AN ASSESSMENT OF THE RISKS OF
STRATOSPHERIC MODIFICATION
Volume I: EXECUTIVE SUMMARY
Submission to the
Science Advisory Board
U.S. Environmental Protection Agency
By
Office of Air and Radiation
U.S. Environmental Protection Agency
October 1986
Comments should be addressed to:
John S. Hoffman
U.S. Environmental Protection Agency, PM 221
401 M Street, S.W.
Washington, O.C. 20460
USA
The following report is being submitted to the Science Advisory Board and to
the public for review and comment. Until the Science Advisory Board review
has been completed and the document is revised, this assessment does not
represent EPA's official position on the risks associated with stratospheric
modification. This report has been written as part of the activities of the
EPA's congressionally-established Science Advisory Board, a public group
providing extramural advice on scientific issues. The Board is structured to
provide a balanced independent expert assessment of scientific issues it
reviews, and hence, the contents of this draft report do not necessarily
represent the views and policies of the EPA nor of other agencies in the
Executive Branch of the Federal Government. Until the final report is
available, EPA requests that none of the information contained in this draft
be cited or quoted. Written comments can be sent to the Science Advisory
Board and would be appreciated by November 14, 1986. Public comments should
be submitted to John Hoffman by December 15, 1986.
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SUMMARY
Rising concentrations of chlorofluorocarbons (CFCs) and Halons have the
potential to deplete stratospheric ozone and to allow additional quantities of
the biologically damaging part of the ultraviolet radiation spectrum (UV-B) to
penetrate to the earth's surface, where it would harm public health and the
environment. While considerable scientific uncertainties remain, substantial
advances have taken place in understanding of this issue since the development
of the theory linking CFCs to ozone depletion in 1974.
Over the past decade, non-aerosol CFC use has risen as the global economy
has grown. A variety of studies indicate that the long-term growth of CFCs,
in the absence of additional regulation, is likely to be between 1% and 4%
annually.
Atmospheric concentrations of other trace gases (e.g., carbon dioxide,
methane, and nitrous oxide) are also growing. The sources of carbon dioxide
increases can be linked primarily to expanded use of fossil fuels, and
secondarily to deforestation. In contrast, far less is understood about the
sources and sinks of methane and nitrous oxide. Unlike CFCs and halons, these
gases either add to the amount of ozone or reduce the rate of depletion. Like
CFCs, these gases are greenhouse gases that are predicted to increase global
temperatures and change global climate. Since future trends in emissions of
these gases are important factors in determining ozone modification and
climate change, assumptions about their growth must be carefully considered.
Models of stratospheric chemistry and physics are used to predict future
changes in the ozone layer. While these models fail to accurately reflect all
the complex forces which interact in the atmosphere to create and destroy
ozone, nonetheless, they represent the most advanced tools for understanding
possible changes in the ozone layer that could be related to future scenarios
of trace gases. One-dimensional models predict that average global ozone will
decline for all scenarios in which CFCs grow. Two-dimensional models analyze
ozone depletion for seasons and latitudes. These models predict depletion at
higher latitudes even if CFC use is reduced to 1980 levels and other trace
gases continue to grow at recent rates.
Model estimates of total column depletion are sensitive to the continued
release of greenhouse gases that counter ozone loss. If an assumption is made
that emissions of these gases are eventually limited in order to reduce the
magnitude of future global warming, the depletion expected froo any scenario
of CFC emissions would be larger.
Because the current models oversimplify or fail to include processes that
occur in the atmosphere, a critical question relates to how useful they are as
a predictive tool. One method of testing their validity is to compare their
predictions against observations of the atmosphere. Models currently closely
reproduce most atmospheric measurements, but fail to accurately reproduce
some, including ozone in the upper stratosphere and the rapid depletion of
ozone in Antarctica in the last six years. These inconsistencies lower our
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confidence in models, making us less certain that they are not underpredicting
or overpredicting depletion. At this time, however, analysis of Antarctic
data has not proceeded far enough to justify abandoning current models as the
best tools for risk assessment.
Many inputs to these models are based on laboratory measurements.
Uncertainty about the accuracy of these measurements is one potential area
responsible for the inadequacies of current model predictions. Analyses of
the implications of this class of uncertainties indicate that if CFCs grow,
there is only a small chance of no depletion even if laboratory measurements
change within the ranges tested. The chances of a depletion significantly
greater than the average predicted appears larger than the chances of one
significantly smaller.
If depletion in column ozone takes place, increases will occur in basal
and squamous skin cancer cases and are considered likely for melanoma skin
cancer. Deaths from these cancers would also increase. If depletion occurs,
additional cataract cases could be expected, along with increased suppression
of the immune system. The effect of this immune suppression on infectious
diseases like herpes and leishmaniasis would be to reduce the body's capacity
to prevent spread or outbreaks. Little is known about effects on other
cutaneous infectious diseases.
While quantitative assessments of the risk to crops and terrestial and
aquatic ecosystems from higher UV-B associated with depletion are not yet
possible, evidence appears to indicate that significant risks exist. While
some cultivars of plants are less susceptible and photorepair mechanisms may
reduce losses, field tests to date have shown damaging effects on yield. In
the case of aquatic organisms, experimental design is far more complicated.
Initial studies suggest that some species are damaged more than others. The
net effect on productivity and any implications for the aquatic food chain
cannot yet be determined.
If ozone depletes, polymers would be expected to degrade more quickly,
although quantitative estimates are available for only one polymer. Finally,
based on one study, depletion is predicted to increase both tropospheric ozone
(i.e., smog) in urban areas and the production of hydrogen peroxide (an acid
rain precursor).
Increases in CFCs and other trace gases and resulting stratospheric
modification all are expected to contribute to global wanning and climate
change. According to the National Academy of Science the magnitude of future
warming is very uncertain. The currently accepted range is 3°C + 1.5°C for
doubled C02 or its equivalent in radiative forcings from other gases. Cloud
response to warming is the major uncertainty with regard to the magnitude of
warming. The timing of the warming is also uncertain. Oceanic heat
absorption is the major question with regard to "the speed which the world's
temperature can expect to increase.
Global warming is likely to cause thermal expansion of the oceans and
alpine melting, raising sea level. The contribution of ice deglaciation to
sea level rise is much more uncertain.
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Sea level rise can be expected to innundate land, especially wetlands,
erode recreational beaches, and cause increased flooding and saltwater
intrusion into freshwater areas. River delta areas are expected to be most at
risk. Case studies in two U.S. cities indicate that sea level rise can be
expected to cause significant economic damage, some of which could be
mitigated by anticipatory actions.
The climate change (e.g., shifts in rainfall, storm tracks, etc.) that
would be associated with global warming is more difficult to predict than sea
level rise, as are the effects of that climate change. Nevertheless, studies
suggest that forests, water resources, agriculture, and health will all be
affected.
An integrated analysis of the likely emissions, atmospheric response, and
effects (based on a one-dimensional model) indicates that under the central
case assumptions the U.S. can expect 40 million additional skin cancer cases
and 800,000 deaths for people alive today and those born during the next 88
years if there is no further action taken to limit CFCs. Two-dimensional
models, because they include estimates of depletion by latitude, may be more
suitable for estimating impacts. Preliminary analysis using these models
suggests that the effects could be twice as high. In addition, estimates of
ozone depletion would be much higher if greenhouse gases are eventually
limited, approximately doubling for a case which assumed that greenhouse gases
are limited in order to hold warming to 3°C (assuming 3°C for doubled C02; the
actual limitation imposed by such a reduction in greenhouse gases could be
1.5°C or 4.5°C, based on the NAS range).
Integrated analyses show that estimates of damages are sensitive to the
rate of CFC and other trace gas growth. Quantitative estimates of damage are
also sensitive to assumptions underlying relationships between exposure and
impact in each of the effects area.
A further underlying uncertainty exists about risk estimates -- no
experiments can be conducted with the earth to validate these models. Thus,
there is no guarantee that models are not under or overpredicting the
magnitude of the risks.
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SUMMARY OF FINDINGS
1. IN THE ABSENCE OF REGULATION, ATMOSPHERIC CONCENTRATIONS OF POTENTIAL
OZONE-DEPLETING CHEMICALS ARE LIKELY TO INCREASE WITH WORLD ECONOMIC
GROWTH.
la. Estimates of chlorofluorocarbons (CFCs) 11 and 12 based on economic
analysis indicate that average long-term growth is likely to be 2.5%
per year; growth of CFC 113 and 22 is expected to be higher.
Ib. While significant uncertainty surrounds long-term growth, estimates, a
variety of studies indicate that growth is unlikely to be negative
nor greater than 5%; several studies indicate that a long-term growth
rate between 1.2% and 3.8% is more likely.
Ic. Halon 1211 and 1301, two brominated fire extinguishants, may grow
fast enough to become significant contributers to ozone depletion.
2. CONCENTRATIONS OF OTHER TRACE SPECIES (CARBON DIOXIDE. METHANE. NITROUS
OXIDE) THAT COUNTER OZONE DEPLETION ARE ASSUMED TO INCREASE AT
APPROXIMATELY THE SAME RATE AS IN RECENT YEARS. THESE TRACE SPECIES ARE
ALSO GREENHOUSE GASES THAT WILL ADD TO GLOBAL WARMING.
2a. A variety of studies based on future fossil fuel consumption have
estimated carbon dioxide (C02) growth. Assuming moderate economic
growth and technological change, C02 emissions were predicted to grow
at 0.6% annually.
2b. Recent measurements of nitrous oxide (N20) show growth of 0.25% per
year. Continuation of the trend was used in the central case.
2c. Recent measurements of methane (CH4) show 1.0% per year increase.
Continuation of the trend was assumed in the central case.
2d. Significant uncertainty surrounds all these trends. Because little
is understood about the sources and sinks of methane, and it has a
relatively short atmospheric lifetime, assumptions about future
trends of this gas are particularly uncertain.
2e. The standard assumption the modeling community has used in developing
scenarios has been that long-term projections of trace gases that
counter ozone depletion will not be limited by future decisionmakers
in order to reduce the magnitude of global warming.
3. MODELS OF THE STRATOSPHERE PREDICT DEPLETION FOR SCENARIOS IN WHICH CFCS
AND OTHER TRACE GASES CONTINUE TO GROW. MODELS PREDICT DEPLETION AT
HIGHER LATITUDES EVEN FOR SCENARIOS IN WHICH THE EMISSIONS OF POTENTIAL
OZONE DEPLETERS ARE LOWER THAN TODAY'S EMISSIONS.
3a. While different models produce slightly different changes in ozone
for the same scenario, they generally provide roughly consistent
estimates.
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3b. Estimated changes in ozone levels are dependent on assumptions about
trace gas growth. For example, if CFCs do not grow and other trace
gases continue to increase, greater amounts of ozone are likely.
3c. Based on a two-dimensional model, depletion with 3* growth of CFCs
and standard assumptions for gases that counter depletion is
predicted to be 7% by 2030 at 50°N.
4. PREDICTED OZONE DEPLETION IS SIGNIFICANTLY GREATER FOR SCENARIOS IN WHICH
GROWTH IN C02. N20. AND CH4 IS NOT ASSUMED TO CONTINUE UNABATED FOR THE
NEXT CENTURY.
4a. Depletion estimates would be doubled if greenhouse warming were
ultimately limited to 3°C (the limitation assumes 3°C temperature
sensitivity for double CO.; the actual limit could vary by +50%).
4b. Depletion would be even greater for a more stringent temperature
limit.
5. A NUMBER OF INCONSISTENCIES BETWEEN OBSERVATIONS AND PREDICTIONS LOWERS
OUR CONFIDENCE THAT MODELS ARE NOT UNDER OR OVER PREDICTING DEPLETION.
HOWEVER. CURRENT MODELS DO ACCURATELY REPRESENT MANY ELEMENTS OF THE
ATMOSPHERE AND STILL APPEAR TO BE THE MOST RELIABLE METHOD OF ESTIMATING
THE RISKS ASSOCIATED WITH FUTURE SCENARIOS OF TRACE GAS EMISSIONS.
5a. Models reproduce most observations of the current atmosphere
relatively well, supporting the belief they can usefully be used as
tools to predict the future.
5b. Discrepancies exist between some predictions and both observations
and measurements of various species in the current atmosphere thus
lowering our confidence that the models will not under or over
predict depletion.
5c. From 1970-83 models have predicted depletion in upper layers of the
stratosphere. This is consistent with actual measurements at 40 km.
5d. Analyses of the uncertainties of laboratory measurements used as one
class of inputs to atmospheric models indicate that if chlorine
grows, depletion is likely. The analyses also demonstrate that a
depletion significantly larger than that yielded by the standard
inputs is more likely than a depletion that is significantly lower.
6. THE FAILURE OF MODELS TO PREDICT THE ANTARCTIC OZONE DEPLETION RAISES
SERIOUS QUESTIONS ABOUT MODEL RELIABILITY. HOWEVER. UNTIL A BETTER
UNDERSTANDING AND ANALYSIS OF THIS PHENOMENON IS ACHIEVED. CURRENT MODELS
ARE STILL THE MOST APPROPRIATE TOOLS FOR RISK ASSESSMENT.
6a. The seasonal Antarctic depletion has been verified by several
different types of instruments; models with conventional chemistry
cannot explain the Antarctic depletion.
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6b. Several chemical and dynamical theories have been proposed to
explain the seasonal Antarctic depletion. Current observations are
insufficient to determine which, if any, are true or false.
6c. At this time, it is unclear whether the seasonal Antarctic depletion
is a precursor to a general atmospheric phenomenon, will be an
anomaly that remains in this unique and geographically isolated
region, or will disappear altogether.
6d. Satellite measurements from Nimbus 7 appear to indicate a depletion
in recent years in the Arctic. The scientific community has not
analyzed this data sufficiently to reach a consensus on the validity
of the data as its been interpreted, its meaning, or even to
conclude it is not part of a cyclical trend. Until this data and
its interpretation are verified, and causality is determined, it
cannot be used as a basis for considering the risks from CFCs.
7. OZONE DEPLETION WILL CAUSE AN INCREASE IN SQUAMOUS AND BASAL SKIN
CANCERS; A GREATER RISE WILL OCCUR IN SQUAMOUS SKIN CANCER.
7a. Squamous skin cancer can be anticipated to rise between 2 and 5
percent for each one percent depletion of ozone. Squamous skin
cancer is generally more serious than basal cancer and proves fatal
in a higher percentage of cases.
7b. Basal skin cancer can be anticipated to rise between 1 and 3 percent
for each one percent depletion of ozone.
7c. Although only a very small percentage of cases of these skin cancers
result in mortality, the large number of additional cases will
aggregate to create a substantial increase in total number of skin
cancers.
8. OZONE DEPLETION IS LIKELY TO CAUSE AN INCREASE IN MELANOMA SKIN CANCER.
ALTHOUGH SOME UNCERTAINTY REMAINS ABOUT THIS CONCLUSION.
8a. Melanoma is a deadly form of skin cancer that currently kills 5,000
people in the United States a year.
8b. Although conclusive evidence does not yet exist, many factors
suggest that UV-B radiation plays a substantial role in the
incidence of melanoma skin cancer.
8c. Melanoma incidence is likely to rise between 1 and 2 percent for
each one percent increase in ozone depletion.
8d. Melanoma mortality is likely to increase about 0.8 to 1.5 percent
for each one percent increase in ozone depletion.
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9. OZONE DEPLETION IS LIKELY TO SUPPRESS THE IMMUNE SYSTEM OF HUMANS.
9a. Laboratory evidence and case studies demonstrate that exposure to
UV-B radiation has the effect of suppressing the immune system.
9b. Although quantitative estimates are impossible, depletion is likely
to increase outbreaks of herpes and the severity of leishraaniasis.
9c. The impact of immune suppression on other infectious cutaneous
diseases has not yet been studied.
10. OZONE DEPLETION IS LIKELY TO CAUSE AN INCREASE IN CATARACTS.
lOa. Laboratory evidence and epidemiology studies have shown that
exposure to UV-B radiation is one cause of cataracts.
lOb. A 1% ozone depletion is likely to cause between a 0.3% to 0.6%
increase in cataract cases.
lOc. In the U.S., cataracts are treatable, but are still the third
leading cause of blindness. In developing countries they are also
a primary source of blindness.
11. OZONE DEPLETION IS LIKELY TO REDUCE CROP YIELD IN CERTAIN CULTIVARS. AND
ALTER COMPETITION BETWEEN PLANTS. THE DIMENSIONS OF THE CHANGES ARE NOT
YET QUANTIFIABLE.
lla. Information on the effects of increased UV-B exposure on plants is
very limited. Few plants have been tested under natural conditions.
lib. Some cultivars appear to be more susceptible to UV-B than others.
Inadequate information exists to determine why this occurs and if
selective breeding could be an effective defense to mitigate
damages from ozone depletion.
lie. Two out of three cultivars of soybeans tested were sensitive to
enhanced UV-B. One cultivar that was tested extensively showed a
yield loss of up to 25% for a 20% depletion.
lid. Field experiments show UV-B may affect competition between plant
species. Ozone depletion, particularly in conjunction with other
stresses, might alter ecosystems in ways not yet understood.
12. OZONE DEPLETION IS LIKELY TO ALTER AQUATIC ECOSYSTEMS AND POSSIBLY AFFECT
THE AQUATIC FOOD CHAIN. THE DIMENSIONS OF THE POSSIBLE CHANGE ARE NOT
YET QUANTIFIABLE.
12a. Limited experiments suggest that increased UV-B can alter the
community composition of phytoplankton that form the base of the
aquatic food web, can curtail the survival of zooplankton, and can
shorten breeding seasons.
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12b. Uncertainties in the lifecycles of these organisms prevents
quantitative estimation of effects, although some data exist which
suggest that relatively low thresholds of tolerance to increases
in UV-B could affect commercially important species. However,
movement to limit exposure, and turbulence or mixing may limit
damage to organisms.
13. OZONE DEPLETION WOULD DEGRADE POLYMERS. SHORTENING THEIR USEFUL LIFE.
COUNTERMEASURES WOULD ADD COST AND POSSIBLY REDUCE PRODUCT QUALITY.
13a. Current usage shows that UV-B damages physical and chemical
properties of certain polymers.
13b. Stabilizers can be added to mitigate damage from increased UV-B,
but at a price and possible loss in product quality.
13c. Uncertainty exists about effects of higher UV-B on polymers due to
a lack of an adequate experimental data base relating UV-B dose to
degradation.
13d. One study that examined the effects of UV-B on polyvinylchloride
showed substantial losses from future ozone depletion.
14. BY INCREASING UV-B. OZONE DEPLETION MAY INCREASE URBAN OZONE. A
POLLUTANT REGULATED UNDER THE CLEAN AIR ACT. IT MAY ALSO INCREASE
HYDROGEN PEROXIDE. AN ACID RAIN PRECURSOR.
14a. The only study on this issue stated that increased UV-B could cause
increases in ground-based ozone (i.e., smog). In addition, because
the ozone formed earlier in the day, it would affect larger
populations.
14b. It also showed that global warming could enhance the negative
effect of enhanced UV-B on ground-based oxidants.
14c. The study also predicted that hydrogen peroxide production was
extremely sensitive to increased UV-B.
14d. Continued studies on the effects of UV-B on ground-based oxidants
and hydrogen peroxide formation are needed to validate this initial
effort.
15. INCREASES IN TRACE SPECIES THAT MODIFY OZONE ARE ALSO EXPECTED TO CAUSE A
SIGNIFICANT GLOBAL WARMING.
15a. The National Academy of Sciences estimated a warming or 3°C +
1.5°C for doubled C02. This range is attributable to uncertainty
as to whether changes in clouds will amplify or dampen global
warming.
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15b. The tuning of the warming is expected to lag the emission of gases
by 10 to 40 years. Uncertainty about the timing is due to a lack
of knowledge about the rate of oceanic heat absorption.
15c. Changes in stratospheric water vapor would raise global
temperatures. Changes in vertical structure of ozone would add to
warming until depletion became large, at which point it would begin
decreasing temperatures.
15d. Due to deficiencies in model representations of a variety of
phenomena, regional characteristics of the climate change that
would accompany the global warming are largely uncertain. In
general, temperatures will increase the further one goes from the
equator, the hydrological cycle will intensify, and areas of
wetness and dryness will shift. Little else about climate changes
can be stated with certainty.
16. SEA LEVEL IS LIKELY TO RISE AS A RESULT OF GLOBAL VARMING. PREDICTIONS
ARE UNCERTAIN. BUT SEVERAL STUDIES HAVE ESTIMATED A RANGE FROM 50 CM TO
200 CM BY 2100 IF GREENHOUSE GAS GROWTH IS NOT CURTAILED.
16a. The primary cause of sea level rise will be thermal expansion and
alpine ice melting. Only for the higher estimates will Antarctic
deglaciation contribute significantly.
16b. Sea level rise can be expected to innudate asd erode coastal land,
to increase flooding, and to produce saltwater intrusion into
freshwater areas.
I6c. Wetlands and river deltas will be most adversely affected. By 2100
the U.S. could lose up to 50% to 80% of its coastal wetlands.
16d. Preliminary studies suggest adverse economic effects, which could
be substantially reduced by anticipatory planning.
17. GLOBAL WARMING CAN BE EXPECTED TO ALTER REGIONAL CLIMATES AND AFFECT
MANY ASPECTS OF THE ENVIRONMENT.
17a. Based on analyses of past climatic changes of roughly similar
magnitude (but which occurred over far longer periods of time),
forests will be altered significantly.
17b. Limited assessments suggest that important changes in farm
productivity can be expected throughout the world.
17c. The location and design of water resource projects are likely to be
altered by climate change.
17d. Human morbidity and mortality could be influenced. According to
the one study on this issue, in the absence of full acclimatization
(which is doubtful in built-up cities like New York) mortality from
extreme temperatures is likely to increase.
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18. FOR THE MOST LIKELY ASSUMPTIONS ABOUT EMISSIONS. ATMOSPHERIC RESPONSE.
AND EFFECTS. SIGNIFICANT IMPACTS ARE EXPECTED FOR HUMAN HEALTH AND THE
ENVIRONMENT. HOWEVER. MAJOR UNCERTAINTIES EXIST ABOUT EACH AREA.
CONSEQUENTLY THE SENSITIVITY OF RISK ESTIMATES TO THOSE UNCERTAINTIES
MUST BE EXAMINED. ESTIMATES OF RISKS IN THIS STUDY ASSUME NO ACTION IS
TAKEN TO REDUCE DEPLETION.
18a. For the central case (2.5% CFC growth, 0.6% C02 growth, and recent
trends for other gases), an additional 40 million skin cancer cases
and 800,000 deaths are projected for people alive today and those
born in the next 88 years in the United States. An additional 12
million cataract cases could occur.
18b. The earth's equilibrium temperature would rise from 3°C to 9.5°C by
2075.
18c. Estimates of risk from ozone depletion are highly sensitive to the
assumptions about growth in greenhouse gases that counter such
depletion. Limiting equilibrium global warming to 3°C (assuming
3°C sensitivity for doubled C02) would more than double the risks
of ozone depletion from CFC and haIon growth.
18d. Estimates of risks are highly sensitive to CFC and halon growth
rates. If one assumes half the CFC growth rate of the standard
case, that is 1.2% instead of 2.5%, estimated damage can be reduced
by 90%. If one assumes a growth rate of 3.8%, estimated damages
would increase 400%.
18e. Damage estimates are sensitive to the atmospheric model used. With
two-dimensional models, estimates of all damages would
approximately double.
18f. Uncertainties about dose-response relationships lead to changes in
estimates of the number of cases by 35% for nonmelanoma and by as
much as 60% for melanoma.
18g. Quantitative estimates of damages for other areas -- crops,
aquatics, ground-based ozone, sea level rise, and polymers --
cannot yet be calculated.
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INTRODUCTION
Moving from the surface of the earth towards space, the temperature falls
until the stratosphere is reached at 10-15 kilometers above the earth's
surface. At this point temperatures begin to rise (Exhibit 1). The
stratosphere sustains unique conditions in which ozone (03) is constantly
produced and destroyed, providing an abundance that varies latitudinally,
seasonally and annually around long-term means.
EXHIBIT 1
Temperature Profile and Ozone Distribution in the Atmosphere
1 .
Small quantities of chlorine, nitrogen, hydrogen, or bromine can combine
in chemical reactions with ozone molecules to produce bimolecular oxygen
(02). These substances act as a catalyst. They are freed following a series
of reactions and can repeatedly combine with ozone. Chlorofluorocarbons,
methyl chloroform and carbon tetrachloride can carry chlorine to the
stratosphere, halons can carry bromine, and nitrous oxide can carry nitrogen.
The chlorine and bromine from chlorofluorocarbons and halons act as strong
depleters of ozone. Nitrous oxide, in the face of growing chlorine, can
interfere with the destruction of ozone by chlorine. Carbon dioxide cools the
stratosphere, reducing the destruction rate of ozone. Methane creates ozone
in the troposphere (which contains 10% of the column ozone) and interferes
with ozone destruction in the stratosphere. It also increases stratospheric
water vapor. All of these molecules are greenhouse gases. Exhibit 2
summarizes their atmospheric effects.
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EXHIBIT 2
Stratospheric Perturbants and Their Effects
Nitrous oxide
Chlorofluorocarbons
Direct Effect
on Global
Temperature from
Tropospheric
Presence
Physical
Effect on
Stratosphere
Effect on
Column Ozone
Carbon Dioxide
Methane
Increases1 Cools2
Increases1 Adds water
vapor;
hydrogen*
Increases ozone3
Increases ozone at
some latitudes',
interferes with
depletion at high
altitudes
Increases
Increases
Adds nitrogen*
Interferes with
catalytic efficiency
of chlorine6
Adds chlorine* Decreases ozone*
Other Trace Gases
(methyl chloroform,
carbon tetrachloride,
haIons)
Increases3
Adds catalytic
species to
stratosphere*
Decreases ozone*
1 Ramanathan et al., 1985.
2 Connell and Wuebbles, 1986.
1 Isaksen, personal communication.
* National Academy of Sciences, 1984.
* Isaksen and Stordal, 1986.
* National Academy of Sciences (1984) notes the direct effect of N20 on
column ozone. In the presence of high levels~of chlorine, N20 may interfere
with the catalytic cycle of chlorine, reducing net depletion (Stolarski,
personal communication).
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Depletion of ozone would allow more ultraviolet radiation to reach the
earth's surface where it could harm human life, plants and aquatic organisms,
and materials. Less ozone would allow for increased penetration of the
biologically damaging, shorter, part of the ultraviolet radiation spectrum,
generally referred to as UV-B radiation (Exhibit 3).
EXHIBIT 3
Percent Increase in UV-B Radiation for a 10% Depletion
29;
307 317
Wavelength (nanometers)
337 DNA Action Spectrum
Results for Washington,D.C., for clear skies in June.
Source:NASA UV model results
RISING CONCENTRATIONS OF TRACE SPECIES
Past emissions of CFC 11 and 12 have caused a rise in their atmospheric
concentrations (Exhibit 4). These CFCs have been rising at 5% annually.
Atmospheric measurements show that CFC 113 has grown at 10% annually, and
Halon 1211 at 23% annually. Chlorofluorocarbons are used in foam blowing,
refrigeration and air conditioning, as a solvent in electronics and metal
industries, as aerosol propellants, and in a variety of specialty
applications. Halons are used in many applications as a fire extinguishant.
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EXHIBIT 4
Historical Production and Atmospheric Concentrations of CFC-11 and CFC-12
Historical Production
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Based on past trends, emissions of CFC 11 and 12 have closely tracked GNP,
growing about twice as fast (Exhibit 5) since the early 1960s. CFC-113 has
grown at an even faster pace.
EXHIBIT 5
Nonaerosol Production Per Capita of CFC-11 and CFC-12 Has Been
Correlated With Gross Domestic Product (GDP)
Per Capita in Developed Countries
(1962 to 1980)
0.8
Production
Per 0.6
Capita
(kg) 0-4
0.2
0
0246
GDP Per Capita
(Thousands 1975 US $)
8
Production per capita of CFC-11 «nd CFC-12 for nonaeroaol applications has bean correlated with COP per capita In the united
States ind other OtCO countries.
Source: CFC production, population, and COP data obtained rraai: Glbos. Nlchael J., (1986). Scenarios of CfC Use: 1985 to 20?5.
ICF Incorporated, prepared for the g.S. Environmental Protection Agency.
Concentrations Are Predicted to Rise
Market studies based on extensive economic analysis by several authors for
a variety of geographic areas predict continued growth in these chemicals.
Longer-term studies suggest growth rates of between 1-4% per year. Based on
these analyses, from now until 2050, an average growth of 2.5% appears most
likely.
* * * DRAFT FINAL * * *
-------
-16-
EXHIBIT 6
Short-Term
Non-Aerosol Projections:
CFC-11 and CFC-12
(1985-2000)
Long-Term Projections
CFC-11 and CFC-12 -- World Production
(2000-2050)
I
B
MXWW
-U U U U M
(«|
04) 1.0
24)
4J» SJO U
7.0 U
Source: "Overview ?»per lor Topic 12: Projection* 3f ?utor«
TJ2? Workshop. May 1916
Based on these projections, the future growth of CFCs would be below
historical levels. Exhibit 7 shows that world GNP per capita in 2050 is
expected to roughly be equivalent to that of Europe today and slightly more
than half that of the U.S. Despite the growth in world income, global CFC use
would be considerably less than that of either the U.S. or Europe today. This
analysis suggests that, in the absence of regulation, CFC use will continue to
grow, but at reduced rates as technological change improves the efficiency of
use or shifts consumers to alternatives.
EXHIBIT 7
Current and Projected Future CFC-11 and CFC-12
Use Per Capita and GNP Per Capita
i IJH mot
\
(197V
'CSS,
•"*»« «M •»«l*nw'l* tMMC M «.*"' *
m»x»: 'fti^nt «mm«v P*M*. IwK ft.*
* * * DRAFT FINAL * * *
-------
-17-
Projections of future trends in C02 are based on extensive energy
modelling and analysis. Exhibit 8 shows a wide range of estimates based on
varying assumptions about economic growth, non-fossil alternatives, energy
conservation, etc. For the purposes of the central case, we have relied upon
the 50th percentile case developed by Nordhaus (NAS 1983).
EXHIBIT 8
Projected Carbon Dioxide Emissions and Doubling Time of Concentrations
Cfl'-ben Oi
Em i ••ton*
«nfl DouA I t n? T <
C02 eaission projections are shown for EPA (Seidel and Keyei 1983); NAS
(Nordhaus and Yohe 1983): and Edmonds (Edmonds et al., 1984). The brackets
indicate the approximate time at which concentrations reach twice the
pre-industrial level.
N20 measurements and analysis of sources and sinks have been more
limited. However, recent atmospheric measurements show a 0.25% annual
increase. For the purposes of developing scenarios, this annual growth rate
has been extended into the future.
Future trends in methane concentrations are difficult to determine.
Scientific understanding of its sources and sinks is limited. However, its
relatively short atmospheric lifetime (of about 10 years), suggests that
changes in emissions over time could substantially Influence atmospheric
levels. In the absence of better information, we assume that recent increases
of approximately 1.0% per year will continue in the future.
For evaluating risks, a critical relationship exists between emissions and
atmospheric concentrations. CFC 11, 12, and 113 have atmospheric lifetimes of
75, 110, and 90 years respectively. This means that about 1/3 of current
emissions will still be in the atmosphere for that length of time into the
future. Since current emissions greatly exceed losses to the stratosphere,
concentrations will rise even if emissions stop growing (Exhibit 9).
* * * DRAFT FINAL * * *
-------
-18-
EXHIBIT 9
Relationship Between Emissions and Concentrations
CFC-12: Emissions
CFC-12 Atmospheric Concentrations
0.40
0.30 •
0.20
0.10 •
1830
IMS
2100
1830
1985
2100
» ntectlo. o< in i. CTC-12
caae«nr«lou contra (I).
•owe. md lo» turn SM
lou U) mid b. rnlrad to holt
»itk 11—nfl.d mat»l at
ATMOSPHERIC RESPONSE
To explore the effects on ozone of changes in the atmosphere's chemical
composition two approaches are utilized. First, measurements of recent
changes in ozone levels and other atmospheric constituents can be compared to
measured increases in CFCs and other trace gases. Second, models can be
developed which attempt to replicate atmospheric processes affecting ozone
levels. Moreover, the first approach can be .used as an important source of
information and validation of the second.
Ozone Monitoring
A range of monitoring using balloons and Umkehr readings show small, but
significant, decreases of approximately 3 percent in the upper atmosphere at
mid-latitudes and a 12 percent increase in ozone (from a smaller base) in the
lower troposphere. Because of a lack of global distribution of ozone
monitoring equipment, no acceptable method has yet been developed to aggregate
stations to determine if net change has occurred on a global basis. Analysis
using data for the period from 1970-80 suggests, however, that no significant
net change in total column ozone has occurred.
Model Predictions
A relatively good consensus exists among models that treat the world as a
single column of air (one-dimensional models), and among two-dimensional
models (2-D) that consider seasonality and latitude. Of these model types,
2-D models project higher average depletion and show more depletion the
further one moves from the equator (Exhibit 10).
* * * DRAFT FINAL * *
-------
EXHIBIT 10
Model Comparison for Coupled
Scenario: 1-D and 2-0 Model,
Global Average
Two Dimensional Model: CFC Emissions
Rolled Back to 1980 Levels
Depletion by Latitude for 3% Growth CFCs
-10
Global average change In total eoluan O>OD« aa calculated by aeversl
node ling group! (or a rnaann scenario of:
Compound Growth late (X par T««r)
Clta 1.0 (eeUeelons)
CB4 1.0 (concentrations)
N20 0.2> (concentrations)
C02 -0.60 (concentrations)
leaulta ahown (or 2-D eodols of leaasen and a£R, I'D etodels o(
Iraaaaur and Vuabbla*, and Connall'a paraatetarizatlon of th« LLNL
1-D axxael
toutca: CheeUcal Haaufacturara aaaoclatloo. (I in
growth per year in CFC eeiiaaiooa; IX growth io CH4 concent rat ii
growth in N20 concentratlona. and approxiatately 0.1X growth to i
concentratlona. Changes ahown for M)*N. SO*N. and tO*N. Teaape
cooaidered In •odal.
Source: laefcaao (peraonal coaaaunteat ion).
» (or n
O.liX
C01
irature (aedherfc
-------
-20-
Testing Model Validity
As one test of their validity, model predictions can be compared against
current atmospheric observations and historical changes. These comparisons
show that current models do a relatively good job replicating most
observations, but inconsistencies with some measurements of atmospheric
constituents do occur. These inconsistencies reduce our confidence in the
predictive capabilities of the current models.
Comparisons of models against upper stratospheric depletion estimates from
the 1970 to 1980 timeframe show relative consistency (Exhibit 11).
EXHIBIT 11
Calculated Ozone Depletion for 1970 to 1980
vs. Umkehr Measurements
nt
1*43
OCCAOM. OZONICMANOCS
In contrast, comparison of model results to the Antarctic ozone hole and
to the alleged Arctic hole suggest that factors influencing this seasonal loss
of ozone may not be incorporated in current models (Exhibit 12).
EXHIBIT 12
It
It
14
li
II
1
t
4
2
174
\»
s;
\
x
V
&
yimmm j ••Mint*
l*f.«-l*M
*•
^ r< 2.4 14 *
T-*
KS
1 1
lialm
* * * DRAFT FINAL * * *
-------
-21-
Until more information is available concerning the cause of the changes in
Antarctica, revisions to these models would be unwarranted. Inadequate
scientific evidence is available to determine whether the phenomenon is a
precursor to future atmospheric behavior or merely an anomaly created by
special geographical conditions unique to Antarctica.
Scientific analysis of the alleged "Arctic hole" has not proceeded far
enough to draw any conclusions about whether it is real or temporary, or to
determine its cause. Consequently, neither phenomenon provides a basis for
revising model depletion estimates, although they clearly raise the
possibility of missing chemistry (or aerosols, for example). Continued
research and analysis could in the future necessitate a revision of risk
estimates.
Uncertainties in Laboratory Inputs
The uncertainties about kinetic rates based on laboratory experiments were
examined in several studies. This represents one possible area of
uncertainties in current model configurations. These studies suggest that
depletion is likely if CFCs grow, and that depletion significantly greater
than predicted in the standard case is more likely than depletion
significantly smaller.
Global Warming
Global warming is considered likely as a result of increases in these
trace gases, including vertical reorganization of ozone in the stratosphere
and increased water vapor. As a benchmark, the magnitude of warming has been
estimated as 3°C + 1.5°C for doubled C02 or the radiative equivalent in other
gases. The primary source of uncertainty is the feedback from clouds. The
timing of this warming is considered uncertain because of delays currently
estimated of 10-40 years due to oceanic heat absorption. Regional climatic
change cannot yet be reliably predicted. Only gross characteristics are
possible such as, increased warming the further one moves toward the poles,
intensified hydrological cycles, and changes in the wetness or dryness of most
of the world's regions. The global warming predicted for standard scenarios
is shown in (Exhibit 13).
RISKS TO HUMAN HEALTH
Because UV-B varies by latitude under current conditions, a natural
experiment exists with more UV-B radiation affecting those living closer to
the equator than those located nearer the poles. Based on extensive
laboratory studies and epidemiological analysis, basal and squamous skin
cancer have been demonstrated to be related to UV-B radiation and can be
expected to increase with ozone depletion (Exhibit 14). Death is fairly
infrequent for these cancers'-- about 1% of cases are fatal with the
preponderance of deaths resulting from squamous cancers.
* * * DRAFT FINAL * * *
-------
EXHIBIT 13
A 3-D Time Dependent Model Projection
, Realized Temperature Increases
A 1-D Tine Dependent Model Projection
of Equilibrium Temperature
Results of Transient Analysis Using a General Circulation Model
H
$
MSI
tCtN
set*
*L
N
J illi
»V»TI
ARID
ARID
fc/*
mi
t
;•""'
f^v
mi
•j
IIII
/"*'••
-..-•
nn
if'
ii ii
nn
..,-••
/
nn
,-
IIII
• •'
1111
mi
..'*
in i
in i
ii 1 1
I
ro
to
i
I9SS
1«9S
3008 JO1S
JOiS 2 CMS 3085 1O69
1078
1960 1970 1980
1990 2000
DATE
2010 2020 2030
Exhibit 13
Only two time-dependent simulations have been conducted using a general
circulation model. The results, shown above, indicate an increase in global
average temperature of approximately 0.9°C by the year 2000 for Scenario A
(which is a continuation of current rates of growth in trace gases). Scenario
B (which reflects reduced rates of trace gas growth) indicates a waiving of
about 0.5°C by 2000. Scenario A achieves a radiative forcing equivalent to
that of doubled C02 about 40 years from now; Scenario B requires 75 years.
Temperature equilibrium warming In this model is 9°C for doubled C02.
* Cooput*d Msunlns that the cliMt* m«n«ltlvity to a doubling of carbon
dioxida i* 3*C. Thla assumption la in th« aiddl* of th« NAS rang* of l.S'C to
4.5*C (>•• Chaptar 6). Nota that tha actual waning that m*j b» raallud Mill
lag by aavaral dacada* or •or*.
Source: Hansen 198S
-------
EXHIBIT 1l»
Relationship Between 0V and Skin Cancer Incidence
Project Percentage Change in Incidence of Basal and
Squamous Cell Skin Cancers for a Ton Percent Depletion
in Ozone for San Francisco Using DNA Action Spectrum
I!
o -
C «
Basal
Male
Female
Squaaoua
Mala
Paula
LOW
21. 15
6.72
33.95
35.3U
Set low ONA
Mid
30.*4l
16.43
51.87
57.93
High
J|0
26.97
f/.. 19
8'4.6»
ro
to
i
' i
I 51 *
• si
i ' i
•* •
: 1
3 i i
5; 1
1 . 1
i 1
° i
1 ;
UV ( count*)
2 According to annual UVB measurements at selected areas of the United States
with regression lines based on an exponential model.
Source: Scotto and Fraumeni (1982).
-------
-24-
Melanoma is a more deadly form of skin cancer and there is greater
uncertainty attached to its relationship to UV-B. While there is not proof
that UV-B causes melanoma, overall the evidence supports a judgment that it is
an important contributing factor (Exhibit 15).
EXHIBIT 15
Information That Has Been Interpreted As Supporting the
Conclusion that Solar Radiation is One of Causes of Cutaneous
Malignant Melanoma (CMM)
• Vhites have higher CMM incidence and mortality rates than blacks.
• Light-skinned whites including those who are unable to tan or who tan
poorly, get more CMM than darker-skinned whites.
• Sun exposure leading to sunburn apparently induces melanocytic nevi.
• Individuals who have more nelanocytic nevi, develop more CMM; the greatest
risk is associated with a particular type of nevus--the dysplastic nevus.
• Sunlight induces freckling, and freckling is an important risk factor.
• Incidence has been increasing in cohorts in a manner consistent with
changes in patterns of sun exposure, particularly with respect to
increasing intermittent exposure of certain anatomical sites.
• Immigrants who move to surjtier climates have higher rates of CMM than
populations in their ccuntry of origin and develop rates approaching th^se
of the adopted country; this increase in risk is particularly accentuated
in individuals arriving before the age of puberty (10-14 years).
• CMM risk is associated with childhood sunburn; this association may
reflect an individual's pigmentary characteristics or may be related to
nevus development.
• Most studies that have used latitude as a surrogate for sunlight or UVB
exposure have found an increase in the incidence or mortality of CMM as
one approaches the equator.
• Patients with xeroderma pigmentosum who cannot repair CVB-induced lesions
in skin DNA have a 2000-fold increased risk of CMM by the age of 20.
• One form of CMM, Hutchison's melanotic freckle melanoma, appears almost
invariably on the chronically sun damaged skin of older people.
Information That Has Been Interpreted As Not Supporting the
Conclusion that Solar Radiation is One of Causes of Cutaneous Melanoma
• Some ecologic epidemiology studies have failed to find a latitudinal
gradient for CMM.
• Outdoor workers generally have lower incidence and mortality rates for C>
than indoor workers.
• t'nlike basal cell and sc.anous cell carcinomas, most CMM occurs on sites
that are not habitually exposed to sunlight.
*"*"*•-DRAFT FTflM
-------
-25-
Laboratory experiments and case studies demonstrate that UV-B can suppress
the immune system in animals and humans. This response is thought to be a
factor in the development of skin cancer. In addition, two infectious
diseases, herpes and leishmaniasis, appear to be affected by UV-B, in part,
due to suppression of the immune system. Other diseases have not been studied.
Although scientific understanding of the causes of cataracts is
incomplete, UV-B exposure appears to be one contributing factor to their
development. Epidemiological studies, animal studies, and biochemical
analysis provide support for linking UV-B and cataracts, though other factors
including exposure to UV-A also play a role (Exhibit 16).
EXHIBIT 16
Estimated Relationship Between Risk of Cataract
and UV-B Flux
Ftrccnt
Increase
la
Cataract
Prevalence
20
18
16
14
12-
ID-
S'
6-
4
2
0
ACE - in
AGE - 60
AGE • 70
10 15 20 15
Percent Increase la UV-B Flux
30
Although curable, cataracts in the U.S. still cause one-third of all
blindness. In less developed countries, the health hazards are more severe.
RISKS TO TERRESTIAL CROPS AND AQUATIC ECOSYSTEMS
Because the current species of plants have evolved under existing
radiation conditions, the question arises as to their ability to grow under
elevated exposure to UV-B. Early studies tested tolerance to UV-B in
greenhouses and showed substantial susceptibility for many cultivars.
However, limited experiments under field conditions have demonstrated that to
some extent a photorepair mechanism reduces damage.
* * * DRAFT FINAL * * *
-------
-26-
Soybeans are the crop that has been tested most extensively. These field
studies conducted for a period of over five years show that for a particular
cultivar reductions in yield of up to 25 percent are possible for a 20 percent
depletion of ozone.
Field experiments have also demonstrated that competitive balances between
planes can be influenced by higher UV-B. The implications cannot be
calculated, however, due to the lack of understanding about current ecosystem
dynamics and the paucity of field experiments on the subject.
The use of selective breeding to choose genotypes insensitive to UV-B may
be possible. However, because the genetic basis for resistance is not
adequately understood, this mitigation approach remains uncertain.
Consequently, while evidence indicates that yield from some cultivars of
crops may be reduced, the magnitude and dimensions are uncertain.
Based on laboratory experiments aquatic organisms appear to have low
thresholds to UV-B exposure. Enhanced UV-B would probably alter the community
composition of phytoplankton, which are at the bottom of the food chain and
which must remain close to the waters surface to absorb sunlight. Larvae of
commercially important aquatic organisms also appear subject to damage from
enhanced UV-B. The great uncertainties, however, are the extent of exposure
to enhanced UV-B in natural conditions in which water mixing and turbulence
may play a role, and the life cycles of the organisms. Current information
suggests a significant risk. For example, one study showed a 8% anchovy loss
for a 9% depletion. But current knowledge is insufficient to determine the
actual dimensions or magnitude of the risk.
RISKS TO POLYMERS
Ultraviolet-B radiation harms polymers, causing cracking, yellowing, and
other effects that reduce their useful life. Stabilizers can be added, at a
cost, to reduce damage, although in some cases they may also reduce product
viability. Increases in humidity and temperature could exacaberate harm to
polymers.
Due to a lack of experimental data, uncertainty exists about the effects
of UV-B and ozone depletion on polymers, requiring approximate estimation
methods to be used.
Only one polymer has been analyzed in detail -- polyvinylchloride (PVC).
Based on a single study, 26% ozone depletion by 2075 would cause a cumulative
economic damage of 4.7 billion dollars (undiscounted) in the U.S.
RISKS TO TROPOSPHERIC AIR POLLUTION
One study recently analyzed the effects of increased UV-B on the formation
of ground-based oxidants (i.e., smog). It showed that in three cities
increases in UV-B could increase ground-based ozone (regulated by EPA at 0.12
ppm), with global warming excaberating the situation (Exhibit 17). Ground-
based ozone would also form earlier on the day, exposing larger numbers of
people to peak values.
* * * DRAFT FINAL * * *
-------
-27-
EXHIBIT 17
Global Warming Would Exacerbate Effects of
Depletion on Ground-Based Ozone
Nashville
41.5%
17% Depletion
and
4°C Temperature <
Rise ^
17.7%
4° C Temperature
Rise
17% Depletion
Only
Increase in Ground-Based Ozone
Philadelphia
19.6%
17% Depletion
and
4°C Temperature
Rise
6.3%
y///////.
4° C Temperature
Rise
17% Depletion
Only
Increase in Ground-Based Ozone
17% Depletion
and
4° C Temperature
Rise
Source: Whitten and
Gery (1986)
Los Angeles
10.4%
4° C Temperature
Rise
17% Depletion
'Only
Increase in Ground-Based Ozone
* * * DRAFT FINAL * * *
-------
-28-
In addition, a preliminary study indicates a strong relationship between
UV-B and hydrogen peroxide, an oxidant and acid rain precursor. In Los Angeles
the effect of 33% depletion was to double hydrogen peroxide; in Philadelphia
it would increase by a factor of 16. These findings need to be verified in
chamber tests.
RISKS FROM CLIMATE CHANGE
CFCs and stratospheric modification may contribute as much as 40-50% of
total predicted global warming in high trace gas growth cases and 20-30* in
the central case. Estimates of the effects of climate change are in early
stages of research.
Potential Increases and Effects of Sea Level
Different studies have analyzed the potential contributions to sea level
rise from different sources. Several have made estimates of thermal expansion
due to global warming. One study has also estimated alpine mountain runoff
and its contribution to sea level rise, while others have looked at the
potential contribution from deglaciation. The estimates are quite consistent
(Exhibit 18).
EXHIBIT 18
Estimates of Future Sea Level Rise
(centimeters)
Year 2100 by Cause (Year 2085 for Revelle 1983):
Thermal Alpine
Expansion Glaciers Greenland Antarctica
Total
Revelle (1983)
Hoffman et al
Meier et al.
Thomas (1985)
Hoffman et al
. (1983)
(1985) c/
. (1986)
30
28-115
-
-
28-83
12
b/
10-30
-
12-37
12
b/
10-30
-
6-27
2
b/
-10-+100
0-200
12-220
70
56-345
50-200
-
57-368
a/ Revelle attributes 16 on to other factors.
b/ Hoffman et al. (1983) assumed that the glacial contribution would be
one to two times the contribution of thermal expansion.
c/ 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).
* * * DRAFT FINAL * * *
-------
-29-
Sea level rise can be expected to innundate marshes, erode coastal areas,
increase flooding, and cause saltwater intrusion (Exhibit 19).
One study estimated that a 100 to 200 cm sea level rise would eliminate 50
to 80% of coastal wetlands depending, in part, on whether new wetlands are
allowed to form or whether developed areas are protected. Several case
studies have demonstrated that specific recreational beaches would disappear,
unless periodic beach and island nourishment with sand occurred. Case studies
of Galveston and Charleston indicate that significant economic damage would
occur, particularly from flooding. These studies also show that anticipatory
planning can significantly reduce damages.
Other studies suggest river deltas are particularly at risk from sea level
rise. Much of the Mississippi delta is already expected to disappear over
time due to subsidence; sea level rise would accelerate this problem. In
Bangladesh and Egypt, one study estimated that subsidence and global sea level
rise could cause displacement of 16-21 percent of Egypt's population and 9-21
percent of the population of Bangladesh.
Possible Effects on Forests
Climate models predict that a global warming of approximately 1.5°C to
4.5°C will be induced by a doubling of atmospheric C02 or equivalent radiative
increases from other trace gases. This C02 doubling or its equivalent is
likely to take place during the next 50 to 100 years. The period 18,000 to 0
years B.P. is one possible analog for a global climate change of this
magnitude. The geological record from this glacial to inter- glacial interval
provides a basis for qualitatively understanding how vegetation may change in
response to large climatic change, though historically this occurred over a
much longer time period.
The paleovegetational record shows that climatic change as large as that
expected to occur in response to a C02-doubling is likely to induce
significant changes in the composition and patterns of the world's biomes.
Changes of 2°C to 4°C have been significant enough to alter the composition of
biomes, and to cause new biomes to appear and others to disappear. At 18,000
B.P., the vegetation in Eastern North America was quite distinct from that of
the present day. The cold/dry climate of that time seems to have precluded
the widespread growth of birch, hemlock, beech, alder, hornbeam, ash, elm and
chestnut, all o2 which are fairly abundant in present-day deciduous forest.
Southern pines were limited to Florida along with oak and hickory.
Limited experiments conducted with dynamic vegetation models for North
America suggest that decreases in net biomass may occur and that significant
changes in species composition are likely. Experiments with one model suggest
that Eastern North American biomass may be reduced by 11 megagrams per hectare
(10% of live biomass) given the equivalent of a doubled C02 environment.
Plant taxa will respond individually rather than as whole communities to
regional changes in climate variables. At this time such analyses must be
treated as only suggestive of the kinds of change that could occur. Many
critical processes are simplified or omitted and the actual situation could be
worse or better.
* * * DRAFT FINAL * * *
-------
Evolution of March as Sea Level Rises
EXHIBIT 19
Erosion; The Bruun Rule
Saltwater Intrusion
5000 Yean Ago
Today
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Future
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tc*narloi TTi* 210 «| CI/I U>-«l U ch« EPA drinking w«t*r
-------
-31-
Possible Effects on Crops
Climate has had a significant impact on farm productivity and geographical
distribution of crops. Examples include the 1983 drought which contributed to
a nearly 30% reduction in corn yields in the U.S., the persistent Great Plains
drought between 1932-1937 which contributed to nearly 200,000 farm
bankruptcies, and the climate shift of the Little Ice Age (1500-1800) which
led to the abandonment of agricultural settlements in Scotland and Norway.
The main effects likely to occur at the field level will be physical
impacts of changes in thermal regimes, water conditions, and pest
infestations. High temperatures have caused direct damage to crops such as
wheat and corn; moisture stress, often associated with elevated temperatures,
is harmful to corn, soybean and wheat during flowering and grain fill; and
increased pests are associated with higher, more favorable temperatures.
Even relatively small increases in the mean temperature can increase the
probability of harmful effects in some regions. Analysis of historical data
has shown that an increase of 1.7°C (3°F) in mean temperature changes the
likelihood of a five consecutive daily maximum temperature event of at least
35°C (95°F) by about a factor of three for a city like Des Moines. In regions
where crops are grown close to their maximum tolerance limits, changes in
extreme temperature events may have significant harmful effects on crop growth
and yield.
Current projections of the effects of climate change on agriculture are
limited because of uncertainties in predicting local temperature and
precipitation patterns using global climate models, and because of the need
for improved research studies using controlled atmospheres, statistical
regression models, dynamic crop models and integrated modeling approaches.
Higher ambient C02 levels may enhance plant growth, decrease water use,
and thereby increase crop yield and alter competitive balances in ecosystems.
These factors must be evaluated in conjunction with changes in climate
regimes. Large uncertainties exist because few long-term and multiple stress
studies have been completed.
Possible Effects on Water Resources
There is evidence that climate change since the last ice age (18,000 years
B.P.) has significantly altered the location of lakes although the extent of
present day lakes is broadly comparable with 18,000 years B.P. For example,
there is evidence indicating the existence of many tropical lakes and swamps
in the Sahara, Arabian, and Thor Deserts around 9,000 to 8,000 years B.P.
The inextricable linkages between the water cycle and climate ensure that
future climate change will significantly alter hydrological processes
throughout the world. All natural hydrological processes -- precipitation,
infiltration, storage and movement of soil moisture, surface and subsurface
runoff, recharge of groundwater, and evapotranspiration -- will be affected
* * * DRAFT FINAL * *
-------
-32-
be affected if climate changes. Until models of regional climate change are
improved, it will be difficult to obtain an understanding of the risks
associated with gloal warming.
Possible Effects on Human Health
Weather has a profound effect on human health and well being. It has been
demonstrated that weather impacts are associated with changes in birth rates,
outbreaks of pneumonia, influenza, and bronchitis, and related to other
morbidity effects and linked to pollen concentrations and high pollution
levels.
Large increases in mortality have occurred during previous heat and cold
waves. It is estimated that 1,327 fatalities occurred in the United States as
a result of the 1980 heat wave and Missouri alone accounted for over 25% of
that total.
Hot weather extremes appear to have a more substantial impact on mortality
than cold wave episodes. Most research indicates that mortality during
extreme heat events varies with age, sex, and race. Acclimatization may
moderate the impact of successive heat waves over the short-term.
Threshold temperatures for cities have been determined which represent
maximum and minimum temperatures associated with increases in total
mortality. These threshold temperatures vary regionally, i.e., the threshold
temperature for winter mortality in mild southern cities such as Atlanta is
0°C and for more northerly cities such as Philadelphia, the threshold
temperature is -5°C. Humidity and precipitation also have an important impact
on mortality, since it contributes to the body's ability to cool itself by
evaporation of perspiration.
If future global warming induced by increased concentrations of trace
gases does occur, it has the potential to significantly affect human
mortality. In one study, total summertime mortality in New York City was
estimated to increase by over 3,200 deaths per year for a 7°F trace
gas-induced warming without acclimatization. If New Yorkers fully
acclimatize, the number of additional deaths is estimated to be no different
than today. It is hypothesized that, if climate warming occurs, some
additional deaths are likely to occur because economic conditions and the
basic infrastructure of the city will prohibit full acclimatization even if
behavior changes.
* * * DRAFT FINAL * * *
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-33-
AN INTEGRATED ANALYSIS OF RISKS OF STRATOSPHERIC MODIFICATION
In order to assess risks from stratospheric modification in the absence of any
future regulatory action, the various assumptions (e.g., trace gas growth,
atmospheric response, incidence of skin cancer, etc.) have to be linked in an
integrated modelling framework. Since significant uncertainty exists about each
component, a central case was estimated along with alternative assumptions.1
1 The central case estimates reflect the most likely values of key
assumptions and inputs used to model risks:
• Annual production of CFC 11 and 12 grow at an annual average rate of 2.5
percent from 1985 to 2050, and remains constant following 2050; growth rates
for other chlorine and bromine substances as described in Chapter 3. The
compounds analyzed include: CFC-11, CFC-12, CFC-22, CFC-113, methyl
chloroform, carbon tetrachloride, Halon-1211, and Halon-1301. Emissions
estimates reflect the storage of some substances in their end-use products for
many years.
• Consensus estimates of the annual rates of increases in atmospheric
concentrations of other trace gases are used: carbon dioxide (C02) at 0.6
percent; methane (CH4) at 1.0 percent; and nitrous oxide (N20) at 0.25
percent. Trace gas assumptions are discussed in Chapter 4.
• A parameterized relationship between emissions of ozone modifiers, trace gas
concentrations and global ozone depletion is used. This equation reflects the
results of a one-dimensional model of the atmosphere using the most recent
estimates of reaction rates. The parameterized atmospheric model (described
in Chapter 17) was derived from the LLNL Model developed by Wuebbles (reported
in Chapter 5).
• The latitudinal distribution of ozone depletion is evaluated using the
results of a time-dependent two-dimensional model of the atmosphere. The
latitudinal analysis of ozone depletion is presented in Chapter 17.
• The relationship between changes in ozone abundance and changes in UV flux
reaching the earth's surface is based on estimates of a radiation model of the
atmosphere. The estimates of UV flux are described in Chapter 17.
• The risks to human health due to increases in UV are evaluated using middle
estimates of dose-response coefficients developed in epidemiologic analyses in
the U.S. The quantifiable risks to human health are described in Chapters 7,
8, and 10.
• The middle estimate by the National Academy of Sciences (NAS) for the
sensitivity of the global climate to greenhouse gas forcings is used -- 3.0°C
equilibrium warming for a doubling of the concentration of C02. The National
Academy of Sciences estimates are presented in Chapter 6. Recent analyses of
climate sensitivity indicate that a 4°C sensitivity may be a preferred central
case assumption (Manabe and Wetherald 1986; Washington and Meehl 1984; Hansen
et al. 1984).
* * * DRAFT FINAL * * *
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-34-
Exhibit 20 shows predicted depletion for a range of cases with varying
assumptions about trace gas growth.
EXHIBIT 20
Global Average Ozone Depletion: Emission Scenarios
(LLNL 1-D Model Results)
2
u
O
N
0
-10 -
-15 -
-20 -
-25 -
-30
1935
2005
2025
2045
2065
2085
Key Assumptions:
Common to Each Scenario
• CH4 concentrations: 1% per year
• C02 concentrations: 0.6% per year
• N20 concentrations: 0.25% per year
Varying in Each Scenario
Annual Growth in CFC-11 and CFC-12 production
(%/year)
Lowest
Low
Central
High
Highest
0.0
1.2
2.5
3.8
5.0
Other CFCs, and chlorinated and brominated compounds
also growing.
* * * DRAFT FINAL * * *
-------
-35-
Exhibit 21 shows predicted health effects in the U.S for the central case
assumptions.
EXHIBIT 21
Human Health Effects: Central Case
(Additional Cumulative Cases and Deaths by Population Cohort)
HEALTH EFFECT
POPULATION
ALIVE TODAY
a
NUMBERS
BORN 1985-2029*
NUMBERS
BORN 2030-2074°
Non-Melanoma Skin Tumors
Additional Basal Cases
Additional Squmaous Cases
Additional Deaths
Melanoma Skin Tumors
Additional Cases
Additional Deaths
Senile Cataract
Additional Cases
630,600
386,900
16,500
12,300
3,900
593,600
5,012,900
3,185,800
135,000
109,800
32,200
3,463,400
17,630,500
12,122,400
509,300
430,500
115,100
8,295,800
Analysis period for health effects: 1985-2074.
Analysis period for health effects: 1985-2118.
Analysis period for health effects: 2030-2164.
Exhibit 22 presents limited evidence from case studies for other key
effects based on the central case assumptions.
Sensitivity to Assumptions About Greenhouse Gases that Counter Depletion
The above case assumes unconstrained greenhouse gas growth. Exhibit 23
examines an alternative set of assumptions which consider the possibility that
future actions might be taken by governments to limit climate change.
* * * DRAFT FINAL * * *
-------
-36-
EXHIBIT 22
Materials, Climate and Other Effects: Central Case
TYPE OF EFFECT EFFECT UNITS
Effects Estimated Quantitatively for the U.S.
Materials Damage a/ 550 Present Value
(millions of 1985
dollars)
Rise in Equilibrium 6.2 Degrees Centigrade
Temperature by 2075 b/
Sea Level Rise by 2075 101 Centimeters
Effects Based on Case Studies and Research in Early Stages
Cost of Sea Level Rise 1,145-2,807 Present Value
in Charleston and Galveston c/ (millions of 1985
dollars)
Reduction in Soybean Seed 14.3 Percent in Year 2075
Yield d/
Increase in Ground-Based 5.1-27.2 Percent in Year 2075
Ozone e/
Loss of Northern Anchovy 3.8-19.8 Percent in Year 2075
Population f/
a/ Discounted over 1985-2075 using a real discount rate of 3
percent.
b/ Estimated using an assumed climate sensitivity of 3°C (middle
NAS estimate). Recent analysis indicates that 4°C may be a
preferred central case assumption. Using a 4°C sensitivity, the
estimated equilibrium warming in 2075 is about 8.4°C.
c/ Lowest estimate with anticipation of sea level rise; highest
estimate without anticipation.
d/ Essex cultivar only in years of average current climate.
e/ Lowest estimate is for Los Angeles, California; highest
estimate is for Nashville, Tennessee.
f/ Lowest estimate assumes 15-meter vertical mixing of the top
ocean layer; highest estimate assumes 10-meter vertical mixing.
* * * DRAFT FINAL * * *
-------
•37-
EXHIBIT 23
Global Average Ozone Depletion: Scenario of Limits
to Future Global Warming
2
u
0
M
0
19S5
2005
2025
2045
2065
2035
It shows the effects of ozone depletion if steps were taken to limit growth as
trace gas emissions to the level of greenhouse warming of 3°C. By limiting
the buffering of ozone depletion by the growth in these greenhouse gases, the
negative effects of CFCs and halons on ozone in the stratosphere is increased.
Exhibits 24 and 25 show the effects on health effects and other factors
for the same assumptions of limited greenhouse gas growth.
Comparison of One-Dimensional Model to a Two-Dimensional Model
The estimates given above are derived from the one-dimensional model used
throughout this review. Comparison of these global ozone depletion estimates
to those from a two-dimensional model, indicate that it produces levels of
ozone depletion slightly less than half of those by a two-dimensional model
(Exhibit 26).
* * * DRAFT FINAL * * *
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-38-
EXHIBIT 24
Cumulative Health Effects for People in U.S. Alive Today and
Born in Next 88 Years With Greenhouse Gases Limited
HEALTH EFFECT
LIMITS TO FUTURE GLOBAL WARMING
* Central Case
3°C + 1.5°C (no limit)
Non-Melanoma Skin Tumors
Additional Basal Cases 50,984,500 23,274,000
Additional Squamous Cases 41,814,400 15,695,100
Additional Deaths 1,726,000 660,800
Melanoma Skin Tumors
Additional Cases 1,137,600 552,600
Additional Deaths 308,500 151,200
Senile Cataract
Additional Cases 22,817,600 12,352,800
* Uncertain of +1.5°C due to uncertainty about true sensi-
tivity of earth to radiative forcing (e.g., same greenhouse gas
increase).
* * * DRAFT FINAL * * *
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-39-
EXHIBIT 25
Materials, Climate, and Other Effects: Scenarios of Limits
to Future Global Warming
(Figures in Parentheses are Percentage Changes from Central Case)
TYPE OF EFFECT
LIMITS TO FUTURE GLOBAL WARMING
3 C Central Case
(no limit)
UNITS
Effects Estimated Quantitativetv for the U.S.
Materials Damage a/ 726 550
Ri se in EquiIibrium
Temperature by 2075
Sea LeveI R i se by 2075
3.0
(-52)
76
(-25)
Effects Based on Case
Studies and Research in Early Stages
Cost of Sea Level Rise in
Charleston and Calveston b/
Reduction in Soybean Seed
Yield c/
Increase in Ground-Based
Ozone d/
Loss of Northern Anchovy
Population §/
967-2328
6.2
101
11U5-2807
>19.0 1U.3
>9.U->50.0 5.1-27.2
>11.0->25.0 3.8-19.8
Present Value
(millions of 1985 dollars)
Degrees Centigrade
Centineters
Present Value
(mill ions of 1985
dol lars)
Percent in Year 2075
Percent in Year 2075
Percent in Year 2075
a/ Discounted over 1985-2075 using a real discount rate of 3 percent.
b/ Lowest estimate with anticipation of sea level rise; highest estimate without
anticipation.
c/ Essex cultivar only in normal years.
d/ Lowest estimate is for Los Angeles, California; highest estimate is for Nashville,
Tennessee.
e/ Lowest estimate 15-meter vertical mixing of the top ocean layer; highest estimate
10-meter vertical Mixing.
* * * DRAFT FINAL * * *
-------
-40-
EXHIBIT 26
Global Average Ozone Depletion: Comparison to
Results with a 2-Dimensional Atmospheric Model
1-0 3 Permit
Emissions
1985
IMS
2005
2015
202S
Sensitivity to Rate of CFC Growth
As shown in Exhibit 20, the amount of ozone depletion is sensitive to the
assumption about future growth of CFCs and other trace gases (Exhibit 23).
Assuming that other gases continue to increase, Exhibit 27 shows the impact on
human health for different CFC growth scenarios.
Uncertainty About Health Dose-Repose Relationships
Uncertainty exists about the appropriate dose-response relationship for
each of the human health effects. Exhibit 28 shows an analysis of the
statistical uncertainty for each of thes areas.
OVERALL ASSESSMENT OF UNCERTAINTY
The largest quantitative uncertainties involve assumptions concerning
future emissions of CFCs; future greenhouse gas growth; the use of 2-D models
for predicting depletion, and uncertainties about dose-response parameters.
Qualitatively the uncertainties for effects include implications of increased
immune suppression; dose-response relationships for aquatics, crops,
terrestial ecosystems; and a vary of climate impacts. With respect to
modeling the atmospheric consequences of trace gas growth, there exists the
possibility that some overlooked or missing factor or oversimplified process
has lead to under- or over-predictions of changes in ozone.
* * * DRAFT FINAL * * *
-------
-41-
EXHIBIT 27
Human Health Effects: Emissions Scenarios
Additional Cumulative Cases and Deaths Over Lifetimes of People Alive Today
(Figures in Parentheses are Percent Changes from Central Case)
EMISSIONS SCENARIOS EXTREME CASES
HEALTH EFFECT Low Central High Lowest Highest
Non-Melanoma Skin Tumors
Additional Basal Cases 1,599,500 23,274,000 83,755,700 -1,616,100 135,317,800
Additional Squamous Cases 823,400 15,695,100 71,808,100 -856,600 117,809,800
Additional Deaths 35,700 660,800 2,952,400 -36,700 4,837,400
Melanoma Skin Tumors
Additional Cases 47,300 552,600 1,897,400 -40,500 3,079,500
Additional Deaths 12,100 151,200 502,800 -11,200 809,700
Senile Cataract
Additional Cases 885,000 12,352,800 34,226,900 -1,112,100 53,429,800
* * DRAFT FINAL * * *
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-42-
EXHIBIT 28
Human Health Effects: Sensitivity to Dose-Response Relationship
Additional Cumulative Cases and Deaths Over Lifetimes of People
in U.S. Alive Today and Born in Next 88 Years
SENSITIVITY OF EFFECT TO UV DOSE
HEALTH EFFECT Low Central High
Non-Melanoma Skin Tumors
Additional Basal Cases
Additional Squamous Cases
Additional Deaths
Melanoma Skin Tumors
Additional Cases
Additional Deaths
Senile Cataract
Additional Cases
14,046,400
9,242,000
109,200
384,300
134,300
6,600,200
23,274,000
15,695,100
660,800
552,600
151,200
12,352,800
34,130,500
24,385,300
10,203,000
732,100
168,500
17,038,300
* * * DRAFT FINAL * * *
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*" ^ \ UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
Dear Collegue:
Enclosed is a copy of the draft document you requested
entitled, An Asj5es,j>raent. of_ the Ri..s.ks_ of. St.jra£os_p_he]:.ic_
Modification prepared by the Strategic Studies Staff of the U.S.
EPA. This document was submitted to the Science Advisory Board
on October 23,1986. On November 24 and 25 the Science Advisory
Board, chaired by Dr. Margaret Kripke will meet to review the
document.
The review process of this document follows the traditional
procedure used by the Science Advisory Board. This includes:
- Public notice of the Subcommittee's November 24-25 meeting
in the Federal Register (in order to conform to the legal
requirements of the Federal Advisory Committee Act).
- Opportunity for succinct technical presentations to the
Subcommittee by interested members of the public (the total
amount of time allotted for such comments will not exceed one
hour)
- A copy of the risk assessment document and comments
received will be available for review at the Public Information
Reference Unit, (202) 382-5926, EPA Headquarters Library, 401 M
St, SW Washington, DC between the hours of 8:00 am and 4:30pm.
The public docket number is A-86-18.
- When the SAB Subcommittee meets in November, there will be
an exchange of scientific views between the Committee and the EPA
staff. This informal exchange of views will cover any questions
concerning the validity of the scientific assumptions, as well as
the methodologies and conclusions of the assessment document.
The Subcommittee will then develop a consensus position paper and
a final report will be prepared. Following the finalization of
the text, the report will be sent to the Science Advisory Board
Executive Committee and then directly to the EPA Administrator.
EPA will then have time to respond to the Subcommittee's report.
Written comments should be addressed to John S. Hoffman, at
PM 220, U.S. EPA, 401 M St,SW , Washington, DC 20460. Comments
are due to the SAB by November 14. The public comment period
will be open until December 10.
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GLOBAL MODELING OF THE ULTRAVIOLET SOLAR FLUX INCIDENT ON
THE BIOSPHERE
George N. Serafino
Applied Research Corporation
8201 Corporate Drive
Landover, Maryland 20785
and
John E. Frederick
Department of the Geophysical Sciences
The University of Chicago
5734 South Ellis Avenue
Chicago, Illinois 60637
-------
Abstract
Thi* report Summarizes an algorithm designed to
estimate the ultraviolet solar flux that reaches the Earth's
surface at any location on the globe and time of year.
Inputs consist of global ozone abundances, terrain height»
the distribution of cloudcover, and the albedos of clouds
and the underlying surface. Intended users of the algorithm
include atmospheric scientists* the photobiology community,
and environmental policymakers.
-------
I. Introduction
The interaction of solar radiation with the Earth and
it* atmosphere is closely coupled to the planet's ability to
support life. Ultraviolet solar radiation likely initiated
the chemical processes which led to formation of the first
organic molecules on the primitive Earth (eg. Ponnamperuma»
1981)i while the development of a substantial ozone layer
created a surface environment where complex self-replicating
molecules could evolve. The decreases shown by both the
absorption cross section of ozone and the DNA action
spectrum at wavelengths between 280 and 320 nm provide
persuasive evidence of the coupling that has existed between
the geophysical and biological realms which ultimately
provided for the evolution of higher life forms.
Issues of more immediate practical concern center on
the observation that the incidence of various skin cancers
shows latitudinal variations. This appears related to the
biologically active ultraviolet flux reaching the surface of
the Earth. While this fact alone is of great significance*
couplings of a more subtle nature apparently exist between
the radiation environment and biological systems. A prime
example is the work by DeFabo and Noonan (1983) which
indicates a link between ultraviolet radiation dosage and
suppression of the immune system in laboratory mice.
Photobiologists have adopted the term UV-A to refer to
radiation over the wavelength range 320-^00 nm, while UV-B
-------
denotes the region 280-320 nm. Absorption by ozone and
atmospheric scattering reduce the solar UV-B flux at the
surface of the Earth to a small fraction of what Mould
otherwise exist. The UV-A, being outside the range of
strong absorption by ozone* experiences much less
attenuation.
This report describes the conceptual formulation of an
algorithm designed to predict the UV-B and UV-A radiation
fluxes as functions of wavelength at any point on the Earth
for any time of year. Papers which summarize the
mathematical methods used in the code already exist in the
published literature. We make reference to these rather
than presenting details here. The algorithm utilizes global
scale ozone measurements obtained by the Solar Backscatterea
Ultraviolet (SBUV) Spectral Radiometer carried on the Nimbus
7 satellite. Ue combine this data set with additional
information on cloudcover and cloud transmission obtained
from independent sources. While the development of the
algorithm is an exercise in radiative transfer and
atmospheric science* we intend the final product to be a
tool for use by the photobiology community and environmental
policymakers.
-------
II. The Radiative Transfer Formulation
We divide the atmosphere into two parts* (1) the clear
atmosphere above any cloudtops and (S) the cloud layer» the
atmosphere beneath the cloud (the "sub-cloud layer"), and
the ground. In the absence of clouds only case 1 is
required. When clouds are present Me merge a model of this
portion of the atmosphere onto the base of the clear sky
calculation. We assume that the lower boundary of the clear
atmosphere> being cloudtops or ground* is a Lambertian
surface of known albedo. A radiative transfer calculation
which includes all orders of multiple scattering and
absorption by ozone then gives the direct and diffuse
components of solar flux incident on the cloudtops or, for
clear skies* on the ground.
The downward diffuse flux, F (> ,6»T>, for a wavelength
% » solar zenith angle 6* and optical depth T» can be
expressed as the sum of an atmospheric scattering component
FC - R / C1-RS(A »T->] (2)
-------
Here T» i« the atmospheric optical depth above the
reflecting surface (ground or cloudtop) of albedo R»
S< A »T"> represent* the backseattering power of the
atmosphere* and F (A »6,T) measures the contribution from
flux that has already reflected from the lower boundary and
is then scattered back into the lower hemisphere. The
advantage of the formulation in equations 1 and 2 is that
the quantities FQ * F, » and S can be computed without
knowledge of the surface albedo. In practice* we calculate
these terms using the Herman and Browning (1965) clear sky,
multiple Rayleigh scattering model.
For clear sky conditions the formulation summarized
above produces the UV-B and UV-A flux at the ground as a
function of wavelength* solar zenith angle (local time)* and
ozone amount. Under cloudy sky conditions* however* we must
define the transmission and reflectivity of the cloud-
subcloud-ground layer. For this we use a two stream
radiative transfer model coupled with the "adding method"
for a multi-layer atmosphere developed by Lacis and Hansen
(1974). This approach divides the atmosphere into a series
of homogeneous layers where each layer has a known
reflectivity and transmission. Clouds occupy the uppermost
layers* while the bottom layer is the ground with a
transmission of zero. The composite reflectivity and
transmission of the multilayer system is determined by
combining the reflectivities and transmissions of the
individual layers with proper account taken of multiple
-------
reflection* of upward and downward directed fluxes. Lac is
and Hansen <197*»> have presented quantitative details of the
technique. The model adopts fractional cloudcover as a
function of latitude from Hughes (198<*>. We assume a
mixture of thick low clouds* with an optical depth for
scattering of 30* and middle level clouds of optical depth
15 (Stephens* 1978). We assume cloud drops to be non-
absorbing in the UV-B and UV-A. However, absorption of
radiation still occurs in the clouds owing to the
tropospheric ozone amount included in the model. The
calculations assume that 85 percent of the downward
radiation incident at the cloudtops is scattered into the
lower hemisphere. The derived transmission of the cloud-
subcloud system multiplied by the total (direct plus
diffuse) flux incident on the cloudtops from equation 1
gives the flux at the ground. Note that Me assume all
radiation transmitted through the cloud to be isotropic over
the lower hemisphere* consistent with a large optical depth
for scattering.
The reflectivity and transmission of atmospheric layers
beneath the cloud deck are defined by expressions for a two
stream model as given by Coakley and Chylek (1975) and
Joseph et al. (1976). Each layer ha* a known optical depth
and an ozone amount based on climatology supplied with the
SBUV data set. To obtain the flux at the ground for a
c1imatological fractional cloudcover* we simply combine
values derived separately for clear and cloudy skies using
-------
e
the weights 1-f and f respectively* where f is the
fractional cloudcover at the latitude of interest.
In principle on* could compute the UV-B and UV-A fluxes
at the gro.und using a complete radiative transfer
calculation for any combination of wavelength, ozone
abundancet cloudcover* solar zenith angle* and ground
reflectivity. In practice this is not necessary. Instead
we generated three sets of flux tables* one with the base of
the clear atmosphere at 10OO mb* another at 700 mb> and the
last with the base at 400 mb. Each table contains the
radiative transfer quantities of equations 1 and 2 for S3
wavelength bands which span the wavelength range 290 to 400
nm, 9 total column ozone amounts* and 13 solar zenith
angles. Surface reflectivities corresponding to the ground
or cloudtops need not enter the tables in view of the form
of equation 1. Each table allows interpolation to obtain
surface fluxes for any ozone value and local time* while a
combination of all three tables provides fluxes for varying
terrain heights and cloudcover conditions. This flexibility
allows the algorithm to predict the ultraviolet radiation
environment at any location on the globe for any time of
year by interpolation based on precomputed radiation tables.
Surface fluxes may refer to specific local times or to
averages over the daylight period at any location and date.
-------
III. The Input Data Sett
The SBUV instrument provides the total column ozone and
vertical ozone profiles needed to evaluate terms in the
radiative transfer calculations. We use SBUV column ozone
amounts averaged over one month time intervals and over all
longitudes in 10 degree wide latitude bands. We associate
these means with the center of each month and latitude bin.
Interpolation in latitude and time then provides the ozone
amount for a specific location and day of the year. Figure
1 illustrates the behavior of column ozone as a function of
latitude and month derived from SBUV. We note that a very
recent revision in the SBUV data set uses improved
absorption cross sections and yields values approximately 6'/<
greater than those shown in Figure 1. The current version
of the global radiation algorithm uses the updated ozone
results. The extraterrestrial solar irradiance. ozone
absorption cross sections, and Rayleigh scattering cross
sections used in the calculations are from Chapter 7 of
WHO/NASA (1986).
-------
10
IV. Algorithm Operation and Sample Results
The algorithm allows the user a high degree of
flexibility in selecting parameters for a given calculation.
Mandatory input* supplied by the user arei (1) latitude and
longitude* (S) day number of the year, 1 through 365, and
(3) local time. As an alternative to local time the user
can choose to compute mean fluxes over the daylight portion
of a 5
-------
11
largest fluxes* <» watts per square meter, reach the ground
in the tropic* because the sun is most nearly overhead here*
•nd the atmospheric ozone Amounts are relatively small. The
major feature of Figure 2 is the large variation in
radiation flux with latitude* especially during the winter
season. In the Northern Hemisphere for December and January
the flux decreases by a factor of 10 between the equator and
50 degrees latitude. During summer the latitudinal
gradients are much less pronounced than in winter, and one
must move from the tropics to 60 degrees to experience a
factor of two decrease in flux at the ground. There is very
little change in the 10:00 A.M. fluxes in the tropics 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 that in Figure 2 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 3
illustrates this behavior by giving contours of the ratio of
UV-B to UV-A fluxes as a function of latitude and month at a
local time of 10:00 A.M. Clearly* the UV-B flux is much
smaller than the UV-A* with the ratio ranging from 2 to
7.SVC. The most significant information in Figure 3 is the
differing latitudinal and seasonal gradients shown by the
UV-B and UV-A. As one moves from the tropics to 60 degrees
-------
latitude in winter, the UV-B flux decreases more rapidly
than the UV-A by a factor of three to four. In summer the
relative variation it much less than a factor of two.
The example* presented above illustrate latitudinal and
seasonal variations. Future updates of the algorithm for
use in truly global studies should include longitudinal
variations in both fractional cloudcover and ozone. Par
many applications* however* the focus is on the radiation
environment at a specific location as well as on changes in
dose rates with parameters such as the ozone amount and
fractional cloudcover. A separate report by H. Pitcher and
J. Scotto now in preparation will describe such studies*
including the comparison of model predictions with ground-
based measurements from Robertson-Berger meters.
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13
Reference*
Coakley, J. A., Jr.i and P. Chylek, 1973: The two-stream
approximation in radiative transfer! Including the angle of
incident radiation* J. A_tmp_». Sc_i_. » 32, 409-418.
Dave* J. V.» and P. M. Furukawa, 1966: Scattered Radiation
in the Ozone Absorption Bands at Selected Levels o_f_ a
Terrestrial Ravleiqh Atmosphere, Meteor. Monogr . , Vol. 7,
No. 29.
DeFabo» E. C., and F. M. Noonan, 1983: Mechanism of immune
suppression by ultraviolet radiation in vivo I. Evidence
for the existence of a unique photoreceptor in skin and its
role in photoimmunnology» J. E*p. Med. > 15?» 8<»-98.
Herman. B. M., and S. R. Browning, 1965: A numerical
solution to the equation of radiative transfer» J. Atmos.
Sci.. 22, 559-566.
Hughes, N. A., 1984: Global cloud climatologies: A
historical review, J. Climate Appl. Meteor., 23, 724-751.
Joseph, J. H., W. J. Wiscombe, and J. A. Weinman, 1976: The
delta-Eddington approximation for radiative flux transfer,
J. Atmos. Sci.. 33, 175-204.
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Kalnay, E., et al., 1983: Documentation o_f the GLAS Fourth
Order GDI. Vo1ume li Model Documentation, internal report,
Laboratory for Atmospheric Science** NASA/Goddard Space
Flight Center, Greenbelt, MO. 20771.
Lacis, A. A., and J. E. Hansen, 1974: A parameterization for
the absorption of solar radiation in the earth's atmosphere,
J. Atmos. Sci . . 3J., 118-133.
Ponnamperuma, C.» 1981: The quickening of life, in Fire of
Life, Smithsonian Exposition Books, W. W. Norton and
Company, New York, 118-125.
Stephens, G. L.« 1978: Radiative properties of extended
water clouds: Part 11, J. Atmos. Sci.. 35, 2111-2132.
WHO/NASA, 1986: Atmospheric Ozone 1985, World Meteorological
Organization, Geneva, Global Ozone Research and Monitoring
Project, Report Number 16.
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15
List of Figure*
Figure 1. Contours of total column ozone (mi 11i-atmosphere-
centimeter*) •• a function of latitude and month derived
from the SBUV instrument.
Figure 2. 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 wavelengths between 290 and 320
nm.
Figure 3. The ratio of solar energy flux in the UV-B from
Figure 2 to that in the UV-A (320-400 nm) as a function of
month and latitude. 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 flux
is 7.5V. of that in the UV-A).
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N
- COLUMN OZONE
60
20
LU
O
1 °
-20
-40
-60
-80
S
N
M A M J J
MONTH
S O
Figure 1
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.-2,
N
CD
85
65
45
25
5
-5
-25
-45
-65
-85
Total UV-B Flux at Ground (W-M )
N 0 J F
N
0.4
I i I J I x
MAMJJASO
Month
Figure 2
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Ratio UV-B UV-A (Units: |Q )
N
a>
-25-
-45 ;c
r-65
-85
N 0
JFMAMJJA
Month
S 0
Figure 3
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IMPORTANT NOTE TO READERS
EPA hatt .submitted a draft document, An Assessment of the
Risks'of Stehcospheric Modification, to the Science Advisorv
Board today (October 23,198*), and also has released it for public
review and comment. On November ?4 and 25 the Science Advisory
Board, chaired hv Dr. Margaret Kripke of The University of Texas
Departnent of Immunoloav, will meet to review the document.
Until the SAR review is completed and the document revised,
the Assessment will not represent the official views of EPA. The
estimates of risks in the document and the numbers contained in
it should be viewed as preliminary. and EPA requests that thev not
be cited or quoted.
The document contains no recommendations for risk management
actions. Rather, it is a compilation of scientific assessments of
risks. 'Vhen reviewed and revised it will serve as the basis for
EPA decisionmaking. Thus the review that in now being initiated
is solely a scientific review.
The Assessment builds on the atmospheric assessments conducted
bv the World Meteroloaical Organization, NASA, NOAA, CMA, and other
national and international scientific organizations. Much of
this previous work has already been peer reviewed.
The Assessment covers and integrates information in a variety
of areas: industrial emissions of trace gases that can modify
t^e stratosphere; biogenic emissions of such gases; possible
changes in atmospheric concentrations which mav occur in response
to these atmospheres; the response of ozone in the stratosphere
to these changes; the response of the global climate system to
stratospheric modification and trace gas build up; basal and
squamous skin cancers; melanoma; immune suppression bv ultra-
violet radlation;crop and terrestial ecosvstem effects; aquatic
systems effects; the effects of UV-R on polvmers; the effects of
iTV-3 on trooospheric air quality; sea level rise; and the effects
of climate chanee.
In some cases qualitative assessments are made of these
impact areas; in other cases quantitative estimates are made.
In all cases, uncertainties are identified and their ramifications
examined. An effort is nade to examine how these areas are
linked together so that the risks can he examined over time.
The general conclusion of the Assessment as it now stands
is that a number of health and welfare impacts are likelv if emis-
sions of chlorofluorocarbons grow. A variety of uncertain factors are
found to be important in determining the magnitude of likelv
effects, including: the future growth of greenhouse gases that
could warm the earth which would counter ozone depletion; the
exact dose-response relationships for health effects; the rate
of chlorofluorocarbons and halon growth; and the actual response
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of che acraoaphere to changes in crace eases. As it now stands che
Assessment uaes conventional atmospheric chemistry in assessing
risks, arguing chac coo Liccle is underscood ahouc che Ancarccic
ozone hole co use ic co re-evaluate currenc models of che resc
of che world.
The reviewed and revised Assessment will serve as a basis
for decisionmaking in FPA'S regulatory program. F.PA is scheduled
co make a proposal which suggescs regulations or states there
is no need for regulation on Mav 1,1987 and to make a final
regulatorv decision November 1 , 1^87. In addition, internacional
negociacions are underway under che Uniced Nacions Environmental
Programme Co develop a prococol Co limic chlorofluorocarbons
globally.
For addicional informacion call:
John S. "offman
Chairman,Scracospheric Proceccion Task Force
EPA.PM-221
401 M Street, SW
Washington, DC 20460
(202) 3*2-4036
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