicals is one thing, limiting emissions of carbon dioxide
from coal and oil burning processes is quite another. The 1985 assessment of
the carbon dioxide/climate question at Villach provided the international
community and, one hopes, governments with a broad program to follow. This
includes a comprehensive menu of research needs and a requirement to undertake
analysis of regional socioeconomic impacts of climate change. Our under-
standing of future regional climates is currently limited and a wide range of
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possible as well as probable scenarios will have to be considered in the
assessment process. UNEP will support a limited number of these regional
exercises and will encourage governments to examine the consequences of
climate change in their own regions. The methods for carrying out such policy
exercises are under discussion. One can be sure a wide range will be
considered. Some idea of the kind of thing that can be done is described by
Parry (this volume) respecting the vulnerability of agriculture to climate
variability and change in the climatic sensitive regions.
What UNEP would hope is that the large international effort will be
closely coordinated and that the WMO/UNEP/ICSU Advisory Group on Greenhouse
Gases established in response to a Villach recommendation can have a role to
play. Only after considerable research and assessment will we be convinced
that a global response is or is not necessary. The need for a climate conven-
tion is not as obvious as the need for a convention to protect the ozone
layer. It remains an option that governments will have to consider, but
presently we would urge them not to waste the time we have available for
action, whether in cooperation with neighboring countries or by themselves,
but to join in the policy analysis process.
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THE POLICY CONTEXT
Gus Speth
World Resources Institute
Washington, D.C. USA
This report is another important step toward understanding and recog-
nizing the threats to human health and the world environment posed by ozone
modification and climate change from a greenhouse warming. In a remarkably
short period of time, an issue of concern to a small group of scientists has
become an important policy problem as well. The focus of scientists and
policymakers is no longer "whether", but "when", and with what effect. We
have even begun to hear talk of the most difficult question of all: what can
we do?
Consider what has been accomplished during the past 15 months:
• In March 1985, twenty countries signed the Vienna Convention for the
Protection of the Ozone Layer, the first international agreement
calling for action to prevent an environmental problem rather than
simply respond to it.
• In October 1985, eighty scientists from twenty-nine countries met at
Villach, Austria to assess our knowledge of the greenhouse problem.
They concluded that the problem is not only real, but occurring much
faster than had been thought, and recommended an "active
collaboration" between scientists and policymakers.
• In January 1986, the National Aeronautics and Space Administration
issued a report to Congress on processes controlling ozone, based on a
two-year study by 150 scientists from around the world. While
strictly a scientific study, the report warns that "we are conducting
one giant experiment on a global scale by increasing the
concentrations of trace gases in the atmosphere without knowing the
environmental consequences."
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e In the spring of 1986, the U.S. Department of Energy released four
volumes summarizing our current understanding of the climate change
issue. This effort also reflected extensive international scientific
participation and peer review. The review of the global carbon cycle
concludes with the recognition that "human effects on atmospheric
composition and the size and operations of the terrestrial eco-systems
represent major excursions that may yet overwhelm a life-support
system crafted in nature over billions of years."
• On June 10 and 11, 1986, a Senate subcommittee chaired by Senator John
Chafee held two days of hearings on the greenhouse and ozone issues.
Unlike prior hearings on the subject, this one gave equal time to what
can and ought to be done, as well as the status of scientific
knowledge. Senator Chafee proposed six policy initiatives, and
representatives of government agencies were pressed about their plans
to address these problems.
Government officials, for the most part, have responded to this explosion
of scientific concern with predictable and complacent calls for more research,
but no action. For example, William Graham, the President's nominated science
adviser, told the Senate hearing that "projections for the future have a large
uncertainty to them and have to be reduced before we take actions." He
suggested we need a "comprehensive understanding of the global environment,"
which might take a decade.
There is no denying the existence of major scientific uncertainties.
However, I draw a conclusion opposite to Dr. Graham's. When dealing with
risks that are grave but cumulative and irreversible, uncertainty is a strong
argument in favor of action. We must take whatever steps are feasible as soon
as possible to reduce the dangers. Inaction is not a neutral, low risk
policy, but rather a gamble that risks much greater harm. As the Villach
statement concludes, "While some warming of climate now appears inevitable due
to past actions, the rate and degree of future warming could be profoundly
affected by governmental policies on energy conservation, use of fossil fuels,
and the emission of some greenhouse gases."
A wait-and-see approach also only makes sense if we can be certain that
the changes will be gradual and detected in time to prevent catastrophe. The
recent discovery of an "ozone hole" over the Antarctic in springtime demon-
strates that natural systems can experience very rapid, marked changes almost
before we have time to confirm our measurements. This phenomenon was not pre-
dicted and cannot be explained by the best available models; nevertheless, it
happened over a period of less than a decade.
There are other negative consequences of delay. Some strategies, such as
developing solar energy or air conditioning equipment that does not require
CFCs, can only be implemented over a long period of time. Unless the develop-
ment of these technologies is accelerated today, these options will not be
available when rapid reductions in emissions become necessary.
The necessary policy responses will almost certainly become more severe
as atmospheric concentrations increase. For example, we can limit long-term
increases in the atmospheric concentration of CFCs by moderate action today,
such as cutting aerosol uses and capping total production. Conversely, if
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emissions are allowed to grow unchecked, future reductions will have to be
much more abrupt, without the benefit of time to search for acceptable substi-
tutes.
To allow the world's environment to deteriorate into a situation in which
we are dependent on rapid and extreme responses is irresponsible. This "cure"
may be as bad as the disease. As former EPA Administrator William Ruckelshaus
(1984) has said, "The ultimate danger is that by remaining reliant on the
'catastrophe theory of planning' in an era producing catastrophes of a magni-
tude greater than in the past, we can place our institutions in situations
where precipitate action is the sole option—and it is then that our
institutions themselves can be imperilled and individual rights overrun."
It is also likely to take far longer to resolve the major scientific
uncertainties than the decade suggested by Dr. Graham. In all likelihood we
will experience major impacts before we fully understand them. The recent DOE
assessment of the greenhouse problem, for example, concludes that it is impos-
sible to predict when C02 induced changes will be identified with statistical
confidence with greater precision than "over the next few decades." The
problem, they warn, "may be too gradual to detect until it is well advanced,
too advanced to stop by the time it is detected, and capable of inducing
profound changes in the delicate environmental balances ..."
The history of the ozone depletion issue reveals repeated assertions that
further research will provide much better insights on the need for policy in
three, five, or ten years time. When the designated period passed, the plea
for "just a few more years" has been renewed. Since research constantly
generates more questions, the process can be repeated many times.
Research will also not resolve the inherent and unavoidable uncertainty
attributable to human behavior, the determinant of growth rates for CC^, CFCs
and quite likely an important factor in emissions of the remaining trace
gases. The greatest uncertainty involved in predicting CC>2 emissions is the
rate of growth in fossil fuel use, a variable that can be influenced by
government policy, but not predicted through scientific research alone.
We must assume that many years will be needed to devise and implement
effective international solutions to these problems. To avoid future
political as well as environmental crises, we should adopt certain measures
that are feasible now, recognizing that they will be only first steps. While
multilateral and international cooperation will ultimately be required, this
should not preclude short-term domestic action. The U.S. has a tradition of
international environmental leadership, the best sources of scientific
understanding, and the greatest resources. We can, and should be, a model for
the world.
Several steps should be taken immediately, among them:
• An international effort to halt tropical deforestation, which accounts
for a large share of CC^ emissions attributable to biotic sources.
Emissions from biotic sources are currently estimated to be equal to
20 to 40 percent of CC^ emissions from fossil fuel use. A detailed
program for large-scale planting and forest management is outlined in
a recent report of the World Resources Institute, the World Bank, and
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the United Nations Development Programme, Tropical Forests: A Call for
Action. This program has received international support for many
reasons, but it would also be highly beneficial from the standpoint of
climate change.
• A ban on nonessential uses of CFCs and a production cap to limit
future growth. There are proven, accepted substitutes for almost all
aerosol uses of CFCs as demonstrated by the experience of the United
States, Canada, and Sweden. There is also no reason to continue using
CFCs for retail food packaging, whipped cream stabilizers, and other
such uses. Greater use of recovery and recycling methods could reduce
CFC use for solvents, foam blowing, and refrigeration and air
conditioning. Over the next decade, we can redesign refrigeration
equipment to operate on CFC-22 or other substitutes that present much
less risk of ozone modification and climate change.
• An increase in energy efficiency. Numerous studies have shown oppor-
tunities for large reductions in the energy needed to power our cars,
appliances, lighting, electric motors, and industrial processes. This
could reduce our dependence on coal-generated electricity, producing
substantial economic benefits while at the same time ameliorating the
global acid rain problem. Such efficiency improvement would be of
even greater benefit in the developing countries, where the cost of
capital is greater and the infrastructure requirements for increasing
coal production are enormous.
• Adoption of advanced technologies for producing electricity from
natural gas. This could increase power supplies, lower costs, and
reduce carbon dioxide emissions simultaneously. Technologies like
advanced combined-cycle systems and steam-injected gas turbines are
technically feasible, cheaper than coal, and environmentally superior
in almost all respects. Substituting them for existing gas turbines
would not increase our gas dependence and would significantly reduce
the need for coal power.
• Tighter regulations to limit carbon monoxide emissions from auto-
mobiles. This would reduce a suspected indirect source of methane
accumulation. Further reductions could also be attained by efforts to
control leakage from gas pipelines and abandoned coal mines.
• Preparation of environmental impact statements on all projects that
may contribute to or be affected by climate change and ozone
modification, as recommended by Senator Chafee. This is not being
done, although we believe it is legally required by the National
Environmental Policy Act. The impact statement process is valuable
because it expands awareness of the issue throughout the government
and would help to identify further opportunities to prevent and adapt
to climate change.
These steps can all be justified not only because they reduce the dangers
of ozone modification and climate change but because they are environmentally
sound. As the Villach statement notes, "Reduction of coal and oil use, and
energy conservation undertaken to reduce acid deposition will also reduce
concentrations of greenhouse gases; reduction in emissions of CFC will help
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protect the ozone layer and will also slow the rate of climate change." Imple-
mented today, they would substantially reduce the risks we face.
More aggressive action will be needed in the long run. We should
seriously study carbon taxes to discourage future use of coal and shale and to
finance reforestation, solar energy development, and energy efficiency tech-
nologies. We must begin the transition now or find ourselves increasingly
dependent on fossil fuels for our prime source of energy.
International cooperation on these issues must be continued, building on
the model of the Vienna Convention for the Protection of the Ozone Layer.
China and the Soviet Union consume as much coal as the United States and
currently plan to significantly increase their use. I strongly support
Senator Chafee's proposal for high level government meetings on these issues,
including the next US/USSR summit. It is also time to plan an international
convention to respond to climate change. A convention could be a mechanism for
developing common policy approaches as well as cooperation on scientific
concerns.
It would also be a terrible mistake if these problems were viewed as
primarily concerns of the industrialized countries. In the developing
countries, increased use of fossil fuels and CFCs could largely offset
reductions achieved elsewhere. Some developing countries, particularly those
with populations concentrated in low lying coastal areas, would be among those
to suffer most from the effects of climate change and ozone modification. A
major focus of international efforts must therefore be to meet the legitimate
needs of the developing countries for energy and refrigeration without greatly
adding to the buildup of greenhouse gases.
Lest these proposals be viewed as opposition to further scientific
efforts, I should emphasize my belief that increased research—particularly
research on health and environmental effects—is also essential. This is so
not only because we need to improve our knowledge of the risks we face, but
also in order to allow preparations for changes that are now inevitable. Past
emissions of trace gases may have already committed the world to an average
warming of one degree or more, and therefore perhaps twice that in high lati-
tudes. As a practical matter, we are committed to still more warming and
climate change because of built-in momentum in our patterns of energy supply
and use. It will take years to develop and implement emission control strate-
gies and to replace the existing energy and industrial infrastructure.
Research on effects is also important to help define the risks of these
problems in widely understood terms. A major reason for the extensive media
interest in the Senate hearings was undoubtedly the detailed description of
potential impacts from ozone modification and climate change. The public was
told not only that global average temperatures could rise several degrees, but
that the number of Washington days hotter than 100° could rise from 1 to 12
(see Hansen et al., this volume). Similarly, graphic terms were used to
characterize the potential devastation of U.S. forests and shoreline
development.
We must take on these problems as part of our responsibility to conserve
and protect the community of life on the planet. Although our dominion over
the earth may be nearly absolute, our right to exercise it is not. The
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responsibility for the greenhouse and ozone problems is ours. As trustees of
the earth for future generations, we must correct what we have wrought.
REFERENCE
Ruckelshaus, W. 1984. Forward. In Greenhouse effect and sea level rise, eds.
Barth, M.C. and J.G. Titus. New York: Van Nostrand Reinhold.
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The Need for Responsible CFC Policy
Richard Barnett
Alliance for Responsible CFC Policy
Rosslyn, Virginia USA
I am honored to present my views on the issues confronting us as scien-
tists, policy-makers, business representatives, interested participants, and
most importantly, inhabitants of our earth. The tasks we perform in our
efforts to better understand the effects of potential ozone depletion, global
climate warming, and climate modification are important to all as we assess
these issues.
They have received a great deal of attention lately as a result of the
hearings held by Senator Chafee's Environmental Pollution Subcommittee.
Unfortunately, the media accounts of those hearings could not explain the
enormous scientific complexities and uncertainties surrounding the ozone
depletion and climate change issues. The scientific uncertainties of these
issues are difficult for the general public to comprehend and they cannot be
adequately conveyed on thirty seconds of network news coverage or a brief news
article.
Hearings such as these are useful if they help us to remain alert and
responsive to the issues and the policy questions they engender; if they serve
to inform, not to alarm; and if they promote rational discourse and action,
rather than responses based on emotion.
It is critical, therefore, that these meetings are held and that reports
such as this are generated to ensure the development of international scienti-
fic consensus on these important issues.
Much has been made of the statement from the National Aeronautics and
Space Administration (NASA)XWorld Meteorological Organization (WMO) Science
Assessment that we're conducting an experiment "on a global scale by increas-
ing the concentrations of trace gases in the atmosphere." Evolutionary
history tells us that the composition of the global atmosphere has naturally
been in a dynamic state. The significant difference between the human race
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today and our evolutionary predecessors is that today society has the capa-
bility to change the earth's atmosphere and also has some ability, albeit
limited, to understand the consequences of our actions and to try to avoid any
adverse effects of our so-called "experiment."
It is somehow ironic that the same capacity that allowed us to have an
Industrial Revolution, to develop new technologies, and to land men on the
moon, now leads us into the maze of complex questions we must now address.
Such is the case with the development of chlorofluorocarbons, or CFCs as
they are commonly known. These synthetic compounds were first developed in
1931 as a result of an intensive research effort to identify an efficient,
safe refrigerant for home use. Since that time they have come to be used in a
wide variety of applications besides refrigeration, most notably for air-
conditioning, foam product manufacturing, cleaning solvent for the electronics
industry, and many other applications. Their uses have become so widespread
because of their many desirable properties. They are nonflammable, noncarcin-
ogenic, noncorrosiva, extremely energy efficient, and they have low toxicity.
The contribution of these substances to worker safety and consumer health
is substantial considering the products in which they are utilized and the
contribution of such products to our quality of life. It is incumbent on us,
however, to examine these substances and their potential for harming the
environment in the long run. On the other hand, we should not rush into
short-term regulatory decisions that result in the use of alternatives that
present immediate, real threats to worker and consumer safety with little or
no environmental benefit. In this case, it appears that the penalties of
premature regulation could be real in terms of an immediate increase in expo-
sure to more toxic substances or increased energy consumption.
We must not forget that other substances also have the potential to
modify the ozone layer and to increase the earth's average surface tempera-
ture. Even if CFCs had never been discovered, these two issues would still be
with us today.
The Alliance for Responsible CFC Policy dismisses the notion of "wait and
see" on the ozone depletion and climate change issues as unacceptable. I
would hardly characterize the activities over the last twelve years as "wait
and see."
The United States and many other countries developed scientific programs
to understand the ozone layer and the processes that control it. Practically
all we know about the stratosphere has been learned in the last ten to fifteen
years. Furthermore, intensive programs to study climate and possible climate
modification are continuing. In addition, U.S. industry strongly supported
efforts to develop the international framework for addressing the ozone deple-
tion issues through the Vienna Convention for Protection of the Ozone Layer.
Given the enormous complexities of the issues we are confronting, I believe
that the progress from the scientific and policy development perspectives has
been remarkable.
In our view, these global issues can only be addressed at the inter-
national level. Further unilateral actions by individual countries would
provide no significant environmental benefit. To this end, the progress made
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to date on international scientific and policy consensus is substantial but
much remains to be done. The science, as we currently understand it, tells
us, however, that there is additional time in which to solidify international
consensus. This must be done through discussion and negotiation, not through
further unilateral regulation in the name of "leadership." Experience tells
us that other countries do not regulate simply because the United States
does. In fact, the opposite may be true. Other nations may view our uni-
lateral actions as solving the problem; thus, giving them reason to do
nothing.
We are not saying, however, that industry should not take precautionary
measures while the research and negotiations continue at the international
level. As Chairman of the CFC Alliance, and as the Chief Operating Officer
for a major air-conditioning manufacturer, I believe we can, we have, and we
will continue to examine and adopt such prudent precautionary measures,
including:
• Recapturing, recycling, and recovery techniques, where cost-effective,
during manufacturing processes to control CFC emissions
• Efforts to transition to existing alternative fluorocarbons that are
considered to be more environmentally acceptable
• Equipment change-out practices to replace, where possible, existing
systems at the expiration of their useful life to equipment utilizing
other CFC formulations
• Technical practices in the field to prevent CFC emissions where practi-
cal
* Encouragement of CFC users to continue to look for technologies, pro-
cesses, or substances that are as efficient, safe, productive, -or
better than what is presently available.
I believe such actions respond to the concerns raised by the issues
discussed at the International Conference on the Effects of Ozone Modification
and Climate Change. I know, for example, that many of these practices have
been put into effect already. For example, unitary air-conditioning equipment
has converted substantially over the last twenty years to R-22 from R-12.
Many manufacturers have instituted recycling and recapturing techniques in
their plants. But as the history of humanity has shown, we are always striv-
ing to improve. What we must guard against is a solution that could be viewed
as a step backwards. Many of the CFC uses have no technically feasible alter-
native CFC formulations. Other substances discussed as substitutes for CFCs,
including sulfur dioxide, ammonia, and methyl chloride raise immediate
concerns for environmental safety, and worker and consumer protection.
The using and producing industries of the CFC Alliance are committed to
being active participants in the exploration and the successful resolution of
these issues. We would like to think that the reasons our companies succeed
are because the products we offer contribute to the quality of life for us
all, and we hope to continue to do so in a responsible fashion.
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The potential effects discussed in this report are serious. Through
continued pursuit of scientific research relating to ozone depletion and
climate change we can understand the nature and extent of any effects that may
actually occur and how we can best deal with them. I also hope that prudent
and responsible actions on the part of government, the private sector, and
industry will minimize any deleterious impacts on society as a result of
premature or unwise regulatory decisions.
As I indicated above, we have established the framework of an inter-
national plan to address these important environmental concerns. These
environmental concerns are serious, but their successful resolution will
require greater global cooperation in conducting the necessary scientific
research and monitoring, and in developing coordinated, effective, and
equitable policy decisions for all nations.
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Cooling the Chemical Summer:
Some Policy Responses to
Ozone-Destroying and Greenhouse Gases
David D. Doniger and David A. Wirth
Natural Resources Defense Council
Washington, DC USA
This exciting report has produced the most comprehensive international
exchange of knowledge ever seen on the known and potential consequences of
unabated release of ozone-destroying and greenhouse gases. We will not
attempt to summarize the papers or discussion, except to say that the picture
of our future being painted by the world's best scientific minds is, to use
the word without exaggeration, disastrous. Unless the private and public
institutions of the world respond, we can look forward to steady increases in
UV-B radiation due to ozone-destroying gases, including CFCs, halons, and
other compounds. Indeed, Watson (this volume) reports that 2 to 3 percent
ozone depletion may already have been observed, taking into account the
contribution of atmospheric aerosols. As a consequence, we can expect
increases in fatal and nonfatal skin cancer; broad, systemic disruption of
human immune responses; cataracts and other vision disorders; and possibly
many other illnesses. We can expect many serious environmental harms from the
increased UV-B, including widespread damage to crops and natural vegetation
(Teramura, this volume), possible disruption of microbial populations on which
the terrestrial ecology depends, and possible disruption of critical aquatic
food chains (Worrest, this volume). We can expect a certain amount of climate
change solely from the redistribution and overall loss of ozone.
From the greenhouse gases—carbon dioxide, methane, nitrous oxide, CFCs,
and others—we can expect a steady global warming to temperatures that even
within a decade may exceed the range experienced in the last one hundred
thousand years. The warming promises major consequences for rainfall and
other weather patterns (Manabe, this volume) and a sharply higher sea level
(Titus, this volume). Agricultural and forest belts are likely to shift,
possibly by hundreds of miles (Parry, this volume). Even the major currents
and circulation patterns of the ocean may change; northern Europe may plunge
into cold even as the world as a whole heats up. The direct and indirect
health effects of the warming are likely to be massive, ranging from large
increases in summertime urban death-rates to death and disease brought about
by drought, storm, and flood.
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These catastrophic prospects should bring home to governments and
ordinary citizens the simple concept that the atmosphere and climate are
fragile. The only thing objectively good about the current atmosphere and
climate is that they are the ones we are used to. Life and civilization are
adapted to this environment; change necessarily will be disruptive.
Especially because so much of the world's population lives with but a small
agricultural and economic safety margin, almost any stratospheric or climatic
change will be for the worse.
Yet, except in parts of the world where the weather is traditionally
variable and where life is lived close to the margin, most governments and
most people take the stability of climate for granted. The common conception,
to this point, has been of an atmosphere resilient enough to absorb stresses
of human origin without danger to existing ecosystems and the economies which
depend on them. Even more dangerous is the Panglossian view, encountered in
some governmental quarters, that greater radiation and heat will be good for
life on earth. These illusions must be rapidly dispelled.
Senate hearings held in June 1986 on the greenhouse effect and threats to
the stratosphere went a long way to dispel these illusions in this country and
to awaken our public and political system. It is hoped that the participant
in this international conference will carry the same message to his or her
country. The message, however, requires persistent repeating by scientists,
governmental officials, nongovernmental organizations, and ordinary citizens
around the world.
To be sure, much of the scientific data is incomplete. Yet the tip of
the iceberg which is visible argues strongly for changing course now. As EPA
Administrator Lee Thomas recognized in his Senate testimony and in this
volume, with the health and environmental stakes so high, the world cannot
afford the luxury of waiting for certainty. In fact, with the stakes so high,
uncertainty is an even more powerful argument for taking early action. How
many unexpected surprises, like the Antarctic ozone hole, can the world afford
to risk? The appropriate standard of proof for this problem is aptly captured
in the American Clean Air Act, which requires action to protect the
stratosphere when damage to it, and damage to health and welfare down below,
"may reasonably be anticipated."
Even though some degree of warming and ozone destruction are now inevit-
able, the future extent of the damage is dependent on decisions to be made in
the coming few years. The magnitude and timing of these changes are fully
under human control.
In this country, it is most encouraging to see the keen awareness and
interest of key legislative leaders such as Senators Chafee and Gore, who were
joined in the landmark hearings by Senators Stafford, Mitchell, Baucus, and
others. We are also encouraged, thus far, by EPA's conduct of the scientific
assessment and decision-making process pursuant to the Stratospheric Ozone
Protection Plan, of which this conference is a part, and by preparations for
resumption of CFC protocol negotiations next fall.
Senators Chafee and Gore have laid out a number of important, positive
policy initiatives which NRDC strongly supports. This report has demonstrated
to us, however, that an even stronger policy response is required by the
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magnitude of the threat to global health and welfare. Our purpose in the
remainder of this paper is to set forth some additional, though surely incom-
plete, proposals on CFCs and CC^.
CFCs: SHARP REDUCTIONS ARE NECESSARY
CFCs are the dominant chemicals in ozone depletion. They also account
for at least one sixth of the current atmospheric stock of anthropogenic
greenhouse gases, and they are growing more rapidly than others.
Domestic and international discussion has focused up to this point on
alternatives for CFC controls which range from very modest measures to, at
most, a cap on production at current levels. But there are now compelling
reasons to conclude that it is no longer sufficient to talk just about avoid-
ing increases in CFC production. Even with such a cap, CFC levels in the
stratosphere will continue to increase. Given the gravity of both problems
and the relative difficulty of rapidly affecting emissions of other gases, CFC
reductions clearly present the best present opportunity to stave off ozone
depletion and to limit the global warming.
Consequently, MRDC supports actual, rapid reductions in production of
CFCs and related chemicals. We offer the outlines of such a proposal here,
acknowledging that many details need to be developed. We propose, both for
domestic regulation and international agreement, an 80 percent cut in permis-
sible production of CFC^, CFC^r halons, and perhaps other compounds, over
the next five years, and a total phaseout over the next ten years.
We would exclude from these production limits substances such as
and CFC^oij^. These are promising alternatives for air conditioning and refri-
geration. They are safer, at least from a stratospheric ozone perspective,
because they break down in the troposphere. At this point we are not sure how
to treat CFC22> which could be substituted in mobile air conditioning. It is
also an ozone depleter, but at a lower rate than CFC^o- Much will depend on
whether CFC ^3 °r ^^134A become adequate substitutes and on whether the world
requires mobile air conditioning at all.
In this connection it was most distressing to hear the major domestic
producers of CFCs state, at the March 1986 workshop and subsequently, that in
the early 1980s they essentially stopped product development and toxicological
testing on potential alternatives to CFC^ and CFCip- Even so, currently
available information indicates that CFC^Q anc* ^^134A can ^ reaclily
developed into feasible alternatives. American industry representatives to
the recent Rome meeting are reported to have said that they can produce these
compounds for three to six times the amount of CFC^ and CFC12- Tne cost
should drop off with volume and time; but even if it did not, it still would
amount to less than a $10 rise in the price of a refrigerator. It is also
most distressing, given the industry's prior opposition to projections that
CFC production will grow, to read that the major American company, DuPont, is
planning to expand production of CFCs in Japan.
We recommend consideration of proposals to give credits against these
production limits for uses from which producers can prove, to domestic and
international authorities, that no emissions result. Such an approach would
encourage closed systems and product recovery and recycling. Any such system
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of exceptions, however, would have to be based on rigorous demonstrations,
with the burden of proof strongly on the producer.
A market-oriented phaseout should be supplemented with a ban on specific
frivolous uses. In the United States, substantial strides have been taken to
eliminate non-essential aerosol uses. But even here certain absurdities are
still cherished. We ought to be able to reach reasonably quick agreement that
the modest virtues of using CFC^c as a whipped topping stabilizer or CFC^ in
chewing gum remover, boat horns, and pressurized drain cleaners should give
way to protection of the atmosphere and climate.
A phase-out over this period would allow time for an orderly transition
to other chemicals, other processes, and other end-products. The gravity of
the situation demands nothing less." Cuts of this magnitude will not even
prevent increases in the level of ozone-destroying CFCs reaching the strato-
sphere; that appears to require an 80 percent cut in today's CFC production,
not production five years from now.
C02: THE NEED TO LIVE WITHIN BUDGETS
We do not pretend to comprehensively address strategies for C02 control
in this paper. We want to emphasize, however, the enormous opportunity to
stabilize or even cut CC^ emissions from industrialized nations' electric
power generation through conservation and efficiency improvements. We have
borrowed heavily here from the work of our colleagues Ralph Cavanaugh and
David Goldstein in NRDC's San Francisco office. Here are some startling
statistics they have compiled:
• The typical American office building is lit by electric lights that
consume six to nine kilowatts of electricity per square foot per
year. Commercially available state-of-the-art technology can reduce
consumption to 1.5 kilowatt hours per square foot without sacrificing
reading ability or other functions of lighting.
• Typical residential water heaters use 4500-6000 kilowatt hours of
electricity per year; state-of-the-art technology only uses 800-1200
kilowatt hours per year.
The National Resources Defense Council estimates that American residential and
commercial electricity use can be cut in half through efficiency improvements
such as these. NRDC estimates that industrial electricity use could be cut by
25 percent through conservation and efficiency improvements. In California
and in the Pacific Northwest, utilities have invested more than half a billion
dollars in residential efficiency improvements, i.e., buying efficient
refrigerators instead of building new power plants. These efficiency invest-
ments, moreover, are clearly cheaper. Measures such as these, applied nation-
wide, could substantially trim projected C02 emissions.
On the basis of this potential, we wish to offer the outlines of a modest
proposal for establishing "C02 budgets" for the utilities and industries of
the United States. For a start, Congress should enact legislation requiring
each utility to develop scenarios for alternative C02 futures, in conjunction
with state regulatory authorities, EPA, and other agencies, through an open,
objective public process. These scenarios should include low- and no-C02
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growth futures, and they should place primary reliance on efficiency improve-
ments and alternative energy sources, without increased dependence on nuclear
power. Similar efficiency analyses should be required for major energy-
consuming industries, including the transportation sector. Once the opportu-
nities for saving energy through attractive conservation and efficiency
investments are apparent, we will be able to take concrete steps toward reduc-
ing emissions of CC>2 and the global warming that results.
CONCLUSIONS
We have no illusions that these proposals on CFCs and COp are either
fully developed or sufficient alone. But as Senator Gore (this volume)
suggests, the institutions of government, science, business, and other sectors
must not be paralyzed by the enormity of the total problem. Rather, we must
break the problem down and come to grips with as many of the pieces as
possible, as fast as we can. Even if significant stratospheric and climatic
change still results, our efforts will be justified, for surely we will know
that without them, things would be even worse.
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Climate Change and Stratospheric Ozone Depletion:
Need for More Than the Current Minimalist Response
John C. Topping, Jr.1
Topping & Swillinger
Washington, DC USA
Devotees of late night television in the United States may have seen the
celebrated W.R. Grace and Company deficit trial advertisements. An elderly
man, presumably of our generation, is on trial for failing to halt the mush-
rooming federal deficit. This courtroom scene in the year 2017 has the
defendant fading a jury of children and an adolescent prosecutor who asks, "In
1986 the national debt reached $2 trillion. Didn't that frighten you?" Our
contemporary lamely replies, "No one was willing to make the sacrifice."
Stepping down from the witness stand, he implores, "Are you ever going to
forgive us?"
While this advertisement may be too strong for the sensibilities of the
television networks, it may be an accurate representation of how our grand-
children will view our mortgaging the future of the global environment. By
2017 our grandchildren will be struggling with a radically warming world
climate causing environmental changes beyond anything ever witnessed by our
species. Unless humanity profoundly alters energy consumption and emission
practices, the global environmental trauma could become the ecological equiva-
lent of the hyperinflation in Weimar Germany in the 1920s, with perhaps as
profound consequences for the health of democratic government.
Mid-range projections of average global surface temperature warming by
2100 are generally at or above 5°C. Virtually all plausible energy-use
projections (other than those hypothesizing the destruction of humanity in a
final world war) point toward a doubling of the preindustrial levels of carbon
dioxide well before the end of the twenty-first century. We are told by an
eminent climatologist that this C02 doubling alone would warm the earth by an
average of 3°C. As a result of recent calculations in some of the more
The author served from September 1983 through January 1986 as Staff Director
of the Office of Air and Radiation of the U.S. Environmental Protection
Agency.
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sophisticated climate models of various feedback effects associated with a CC>2
doubling, the likely warming due to such growth of carbon dioxide in the
atmosphere may prove to be at least 4°C (Hansen, this volume).
Although fossil fuel burning alone could produce a doubling of preindus-
trial CC>2 levels in the next seventy-five years, such a doubling could be
accelerated by a decade or more if we continue to clear the world's forests at
current rates. The biosphere, especially forests, constitutes a major sink
for taking up carbon dioxide so that it does not build up in the atmosphere.
Yet the largest source of such uptake, the tropical rain forests, is often
severely pressed by development pressures in Third World countries from both
indigenous sources and multi-national companies.
Despite abundant evidence that the buildup of carbon dioxide levels alone
could produce an average global climate warming of 5°C by 2100, the most
plausible current projections indicate that this COo-induced temperature
warming will be roughly matched by a temperature rise due to a simultaneous
buildup in other trace gases as chlorofluorocarbons, carbon tetrachloride,
nitrous oxide, carbon monoxide, methane, and compounds of bromine.
The long-term implications of such a rapid climate warming for humanity
and most other animal and plant species on this planet are staggering. These
involve losing tens of millions of acres of coastal land to the sea, the
impairment of many of the world's port facilities, the loss of countless lives
of coastal and lowland dwellers to increasingly destructive storm surges, and
massive salt water intrusion on fresh water supplies. The greatest human toll
is likely to come in famines that could ultimately claim the lives of hundreds
of millions in Third World countries. The tragic famine we are now witnessing
in Africa may be but a small harbinger of the catastrophe that will unfold as
desertification claims arable land and shifts in rainfall patterns disrupt
already marginal food production and distribution systems. Although many
plants will grow more rapidly in a higher C02 environment, it is unlikely over
the next century that such potential gains in the food supply would match the
losses caused by migration of food belts. Moreover, the non-COn greenhouse
gases provide no such benefits but could disrupt the climate just as much.
Besides its potentially large toll in human lives, this rapid climate
change will probably destroy the habitats of thousands of animal and plant
species, thus robbing our planet of much of its biological diversity. In
addition to its direct human and ecological toll, adjustments to this rapid
climate change could be expected to consume the entire growth dividend
humanity would have used to improve living standards of future generations and
to redress the impoverishment of the Third World. Huge sums would be required
for dikes to preserve many coastal areas, and much of our planet's great
investment in agriculture would be made obsolete by a rapid change in climate.
As apocalyptic as the consequences of such climate shock would appear to
be over the long haul, people tend to glaze over at discussions that seem more
relevant to their great grandchildren. Economists have developed the concept
of discounting the value of human lives saved in the future. As some have
pointed out, by adopting a high enough discount rate, one could conclude that
the destruction of human civilization one or two centuries from now is of
little or no economic consequence in present value terms, even if such a
certain fate results from today's decisions. Sadly the calculations of most
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public policy-makers seem equally unmindful of the injunction of that great
political philosopher Edmund Burke that government owes a duty not only to the
living, but also to the dead and to those who are yet to be born.
Yet, as some eminent NASA scientists have recently projected, climate
change is no longer merely a concern for future generations. By 1990, they
suggest, we are likely to see temperature changes outside of the normal range
of variation with an increase of about 1°C in average global surface tempera-
ture between now and the year 2000. At the end of this century humanity could
face a warmer world than at any time in the last hundred thousand years with
the prospect of a continued warming at an ever-accelerating rate.
A major factor in the acceleration of these climate warming projections
has been a late-blooming recognition of the important role of highly absorp-
tive greenhouse gases, such as chlorofluorocarbons, carbon tetrachloride, and
various bromine compounds, which remain in the atmosphere for decades if not
centuries before breaking down. Methane growth due to agriculture, and
nitrous oxide and carbon monoxide growth from fuel combustion have also caused
the warming projections to rise.
Because of their powerful bonding and insulating qualities, chlorofluoro-
carbons are being used for a profusion of uses well past refrigeration and air
conditioning to such diverse purposes as computer manufacturing and preserving
the taste of a "McDLT" sandwich from a fast-food restaurant. These same
qualities that make chlorofluorocarbons such readily adaptable commercial
compounds also make them powerful greenhouse gases and effective depleters of
our stratospheric ozone layer.
Due to the rapid growth in CFC use during the 1980s and the rapid buildup
of bromine compounds, the danger to the stratospheric ozone layer appears
greater than was originally thought when concern first arose in the mid-
1970s. Yet much more important than the sizable increases in skin cancer,
potential weakening of the human immune system, and likely crop and materials
damage resulting from a chlorine and bromine compound induced depletion of the
stratospheric ozone layer are the sizable boosts that such gases will provide
to climate warming.
Given present CFC-use projections, it is conceivable that these compounds
alone will produce an amplification of 1° to 1.5° C in the total global
temperature warming over the next several generations. A small increment in
the greenhouse warming can also be anticipated from the growth of such
chlorine compounds as carbon tetrachloride and methyl chloroform as well as by
a profusion of bromine compounds.
These stratospheric perturbants would be the first targets of any effec-
tive international effort to slow the greenhouse warming. They are all
industrially-produced compounds, many virtually unknown two generations ago.
Many have some available substitutes, which are neither stratospheric pertur-
bants nor greenhouse gases for most commercial applications. Regulation of
these compounds could afford dual benefits by providing stratospheric protec-
tion and slowing the greenhouse warming. Control of even small volumes of
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these chlorine and bromine compounds can have a highly beneficial effect, due
to their long persistence in the atmosphere and their tremendous absorptive
potential (sometimes several thousand times an equivalent molecule of carbon
dioxide).
Any effective U.S. and international effort to address the dual problems
of greenhouse warming and stratospheric ozone depletion will require a much
more tangible commitment of resources and attention by senior policy-makers in
the major industrial nations. In the United States there recently have been
some encouraging indications of intellectual recognition by senior policy-
makers of the importance of the problem of climate change. William
Ruckelshaus' strong foreword to the provocative work Greenhouse Effect and Sea
Level Rise (Earth and Titus 1984) and Lee Thomas' clarion call in March 1986
for stratospheric ozone protection pointed out the critical importance of
these issues.
Yet recognition of these issues has not translated into a tangible
resource commitment. Despite indications that prospective climate change
dwarfs all other environmental problems combined, fewer than nine EPA
employees out of a workforce of about 12,000 work full-time on either the
issue of greenhouse warming or stratospheric ozone depletion. Although the
proportion has grown considerably in the past year, still only about one-tenth
of one percent of EPA's total resources is devoted to addressing these
issues. This minimalist resource commitment is not due to a lack of will on
the part of EPA's senior leadership but to the statutory ambiguity of EPA's
role and the deep-seated hostility that the Office of Management and Budget
(OMB) has exhibited toward EPA's addressing such first-order environmental
issues as climate change, indoor air, and radon. OMB has resisted giving EPA
resources in apparent fear that the agency might uncover problems with result-
ing budgetary or regulatory consequences. While somewhat greater sums have
been directed at studying aspects of climate change at the National
Aeronautics and Space Administration, the National Oceanographic and
Atmospheric Administration, and the Department of Energy, no coherent federal-
wide focus exists on these problems, which will ultimately affect virtually
every agency in government.
With a few exceptions the resource commitment to seriously addressing
these issues by U.S. environmental groups has been equally fainthearted. Some
environmentalists, by reflexively opposing all forms of nuclear power, have
helped increase our dependence on fossil fuels. Moreover, both greenhouse-
induced warming and stratospheric ozone depletion are global problems, and
environmental policy-makers and environmental organizations in other
industrialized countries have often lagged behind those in the U.S. in addres-
sing these problems.
Despite the clear inadequacy of the present response to the prospect of
climate change, a number of tangible steps can be taken by the U.S. and other
countries to make the problem more manageable. These include:
• Preservation of critical satellite tracking research and climate
modeling concerning ozone depletion and greenhouse warming. The
recent turmoil at NASA, the destruction at launch of a key weather
satellite, and the general environment of federal budget austerity
have placed some critical research in jeopardy. Its loss could
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greatly hinder our developing a clear understanding of the likely pace
and regional implications of climate change.
Development of a serious external constituency for climatic stability
including environmentalists, scientists, coastal dwellers, farmers,
the nuclear and the solar industry, and others. If such coalitions
are organized in the major industrial democracies, they can help to
ensure the attainment of broadscale international agreements essential
to responding to climate change.
Immediate phasing out of such relatively frivolous and easily substi-
tutable uses of CFCs as aerosols, egg cartons, and fast food
containers through a combination of consumer boycotts, industry
voluntary action, national regulation or taxes, and international
agreement. Concerted activity by consumers to avoid CFC aerosols
preceded U.S. regulatory action. A similar focus on the threat to the
environment posed by such environmentally dangerous and frivolous uses
of CFCs might trigger a similar scramble by fast food retailers to
point out that their products are not only tastier, but safer for the
environment, than those of their competitors.
Approaching regulation of CFCs and other trace gases such as carbon
tetrachloride, methyl chloroform, and bromine compounds by weighing
their greenhouse absorptive potential, their residence time, and their
ozone depleting capacity. Thus, even among CFCs, substitutions might
be encouraged of longer residence time compounds by shorter residence
time compounds.
Where appropriate, amend environmental statutes to address possibly
harmful substitution effects caused by proposed environmental regula-
tions. EPA recently issued a notice of an intent to list perchloro-
ethylene, a significant dry cleaning solvent, as a hazardous air
pollutant under Section 112 of the Clean Air Act. Such listing and
subsequent regulation could conceivably trigger a rapid movement in
the dry cleaning industry to CFCs, on balance likely to pose much
greater environmental dangers than perchloroethylene. Language
specifically permitting consideration of greenhouse warming and ozone
depleting effects of available substitutes would facilitate more
rational regulation.
Requirements that long-term projects reviewed under the National
Environmental Policy Act consider climate change and sea level rise.
This might be accomplished through amendment of implementing regula-
tions or by a suit directed at an appropriate project, such as a
coastal highway that has failed to consider likely sea level rise.
Institutionalization of climate change considerations into the project
planning process for long term public and private sector investments
should ultimately save taxpayers and investors billions of dollars and
ensure that we leave future generations a sounder environment.
Insistence by bilateral and multilateral lending institutions that
their funds not finance the destruction of tropical rain forests and
other important global forest resources. Recognition of the global
stake in preserving these resources, located largely in developing
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countries, may ultimately require the industrialized countries to
finance some of the economic loss developing countries would perceive
occurring should they forego development in the tropical rain forests.
• Recognition, even in the face of the tragedy at Chernobyl, that along-
side energy conservation nuclear power remains the likely principal
alternative to fossil fuel burning over the next generation or two.
Besides strengthening the powers of the International Atomic Energy
Agency to improve safety standards and ensure against diversion of
nuclear materials to nonpeaceful uses, recapturing public confidence
in the safety of nuclear power will require implementing environ-
mentally sound radioactive waste policies. It is likely that
environmental and energy considerations may militate toward large
scale nuclear plant construction before the end of this century. Yet
to meet deep public concerns about the safety of nuclear power may
require the development of a new generation of technology that is
relatively invulnerable to nuclear meltdown. Governments,
environmental groups, and the nuclear power industry have a common
interest in the success of such an effort. Simultaneous satisfaction
of safety concerns and economic considerations will require very
rigorous safety standards coupled with a virtual regulatory certainty
that careful adherence to such standards will ensure expeditious
licensing and avoid protracted litigation.
• Renewed international research focus on improving the efficiency of
such alternative energy sources as solar power and perfection of such
potential breakthrough technologies as hydrogen powered vehicles.
• A concerted public-private sector effort to mitigate the costs of
climate change by adjusting land use and coastal development policies
to allow for the prospect of increasing sea level rise, by encouraging
the development of crops that can flourish under rapidly changing
climatic conditions, by factoring climatic change and rising CC^
levels into the strategic planning of industry, and by incorporating
the prospect of a rapidly warming climate into calculations of utility
peak load demand and necessary future capacity.
Due to the enormous momentum in the earth's climate system already
present from our massive increase in fossil fuel burning and release of many
manmade greenhouse gases, adaptation will be an essential part of our
response. The sooner we incorporate climate change considerations into our
societal planning the better our prospect will be for turning the greenhouse
warming from an unprecedented catastrophe to merely an enormous societal
challenge. Yet, even the best adaptation and mitigation strategy may be of
little avail if present energy use and gas release trends remain unabated.
Action by EPA and UNEP to sharply curtail emissions of the greenhouse gases at
issue may afford us the time to fashion the more comprehensive response that
will ultimately be required.
REFERENCE
Barth, M.C., and J.G. Titus. 1984. Greenhouse effect and sea level rise. New
York: Van Nostrand Reinhold.
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The Implications of Health and Environmental
Effects for Policy
Daniel J. Dudek and Michael Oppenheimer
Environmental Defense Fund
New York, New York USA
ABSTRACT
In approaching the question of whether the protection of stratospheric
ozone requires the control of CFCs and/or other ozone-depleting agents, the
U.S. Environmental Protection Agency (EPA) has divided the problem into a
consideration of future emissions and atmospheric and health effects. The
first workshop was devoted to the former topic. From that session it is clear
that in the absence of policy action, CFC use will continue to grow in the
future. While the papers presented provided a wide range of possible future
CFC levels, it is important to emphasize that no credence can be given to zero
growth assumptions for either long term production or emissions.
The various papers in this report focus on the consequences of failing to
manage emissions of ozone-depleting substances. These environmental and
health effects are the damages that can be avoided by controlling emissions.
These impacts can be distributed into direct and indirect categories stemming
from UV-B radiation or climate change. The effects documented involve primary
production sectors such as agriculture and fisheries, as well as higher-order
damages to human health, materials, and coastal property. Little of the
research has generated information in sufficient detail to estimate dose-
response relationships. However, when we compare our current knowledge
against the information on effects available in the late 1970s, we can see
that there has been substantial learning on this issue. Several of the papers
presented a sufficient range of responses to allow a preliminary examination
of the benefits of controlling emissions.
Two trajectories of ozone depletion in response to alternative scenarios
of chlorofluorocarbon (CFC) and trace gas emissions were selected to represent
the 'with' and 'without1 action extremes. These depletion predictions formed
the basis for predicting effects in the United States. Control action is
simulated in the atmospheric model by holding emissions constant at 1980
levels which is broadly similar to a production capacity limit. The main
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analysis focuses on nonmelanoma skin cancers and the damages to PVC. Indirect
effects of increased UV-B radiation are illustrated by extrapolating
photochemical oxidant production and its yield-reducing impacts on major crop
commodities. The avoided damages from now until the year 2025 were estimated
to be approximately 1.65 million cases of nonmelanoma skin cancer and approxi-
mately $7 million of PVC damage. Yield reductions due to increased ambient
ozone would be significant for soybeans and cotton beginning in 2010.
Numerous effects not quantified are described qualitatively.
To complete the analytical illustration of stratospheric ozone
management, the focus naturally shifts to the estimation of the costs of
control action. The changes in economic surplus associated with the position
of a production cap were derived from existing research results. Average
annual present value control costs were estimated to range from $196 million
to $455 million, depending upon the ease of substitution of alternatives.
Transition costs might also be substantial if policy action is implemented
with little advance notice. The safety implications of the substitutes also
were neglected. However, given the relative magnitude of benefits and cost,
the prudent course would be to focus on the design of efficient and equitable
management strategies for limiting CFC emissions.
Consequently, the current focus of research resources should be to assess
consequences of possible policy choices. What are the effects of differences
in policies, timing, and force? If we delay policy action, will it be more
difficult in the future? Delay would not provide the needed stimulus for
research into substitutes or reduced emission technologies. What are the
opportunity costs of deferring control? To address these policy questions and
deliver information to a rational policy process, we need to focus our
research resources in the next year on the articulation of our uncertainty and
its explicit incorporation into policy analysis. What are the consequences of
being wrong and what is the least risky alternative? The real challenge is
the design of policies to limit CFC emissions with associated monitoring and
enforcement components that will protect the environment but allow all nations
to share in the benefits of these chemicals.
INTRODUCTION
This report presents results of scientific analyses of various effects
associated with changes in stratospheric ozone. This document and the
conference on which it reports is one part of a process that started in the
fall of 1985. In approaching the question of whether the protection of
stratospheric ozone requires the control of CFCs and/or other ozone-depleting
agents, the U.S. EPA has divided the problem into a consideration of economic
and technical issues associated with emissions, and the resulting atmospheric
and health effects. The process is designed to provide the best possible
information on potential ozone-depleting substances, their quantities and uses
now and in the future, and the consequences associated with depletion. In
organizing this massive amount of information, economists divide it into the
broad categories of benefits and costs. Using this framework, then, we can
establish a correspondence between the various conferences and reports and the
information that economists believe is useful for policy analysis.
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In the fall of 1985, there was a World Meteorological Organization (WHO)
Climate Conference convened "to provide governments around the world with the
best scientific information currently available on whether any human
activities represent a substantial threat to the ozone layer" (Watson 1986).
The executive summary from the conference report succinctly concludes that:
Given what we know about the ozone and trace gas-
chemistry-climate problems we should recognize that we
are conducting one giant experiment on a global scale by
increasing the concentrations of trace gases in the
atmosphere without knowing the environmental
consequences. (Watson 1986)
The next set of workshops attempted to delimit the size of this
experiment by assessing current and expected future demands for CFCs. The
effects and efficiencies of existing control policies were also reviewed. In
our benefit-cost language, this information would enable us to assess the
costs of any control action. The international component of this process was
concluded in a May 1986 meeting in Rome. While there were disagreements among
the delegations about the precise future for CFC production, use, and
emission, there was a consensus that annual growth in CFC demand would likely
be above zero but less than five percent.
This report represents an articulation of our best understanding of the
benefits associated with any decision concerning the management of strato-
spheric ozone. These effects are viewed as benefits because they represent
the consequences that would be avoided by pursuing a particular alternative
course of action. Clearly, the range of alternatives includes the possibility
of doing nothing.
This paper highlights the process by establishing a correspondence
between seemingly diverse activities; summarizes the information presented in
this report within the context of that process; and previews the next step in
the process, which will consider general control strategies. The paper is
divided into several sections which focus on the general methodology, the
estimation of costs associated with control action, the evaluation of the
associated benefits, and the implications of this preliminary assessment for
further research.
THE GENERAL APPROACH
Attributes of the Problem
Before elaborating on the economist's world view of policy analysis, it
is important to briefly consider several salient aspects of the stratospheric
ozone depletion problem. One of the most interesting, yet vexing,
characteristics of the problem is its global nature. This attribute is impor-
tant if we think of the problem as one of managing a global commons. Mo
individual, firm, or nation can capture the benefits from reducing
emissions. We cannot exclude others from enjoying the benefits from our
emissions reductions even if they do not contribute. Consequently, no indivi-
dual actor bears the full consequences of their decisions to emit or not.
This condition creates an imperative for concerted global action.
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The lengths of lags in the atmospheric system due to the very long resi-
dence times of these chemicals result in two additional attributes of
concern. The first is irreversibility: if the earth's systems are being
severely perturbed, what will the new equilibria be like? Can we ever regain
the old? Will the simultaneous changes wrought by ozone depletion and climate
change irrevocably alter the biosphere? Further, what are the implications
for future generations? These long lags necessitate long planning horizons
and drive us headlong into the question of intergenerational equity. What are
the responsibilities of the present to the future? Mishan and Page (1982)
have argued that we should adopt the view that:
the means for future well-being (should) be at least as
good as our own, thus focusing attention on the future
condition of the resource base and its ultimate
renewability and the portfolio of catastrophic risks
that are passed from one generation to another.
As a current custodian of this planet, I believe that this is an
appropriate vantage from which to review the information presented in this
report.
General Framework
As indicated in the introduction, the general framework of organization
for this paper draws from the policy process in which we are engaged.
Economists view this process as one of assessing the benefits and costs
associated with alternative courses of action. In each case, it is important
to evaluate the effects of a policy with respect to a particular baseline.
This necessity is imposed upon us because we wish to ascertain which changes
can be ascribed to the action of the policy and because the problem involves
chemical substances with extremely long lifetimes.
Costs. In the case of stratospheric ozone, costs will be the net economic
effects on CFC producers, consumers, and the economy as a whole. These
effects are expected to fall under several categories: surplus losses,
efficiency losses, nonrecoverable resource cost, safety cost associated with
alternatives, and administrative costs (Yarrow 1986). Of these,
administrative and transition costs can be effectively assumed to be zero.
Administrative cost should be small because the number of CFC producers is
small. Transition cost would be expected to be a function of the timing of
the policy action. If the policy intent and its implementation date are
announced well in advance of the proposed action, firms producing CFCs should
have the opportunity to alter their resource allocations. A commonly employed
measure of economic welfare is the sum of economic surpluses. Graphically,
using linear supply and demand functions we can illustrate several of these
concepts (Figure 1). In this simplified example, consumers' surplus is repre-
sented by the area under the demand curve DD1 above the equilibrium price
p*. Because the supply curve is depicted as a horizontal line and producers'
surplus is normally the area below the equilibrium price level but above the
supply curve, producers' surplus is zero. For any proposed policy we can
compute the change in economic welfare as the sum of consumers' and producers'
surplus.
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Price _,
-,**
Q1980
Quantity
Figure 1. Conceptual Illustration Of Surplus Losses
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To more effectively describe the approach pursued in this paper, it is
necessary to consider the specific range of policies to be evaluated.
Policies considered for the control of CFCs have either involved the prohibi-
tion of specific uses or limits on the total amounts that could be produced.
Each policy type has its adherents and detractors. For expository purposes
only, we evaluate a production capacity limit set at 1980 production levels.
Because our intent is to summarize the large quantity of existing research on
this topic into a useful integrated framework, the choice of policy for analy-
sis was conditioned on the available literature (Palmer and Quinn 1980). Such
a production capacity limit can be represented as a vertical line segment LL'
set at the existing 1980 production level.
As demand for CFCs continues to grow, we would expect competition among
users for the privilege of using some of the limited quantity of CFCs. This
competition would likely take the form of increased prices for the
chemicals. Such intensified competition is expected to result in the alloca-
tion of this limited supply to highly valued uses only. Thus, early in the
adjustment process we would expect to see most aerosol applications of CFCs
disappear due to their substantially increased cost. Figure 1 illustrates
this process. Demand shifts to dd' but the quantity available cannot increase
beyond the 1980 production level LL'. Depending on the feasibility of substi-
tution in both technical and economic terms, CFC users will either switch to
alternatives or compete for the limited supplies. The resulting change in
economic surplus is measured as the shaded area p*p**abc in Figure 1.
Benefits. Noneconomists are often confused by the convention that the
benefits associated with any environmental improvement are the damages avoided
as a result of the policy action. We compute the production, use, and
emissions of CFCs expected in the future in the absence of any policy
action. These emission trajectories can then be transformed into estimates of
ozone depletion over time through atmospheric models. The depletions are then
translated into the effects that are addressed in the various volumes of this
report. Similarly, a trajectory of emissions associated with the imposition
of a production capacity limit can be calculated along with its expected
effects. In real time, we would expect the time path of emissions to be
altered in response to the effects of policy as indicated in the discussion of
cost. Consequently, it is important to evaluate the behavioral adjustments of
the economic actors prior to estimating the impacts of those decisions upon
the atmosphere and environment. Thus we have a "without policy" set of
effects and a "with policy" set; the differences between them represent the
effects avoided. These are the benefits resulting from the policy action.
THE SPECIFIC ANALYSIS
Irrespective of whether we actually perform the benefit-cost computation
and whether discounting is applied and in what degree, it is useful to identi-
fy the intertemporal distribution of benefits and cost. There are a number of
theoretical and ethical issues associated with the application of discounting
techniques across long time scales, and so it is important to take the inter-
generational view alluded to earlier. The practical implication of such
vantage is that most effects will be left in the physical units of occurrence.
As indicated in the preceding section, this type of analysis requires
time dependent scenarios describing the evolution of the atmosphere in
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response to emissions. This analysis utilized Scenarios A and C from the
time-dependent, two-dimensional model presented by Stordal and Isaksen (this
volume). Scenario A assumes that emissions of chlorocarbons will be held
constant at 1980 levels. The specific chlorocarbon emissions considered are
methyl chloride, carbon tetrachloride, methyl chloroform, F-11, F-12, F-22,
and F-113. Detailed emission rates for the individual constituents are given
in Table 2 of Stordal and Isaksen. Scenario A is assumed to approximate the
effect of imposing a production limit at 1980 levels. This is an assumption
since there is not a strict equivalence between production and emissions. For
example, production could increase over time while emissions were held
constant. This could be accomplished by reducing prompt emissions, improving
recovery and recycling. However, this approximation is quite useful in
allowing us to simulate the effects of the imposition of a production limit.
The specific assumptions and effects associated with Scenario A, the "with
action" alternative, are presented in Table 1.
Extension of the status quo, i.e., continued chlorocarbon production
growth, is represented by Scenario C. Of the four time paths presented by
Stordal and Isaksen, this is the most pessimistic in that it projects a high
rate of sustained annual growth in emissions. While emissions do not neces-
sarily correspond to production, this scenario was specifically derived from
the late market maturation and new market development assumptions of Quinn et
al (1980). These yield approximately a 4% annual rate of growth in production
which was translated into a 2.1% annual increase in the rate of emissions of
individual chemicals. An immediate question arises as to the realism of the
production growth rate. From the UNEP review of CFC projections studies
presented in Rome, 4% is an upper bound within the range of estimates
produced. Thus, the results presented in this paper can be construed to be a
conservative upper limit. It is conservative in the sense that no account is
taken of the potential for demand increases among developing countries or
among Eastern Bloc nations. This "without action" scenario is described in
Table 2.
From the UNEP workshop on demand and controls held in Rome in May 1986,
several facts clearly emerged. First, chlorofluorocarbons have highly desir-
able physical and chemical properties, which account for the wide array of
beneficial applications in which they are found. These characteristics have
resulted in substantial growth in demand and use. Despite the slump in sales
induced by controls on aerosol applications in some countries in the late
1970s and a worldwide recession, production levels have increased beyond
previous peaks. Projections of future CFC demand produced by a variety of
alternative methodologies and authors all indicated that demand would grow.
Major areas of uncertainty were identified as future population growth, the
level of economic activity in the world, and the growth of sales in the
developed countries. From that session it is clear that in the absence of
policy action, CFC use will continue to grow in the future. While the papers
presented provided a wide range of possible future CFC levels, it is important
to emphasize that:
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Table 1. Global Average Ozone Depletion With Constant
Emissions at 1980 Levels
YEAR
1980
1990
2000
2010
2025
PRODUCTION EMISSIONS INDEX
constant 100
" 100
11 100
" 100
11 100
OZONE DEPLETION
0.80*
1 .40*
1.80*
2.00*
2.00*
Source: Stordal and Isaksen (this volume).
Table 2. Global Average Ozone Depletion With
Continued Production Growth
YEAR
1980
1990
2000
2010
2025
PRODUCTION
EMISSIONS INDEX
100
(growth of 4.0* per year)
" 155
" 227
" 299
" 421
OZONE DEPLETION
0.80*
1.80*
3.00*
4.40*
7.50*
Source: Stordal and Isaksen (this volume).
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Under no circumstances do zero growth assumptions appear
to be a reasonable basis for calculating long term
emissions profiles. Moreover, growth rates in production
and emissions of these chemicals will probably be higher
in the next few decades than in the distant future.
Holding other things constant, these findings will tend
to increase expected ozone depletion relative to models
with unrealistic steady state emissions at historical
levels. (Quinn et al. 1980)
Further, it is important to remember that the results produced by Stordal
and Isaksen were spatially, as well as temporally, distributed. In
particular, their estimates indicate that ozone depletion will be
latitudinally distributed with increased depletion at high latitudes. To
illustrate the significance of these spatial differences, Tables 3 and 4
present the ozone depletion effects associated with Scenarios A and C, respec-
tively, for 60°N latitude. Even with emissions held constant at 1980 levels,
depletion is projected to reach 8% by 2025. If production and emissions
continue to grow, 8% depletion would be attained at 60°N by 2000, rising to
M% in 2025. Consequently, the global average depletion trajectories employed
in this analysis are conservative with respect to the extreme experiences that
could result.
Costs
As previously indicated, the social cost of any control action can be
expected to fall into several categories; but we only measure surplus
losses. The costs of controlling emissions through the imposition of a
production capacity limit set at 1980 levels are taken from a study conducted
by Rand (Palmer and Quinn 1981). That study considered each of the major
market outlets for chlorocarbon inputs with a focus on understanding both the
availability and ease of substitution. In generic terms, the alternatives
evaluated ranged from reduced input use from changes in product formulation or
production technology, improved recycling and recovery, and switching to non-
CFC inputs. For each major CFC user these alternatives were arrayed according
to cost so that substitutions would occur in synchrony with increases in the
price of CFCs. These responses were then aggregated for each chemical and for
the industry as a whole.
There are three basic areas of uncertainty in this analysis: the speed
of user responses, the rate at which new alternatives would be commercially
provided, and the precise mechanism for market clearing. These uncertainties
are accommodated by assessing the impact of these rates upon costs for various
assumed rates. While the Rand study evaluated seven alternative scenarios,
only two are considered in this paper. The extremes of the Rand results were
selected to represent pessimistic and optimistic extremes that should bracket
the actual costs. Their results were updated to 1984 terms to facilitate
comparison. The annual cost of a 1980 production cap for the years 1981
through 1990 are displayed in Table 5. Using these annual estimates and
converting to present value terms at an 11% discount rate results in
cumulative control costs for this 10-year period ranging from approximately
$1.9 to $4.5 billion. From Table 5, it is clear that costs would rise over
time as the demand for CFCs continues to grow, as users continue to bid up the
prices of the increasingly scarce chemicals, and as the easy substitutions are
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Table 3. Ozone Depletion With Constant Emission at 1980 Levels
at 60° North Latitude
YEAR
1980
1990
2000
2010
2025
PRODUCTION
constant
it
it
ii
it
EMISSIONS INDEX
100
100
100
100
100
OZONE DEPLETION
2.40$
4.50$
6.00$
7.00$
7.90$
Source: Stordal and Isaksen (this volume).
Table 4. Ozone Depletion With Continued Production Growth
at 60° North Latitude
YEAR PRODUCTION EMISSIONS INDEX
1980
(growth of 4.0$ per year)
1990 "
2000 "
2010 "
2025 "
100
155
227
299
421
OZONE DEPLETION
2.40$
5.00$
7.90$
11.50$
17.00$
Source: Stordal and Isaksen (this volume).
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Table 5. Time Stream of Costs
YEAR OPTIMISTIC PESSIMISTIC
(millions of 1984 dollars)
1981 27.4 49.2
1982 65.5 152.7
1093 135.7 317.2
1984 181.0 578.1
1985 285.2 873.2
1986 425.9 1427.6
1987 571.4 1453.2
1988 664.8 1480.9
1989 926.7 1511.0
1990 1543.5 1558.2
Present Value 1865.3 4543.0
Source: Palmer and Quinn.
achieved. In sum, for this period average annual control cost would be
expected to range between $187 and $454 million.
Benefits
This report presents papers documenting effects upon human health and the
environment from two problems that are linked through CFCs. Increased UV-B
radiation throughout the biosphere is expected as the total ozone column is
reduced through chain reactions in the stratosphere catalyzed by chlorine.
CFCs are also radiatively active, absorbing infrared radiation and contri-
buting to the climate warming due to the greenhouse effect. The direct and
indirect effects induced by these changes are the damages associated with
emissions and thus are the benefits that would result from controlling such
emissions.
Historically, concern with ozone depletion has centered on increased UV-B
radiation and its direct implications for human health. The effects docu-
mented include increased skin cancer, immune system suppression, and ocular
damage. This paper focuses on the implications of skin cancer research for
changes in human health when coupled with alternative trajectories of ozone
depletion. Epidemiological studies conducted by the National Cancer Institute
formed the basis for our effects assessment (Fears and Scotto 1983).
Estimates of ozone depletion can be translated into increases in UV-B radia-
tion through application of an enhancement ratio. In this paper that was
assumed to be a conservative 1:2 (National Academy of Sciences 1984).
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Coupling the alternative ozone depletion scenarios previously discussed with
the enhancement ratio, trajectories of UV-B increase can be predicted. Using
the results from the Fears and Scotto (1983) power model (more conservative
than its exponential counterpart), UV-B increases are mapped into increased
incidences of skin cancer. These UV-B increases are applied to the base case
of 400,000 cases per year and adjusted according to the projections of a
Caucasian population presented in Rundel and Nachtwey (1978).
Time and policy dependent rates and numbers of skin cancers for the
United States are shown in Tables 6 and 7. Table 6 indicates that even with
emissions held constant at 1980 levels, the number of new skin cancers would
rise to approximately 142,000 per year by 2025. A more dramatic change is
associated with growth in chlorocarbon emissions as the number of new cases
for that year is estimated to be roughly 256,000 (Table 7). Our interest here
is the difference between these trajectories, because that is the number of
cases of skin cancer that could be saved by constraining chlorocarbon
emissions and thus slowing the rate of ozone depletion. For example, about
114,000 cases of skin cancer could be prevented in 2025 by controlling chloro-
carbon emissions growth. Table 8 presents this component of the benefits
trajectory as the differences over time for each of the projection years.
However, these results are more easily understood graphically. Figure 2
depicts the number of new cases of skin cancer expected if emissions are
controlled (with action) and if emissions continue to grow (without action).
The shaded area between these two trajectories is the total number of cases
that would be avoided as a result of policy action. In this analysis, 1.66
million skin cancers could be prevented if emissions are controlled at 1980
levels. This result is all the more significant given recent reports citing
the lack of progress in managing cancer and the need to emphasize prevention
(Associated Press 1986). From this vantage, controlling chlorocarbon
emissions would seem to be a judicious investment.
At a more mundane level, other direct effects of increased UV-B include
materials damages, in particular impacts on polymers and elastomers. Andrady
and Horst (Volume 2) identify effects ranging from discoloration to
brittleness. The specific damage depends upon the type of plastic and its
application. For example, in the case of rigid PVC used for home siding, UV-B
causes discoloration which results in an increased rate of rejection.
Increased PVC brittleness due to UV-B radiation in pipelines can cause
premature failure and more serious consequences. In each case, these effects
can be ameliorated by changing the plastic's formulation by adding titanium
dioxide. Andrady and Horst (Volume 2) project the amounts of plastics expect-
ed to be used in the future, the increased UV-B this stock would be exposed
to, and the costs of ameliorating the effects of such exposure.
Their results are interpolated for the two ozone depletion scenarios
analyzed in this paper. Table 6 contains the damage estimates to U.S. PVC if
emissions are controlled. At a maximum, these would be $8 million annually.
In the absence of control, however, this figure would increase to $35 million
per year (Table 7). Consequently, the maximum annual benefit in the form of
foregone PVC damages would be $2? million (Table 8). Using a planning horizon
extending to 2075 and applying a discount rate of 10 percent they estimate
that the present value of PVC damages would range from $10 to $27 million
depending upon the strength of PVC demand. While these damages are relatively
small compared with the costs estimated for the production cap policy, they
illustrate the pervasive nature of the effects of ozone depletion.
368
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280 -i
240 -
200 -
Numbers
of
Cases
(thousands)
160 -
120 -
80 -
40 -
2030
Figure 2. The Incidence of Skin Cancers in the United States
Associated with Alternative Ozone Depletion Scenarios
369
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Table 6. Effects of Global Average Ozone Depletion With
Constant Emissions at 1980 Levels
EFFECTS
YEAR
1990
2000
2010
2025
OZONE
DEPLETION
1 . 40$
1.80$
2.00$
2 . 00$
SKIN CANCERS3
[% increase]
Male/Female
5.6/ 4.2
1.21 5.4
8.0/ 6.0
8.0/ 6.0
U.S.b
[new cases/yr]
51,900
84,800
110,600
141,900
PVC DAMAGE-U.S.C
[millions of
1984 $/year]
5.0
7.0
8.0
8.0
b
c
Based upon a 4x increase in the incidence of skin cancer for males and a
3x increase in incidence for females per unit depletion of ozone (Fears
and Scotto 1983).
Increase from a base level of 400,000 cases/yr.
Interpreted from Andrady and Horst (Volume 2).
Table 7. Effects of Global Average Ozone Depletion With
Continued Production Growth
EFFECTS
YEAR
1990
2000
2010
2025
OZONE
DEPLETION
1.80$
3.00$
4.40$
7.50$
SKIN CANCERS3
[$ increase]
Male/Female
1.21 5.4
12. O/ 9.0
17. 6/ 13.2
30. O/ 22.5
U.S.b
[new cases/yr]
58,900
104,800
152,500
256,400
PVC DAMAGE-U.S.C
[millions of
1984 $/year]
7.2
11.0
17.5
35.0
b
c
Based upon a 4x increase in the incidence of skin cancer for males and a
3x increase in incidence for females per unit depletion of ozone (Fears
and Scotto).
Increase from a base level of 400,000 cases/yr.
Interpreted from Andrady and Horst (Volume 2).
370
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Table 8. Difference Between Constant 1980 Emissions and
Continued Production Growth Scenarios
EFFECTS
YEAR
OZONE
DEPLETION
SKIN CANCERS
[% increase]
Male/Female
U.S.
[new cases/yr]
PVC DAMAGE-U.S.
[millions of
1984 $/year]
1990
2000
2010
2025
1.27.
2.4$
5.5%
1.67 1.2
4.87 3.6
9.67 7.2
22.07 16.0
6,300
20,000
41,900
114,500
2.0
4.0
9.5
27.0
A less obvious category of effects include those generated as indirect
consequences. For example, Whitten and Grey (Volume 2) present research
indicating that increased levels of UV-B irradiance due to ozone depletion
would stimulate increased formation of photochemical oxidants. Their results
indicate that ozone concentrations would peak earlier in the day and at
greater distances from the source, with the result that a larger human popula-
tion would be exposed and at risk. EPA is currently assessing existing ozone
standards in light of new research concerning general health effects.
Further, as many as 24 cities across the nation will not be in compliance with
existing standards by the December 30, 1987 deadline. Increasing levels of
UV-B will definitely exacerbate this problem and increase substantially the
magnitude of investment required to maintain urban air quality.
These effects are not limited to urban areas. Some of the most signifi-
cant damages to date associated with increasing ambient ozone concentrations
have accrued in agricultural areas. As described in the National Crop Loss
Assessment (Adams and McCarl 1985; Garcia et al. 1986), yield reductions and
the consequent impacts upon profitability have cost between $0.7 and $2.0
billion annually. Increases in the ambient concentrations of ozone in rural
areas obviously would increase the extent of these damages. Whitten and
Grey's results were extended to rural areas in an attempt to identify the
possible magnitude of this impact. The increases for ground ozone concentra-
tions in urban areas associated with different levels of ozone depletion from
their research were applied to existing average rural ambient ozone concentra-
tions. The resulting concentrations were evaluated for yield reductions by
using the dose-response relations developed by Heck et al. These yield reduc-
tions for the "with action" and "without action" scenarios are shown in Tables
9 and 10.
371
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Table 9. Indirect Effects of Global Average Ozone Depletion
With Constant Emissions at 1980 Levels
YEAR
OZONE
DEPLETION
CROP LOSS a
% yield reduction
corn
wheat
soybeans cotton
1990
2000
2010
2025
1.40*
1.80%
2 . 00*
2.00*
less than
11
ti
it
1.0* for all
it
it
it
crops
Additional damages from dose response relations given in Heck et al.
Table 10. Indirect Effects of Global Average Ozone Depletion
With Continued Production Growth
YEAR
1990
2000
2010
2025
OZONE
DEPLETION
1.80*
3.00*
4.40*
7.50*
CROP LOSS a
* yield reduction
corn wheat
less than 1 .0*
less than 1 .0*
0.45* 0.45*
1.50* 1.40*
soybeans
for all crops
for all crops
1.20*
2.80*
cotton
1.80*
3.30*
Additional damages from dose response relations given in Heck et al.
372
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The results under controlled emissions show very slight effects
throughout the period of analysis. The increasing depletion associated with
continued emissions growth would cause reductions in soybean and cotton yields
by the year 2010. These would be more pronounced by 2025. The differences in
percentage yield reductions that could be attributed to policy action are
displayed in Table 11. No attempt has been made to translate these yield
reductions into an economic dimension because of the complex interaction of
behavioral and market responses. The four crops examined are major
commodities in the world's food and fiber system, as illustrated in Table
12. When aggregated across the immense acreages and values shown for these
crops, even small changes would produce significant damages.
This paper has been modest in the costs that have been estimated. Table
13 provides an itemization of the effects identified at the EPA/UNEP
conference which have not been included. Despite the lack of attention to
this wider catalogue of effects, this analysis suggests that we have answered
the question of whether to act. Even those effects about which we have great
uncertainty represent incentives to action. Perhaps the most significant
category of such uncertain impacts is that described as environmental
effects. The changes stimulated by the direct and indirect effects of both
increases in UV-B radiation and climate change will be most profound for
natural ecosystems and their inhabitants. Consider, for example, the spatial
shifts in agricultural production regions likely to occur from the combined
stresses of increased UV-B and climate change. Soil moisture changes, direct
yield reductions, changes in the temperature regimen, and enhanced carbon
dioxide concentrations will alter comparative advantage. Production regions
are likely to encroach on currently marginal lands devoted to wildlife
habitat, forestry, and open space. The magnitude of these changes have the
potential to eradicate the substantial investment that we have committed to
maintaining species diversity and wildlands.
A caveat is in order: In valuing future outcomes, we are conditioned by
current prices that reflect the existing pattern of resource and commodity
availabilities. As population grows in the future and as increasing resources
are devoted to maintaining the economic well-being of those future
generations, the availability of natural resources and wildlands can be
expected to decline. This change in physical supply can occur at exactly the
time when demands for the nonconsumptive uses of such resources will be higher
if current tasks and preferences endure. Consequently, they may be much more
precious to future generations.
Our real dilemma in the evaluation of these alternative futures is the
lack of a criterion by which to gauge them. In particular, policy formation
is hampered by the lack of an acceptable ozone depletion management target
framed in terms of public health and environmental systems damage. Until that
target is set and its implications for allowable atmospheric chlorine concen-
trations, CFC growth, and use levels are calculated, we don't really know the
potential implications of widely divergent alternative futures. Further, in
the absence of a policy target for a maximum allowable ozone depletion, it is
difficult to assess the importance of the uncertainties underlying the
alternative long-term forecasts for CFCs. Recall that scientists have
cautioned that "once the predicted change in climatology or ozone depletion
diverges substantially from current conditions, the validity of the models
becomes suspect." Consequently, what is needed is a decision concerning
373
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Table 11. Difference Between Constant 1980 Emissions and
Continued Production Growth Scenarios
OZONE
YEAR DEPLETION CROP LOSS
% yield reduction
corn wheat soybeans cotton
1980 0.0$ 000 0
1990 0.4$ -
2000 1.2$
2010 2.4$ 0.45 0.45 1.20 1.80
2025 5.5$ 1.50 1.40 2.80 3.30
Table 12. Principal Crop Commodity Statistics for 1984
CROP WORLD ACREAGE U.S. ACREAGE U.S. CROP VALUE
— (thousands of acres) (billions 1984$)
Cotton 85,067 10,380 3.66
Corn 312,299 80,434 20.50
Soybeans 130,646 67,735 11.40
Wheat 570,795 79,213 8.70
Source: Agricultural Statistics 1985, U.S. Government Printing Office,
Washington, D.C., 1986.
374
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Table 13. Effects of Ozone Depletion and Climate Change
HEALTH EFFECTS
Direct Effects of UV-B Radiation
melanoma
immune system suppression
ocular damage
Indirect Effects of UV-B Radiation
increased human exposure to increased air pollutants
Direct Effects of Climate Change
temperature thresholds and increased mortality
Indirect Effects of Climate Change
flooding severity from sea level rise
increased frequency of severe weather
AGRICULTURAL EFFECTS
Direct Effect of UV-B Radiation
crop yield reductions
Indirect Effects of UV-B Radiation
changes in competitive balance between plant species
Direct Effects of Climate Change
soil moisture changes
changes in crop suitability
Indirect Effects of Climate Change
comparative advantage and spatial location of production
equipment complements
chemical input use
pest timing and impact
property values and financial stress
FISHERIES EFFECTS
Direct Effects of UV-B Radiation
phytoplankton mortality
larval sensitivity
Indirect Effects of UV-B Radiation
changes in species diversity
endangered species
reductions in commercial catch
MATERIALS DAMAGES
Indirect Effects of Climate Change
coastal property inundation
salt water intrusion
erosion
flooding
ENVIRONMENTAL EFFECTS
species diversity
endangered species
pesticide, herbicide, trace element loadings
habitat reductions
wild and scenic rivers
wetlands disappearance
375
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acceptable public health and environmental impacts associated with alternative
levels of stratospheric ozone depletion.
FUTURE RESEARCH NEEDS
It has become extremely fashionable to highlight the scientific
uncertainties surrounding any particular environmental problem requiring
public decisions to be made. As most of us know, uncertainty is a fact of
life. Its new found vogue in the policy arena belies this normal human exper-
ience. For example, when making a corporate move, new housing is normally
acquired. Such moves typically occur across steep housing gradients. In
today's markets of rapidly appreciating prices and high demand, the potential
buyer must be prepared to make quick decisions or be foreclosed on the possi-
bility of making a decision. Business is not much different except the stakes
are higher. Opportunities present themselves and then vanish. To continue
the analogy, the business of running a global environment has even higher
stakes. We, too, are presented with opportunities for action-decision making,
which may never be offered again. To defer action when the opportunity arises
could mean its irrevocable loss. So, there is uncertainty in the economic
future of CFCs, uncertainty in the atmospheric science and effects, and uncer-
tainty in the opportunities for decision making.
The best way to represent this problem of uncertainty is to view any
policy action that might be taken as insurance. After all, the point to
insurance is the opportunity to manage uncertainty and its attendant risks.
Limiting the emissions of CFCs can be viewed as an insurance policy against
the multifarious potential future damages that are explored by the authors of
this report. What prudent person among us has not purchased insurance? The
consequences of ozone depletion alone should cause us to act, but the possibi-
lity of preventing some of the global warming is further reason. Research is
still needed but it should be focused. The following are some specific
suggestions.
When one considers the potential consequences of climate change and ozone
modification, the relative lack of research on ecological consequences is
striking. Not only is the general level of funding for research in ecology
extremely limited, but there is virtually no focus on the consequences of the
anticipated changes for natural ecosystems.
Other ecological stresses have been explored in some detail. For
example, we have begun to understand the response of freshwater ecosystems to
acid deposition, and a rudimentary and fragmented picture is developing of the
effects of air pollution stresses on mid-latitude forests. These efforts
provide a good launching point for ecological studies of the consequences of
climate change and ozone modification. There are two reasons for this
argument. First, adequate baseline data for the relevant systems are being
developed. Second, as Bruce (this volume) points out, the climate/ozone
reduction stress will act synergistically on these systems with the acid
deposition-air pollution stresses that are the focus of current studies.
A few examples illustrate this point. Mid-latitude forests that are
stressed by air pollution in Central Europe experienced rather rapid declines
after 1979. Some have suggested that this decline occurred as a natural
climate stress (successive warm periods) was superimposed on a long term air
376
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pollution stress. It is possible that this large, rapid change in forest
status is a precursor to the effects of climate change, acting in combination
with air pollution. One might suppose that this synergistic effect will
accelerate the effect of climate change alone in altering forest distributions
on the earth's surface. This particular synergy obviously links with the
Whitten study; the enhanced ultraviolet flux from ozone modification will
increase oxidant concentrations, which act as phytotoxins.
From a policy perspective, the interactive effects of these stresses are
very important. By accelerating the consequences of climate change, they will
put that stress in a current context, and signal large ecological changes
sooner than otherwise expected. Timing becomes especially important if
extreme temperature periods are ecologically significant because the number of
such periods exceeding a given temperature will increase as climate changes.
As an unfortunate consequence, heavily polluted areas become a testing ground
for the effects of climate change. We would urge a mid-latitude forest
"watch" as an ecological early warning area.
Both the nitrogen and the sulfur cycles will be affected by global
warming, providing another set of synergisms and critical ecosystems.
Clearly, we have massively disturbed these cycles, and will do so more in the
future, without knowing either the implications or where we are headed.
Increases in global nitrogen and sulfur deposition and the effects of such
deposition are already measured. The interaction of these increases with
climate change and enhanced ultraviolet flux should be an important research
focus.
These interactions also underscore the linked nature of climate change
and other air pollutant stresses both at their sources and at the effects
levels. They emphasize the efficacy of strategies to limit trace gas
emissions in general and add a note of urgency to such action. In a way, the
effects are already upon us. We should slow them down and let our knowledge
expand faster than the rate at which we're changing the earth.
CONCLUSIONS FOR POLICY
Before identifying the priority policy research needs that this summariz-
ing exercise leaves us with, it is important to make a few observations.
First, most discussions concerning ozone depletion focus on CFCs 11 and 12.
It should be clear by now that we must include a wider range of ozone-deplet-
ing chemicals within our regulatory framework. The remainder of the
commercially produced CFCs plus the halons should be included. The bromine
contained within the halons is many times more effective at depleting ozone
than the chlorine of CFCs. If only F-11 and F-12 are managed and other chemi-
cals are produced for a mature market, we will not attain the desired
objective of protecting the ozone layer. Furthermore, consider the implemen-
tation of the production capacity limit within the European Economic
Community: In that setting, the cap is set to the sum of the nameplate capa-
cities for the various existing production facilities. There are a number of
swing facilities that primarily produce F-11 and F-12 but for a portion of the
year also produce F-22. If the F-11 and F-12 production capacity limits were
to become binding, then these facilities would be dedicated to F-11 and F-12,
and a F-22 facility could be constructed, adding more CFC emissions. We need
a consistent and reliable method of adding these different chemical compounds
377
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together to ensure that their individual depleting effects are accounted for
in any policy.
We need to identify an internationally and environmentally acceptable
limit to stratospheric ozone depletion. Is the intent to limit the rate of
growth of CFCs or is it to constrain the ultimate quantity discharged to the
atmosphere? While we may perceive ourselves to be currently constrained in
our ability to either articulate or implement any policy objective, we should
actively assess the consequences of the possible choices. What if CFCs are
not best conceived as a mature or saturated market? What are the effects of
differences in policies, timing and force? If we delay policy action, will
policy action in the future be more difficult? Delaying would not provide the
needed stimulus for research into substitutes or reduced emission
technologies. What are the opportunity costs of deferring control? To
address these policy questions and deliver information to a rational policy
process, we need to focus our research resources in the next year on the
articulation of our uncertainty and its explicit incorporation into policy
analysis. What are the consequences of being wrong and what is the least
risky alternative? The real challenge is the design of policies to limit CFC
emissions with associated monitoring and enforcement components that will
protect the environment and yet allow all nations to share in the benefits of
the use of these chemicals.
It is important to distinguish between irreversible decisions and
irreversible actions. In the case of stratospheric ozone, an irreversible
action is depletion and its attendant effects which cannot be undone except
with the passage of very long periods of time. By contrast, policy actions to
limit the growth in emissions of CFCs and other ozone-depleting substances do
not represent irreversible decisions. Any agreement can be reconsidered and
changed. The critical point is the irreversibility of the consequences, which
represent an imperative quite distinct from whether policy may be reasses'sed
and changed. This places the policy question before us strictly in the form
of trading off short-term economic advantages for an environment that can be
sustained in the long run.
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