United States
Environmental Protection
Agency
Policy, Planning,
And Evaluation
(PM-221)
21P-2003.2
December 1990
Policy Options For
Stabilizing Global Climate
Report To Congress
Executive Summary
Printed on Recycled Paper
-------
POLICY OPTIONS FOR STABILIZING GLOBAL CLIMATE
REPORT TO CONGRESS
Executive Summary
Editors: Daniel A. Lashof and Dennis A. Tirpak
United States Environmental Protection Agency
Office of Policy, Planning and Evaluation
December 1990
-------
This document has been reviewed in accordance with the U.S.
Environmental Protection Agency’s and the Office of Management and
Budget’s peer and administrative review policies and approved for
publication. Mention of trade names or commercial products does not
constitute endorsement or recommendation for use.
Publishers Note:
Policy Options for Stabilizing Global Climate, Report to Congress has oeen
published in three parts:
21P-2003.1 MAIN REPORT (includes Executive Summary)
21 P-2003.2 EXECUTIVE SUMMARY
21 P-2003.3 TECHNICAL APPENDICES
Those who wish to order the Main Report or Technical Appendices should
inquire at the address below:
Publications Requests
Climate Change Divtsion (PM-221)
Office of Policy, Planning and Evaluation
U.S. Environmental Protection Agency
401 M Street, S.W.
Washington, D.C. 20460
-------
POLICY OPTIONS
FOR STABILIZING GLOBAL
Executive Summary
ABSTRACT 1
INTRODUCTION 2
Purpose of This Study 2
Scope of This Study 2
Current Policy Developments 4
Limitations 4
HUMAN IMPACT ON THE CLIMATE SYSTEM 5
The Greenhouse Gas Buildup 5
The Impact of Greenhouse Gases on Global Climate 8
Natural Climate Variability 10
SCENARIOS FOR POLICY ANALYSIS 10
Defining Scenarios 10
Scenarios with Unimpeded Emissions Growth 12
The Impact of Policy Choices 14
Accelerated Emissions Scenario 14
Scenarios with Stabilizing Policies 19
TECHNOLOGICAL OPTIONS FOR REDUCING
GREENHOUSE GAS EMISSIONS 28
Improve Energy Efficiency 30
Improved Transportation Efficiency 30
Other Efficiency Gains 30
Carbon Fee 31
Increase Use of Non-Fossil Energy Sources 31
Nuclear Power 31
Solar Technologies 33
Hydro and Geothermal Energy 33
Commercialized Biomass 33
Reduce Emissions from Fossil Fuels 33
Greater Use of Natural Gas 34
Emission Controls 34
Reduce Emissions from Non-Energy Sources 34
CFC Phaseout 34
Reforestation 35
Agriculture, Landfills, and Cement 35
V
-------
A WIDE RANGE OF POLICY CHOICES FOR
THE SHORT AND LONG TERM 37
The Timing of Policy Responses 38
The Need for an International Response 41
NOTES
REFERENCES
VI
-------
FOREWORD
I am pleased to transmit the attached Policy Options for
Stabilizing Global Climate , the second of two reports on global
climate change prepared in response to a Congressional request in
the Fiscal Year 1987 Continuing Resolution Authority. The first
report assessed the potential health and environmental effects of
climate change on the U.S. This report examines a range of
possible response options and estimates their potential for
reducing or limiting emissions of greenhouse gases on a global
scale.
The magnitude of the effort required to produce this report
was greater than many had anticipated. The lead authors and many
other contributors have nevertheless created an impressive and
scholarly work that provides a valuable foundation for the
additional research and analysis that will be needed for
determining future policy actions. I would like to congratulate
all those involved.
The report is one of the first to take a comprehensive and
global approach, covering all sectors and all greenhouse gases, in
the analysis of policy options for reducing greenhouse gases. It
carefully describes the types of gases involved, their physical
sources, and the level of emissions by source as well as geographic
location. Based on a wide range of policy options, from energy
efficiency to new methods of rice cultivation, it presents possible
future scenarios of greenhouse gas emissions to the year 2100
depending on the level of response as well as many other
independent factors.
The results demonstrate that greenhouse gas emissions can be
effectively reduced. However, the report acknowledges that the
actual size of these reductions will depend upon a great many
factors, not the least of which are the accuracy of the data and
the inherent limitations of the models employed in the analysis.
Economic growth, population growth, and the extent to which
countries respond to climate change are among the many other
uncertainties.
Another key limitation of the report is that comprehensive
estimates of the costs of achieving these reductions are not
provided. This was a conscious decision based on the time and
resources available for preparing the report, as well as the
interest of several groups in undertaking their own cost analyses.
Cost assessments have been conducted over the last year, both
within EPA and among other agencies. Additional studies are
underway that will improve our information on this important topic.
Since the final draft report was released approximately a year
ago it has undergone a thorough and rigorous review. Several
additional reports on responses to global climate change have also
been issued which have provided a further basis for judging the
-------
quality and thoroughness of the report. These include reports by
the Intergovernmental Panel on Climate Change 1 the Office of
Technology Assessment, the National Research Council, and others.
Remarkably, the final report has required only relatively minor
improvements to meet the standards set by our reviewers as well as
other experts studying the issue.
I believe this is not only due to the excellent effort devoted
to the preparation of this report, but it is also a reflection of
the broad consensus that exists concerning the nature and potential
of the options we have for addressing the problem of global climate
change.
Unfortunately, there is no silver bullet among them. Choosing
among the wide range of options is thus going to be the toughest
challenge we now face.
Terry JDavies
Assistant Administrator
Office of Policy, Planning and Evaluation
-------
EXECUTIVE SUMMARY
ABSTRACT
The composition of Earth’s atmosphere
is changing. The concentration of carbon
dioxide, the most important greenhouse gas
accumulating in the atmosphere, has risen
25% since pre-industrial times. Significant
increases in the concentrations of methane,
chlorofluorocarbons, and nitrous oxide have
also been observed. Present emission trends
would lead to a continuing buildup of these
gases in the atmosphere. Although there is a
good deal of uncertainty about the timing,
magnitude, and regional distribution of climate
change that would occur if these trends are
not reversed, significant global warming over
the next century -- from 0.2 to 0.5 degrees C
per decade -- is predicted by global climate
computer models.
Drastic cuts in emissions would be
required to stabilize atmospheric composition.
Because greenhouse gases, once emitted,
remain in the atmosphere for decades to
centuries, stabilizing emissions at current
levels would allow the greenhouse effect to
continue to intensify for more than a century.
Emissions of carbon dioxide might have to be
reduced by 50-80% to hold its concentration
constant.
While it is not possible to stabilize
greenhouse gas concentrations immediately,
world-wide implementation of measures to
reduce emissions would decrease the risks of
global warming, regardless of uncertainties
about the response of the climate system.
Scenario analyses indicate that if no policies to
limit greenhouse gas emissions were
undertaken, the equivalent of a doubling of
carbon dioxide would occur between 2030 and
2040, and the Earth might be committed to a
global warming of 2-4°C (3-7°F) by 2025 and
3-6°C (4-10°F) by 2050. Early application of
existing and emerging technologies designed
to, among other things, increase the efficiency
of energy use, expand the use of non-fossil
energy sources, reverse deforestation, and
phase out chlorofluorocarbons could reduce
the global warming commitment in 2025 by
about one-fourth, and the rate of climate
change during the next century by at least
60%. A global commitment to rapidly
reducing greenhouse gas emissions might be
able to stabilize the concentrations of these
gases by the middle of the next century,
perhaps limiting global warming to less than
2°C (3°F). The economic and technological
analyses needed to determine the specific
actions that would achieve such a large
reduction at minimum cost have not yet been
done. The economic feasibilities, costs,
benefits, and other social and economic
implications of such actions are not known.
This study identifies a wide range of potential
options and actions which appear promising
based on available technical information.
Further detailed study is required to determine
the effectiveness and economic implications of
each option.
There is a wide range of policy choices
available that have the technical potential to
reduce greenhouse gas emissions. Many also
appear to be consistent with other economic,
development, environmental, and social goals.
Any effective strategy will require a variety of
policies aimed at reducing emissions from
many sources and obtaining the cooperation of
many countries. Although a full assessment of
the costs and benefits of each option has not
been conducted, a number of potential actions
or policies geared toward increasing energy
efficiency, accelerating research and
development, and reversing deforestation
would have important benefits in addition to
reducing greenhouse gas emissions. Decisions
on the timing of U.S. policy responses should
be based on a consideration of the multiple
benefits and costs that might result from each
policy, the additional commitment to warming
caused by delaying action, and the role that
U.S. leadership could play in promoting
international cooperation to limit changes in
climate variables to acceptable levels.
Much of the report’s discussion
necessarily cites information derived from U.S.
experience and data because of the limitations
of information about other regions. However,
the report’s discussion of emissions, potential
response options, and their implications is
from a world-wide perspective. Because of
limitations in our knowledge, particularly
about economic factors in many regions
outside of the U.S., the report’s findings and
conclusions must be viewed as indicative and
preliminary.
I
-------
Policy Options for Stabilizing Global Climate
INTRODUCTION
The composition of the Earth’s
atmosphere is changing (see Figure 1).
Although the specific rate and magnitude of
future climate change are hard to predict, in
the absence of policy responses the observed
trends and projected increases in the
atmospheric concentrations of greenhouse
gases are likely to significantly alter the global
climate during the next centuiy. “Greenhouse”
gases (carbon dioxide, methane, chlorofluoro-
carbons, and nitrous oxide, among others) in
the atmosphere absorb heat that radiates from
the Earth’s surface and emit some of this heat
downward, warming the climate. Without this
“greenhouse effect,” the Earth would be about
30°C (60°F) colder than it is today. Human
activities are now increasing the atmospheric
concentrations of greenhouse gases on a global
basis, thus intensifying the greenhouse effect.
The rate of greenhouse gas buildup during the
next century will depend heavily on future
patterns of economic and technological
development, which are, in turn, influenced by
policies of local, state, national, and
international institutions.
Purpose of This Study
To better define the potential effects of
global climate change and identify the options
that are available to limit human-caused
climate change, Congress asked the U.S.
Environmental Protection Agency (U.S. EPA)
to undertake two studies. Congress directed
that in one of these studies U.S. EPA focus on
Rthe potential health and environmental effects
of climate change.” A companion report, The
Potential Effects of Global Climate Change on
the United States (Smith and Tirpak, 1989),
responds to that request. The second request
was that U.S. EPA undertake --
An examination of policy options
that if implemented would stabilize
current levels of atmospheric
greenhouse gas concentrations. This
study should address the need for
and implications of significant
changes in enei ’ policy, including
energy efficiency and development of
alternatives to fossil fuels; reductions
in the use of CFCs; ways to reduce
other greenhouse gases such as
methane and nitrous oxide; as well
as the potential for and effects of
reducing deforestation and
increasing reforestation efforts.
This study responds to that request by
examining the impact of a wide variety of
policy options under a range of possible
economic and technologic developments. The
analysis shows that while it is not possible to
stabilize greenhouse gas concentrations
immediately, a global commitment to rapidly
reduce greenhouse gas emissions might be able
to stabilize their concentrations by the middle
of the next century and even reduce
concentrations toward current levels by the
end of the next century. While humans may
have already committed the earth to significant
climate change during the next century, efforts
undertaken now to limit the buildup of
greenhouse gases in the atmosphere can
dramatically reduce the rate and ultimate
magnitude of such change.
Scope of This Study
The scope of this study is necessarily
global and the time horizon is more than a
century. To address this complex problem the
Agency enlisted the help of leading experts in
the governmental, non-governmental, and
academic research communities. Five work-
shops, which were attended by over 300
people, were held to gather information and
ideas about factors affecting atmospheric
composition and about response options
related to greenhouse gas emissions from
agricultural and forestry practices, industrial
processes, and energy consumption and supply,
as well as the extent to which developing
countries may be contributing to potential
global warming. Experts at NASA. the U.S.
Department of Energy (U.S. DOE), and the
U.S. Department of Agriculture (U.S. DOA)
contributed to this effort.
Based on the outcome of this
information-gathering process, U.S. EPA
developed an integrated analytical framework
to organize the data and assumptions required
to calculate (1) emissions of radiatively and
chemically active gases, (2) concentrations of
greenhouse gases, and (3) changes in global
2
-------
Executive Summary
FIGURE 1
CONCENTRATION OF CO 2 AT MAUNA LOA OBSERVATORY
AND CO 2 EMISSIONS FROM FOSSIL-FUEL COMBUSTION
(a)
C
0
a-
(5
(5
1
a.
C
0
(5
C
( 5
0
C
0
0
ON
C.)
(b)
5.
4
3
2
1958 1962 1966 1970 1974 1978 1982 1986 1989
Year
Figure 1. Figure 1(a) depicts monthly concentrations of atmospheric CO 2 at Mauna Loa Observatory,
Hawaü. The yearly oscillation is explained mainly by the annual cycle of photosynthesis and
respiration of plants in the northern hemisphere. Figure 1(b) represents the annual emissions of C0 2 ,
in units of carbon, due to fossil-fuel combustion. (Sources: Keeling, 1983, and pers. communication;
Komhyr et al., 1985; NOAA, 1987; Conway et al., 1988; Rotty, 1987, and pers. communication.)
a-
(5
( 5
>-
C.)
(5
E
(5
I-
0 )
(5
(5
C.
(5
C
0
( 5
(5
E
w
O’
C.)
6
3
-------
Policy Options for Stabilizing Global Climate
temperatures. This framework is highly
simplified, as its primary purpose is to rapidly
scan a broad range of policy options in order
to test their general effectiveness in reducing
atmospheric concentrations of greenhouse
gases. This analysis represents the first
attempt to quantify the relationship between
certain underlying forces (e.g., population
growth, economic growth, and technological
change) and emissions of all of the important
greenhouse gases. By using this framework we
were able to estimate how assumed changes in
these underlying forces would affect the
composition of the atmosphere and global
temperatures. It should be kept in mind that
the uncertainties in deriving temperature
changes from changes in greenhouse gas
concentrations are substantial. In constructing
this framework, we used the results of more
sophisticated models of individual components
as a basis for our analysis (see Appendix A for
more discussion of this framework). While we
believe that this framework generally reflects
the current state of scientific knowledge, there
are important limitations.
Current Policy Developments
The primary objective of this report is
to begin discussion of policies that could be
adopted by the global community to respond
to climate change concerns. We have not
specifically focused on policies for the United
States, but current developments in U. S.
policy are an important part of the background
information for readers of this report.
Since this study was completed, many
countries have already made commitments to
goals or actions that help to reduce net
greenhouse gas emissions. In the United
States the focus has been on actions that also
have benefits for reasons other than climate
change. Because of these other benefits, such
actions can be justified despite the very
substantial scientific and economic
uncertainties associated with climate change
issues.
The 1990 Clean Air Act Amendments
contain provisions to attain and maintain
National Ambient Air Quality Standards by
regulating emissions of volatile organic
compounds, nitrogen oxides, and carbon
monoxide. The Amendments will not only
produce cleaner air, but also significantly affect
greenhouse gases or their precursors. Major
reductions of sulfur dioxide to 10 million tons
below 1980 levels and of nitrogen oxides to 2
million tons below projected year 2000 levels
will reduce greenhouse gas emissions by
greatly encouraging energy efficiency. Phasing
out CFCS, carbon tetrachlotide, methyl
chloroform, and hydrochlorofluorocarbons
(HCFCs) in accordance with the Montreal
Protocol and the Clean Air Act will
substantially reduce emissions of greenhouse
gases as well as protect the stratospheric ozone
layer.
The President’s proposed program for
planting a billion trees a year will produce
substantial benefits for wildlife, soil
conservation, and energy saving, as well as
directly take up CO 2 from the atmosphere.
The increase in the Federal gasoline tax
enacted in the Budget Reconciliation Act of
1990 will reduce emissions by encouraging
energy efficiency in road transportation.
Increased funding requested in the FY 1991
budget for research and development in solar
and renewable energy and energy conservation
will be important in identifying and developing
technologies and practices that will allow us to
meet our energy needs in environmentally
efficient ways. New energy saving appliance
standards promulgated by the Department of
Energy will increase energy conservation and
reduce demand.
The U. S. has committed to specific
policy actions without specifying the future
level of aggregate emissions that will be
realized. Several other countries have
committed to quantitative, aggregate, future
emission goals but have not specified the
policy actions that will ensure achievement of
those goals. The U. S. actions may have
effects on emissions as substantial as the target
emissions levels being promised for future
achievement by a number of other countries.
Limitations
The analytical framework used in this
report attempts to incorporate some
representation of the major processes that will
influence the rate and magnitude of
greenhouse warming during the next century
within a structure that is reasonably
4
-------
Executive Summary
transparent and easy to manipulate. In so
doing we recognize a number of major
limitations:
• Because of the scope of the analysis, it
was not possible to come up with
comprehensive estimates of the costs or
benefits associated with each policy option.
We have instead relied on available
engineering cost estimates and judgment to
select options that appear to be the most
attractive. Subsequent studies, currently under
way, will provide more detailed economic
analysis for the next few decades on a country-
by-country basis. In particular there are
serious limitations in economic activity, cost,
and emission factor data for regions outside of
the U.S., particularly for the developing
countries. Thus, the implications of each
policy option for such regions are preliminary
and uncertain. The policy options presented
herein should therefore be viewed as examples
of what could be done to reduce the buildup of
greenhouse gases, not as recommendations of
what should be done.
• Forecasting rates of economic growth
and technological change over decadal time
periods is difficult, if not inherently
impossible. For this reason, the scenarios of
this report should not be viewed as forecasts
or predictions. While we believe that the
scenarios presented in this report provide a
useful basis for analyzing policy options, our
alternative assumptions may not adequately
reflect the plausible range of possibilities. For
example, we have assumed that aggregate
economic growth rates will generally decline
over time from the levels assumed for 1985-
2000; this may not be the case. Similarly,
assumed improvements in energy-consuming
and -producing technology in the No Response
and/or the Stabilizing Policy scenarios (see
Table 2 for a description) may prove to be too
optimistic or pessimistic.
• The use of simplified models also
implies that some potentially important
processes and interactions cannot be
accounted for. These include the
macroeconomic implications of the projected
changes in climate and the options designed to
limit these changes. Similarly, capital markets
are not explicitly considered. This is
particularly significant with regard to
developing countries, as it is unclear if they
will be able to obtain the capital needed to
develop the energy supplies assumed in some
of the scenarios. Additionally, the simplified
atmospheric chemistry and ocean models
employed may not adequately reflect the
underlying processes, particularly as climate
changes. Similarly, the parametric model used
to relate global temperature increases to
concentrations of greenhouse gases may not be
valid for extrapolations beyond 6°C.
• Behavioral changes that might be
stimulated by climate change, by policies, or by
individual choices to limit climate change also
have not been considered. Individual
decisionmakers will take actions to adapt to
any changes in climatic conditions. The
nature, costs, and benefits of these actions and
behavioral changes are not adequately defined
and understood. For example, future
population levels will have an important
impact on greenhouse gas emissions, but
reduced rates of population growth have not
been analyzed as a policy response.
HUMAN IMPACT ON THE
CLIMATE SYSTEM
The Greenhouse Gas Buildup
Many greenhouse gases are currently
accumulating in the atmosphere. The most
important, in terms of past and current
contribution to radiative forcing, is carbon
dioxide (C0 2 ), followed by methane (CH 4 ),
chlorofluorocarbons (CFCs), and nitrous oxide
(N 2 0) (see Figure 2 and Box 1). Carbon
dioxide, a fundamental product of burning
fossil fuels (coal, oil, and gas), is also released
as a result of deforestation. There are many
sources of methane, including rice cultivation,
enteric fermentation in animals, releases
during coal mining and natural gas production
and distribution, waste decomposition in
landfills, as well as many natural sources.
CFCS, however, are produced only by the
chemical industry. The sources of nitrous
oxide are not well characterized, but most are
probably related to soil processes; the most
important anthropogenic sources are fertilizer
use and various land-use changes such as
deforestation and savanna burning.
Greenhouse gases of natural origin include
S
-------
Policy Options for Stabilizing Global Climate
FIGURE 2
GREENHOUSE GAS CONTRIBUTIONS TO GLOBAL WARMING
1880- 1980
CFC-1 1&-1
(14%)
rigure . tsasea on estimates oi me increase in me concentration ot each gas during the specified
period. Other includes additional CFCs, halons, changes in ozone, and changes in stratospheric water
vapor. The other category is quite uncertain. (Sources: 1880-1980: Ramanathan et a!., 1985; 1980s:
Hansen et a!., 1988.)
Other (8%)
CFC-1 1&-12
(8%)
CO 2 (66%)
Other (13%)
N 2 0
(5%)
CH 4 (1
6
-------
Executive Summary
Box 1. Concept of Global Warming Potential
Throughout this Report, relative contributions to climate change by greenhouse gas
are calculated based on changes in atmospheric concentrations of each gas. These
concentration changes alter the radiative balance of the climate system. The scientific
community has in the past calculated contributions to radiative forcing using estimated
changes in atmospheric concentrations over some time interval (e.g., 10 years); this approach
is reflected in the left-hand figure below (and also in Figure 2) based on Hansen et al.
(1988). When discussing the various greenhouse gases in a policy context, however, there
is often a need for policymakers to have some simple means of estimating the relative
impacts of emissions of each greenhouse gas to affect radiative forcing, and hence climate,
without the complex, time consuming task of determining the impacts on atmosphenc
concentrations Since this Report was first prepared, several researchers have developed
indices that translate the level of emissions of the various greenhouse gases into a common
metric an order to compare the climate-forcing effects of the gases The index has been
called the Global Warming Potential (GWP), and is defined as the time integrated
commitment to climate forcing from the instantaneous release of 1 kilogram of a trace gas
expressed relative to that from 1 kilogram of carbon dioxide. For purposes of illustrating
this concept, we have used the GWP methodology evcloped by the Intergovernmental
Panel on Climate Change. for an integration period of 1(X) years (IPCC, 1990) to express
1985 emissions on a C0 2 -equivalent basis in order to compare the results to the
methodology used by Hansen et a!. (1988); see right-hand figure below. These two
approaches produce very different results since Hansen et a!. (1988) base their approach on
the radiative forcing effects of estimated changes in atmospheric concentrations from 1980-90,
while the use of GWPs measures the radiative forcing effects of emissions for a single year
(i e, 1985) over a 100-year time frame (see Addendum to Chapter U for a complete
discussion of this concept) This report uses the Hansen et a! (1988) methodology when
discussing relative current contributions of different gases and source categories. Use of the
IPCC or other alternative integrating methodologies would change the values of these shares
somewhat.
CONTRIBUTION TO RADIATIVE FORCING
By Greenhouse Gas By Greenhouse Gas
Concentrations Emisslona on a C02-Equivalent Basis
Oth.r(1O%)
1 C02(46%)
CH4(1S%) < US2%)
1980s 1985
Bows.: Hanson •t aL (116$) Ss..d on IPCC (1$SO)
GWP values from IPCC (1990) were used and applied to global emission estimates from
the RCW scenario
Oth.rCFCs( -
CFC- 11 &
-12(14%),
N20 (6%) ‘
Oth.r CFCs ( 3 %)Oth.r(3%)
CFC-11&-12(S%)
7
-------
Policy Options for Stabilizing Global Climate
water vapor and all of those listed above
except the chiorofluorocarbons.
Stabilizing emissions of greenhouse
gases at current levels will nor stabilize
concentraiions. Once emitted, greenhouse
gases remain in the atmosphere for decades to
centuries. As a result, if emissions remained
constant at 1985 levels, the greenhouse effect
would continue to intensify for more than a
centuiy. Carbon dioxide concentrations might
reach 440-500 parts per million (ppm) by 2100,
compared with about 350 ppm today, and
about 290 ppm 100 years ago (see Figure 3).
Nitrous oxide concentrations would probably
increase by about 20%; methane
concentrations might remain roughly constant.
Drastic cuts in emissions would be
required to stabilize atmospheric
composition. This assertion is based on the
fact that these gases remain in the atmosphere
for a very long time an4. that constant
emissions at current levels would lead to a
continuing increase in concentrations.
Emissions of C0 2 , for example, would have to
be reduced by 50-80% to stabilize atmospheric
concentrations (see Table 1). Even if all
anthropogemc emissions (i.e., emissions caused
by human activities) of C0 2 , CFCs, and N 2 0
were eliminated, the concentrations of these
gases would remain elevated for decades. It
would take more than 50 years, and possibly
more than a century, following a cut-off in
CO 2 emissions for the oceans and other sinks
to absorb enough carbon to reduce the
atmospheric concentration of CO 2 halfway
toward its pre-industrial value.
The Impact of Greenhouse Gases
on Global Climate
Uncertainties about the impact of the
greenhouse gas buildup on global climate
abound. These uncertainties are not about
whether the greenhouse effect is real or
whether increased greenhouse gas
concentrations will raise global temperatures.
Rather, the uncertainties concern the ultimate
magnitude and timing of warming and the
implications of that warming for the Earth’s
climate system, environment, and economies.
TABLE 1
Approximate Reductions in
Anthropogenic Emissions Required to
Stabilize Atmospheric
Concentrations at Current Levels
REDUCTION
GAS
REQUIRED
Carbon Dioxide
50-80%
Methane
10-20%
Nitrous Oxide
80-85%
Chlorofluorocarbons
75-100%
Carbon Monoxide (CO)
Freeze
Oxides of Nitrogen (NOr)
Freeze
The magnitude of future global warming
will depend, in part, on how geophysical and
biological feedbacks enhance or reduce the
warming caused by the additional infrared
radiation absorbed by increasing concen-
trations of greenhouse gases. The ultimate
global average temperature increase that can
be expected from a specific increase in the
concentrations of greenhouse gases can be
called the “climate sensitivity.” This parameter
provides a convenient index for the magnitude
of climate change that would be associated
with different scenarios of greenhouse gas
buildup. (In this report we use a doubling of
the concentration of CO 2 from pre-industrial
levels, or the equivalent from increases in the
concentrations of a number of greenhouse
gases, as the benchmark case.)
Estimating the impact of increasing
greenhouse gas concentrations on global
climate has been a focus of research within the
atmospheric science community for more than
a decade. This research shows that:
• If nothing else changed in the Earth’s
climate system except a doubling of CO 2 (or
the equivalent in other greenhouse gases),
average global temperature would rise 1.2-
1.3°C.
8
-------
Executive Summary
C
0
I-
.
0
0
0.
500
475
450
425
400 F—
375
350
325
rILyUKt 3
IMPACT OF C02 EMISSIONS REDUCTIONS
ON ATMOSPHERIC CONCENTRATIONS
1985 2000
Y•ar
Figure 3. The response of atmospheric CO 2 concentrations to arbitraly emissions scenarios, based
on two one-dimensional models of ocean CO 2 uptake. The emissions scenarios are relative to
estimated 1985 levels of 5.9 billion tons of carbon per year. (Sources: Hansen et al., 1984; Lashof,
1989; Siegenthaler, 1983.)
Conetant
H
---.--- - ;
2025 2050
2075
2100
9
-------
Policy Options for Stabilizing Global Climate
Increased global temperatures would
raise atmospheric levels of water vapor and
change the vertical temperature profile, raising
the ultimate global warming caused by a
doubling of CO 2 . Changes in snow and ice
cover are also expected to enhance warming.
There is strong consensus that if nothing other
than these factors changed in the Earth’s
climate system, the global temperature would
rise by 2-4°C.
The impact of changes in clouds on
global warming is highly uncertain. General
circulation models now generally project that
the global warming from doubling CO 2 could
cause changes in clouds that would either
enhance this warming or diminish it somewhat.
• A variety of other geophysical and
biogenic feedbacks exist that have generally
been neglected in global climate models. For
example, future global warming has the
potential to increase emissions of carbon from
northern latitude reservoirs in the form of
both methane and carbon dioxide, and to alter
uptake of CO 2 by the biosphere and the
oceans. Modeling analyses attempting to
incorporate feedbacks result in a wider range
of possible warming, i.e., 1.5 to 5.5° C, for an
initial doubling of CO 2 .
Global warming of just a few degrees
would represent an enormous change in
climate. The difference in mean annual
temperature between Boston and Washington
is only 3.3°C, and the difference between
Chicago and Atlanta is 6.7°C. The total global
warming since the peak of the last ice age,
18,000 years ago, was only about 5°C. That
change transformed the landscape of North
America, shifting the Atlantic ocean inland by
about one hundred miles, creating the Great
Lakes, and changing the composition of forests
throughout the continent.
The potential future impacts of climate
change are difficult to predict and are beyond
the scope of this report. Although global
temperature change is used as an indicator of
climate change throughout this report, it is
important to bear in mind that regional
changes in temperature, precipitation, storm
frequency, and other variables will determine
the environmental and economic impacts of
climate change. Predictions of such regional
changes in climate are highly uncertain at this
time.
Sensitivity analyses can be undertaken to
estimate potential impacts, as was done in the
companion volume, The Potential Effects of
Global Climate Change on the United States.
The collective findings of that study suggest
that the climatic changes associated with a
global warming of roughly 2-4°C would result
in
a world different from the world
that exists today. . . . Global
climate change could have
sigmjicant implications for natural
ecosystems; for where and how we
farm; for the availability of water
to irrigate crops, produce power,
and support sh pping for how we
live in our cities; for the wetlands
that spawn our fish; for the
beaches we use for recreation; and
for all levels of government and
indus y (Smith and Tirpak, 1989,
p. m).
Natural Climate Variability
Because of long-period couplings
between different components of the climate
system, for example, between ocean and
atmosphere, the Earth’s climate would still
valy without being perturbed by any external
influences. This natural variability could act
to add to, or subtract from, any human-made
warming. Natural emissions and variations
contribute significantly to climate change.
Climate variations from glacial to interglacial
periods have been caused naturally.
Controlling anthropogenic greenhouse gas
emissions will not prevent natural climate
change.
SCENARIOS FOR POLICY
ANALYSIS
Defining Scenarios
Defining scenarios that encompass more
than a centuly is a daunting task. While this
is an eternity for most economists and
planners, it is but a moment for geologists.
And indeed, decisions made in the next few
10
-------
Executive Summary
decades, about how buildings are constructed,
electricity is generated, and cities are laid Out,
for example, will have an impact on the
climate in 2100 and beyond. Decisions about
what kinds of automobiles and other industrial
products to produce and how to produce them
will also have a profound impact. These
choices, which will affect the amount and type
of fuel we use to travel, to heat and light our
homes and offices, and to run our factories,
will influence the magnitude of greenhouse gas
emissions for many years.
To explore the climatic implications of
such policy and investment decisions, we have
constructed six scenarios of future patterns of
economic development, population growth,
and technological change. These scenarios
start with alternative assumptions about the
rate of economic growth and policies that
influence emissions, such as those affecting
levels of future energy demand, land-clearing
rates, CFC production, etc. These scenarios
are intended to be internally consistent
pictures of how the world may evolve in the
future. They are not forecasts and they do not
bracket the full range of possible futures.
Instead, they were chosen to provide a basis
for evaluating strategies for stabilizing the
atmosphere in the context of distinctly
different, but plausible, conditions.
Specifically, the policy scenarios
discussed in this report are meant to stimulate
further study. They do not constitute
conclusions about what would be the most
feasible and cost-effective strategies or plans
for responding to climate change and should
not be interpreted as such. What they do
show is that no single measure or limited set
of a few measures would be an adequate
response to climate change. They also show
that there are a great many potential options,
each one of which alone would have only a
modest impact. Finally, they show that much
more work is needed to evaluate the physical,
social, and economic implications of each
policy option and to identify the least socially
and economically disruptive approaches.
Deciding on an overall climate ehange
response strategy will be extremely difficult
taking into account all of the unknowns and
uncertainties. The need for world-wide
cooperation in a strategy complicates the
policy-making problem. However, the U.S.
has many potential options from which, if their
implications are well understood, it can
develop a response that is likely to be both
feasible and effective. It is already proceeding
in this manner by immediately implementing a
series of actions that can be justified for other
reasons or by their benefits even in the face of
the uncertainties. However, there are
uncertainties even about how far those actions
which the U.S. is already taking should be
pursued. Not all levels of energy efficiency,
tree planting, or increased levels of R & D are
likely to produce benefits in excess of their
costs. All countries in their specific economic
contexts need to consider the costs, benefits,
and uncertainties of taking various actions.
It should be noted that these scenarios
have not been updated to reflect the current
status of the Montreal Protocol as
strengthened by the London Agreement to
completely phase out CFCs, halons, carbon
tetrachioride, and methyl chloroform, and to
encourage limits on HCFCs.
Two scenarios explore alternative
pictures of how the world may evolve in the
future assuming that policy choices allow
unimpeded growth in emissions of greenhouse
gases (these are referred to as the “No
Response” scenarios). One of these scenarios,
called a Rapidly Changing World (RCW),
assumes rapid economic growth and techno-
logical change; the other, called the Slowly
Changing World (SCW), represents a more
pessimistic view of the evolution of the world’s
economies. A variant of the RCW scenario,
Rapidly Changing World with Accelerated
Emissions (RCWA), assumes that efficiency
improvements occur more gradually and that
policies tend to favor increased greenhouse gas
emissions. Two additional scenarios (referred
to as the “Stabilizing Policy” scenarios) start
with the same economic and demographic
assumptions as the RCW and SCW, but
assume a world in which nations have adopted
policies to limit anthropogenic emissions of
greenhouse gases. These scenarios are called
the Slowly Changing World with Stabilizing
Policies (SCWP) and the Rapidly Changing
World with Stabilizing Policies (RCWP). In
addition, a variant of the RCWP assumes
more Rapid Reductions in greenhouse gas
emissions (RCWR). In all of the scenarios it
11
-------
Policy Options for Stabilizing Global Climate
is assumed that the key national and
international political institutions evolve
gradually, with no major upheavals. An
overview of the scenario assumptions is
provided in Table 2.
The analysis for this study included a
detailed examination of energy demand for the
year 2025. We chose this date because,
although substantial change will have occurred
by then, some currently existing infrastructure
will still be in place and much of the
technology to be deployed over this period is
already under development. Scenarios
extending beyond this date are speculative, but
they are included because they are necessary to
evaluate the full implications of more
immediate decisions and because greenhouse
gases affect warming for many decades.
Projections to 2100 are based on the patterns
and relationships established between 1985
and 2025. The six scenarios analyzed in this
study were developed using the Atmospheric
Stabilization Framework. This analytical
framework was constructed for the purpose of
evaluating the impact of all anthropogenic
activities on the level of greenhouse gas
emissions, and consequently, on the rate and
magnitude of global climate change. For a
description of this Framework, the reader is
referred to Chapter VI and Appendix A.
It should be understood that the
discussions of climate change in Chapter 3 and
the discussions of the climate changes
associated with the various scenarios are
subject to great scientific uncertainties. The
general circulation models, which are the basis
for simulating climate changes, while among
the most sophisticated tools available, are
relatively simple compared to the feedback
mechanisms and processes that operate in the
real atmosphere/oceans system. The model
physics grossly oversimplify the real world.
The models do not yet adequately describe the
present climate and, thus, projections must be
viewed with extreme caution.
Scenarios with Unimpeded
Emissions Growth
In ‘A Slowly Changing World’ (SCW)
we consider the possibility that the recent
experience of modest growth will continue
indefinitely, with no concerted policy response
to the risk of climate change. Per capita
income in developing regions that have very
high population growth is stagnant for several
decades, and shows modest increases
elsewhere. Economic growth rates per capita
increase slightly over time in all developing
regions as population growth rates gradually
decline. The population engaged in traditional
agriculture continues to increase, as does
speculative land clearing and demand for
fuelwood. These factors lead to accelerated
deforestation until tropical forests are virtually
eliminated toward the middle of the next
centuiy. Because of slack demand, real energy
prices increase slowly. Productivity in industry
and agriculture improves at only a moderate
rate. Correspondingly, the energy efficiency of
buildings, vehicles, and consumer products
improves at a slow rate.
In ‘A Rapidly Changing World’ (RCW)
rapid economic growth and technological
change occur with little attention given to the
global environment. Per capita income rises
rapidly in most regions and consumers demand
more energy services, which puts upward
pressure on energy prices. The number of cars
increases rapidly in developing countries, and
air travel increases rapidly in industrialized
countries. Energy efficiency is not much of a
consideration in consumer choices, as income
increases faster than real energy prices, but
efficiency increases do occur as a result of
technological improvements. Correspondingly,
we assume that there is a high rate of
innovation in industry and that capital
equipment turns over rapidly, thereby
accelerating reductions in energy required per
unit of industrial output. An increasing share
of energy is consumed in the form of
electricity, which is produced mostly from coal.
The fraction of global economic output
produced in the developing countries increases
dramatically as services become more
important in industrialized countries and as
industries such as ste , aluminum, and auto-
making grow in developing countries.
Population growth rates decline more rapidly
than in the Slowly Changing World scenario as
educational and income levels rise.
Deforestation continues at about current rates,
spurred by land speculation and commercial
logging, despite reduced rates of population
growth. Note that the SCW and RCW
scenarios are not bounding cases with respect
12
-------
Executive Summary
TABLE 2
Overview of Major Scenario Assumptions
Slowly Chan2in World
Rapidly Chan in2 World
Slow ON? Growth
Continued Rapid Population Growth
Minimal Energy Price Increases
Slow Technological Change
Carbon-Intensive Fuel Mix
Increasing Deforestation
Montreal Protocol/Low Participation
Slowly Changing World
with Stabilizin2 Policies
Rapid ON? Growth
Moderated Population Growth
Modest Energy Price Increases
Rapid Technological Improvements
Veiy Carbon-Intensive Fuel Mix
Moderate Deforestation
Montreal Protocol/High Participation
Rapidly Changing World
with Stabilizing Policies
Slow GNP Growth
Continued Rapid Population Growth
Minimal Energy Price IncreasesfFaxes
Rapid Efficiency Improvements
Moderate Solar/Biomass Penetration
Rapid Reforestation
CFC Phaseout
Rapidly Changing World
with Accelerated Emissions
Rapid ON? Growth
Moderated Population Growth
Modest Energy Price IncreasesiTaxes
Very Rapid Efficiency Improvements
Rapid Solar/Biomass Penetration
Rapid Reforestation
CFC Phaseout
Rapidly Changing World
with Rapid Emissions Reductions
High CFC Emissions
Cheap Coal
Cheap Synfuels
High Oil and Gas Prices
Slow Efficiency Improvements
High Deforestation
High-Cost Solar
High-Cost Nuclear
Carbon Fee
High MPG Cars
High Efficiency Buildings
High Efficiency Powerplants
High Biomass Penetration
Rapid Reforestation
13
-------
Policy Options for Stabilizing Global Climate
to emissions, rather the assumptions are
intended to be logically related, and therefore,
have partially offsetting implications.
Without stabilizing policies, rapid
greenhouse gas buildup and global warming
are likely. The two worlds described above
lead to significant increases in emissions of
carbon dioxide and other trace gases (see
Table 3) and in atmospheric concentrations of
the greenhouse gases (see Figure 4). CO 2
concentrations reach twice their pre-industnal
levels in about 2080 in the SCW scenario. In
the RCW this level is reached by 2055, and
concentrations more than three times pre-
industrial values are reached by 2100. When
all the trace gases are considered, an increase
in the greenhouse effect equivalent to that
which would occur from a doubling of CO 2
concentrations is reached by 2040 in the SCW
and by 2030 in the RCW. By 2100 the total
radiative forcing is equivalent to a tripling of
CO 2 in the SCW and a factor of 5 increase in
the RCW. These results are in good
agreement with those of recent studies that
have made less formal estimates based
primarily on current trends in concentrations
and/or emissions. A notable exception are the
results for CFCs. The June 1990 London
Amendments will result in even lower concen-
urations of CFCs. However, because the
London Amendments were adopted after this
analysis, they are not included in the scenarios.
Even a Slowly Changing World would
produce a 2-3°C temperature increase
during the next century. In the SCW
scenario, realized global warming would
increase by 1.0-1.5°C between 2000 and 2050
and by 2-3°C from 2000 to 2100 (temperature
ranges are based on a climate sensitivity of 2-
4°C unless otherwise noted; see Box 2 and
Figure 5). The maximum realized rate of
change associated with this scenario is 0.2-
0.3°C per decade, which occurs sometime in
the middle of the next century. The total
equilibrium warming commitment is
substantially higher, reaching 3- >6°C by 2100
relative to pre-industnal levels (see Table 4).1
The “equilibrium warming commitment”
is the warming that would eventually result
from a given atmospheric composition
assuming that it were to remain fixed at that
level. Because the oceans adjust thermally
over many years, it takes years or decades to
reach the equilibrium warming. “Realized
warming” is that portion of the equilibrium
warming that has been reached at any point in
time (see Box 2).
Higher rates of economic growth are
certainly the goal of most governments and
could lead to higher rates of climate change as
illustrated by the RCW scenario. The rate of
change during the next century would be more
than 50% greater than in the SCW: in the
RCW, realized global warming increases by
1.3-2.0°C between 2000 and 2050, and by 3-5°C
between 2000 and 2100. The total equilibrium
warming commitment reaches 5-> .6°C by 2100.
In this case the maximum realized rate of
change is 0.4-0.6°C per decade, which occurs
sometime between 2070 and 2100.
The Impact of Policy Choices
Government policies, if applied
globally, could significantly increase or
decrease future warming. The warming
suggested by the Slowly Changing and Rapidly
Changing World cases is not inevitable; it is
the result of the public and private choices
implicit in these scenarios. While some future
warming probably is locked in, the range of
possible future commitments to warming is
enormous.
Accelerated Emissions Scenario
Decisions that will be made in the near
future may lead to increased emissions if there
is no clear policy goal to reduce them. This
potential is illustrated by a series of tests that
were conducted to examine the effect of
accelerated emissions on equilibrium warming
commitment. Starting with the RCW scenario,
eight key parameters were varied as proxies for
recently-proposed policies that have the
potential to significantly increase greenhouse
gas emissions (e.g., accelerated development of
synfuels) or the possible consequences of
government inaction or failure (e.g., high use
of CFCS and deforestation).
14
-------
Executive Summary
TABLE 3
Trace Gas Emissions
1985 2025 2100
CO, (Pg C) 1
SCW 6.0 9.6 10.7
RCW 6.0 12.4 26.1
RCWA 6.0 21.9 54.8
SCWP 6.0 5.2 2.6
RCWP 6.0 5.4 5.3
RCWR 6.0 2.1 0.8
N 2 0 (Tg N)b
SCW 12.5 16.5 15.6
RCW 12.5 16.1 18.1
RCWA 12.5 18.5 22.0
SCWP 12.5 13.1 12.8
RCWP 12.5 13.3 12.6
RCWR 12.5 13.1 12.5
CH 4 (Tg CH 4 )
SCW 510 690 830
RCW 510 730 1,130
RCWA 510 910 1,580
SCWP 510 540 480
RCWP 510 560 525
RCWR 510 520 460
NO 1 (Tg N)
SCW 54 71 69
RCW 54 79 122
RCWA 54 105 187
SCWP 54 48 45
RCWP 54 56 49
RCWR 54 53 48
Co (Tg C)
SCW 500 830 620
RCW 500 720 1,190
RCWA 500 980 1,120
SCWP 500 290 250
RCWP 500 290 230
RCWR 500 270 240
CFC-12 (Gg)
SCW 365 395 425
RCW 365 450 520
RCWA 365 860 1,485
SCWP 365 50 70
RCWP 365 85 90
RCWR 365 85 90
HCFC.22 (Gg)d
SCW 74 405 880
RCW 74 830 3,125
RCWA 74 830 3,125
SCWP 74 405 880
RCWP 74 830 3,125
RCWR 74 830 3,125
Pg C = Petagrams of carbon; 1 Petagram = 101$ grams.
Tg N = Teragrams of nitrogen; 1 Teragram 10” grams.
Gg = gigagram; I gigagram = i0 grams.
d These scenarios were produced prior to the negotiations for the London Amendments to the Montreal Protocol. The CFC
phaseout policy assumed in these policy scenarios is similar overall to, but somewhat more stringent than, the London
Amendments.
15
-------
Policy Options for Stabilizing Global Climate
FIGURE 4
ATMOSPHERIC CONCENTRATIONS
(3.0 Degree Celsius Climate Sensitivity)
CARBON DIOXIDE METHANE
RCWA
6000
5000
C
0
RCW 4000
scw 3000
RCWP
8cwp
RCWR 2000
1000
10000
RCWA
8000
C
8000
RCW 9
•cw 7000
6
; 6000
0
SCWP 5000
RCWP
RCWR
4000
3000
ft.
2000
1000
0
800
400
200
0
600
450
400
350
300
250
1686 2000 2025 2050
NITROUS OXIDE
2075 2100
CHLOROFLUOROCARBONS
1600
1600
1400
1200
1000
800
RCWA
RCW
SCW
RCWP
Scwp
RCWR
C
0
a
U
U
S.
RCWA
RCW
SCW
RCWP
RCW
Scwp
18852000 2025 2080 2071 2100
y..r
16
-------
Executive Summary
FIGURE 5
REALIZED WARMING
NO RESPONSE SCENARIOS
6
5
4-
3
2
1
0—
1985 2000
(Based on 2.0 - 4.0 Degree Sensitivity)
RCW..:..II: H :1:I
Figure 5. Shaded areas represent the range based on an equilibrium climate sensitivity of 2-4°C to
a doubling of CO 2 .
17
0
0
0
0
0
0
1
0
a
Scw
2025
Year
2050
2075 2100
-------
Policy Options for Stabilizing Global Climate
TABLE 4
Scenario Results For Realized And Equilibrium Warming
Realized Warming 2°C Sensitivity
1985
2000
2025
2050
2075
2100
SCW
0.5
0.7
1.2
1.7
2.2
2.6
RCW
0.5
0.7
1.3
2.0
2,9
3.8
RCWA
0.5
0.7
1.5
2.8
4.5
>6.0’
SCWP
0.5
0.7
0.9
Li
1.2
1.2
RCWP
0.5
0.7
1.0
1.2
1.4
1.5
RCWR
0.5
0.7
0.9
0.9
0.9
0.8
Realized Warming - 4°C Sensitivity
1985
2000
2025
2050
2075
2100
SCW
0.7
1.0
1.8
2.6
3.4
4.2
RCW
0.7
1.0
1.9
3.0
4.4
6.0
RCWA
0.7
1.1
2.1
4.2
>6.0*
>6.0’
SCWP
0.7
1.0
1.4
1.7
1.9
2.1
RCWP
0.7
1.0
1.5
1.9
2.2
2.5
RCWR
0.7
1.0
1.4
1.5
1.5
1.4
Equilibrium Warming Commitment - 2°C Sensitivity 1985 2000 2025 2050 2075 2100
SCW 0.7 1.1 1.7 2.3 2.8 3.3
RCW 0.7 1.1 1.9 2.9 4.0 5.1
RCWA 0.7 1.1 2.4 4.3 >6.0’ >6.0’
SCWP 0.7 1.0 1.3 1.4 1.4 1.4
RCWP 0.7 1.0 1.3 1.5 1.7 1.8
RCWR 0.7 1.0 1.2 1.1 1.0 0.9
Equilibrium Warming Commitment - 4°C Sensitivity 1985 2000 2025 2050 2075 2100
SCW 1.5 2.2 3.5 4.7 5.7 >6.0’
RCW 1.5 2.2 3.8 5.8 >6.0’ >6.0’
RCWA 1.5 2.3 4.7 >6.0’ >6.0’ >6.0’
SCWP 1.5 2.0 2.5 2.7 2.8 2.8
RCWP 1.5 2.0 2.6 3.1 3.4 3.7
RCWR 1.5 2.0 2.3 2.1 1.9 1.7
Estimates of equilibrium warming commitments greater than 6°C represent extrapolations beyond
the range tested in most climate models, and this warming may not be fully realized because the
strength of some positive feedback mechanisms may decline as the Earth warms. These estimates are
represented by >6°C.
18
-------
Executivc Summary
Figure 6 illustrates the results of these
tests as compared with the RCW scenario.
The results are illustrated in terms of the
incremental effect of each outcome on the
equilibrium warming commitment in 2050 and
2100. As Figure 6 shows, the measures that
amplify the warming to the greatest extent are
those that reduce the rate of efficiency
improvement (historically, energy efficiency
has improved about 1-2%/year), reduce the
cost of synfuels, and increase the assumed rate
of growth in CFC production and use.
Policies leading to accelerated deforestation
would have a large impact in the near term,
but a relatively small impact in 2100.
The impact of all of these policies in
combination is quite dramatic. In this case,
emissions of CO 2 would be nearly five times
pre-industrial levels. The rate of warming
during the next century would be over 60%
higher than in the RCW scenario.
Scenarios with Stabilizing Policies
Three scenarios were constructed to
explore the impact of policy choices aimed at
reducing the risk of global warming. The
Slowly Changing World with Stabilizing
Policies, the Rapidly Changing World with
Stabilizing Policies, and the Rapidly Changing
World with Rapid Reductions start with the
same economic and demographic assumptions
used in the SCW and RCW scenarios,
respectively, but assume that government
leadership is provided to ensure that a wide
range of measures to reduce greenhouse gas
emissions are implemented beginning in the
1990s.
Box 2. Equilibrium and Realized Warming
Equilibrium Warming commitment
The equilibrium warming commitment for any given year is the temperature increase that
would occur in equilibrium if the atmospheric composition was fixed in that year. This
temperature may not be realized for several decades, and may not be realized at all if
greenhouse gas concentrations fall.
Realized Warming
Because the oceans have a large heat capacity the temperature change realized in the
atmosphere lags considerably behind the equilibrium level (the difference between the
equilibrium warming and the realized warming in any given year is called the unrealized
wartning . Realized warming has been estimated with a simple model of ocean heat uptake.
Climate Sensitivuv
Because the response of the climate system to changes in greenhouse gas concentrations is
quite uncertain due to the role of clouds and other processes, we also consider a range of
“climate sensitivities.” Climate sensitivity is defined as the equilibrium warming commitment
due to a doubling of the concentration of carbon dioxide from pre-industrial levels. Given a
particular emissions scenario and climate sensitivity, the realized warming is much more
uncertain than the equilibrium warming commitment because the effective heat storage capacity
of the oceans is not known. On the other hand, because the amount of unrealized warming
increases with increasing climate sensitivity, for a given scenario, realized warming depends less
on climate sensitivity than does equilibrium warming commitment.
19
-------
Policy Options for Stabilizing Global Climate
FIGURE 6
ACCELERATED EMISSIONS CASES:
PERCENT INCREASE IN EQUILIBRIUM WARMING COMMITMENT
1. High CFC Emissions
b
2. Cheap Coal
3. Cheap Synfuels
4. HIgh Oil & Gas Pric..d
5. Slow Efficiency
Improvements
C I
6. High DeforestatIon
7. High-Cost Solar°
8. High-Cost Nuclear’
Accelerated Emissions
(Combination of 1-8
I
I
Percent Relative to RCW
.
2050
2100
-50 10 20 30 40 50 60 70
Prcnt
2$
-------
Executive Summary
FIGURE 6 -- NOTES
Impact Of Accelerated Emissions Policies On Global Warming
a Assumes a low level of participation in and compliance with the Montreal Protocol, excluding the London
Amendments, which were adopted after these scenarios were completed. The assumptions used in this case are
similar to those used in the “Low Case” analysis described in the U.S. EPA’s Regulatory Impact Assessment report,
i.e., about 75% participation among developed countries and 40% among developing countries. In the RCW case
the U.S. was assumed to participate 100%, other developed countries 94%, and developing countries 65%.
b Assumes that advances in the technology of coal extraction and transport rapidly reduce the market price of coat
at the burner tip. In the RCW scenario, the economic efficiency of coal supply is assumed to improve at a rate of
approximately 0.5% per year. In this case, it is assumed to improve at a rate of 1% per year.
C Assumes that the price of synthetic oil and gas could be reduced by 50% and commercialization rapidly accelerated
relative to the RCW case.
d Assumes that OPEC (or some other political entity) could control production levels and thus raise the border
prices of oil and gas. To simulate this effect, oil and gas resources were shifted to higher points on the regional
supply curves. In addition, extraction costs for oil in each resource grade were increased relative to the assumptions
in the RCW case. In 2025 these assumptions increased oil prices about $1/barrel and gas prices about
$0.25/thousand cubic feet.
e Assumes that technical gains in the engineering efficiency of energy use occur only half as rapidly as assumed in
the RCW case. In the RCW case it is assumed that efficiency improves at rates of approximately 1-2% per year
(approximately equal to historical rates). In the Slow Improvement case the assumed rates were reduced to only
0.5-1.0% per year. The lower rate of improvement is similar to the assumptions in recent projections for the U.S.
DOE’s National Energy Policy Plan.
Assumes annual deforestation increases at a rate equal to the rate of growth in population. In the RCW case the
rate of deforestation increases at a slower rate, reaching 15 million hectares/year in 2097 compared to 34 million
hectares, ’ear by 2047 in the RCWA case.
Assumes that the cost of solar energy precludes the possibility of its making any significant contribution to global
energy supply. In the RCW case costs approached 8.5 cents/kwh after 2050.
b Assumes that the cost of electricity from fission electric systems becomes so high that their contribution to global
energy supply is permanently limited. In this case, an environmental taxof about 6 cents/kwh (1988$) on the price
of electricity supplied by nuclear powerplants was phased in by 2050. In the RCW case nuclear costs were assumed
to be 6.1 cents/kwh in 1985.
All of the above assumptions were combined in one scenario. The result is not equal to the sum of the warming
in the RCW and the eight individual cases because of interactions among the assumptions.
21
-------
Policy Options for Stabilizing Global Climate
No single activity is the dominant
source of greenhouse gases; therefore, no
single measure can stabilize global climate.
Many individual components, each having
a modest impact on greenhouse gas
emissions, can have a dramatic impact on
the rate of climate change when combined.
The Stabilizing Policy scenarios therefore
assume that many policy initiatives are
undertaken simultaneously. These scenarios
assume that policies to promote energy
efficiency in all sectors succeed in substantially
reducing energy demand relative to the No
Response scenarios (which already assume
substantial efficiency improvements).
Research and development investments in
non-fossil energy supply options such as
photovoltaics (solar cells), biomass-derived
fuels and electricity (fuels made from plant
material), and advanced nuclear reactors are
assumed to make these options available and
begin to become competitive by 2000. As a
result, non-fossil energy sources meet a
substantial fraction of total demand in later
periods. There is considerable uncertainty as
to whether these sources could actually be
available on a competitive basis by the year
2000. In addition, whether these technologies
would be economically attractive in the
quantities projected in future scenario years is
quite uncertain. The existing protocol to
reduce CFC and halon emissions is assumed to
be strengthened, leading to a phaseout of fully-
halogenated compounds and a freeze on
methyl chloroform. (The London Amendments
to the Montreal Protocol, adopted after this
analysis was completed, call for the complete
phaseout of CFCs, halons, carbon
tetrachioride, methyl chloroform, and
encourage limits on HCFCs.) A global effort
to reverse deforestation transforms the
biosphere from a source to a sink for carbon
by 2000, and technological innovation and
controls reduce agricultural, industrial, and
transportation emissions. The impact of
these measures on warming commitment in
2050 and 2100 is illustrated in Figures 7 and 8.
The results of this analysis suggest that
accelerated energy efficiency improvements,
reforestation, modernization of biomass use,
and carbon emissions fees could have the
largest near-term impact on the rate of climate
change. In the long run, advances in solar
technology and biomass plantations also play
an essentiai role. These conclusions are based
upon the assumptions made in these scenarios
about these technologies and about competing
technologies, such as nuclear fission. How
sensitive they may be to variations in the
assumptions, particularly to differences
reflecting economic differences between the
industrialized countries and the developing
countries, is not fully understood. While the
same general emissions reduction strategies
are assumed in both the SCWP and RCWP
cases, the degree and rate of improvement are
greater in the RCWP scenario because
technological innovation and capital stock
replacement occur at a faster pace.
The policies considered in these
scenarios do not require fundamental changes
in lifestyles. For example, energy use in
buildings is greatly reduced in the Stabilizing
Policy scenarios relative to the No Response
scenarios, but the floor space available per
person and the amenity levels provided are
assumed to be the same. Similarly, while
automobile fuel efficiency is assumed to be
much higher, restrictions on automobile
ownership are not considered. The potential
impact of policies on personal decisions that
directly change lifestyles has not been
examined.
It should be kept in mind that these
Stabilizing Policy scenarios incorporate
assessments of the technical feasibility of the
measures included and general judgments
about their likely economic character.
Analyses of economic feasibility, market
penetration, costs, benefits, and other
socioeconomic implications have not been
systematically completed. Knowledge is
particularly lacking about these socioeconomic
aspects under developing country conditions
where scarcity of capital and of trained
technical people could complicate efforts to
implement these measures.
These policy assumptions result in a
substantial reduction in the rate of greenhouse
gas buildup, but not an immediate stabilization
of the atmosphere (see Figure 9). In the
RCWP scenario global CO 2 emissions decline
about 10% by 2025 and remain roughly
constant thereafter. This result implies
substantial reductions in emissions from
22
-------
Executive Summary
FIGURE 7
STABILIZING POLICY STRATEGIES:
DECREASE IN EQUILIBRIUM WARMING COMMITMENT
1. Improved Transportation
Eff lclency
2. Other Efficiency Gainsb
3. Carbon Feec
4. Cheaper Nuclear
Power d
Percent Reduction Relative to RCW
5. Solar Technologles _______
6. Commercialized Biomass’
7. Natural Gas Incentives 9
8. Emission Controlsh
9. CFC Phaseout’
10. Reforestation 1
1 1. Agriculture, Landfills,
and Cement K
RCWP (Simultaneous
Implementation of 1-1 1)
o
-------
Policy Options for Stabilizing Global Climate
FIGURE 7 - NOTES
Impact Of Stabilizing Policies On Global Warming
The average efficiency of cars and light trucks in the U.S. reaches 30 mpg (7.8 liters/100 km) by 2000; new cars achieve 40
mpg (5.9 litersTlOO kin). Global fleet-average automobile efficiency reaches 43 mpg by 2025 (5.5 litersflOO kin). In the RCW
case global vehicle efficiencies for cars and light trucks achieve 30 mpg by 2025.
b The rates of energy efficiency improvements in the residential, commercial, and industrial sectors are increased about 0.3-0.8
percentage points annually from 1985 to 2025 compared to the RCW and about 0.2-0.3 percentage points annually from 2025-
2100. In the RCW case energy efficiency improvements averaged about 1-2% annually from 1985-2025, and less than 1% after
2025.
Emissions fees are placed on fossil fuels in proportion to carbon content. Fees were placed only on production; maximum
production fees (1988$) are $1 00/03 for coal (about $25/ton), $0.80/GJ for oil (about $5/barrel), and $054103 for natural gas
(about $0.58/thousand cubic feet). These fees increase linearly from zero, with the maximum production fee charged by 2025.
In the RCW case no emission fees were assumed.
d Assumes that technological improvements in nuclear powerplant design reduce costs by about 0.6 cents/kwh (1988$) by 2050.
In the RCW case we assumed that nuclear costs in 1985 were 6.1 cents/kwh (1988$).
e Assumes that low-cost solar technology is available by 2025 at costs as low as 6.0 cents/kwh. In the RCW case these costs
approached 8.5 cents/kwh, but these levels were not achieved until after 2050.
t Assumes the cost of producing and converting biomass to modern fuels reaches $435/03 (1988$) for gas (about $4.70/thousand
cubic feet) and S6.00/GJ (1988$) for liquids (about $36/barrel) by 2025, with biomass penetrating more quickly than in the RCW
case due to more land committed to production. The maximum amount of liquid or gaseous fuel available from biomass (i.e.,
after conversion losses) is 205 El. In the RCW case these prices were not attained until 2035, and biomass energy penetrates
slowly because research and development is slow and because land is committed slowly to biomass energy production.
Assumes that economic incentives for gas use for electricity generation increase the gas share by 5% in 2000 (thereby reducing
prices about 1.6%) and 10% in 2025 (thereby reducing prices about 3.1%). Gas consumption for electricity generation was
about 21 El in the RCW case.
b Assumes more stringent NO 1 and CO controls on mobile and stationary sources, including all gasoline vehicles using three-way
catalysts, in OECD countries by 2000, and in the rest of the world by 2025 (new light-duty vehicles in the rest of the world use
oxidation catalysts from 2000 to 2025). In the RCW case only the U.S. adopts three-way catalysts (by 1985); the OECD
countries adopt oxidation catalysts by 2000, and the rest of the world does not add any controls. From 2000 to 2025
conventional coal boilers used for electricity generation are retrofit with low NO 1 burners, with 85% retrofit in the developed
countries and 40% in developing countries; starting in 2000 all new coinbustors used for electricity generation and all new
industrial boilers require selective catalytic reduction in the developed countries and low NO 1 burners in the developing
countries, and after 2025 all new combustors of these types require selective catalytic reduction. Other new industrial non-boiler
combustors such as kilns and diyers require low NO 1 burners after 2000. In the RCW case no additional controls are assumed.
100% phaseout of CFCs by 2003 and a [ reese on methyl chloroform is imposed. There is 100% participation by
industrialized countries and 94% participation by developing countries. In the RCW scenario we assumed compliance with the
Montreal Protocol, which called for a 50% reduction in the use of the major CFCS. Note the London Amendments to the
Montreal Protocol, calling for a phaseout of CFCs halons, carbon tetrachloride, methyl chloroform, and encouraging limits on
HCFCs, are not reflected in the scenario; these Amendments were negotiated after this analysis was completed.
The terrestrial biosphere becomes a net sink for carbon by 2000 through a rapid reduction in deforestation and a linear
increase in the area of reforested land and biomass plantations. Net CO 2 uptake by 2025 is 0.7 Pg C. In the RCW case, the
rate of deforestation continues to increase very gradually reaching 15 Mha ’r in 2097.
Assumes that research and improved agricultural practices result in an annual 0.5% decline in the emissions from rice
production, entenc fermentation, and fertilizer use. C l - I 4 emissions from landfills are assumed to decline at an annual rate of
2% in developed countries because of policies aimed at reducing solid waste and increasing landfill gas recovety, while emissions
in developing countries continue to grow until 2025 and then remain flat due to incorporation of the same policies.
Technological improvements reduce demand for cement by 25%. In the RCW case no emission rate changes were assumed
for agricultural practices C F ! 4 emissions front landfills were assumed to remain constant in developed countries and increase
as the population grew in developing countnes
‘Impart on global warming when all the above measures are implemented simultaneously. The sum of each individual reduction
in warming is not precisely equal to the difference between the RCW and RCWP cases because not all the strategies are strictly
add i nv
24
-------
Executive Summary
FIGURE 8
RAPID REDUCTION STRATEGIES:
ADDITIONAL DECREASE IN EQUILIBRIUM WARMING COMMITMENT
a
1. Carbon Fee
b
2. HIgh MPG Cars
3. HIgh Efficiency
Buiidlngsc
4. High Efficiency
Powerpiantsd
5. High Biomass
6. RapId Ref orestation
Rapid Reduction g
(implementation
of 1-6)
Additional Percent Relative to RCW
2050
2100
0 5 10 15 20 25
P•rc•nt
rigure . me impact of additional measures applied to the RCWP scenario expressed as percent
change relative to the equilibrium warming commitment in the RCW scenario. The simultaneous
implementation of all the measures in combination with the measures in the RCWP scenarios
represents the Rapid Reduction scenario.
25
-------
Policy Options for Stabilizing Global Climate
FIGURE 8-- NOTES
Impact Of Rapid Reduction Policies On Global Warming
‘High carbon emissions fees are imposed on the production of fossil fuels in proportion to the CO 2 emissions
potential. In this case, fees of about $4.O0/GJ were imposed on coal ($100/ton), $3.20/CM on oil ($19/barrel), and
$2. 15IGJ on natural gas (S2.00/mct). These fee levels are specified in 1988$ and are phased in over the period
between 1985 and 2025. No fees were assumed in the RCW case.
b Assumes that the average efficiency of new cars in the U.S. reaches 50 mpg (4.7 liters/100 km) in 2000 and that
global fleet-average auto efficiencies reach 65 mpg (3.6 liters/100 km) in 2025 and 100 mpg (2.4 liters/100 km) in
2050. Comparable assumptions for the RCWP case were 40,50, and 75 mpg for 2000,2025, and 2050, respectively.
C Assumes that the rate of technical efficiency improvement in the residential and commercial sectors improves
substantially beyond that assumed in the RCWP case. In this case, the rate of efficiency improvement in the
residential and commercial sectors is increased so that a net gain in efficiency of 50% relative to the RCWP case
is achievsd in all regions. In the RCWP case rates of efficiency improvement averaged 1.5-3.0% per year from
1985-2025.
4 Assumes that by 2050 average powerplant conversion efficiency improves by 50% relative to 1985. In this case,
the design efficiencies of all types of generating plants improve significantly. For example, by 2025 new oil-fired
generating stations achieve an average conversion efficiency roughly equivalent to 5% greater than that achieved
by combined-cycle units today. In the RCW case new oil-fired units achieve an average conversion efficiency equal
to combined-cycle units today.
‘The availability of commercial biomass was doubled relative to the assumptions in the RCWP case. In this case
the rate of increase in biomass productivity is assumed to be at the high end of the range suggested by the U.S.
DOE Biofuels Program. Conversion costs were assumed to fall by one-third relative to the assumptions in the
RCWP case.
A rapid rate of global reforestation is assumed. In this case deibrestation is halted by 2000 and the biota become
a net sink for CO 2 at a rate of about 1 Pg C per year by 2025, about twice the level of carbon storage assumed in
the RCWP case.
5 lmpact on warming when all of the above measures are implemented simultaneously. The impact is much less
than the sum of the individual components because many of the measures are not additive.
26
-------
Executive Summary
FIGURE 9
REALIZED WARMING:
NO RESPONSE AND STABILIZING POLICY SCENARIOS
(Based on 2.0 - 4.0 Degree Sensitivity)
Slowly Changing World
I
Rapidly Changing World
0
1985 2000 2025 2050 2075 2100
Year
4
2
2100
Figure 9. Shaded areas represent the range based on an equilibrium climate sensitivity to doubling
CO 2 of 2-4°C.
• 4
0
0
0
0
02
SCWP
RCWP
H
0
i•es 2000 2025 2080 2075
Year
27
-------
Policy Options for Stabilizing Global Climate
industrialized countries, however. U. S.
emissions, for example, fall 40% by 2025.
Carbon dioxide concentrations increase
gradually throughout the time frame of the
analysis despite roughly constant emissions (as
discussed above). Total radiative forcing is
close to being stabilized by 2100, but the level
is equivalent to almost a doubling of pre-
industrial CO 2 concentrations in the RCWP
and to a 65% increase in the SCWP.
The rate of climate change in the
SCWP and RCWP scenarios is’ at least 60%
less than in the corresponding worlds
without policy responses, but the risk of
substantial climate change is still significant.
The rate of global temperature increase during
the next centuiy in these scenarios is 0.5-1.5°C,
while the maximum rate of change is less than
0.2°C per decade between 2000 and 2025. This
represents much more gradual change than in
the No Response scenarios, but it does not
ensure that the rate of warming will remain
below 0.1°C per decade. Some experts have
suggested that this rate of change represents
the maximum to which many species of plants
and animals could adapt. Total equilibrium
warming commitment could exceed 3.5°C by
2100 in the RCWP case. Given the possibility
that the climate sensitivity could be higher and
that there could be large positive
biogeochemical feedbacks that are not
included in these calculations, there is a
possibility that these scenarios could lead to
extremely rapid climate change. It is also
possible that the policies assumed in these
scenarios could limit climate change to about
1°C if the true climate sensitivity of the Earth
is low.
Only the most a ressive policy case
reverses the greenhouse gas buildup early in
the 21st century. The economic feasibility,
costs, benefits, and other socioeconomic
implications of such policies have not been
determined at this time. The Rapid
Reduction scenario explores the impact of
policies that effect a rapid transition away
from fossil fuels. In the Rapid Reduction
scenario net global CO 2 emissions decline
nearly 15% by 2000 and 65% by 2025. U.S.
emissions decline 20% by 2000 and 50% by
2025. The atmospheric concentration of CO 2
peaks below 400 ppm around 2025, and total
greenhouse forcing peaks at an equivalent CO 2
concentration of less than 450 ppm. After this
point, equivalent CO 2 concentrations decline
until by 2100 they are about equal to current
levels of atmospheric greenhouse gas
concentrations (on a C0 2 -equivalent basis). It
is this level of concentration, and the policy
options necessary to achieve this level, that
Congress specifically requested U.S. EPA to
evaluate. Despite declining concentrations,
however, temperatures continue to rise to.
about 2050, peaking at 0.9-1.5°C above pre-
industrial levels. in this case the maximum
rate of change is 0.09-0.16°C per decade
between 2000 and 2025, but the average rate
of change over the next century is much less
than 0.1°C per decade. The measures that
reduce the warming to the greatest extent in
the Rapid Reduction case relative to the
RCWP case are those that impose stiff carbon
fees on the production of fossil fuels, improve
the energy efficiency of buildings, and increase
the assumed level of renewable resource
availability. Options for phasing in carbon
fees so as to minimize impacts on the global
economy require additional analysis.
To reduce the amount of global
warming to the rates projected in the RCWP
and Rapid Reduction cases, Table 5 lists
several policies that might have to be adopted
by 2000 to begin reducing greenhouse gas
emissions. These examples are meant to
illustrate potential policy responses; a variety
of policy combinations might achieve the
reductions in global warming estimated in each
case.
TECHNOLOGICAL OPTIONS
FOR REDUCING GREENHOUSE
GAS EMISSIONS
There is a wide variety of available, or
potentially available, options to reduce
greenhouse gas emissions that it is believed
would not unduly interfere with meeting
growing demands for goods and services. The
current status and potential of these options
are briefly reviewed below. In most cases, the
costs and benefits of these options for
responding to climate change cannot be fully
quantified at this time, both because of
scientific uncertainties about climate change
itself and because of many economic
28
-------
Executiv Summary
TABLE 5
Examples Of Potential Policy Responses By The Year 2000
RCWP Case
• Research on energy efficiency and non-fossil-fuel technology is accelerated
• New automobiles in the U.S. average 40 mpg
• New automobiles in the OECD use three-way catalytic converters to reduce CO and NO, 1 the rest of world
uses an oxidation catalyst
• Average space-heating requirements of new single-family homes are 50% below 1980 new home average
• Net global deforestation stops
• CFCs are phased out; production of methyl chloroform is frozen
• Fossil fuels are subject to emission fees that are set according to carbon content -- $10/ton on coal, $2/barrel
on oil, $0.20/thousand cubic feet on natural gas
• Accelerated research and development into solar photovoltaic technology allows solar power to compete with
oil and natural gas (U.S. DOE long-term policy goals)
• Available municipal solid waste and agricultural wastes are converted to useful energy
• Accelerated research on biomass energy plantations increases current productivity by 65% (to 25 dry
tons/bectare annually)
RCWR Case
• Research on energy efficiency and non-fossil-fuel technology is accelerated
• New automobiles in the U.S. average 50 mpg
• Major retrofit initiatives reduce energy use in existing commercial buildings by 40%
• Average space-heating requirements of new single-family homes are 90% below 1980 new home average
• Global deforestation stops; major reforestation programs are undertaken
• CFCs are phased out; production of methyl chloroform is frozen
• Fossil fuels are subject to emission fees that are set according to carbon content — $38/ton on coal, $7/barrel
on oil, $0.75/thousand cubic feet on natural gas
• Commercialization incentives lead to significant market penetration for solar technologies
• 250 million hectares globally are committed to biomass energy plantations, i.e., 5% of forest and woodland
area
29
-------
Policy Options for Stabilizing Global Climate
uncertainties about the potential options
themselves.
Improve Energy Efficiency
The introduction of technologies and
practices that use less energy to accomplish
a given task would have the largest impact
on global warming in the near term. Both
industrialized and developing countries can
significantly improve energy efficiency.
Although per capita energy consumption is
veiy low in developing countries, there is a
large potential to increase efficiency because
energy use per unit of GNP is often extremely
high. Indeed, the imperative for energy
efficiency may be even stronger in developing
countries to the extent that expending scarce
capital on expanding energy supply systems can
be avoided. Many of the technical options
described below may be directly applicable in
developing as well as industrialized countries,
but alternative approaches suited to available
resources will also be needed. In many cases
improved management of existing facilities
could have large payoffs. We estimate that
accelerated improvements in energy efficiency
account for about 25% of the difference
between the RCWP and the RCW cases in
2050 (we note that this occurs even though
fairly rapid improvements are already assumed
in the RCW case).
Improved Transportation Efficiency
A number of known technologies have
the technical potential to increase automobile
fuel efficiency from current levels for new cars
(25-33 mpg or 9.4-7.1 liters/100 km) to
significantly higher levels. What could be
achieved in the foreseeable future without
downsizing vehicles and reducing safety and
other desirable characteristics is uncertain.
Given the currently available technical options
and their likely costs of implementation, a
fleet average new car economy level of 40 mpg
by the year 2000 could require size and
performance reductions. The RCWP scenario
assumes that new cars in the industrialized
countries achieve an average of 50 mpg (4.7
liters/100 km) in 2025 and 75 mpg (3.1
liters/100 km) in 2050 (somewhat lower rates
of efficiency improvement are assumed in the
SCWP scenario). In addition, major fuel
efficiency improvements in diesel trucks and
aircraft are possible. The Rapid Reduction
case assumes more aggressive measures to
improve efficiency.
Other Efficiency Gains
More efficient building shells, lighting,
heating and cooling equipment, and appliances
are currently commercially available. The
most efficient new homes currently being built
use only 30% as much heating energy per unit
of floor area as the average existing house in
the United States. Advanced prototypes and
design calculations indicate that it is
technically possible to build new homes that
use only 10% of current average energy
requirements. The economic feasibility, the
likely market penetration, and the costs of
implementing such technological options are
uncertain. About 20% of U.S. electricity is
consumed for lighting, mainly in residential
and commercial buildings. A combination of
currently available advanced technology and
careful design has been shown to cost-
effectively reduce energy requirements for
lighting by more than 75%. The RCWP
scenario assumes that the average reduction in
energy use per unit of residential and
commercial floor space by 2025 in the U.S. is
as much as 75% for fuel and 50% for
electricity. Smaller improvements are assumed
in other regions and in the SCWP scenario.
Advanced industrial processes currently
available can significantly reduce the energy
required to produce basic materials --
especially if these processes are used in
combination with recycling. For example,
estimates of the reductions in energy intensity
of U.S. steel production that are technically
feasible range from 20 to 50 percent. How
much of these savings would be economically
feasible and at what cost is unknown. Electric
motors are estimated to account for about
70% of U.S. industrial electricity use. Several
case studies show that improved motors and
motor controls now commercially available
could reduce energy consumption by electric
motors at least 15% relative to current
averages.
While the promise of technically feasible
efficiency gains is great, the uncertainties
about the rate and scale of implementation of
30
-------
Executive Summary
such measures are also great. Many of these
gains would depend, in the U.S. and other
developed countries, upon the rates at which
the existing capital stock is replaced by new,
more efficient capital equipment and facilities.
Such rates depend upon a host of economic
and other factors that are difficult to assess:
the rates at which potential users learn about
new technologies, the age and value of existing
equipment and facilities, the availability and
cost of credit, the degree that existing capital
capacity is utilized, and so forth. For these
reasons, market penetration rates of new
technologies, and how such rates might be
accelerated, are very uncertain.
Carbon Fee
One way to provide a market signal that
CO 2 emissions have environmental
consequences is to apply a “carbon” fee to the
price of fossil fuels that is proportional to the
carbon content of the fuel. Fees could be used
in conjunction with performance standards and
other strategies to encourage energy
conservation and investments in energy-
efficient technology. A carbon fee would also
affect the relative prices of fossil and non-
fossil energy sources and the relative prices
among the fossil fuels, reinforcing the policies
discussed in the following sections. The
revenues from such a fee could be used to
reduce other taxes, reduce the national debt,
and/or support other national goals. To be
least disruptive, revenues would need to be
offset by reductions in other taxes. Further
analysis is required to determine these impacts
on the economy. In particular, the full social
costs and benefits of substantial reductions in
an energy option, such as coal use, due to high
carbon fees or to command-and-control
regulations, have not been evaluated.
Given the scientific and economic
uncertainties about the changes in climate that
are likely to result from given changes in
greenhouse gas concentrations, and the net
costs to society of such climate changes,
appropriate levels for setting greenhouse gas
fees are unknown.
If greenhouse gas fees and other
controls on emissions are not established on a
comparable basis world-wide, the problem of
emissions-intensive activities migrating to
countries where fees were lower or controls
less stringent could occur, thereby reducing the
net effectiveness of the fees or controls.
Increase Use of Non-Fossil Energy
Sources
There is a critical need for research
on non-fossil energy technologies. The
development of attractive non-fossil energy
sources is critical to the success of any climate
stabilization strategy over the long term.
Under the assumptions of this report’s
scenarios, increased penetration of solar and
advanced biomass technologies contribute little
to reduced warming in - 2025, but they are
responsible for 24% of the difference between
the RCWP and the RCW case in 2050, and
over 25% of this difference in 2100. Figure 10
shows the relative contribution to primary
energy supply of each fossil and non-fossil fuel
under each of our scenarios. The exact mix of
non-fossil energy supply technologies assumed
in the policy scenarios is rather arbitrary, but
makes little difference to greenhouse gas
emissions. Some particularly promising non-
fossil technologies are described below.
Nuclear Power
Nuclear fission produces about 5% of
global primary energy supplies and its share
has been growing. High cost and concerns
about safety, nuclear proliferation, and
radioactive waste disposal, however, have
brought new orders for nuclear powerplants to
a halt in many countries. Advanced designs, in
particular the Modular High Temperature
Gas-cooled Reactor, have recently been
proposed in an attempt to overcome some of
these problems. The role of nuclear power
could be significantly expanded in the future if
these efforts are successful and public
confidence in this energy source is restored.
Nuclear power’s contribution to primary
energy supply in the SCWP case increases to
less than 7% in 2050 and to 8% in 2100 and
in the RCWP case to 10% in 2050 and 18% in
2100. It is possible that the nuclear
contribution could be substantially greater, if
concerns about safety, nuclear proliferation,
and waste disposal could be adequately dealt
with and if costs could be reduced by moving
toward the manufacture of standardized
31
-------
Policy Options for Stabilizing Global Climate
1500
1250
1000
>.
U
750
a
500
250
0
1600
1260
:1000
750
a
500
250
0
3000
2500
) 2000
.1500
1000
500
0
1$S5 2000 2025 2050 2075 2100
y.sI.
Noto: FuN scsl Is deubl.d for th. RCWA cas•.
FIGURE 10
PRIMARY ENERGY SUPPLY BY TYPE
1500
1250
1000
760
600
250
0
1500
1260
1000
760
500
250
0
1500 RCWR
1260 -
1000
::: 4: . .
250 Nucl•sr
0
1966 2000 2025 2050 2075 2100
V.ur
SCwp
Blomass
Coal
Blomass
Solar
Nucl.ar
Hydro
Gas
Oil
Coal
32
-------
Executive Summary
powerplants and away from the construction of
one-of-a-kind facilities.
Solar Technologies
There is a range of solar technologies
currently available or under development that
could increase the use of solar energy. Direct
use of solar thermal energy, either passively or
in active systems, is already commercial for
many water- and space-heating applications.
In some locations wind energy systems are also
currently commercial for some applications.
In recent years engineering advances have
resulted in significant cost reductions and
performance improvements. Solar
photovoltaic (PV) cells are currently
competitive for many remote power generation
needs, especially in developing countries.
Dramatic progress has been made recently in
reducing the costs of producing PV systems,
particularly with thin-film amorphous silicon
technology. If current research and
manufacturing development efforts reach their
objectives, PV could play a major role in
meeting energy needs in the next century. The
degree to which these objectives, particularly
cost reduction, could be achieved by specific
times and the size of the future contribution
are, of course, uncertain. In the SCWP
scenario solar sources of electricity are
equivalent to 6% of primary energy supply
from 2050 onward. A larger contribution is
envisioned in the RCWP scenario: 10% in
2050, increasing to over 13% in 2100.
Hydro and Geothermal Energy
Other renewable resources can also
increase their contribution to total energy
supplies. Hydroelectric power is already
contributing the equivalent of about 7% of
global primary energy production, and
geothermal power is making a small (less than
1%) but important contribution. There is
potential to expand the contribution of these
sources, although good hydro and geothermal
sites are limited and environmental and social
impacts of large-scale projects must be
considered carefully. Significant questions
concerning the economics of remaining
available sites, and the likely environmental
constraints on these sites, have not been
analyzed in detail. Hydroelectric and
geothermal power expands to nearly 13% of
global primary energy production in the SCWP
scenario, but increases only to about 9% in the
RCWP case (this relatively smaller
contribution is due to the higher level of
energy production; i.e., the absolute amount is
higher, but the percentage is lower).
Commercialized Biomass
Biomass is currently being extensively
utilized, accounting for roughly 10% of global
energy consumption, primarily in traditional
applications (e.g., cooking), which are not
included in most official accounts of
commercial energy use. Current and emerging
technologies could vastly improve the
efficiency of biomass use. In the near term
there is substantial potential for obtaining
more useful energy from municipal and
agricultural wastes. More advanced
technologies for producing, collecting, and
converting biomass to gaseous and liquid fuels
and electricity could become economically
competitive within a decade. The prospects
for integrating biomass gasification with
advanced combustion turbines is particularly
promising. While the technical potential for
commercialized biomass is highly promising,
important questions remain about the scale
and degree of the economic potential. In
particular, the availability of productive land
that could be devoted to growing biomass fuels
needs further study. Furthermore,
environmental and societal impacts related to
large-scale biomass use, which would have to
be addressed, include competition with food
production, ecological impacts, and emissions
of volatile organic compounds. In the SCWP
scenario biomass energy supplies 32% of
primary energy needs in 2050 and 48% in
2100. Biomass supplies about 32% of primary
energy by 2050 and 32% by 2100 in the RCWP
scenario.
Reduce Emissions from Fossil
Fuels
Inherent to the burning of fossil fuels is
the generation of large amounts of CO 2 .
Although it is technically possible to scrub
CO 2 Out of central station powerplants, it is
estimated that this would probably at least
double the cost of power generation, and an
33
-------
Policy Options for Stabilizing Global Climate
environmentally acceptable method of disposal
has not been demonstrated. All fossil fuels
are not created equally, however. Burning
coal produces about twice as much CO 2 per
unit of energy released as does natural gas; the
amount of CO 2 produced by oil is about 80%
of the amount produced by coal.
Furthermore, oil and gas have the potential to
be used much more efficiently than coal in
power generation, substantially increasing their
CO 2 advantage. Thus fuel switching among
fossil fuels can significantly reduce CO 2
emissions. Similarly, non-CO 2 emissions from
fossil-fuel burning can be controlled, resulting
in significant impacts on greenhouse gas
concentrations. Also, when new fossil-fuel
facilities need to be built, emissions can be
minimized by installing the most efficient
technologies, such as the use of Integrated
Gasification/Combined Cycle (IGCC) systems
for new coal-fired generation requirements.
The potential timing and market
penetration of more efficient fossil-fuel-fired
technologies are uncertain, particularly in the
developing countries, where most of the
growth in emissions is likely to take place.
The potential impact of these technologies is
significant, but their cost effectiveness is veiy
uncertain.
Greater Use of Natural Gas
Because of its inherent CO 2 advantage
over other fossil fuels, increased use of natural
gas could significantly reduce total emissions.
Two important considerations should be kept
in mind, however. First, natural gas is a finite
resource. Increased use of natural gas during
the next few decades could provide an
essential bridge as non-fossil energy sources
are further developed, but unless a transition
toward reduced dependence on fossil fuels is
accomplished, reduced availability of natural
gas in later periods could offset the gains from
using gas in earlier periods. Second, natural
gas is primarily methane, which is itself a
powerful greenhouse gas. If a substantial
amount of methane reaches the atmosphere
through leaky transmission or distribution
pipes, the advantage of natural gas can be
significantly reduced or offset.
Emission Controls
Emissions of CO contribute to elevating
methane concentrations, and NO emissions
contribute to tropospheric ozone formation,
both of which are important greenhouse gases.
Thus, more stringent and comprehensive
controls on CO and NOR, such as three-way
catalysts on automobiles and low-NOr burners
on boilers and kilns, would reduce greenhouse
gas concentrations as well.
Reduce Emissions from Non-
Energy Sources
CFC Phaseout
Halocarbons (which include CFCs and
halons) are potent stratospheric ozone
depleters as well as greenhouse gases.
Concern over their role as a threat to the
ozone layer led in September 1987 to “The
Montreal Protocol on Substances That
Deplete the Ozone Layer” (or the Montreal
Protocol). The Montreal Protocol came into
force on Januaiy 1, 1989, and has been ratified
by 68 countries, representing just over 90% of
current world consumption of these chemicals
(as of February 1, 1991). The London
Amendments to the Protocol, which call for
the phaseout of CFCs, halons, carbon
tetrachloride, and methyl chloroform, and
encourages limits of HCFCs, were adopted in
June 1990. These amendments were adopted
after this analysis was completed.
Further reductions in CFCs are
needed to slow the buildup of atmospheric
concentrations. The major provisions of the
Montreal Protocol include a 50% reduction
from 1986 levels in the use of CFC-11, -12,
-113, -114, and -115 by 1998; a freeze on the
use of Halon 1211, 1301, and 2402 at 1986
levels starting in approximately 1992; and a
delay of up to 10 years in compliance with the
Protocol for developing countries with low
levels of use per capita. As a result of this
historic agreement, the veiy high growth rates
in CFC concentrations assumed in some
previous studies are unlikely to occur.
However, because of the long atmospheric
34
-------
Executive Summary
lifetimes of CFCs, the probability that not all
countries will participate in the agreement,
and the provision for increased use in
developing countries, CFC concentrations will
still rise significantly in the future unless the
Protocol is strengthened (see Figure 4). An
international meeting to discuss strengthening
of the Protocol was held in June 1990 in
London, England. The Amendments to the
Protocol adopted in London were similar to,
but not as stringent as, the phaseout assumed
in this analysis.
Promising chemical substitutes,
engineering controls, and process modifi-
cations that could eliminate most uses of
CFCs have now been identified. In the policy
scenarios we assume that the use of CFCs and
halons is phased out and that emissions of
methyl chloroform are frozen (no additional
growth in CFC substitutes is assumed as a
result of the phaseout beyond the levels
assumed under the Protocol). Even under
these assumptions total weighted halocarbon
concentrations increase significantly from 1985
levels, in part because the chemical substitutes
contribute significantly to greenhouse forcing,
although the final concentrations are about
one-third of the level in the corresponding No
Response scenarios. The greenhouse forcing
potential of CFC substitutes will have to be
carefully evaluated to improve estimates of
their potential role in climate change. In our
analysis, phasing out CFCs was responsible for
9% of the decrease in warming in the RCWP
in 2050 relative to the RCW.
Reforestation
Deforestation and biomass burning are
significant sources of C0 2 , CO. CH 4 , NOR, and
N 2 0. The world’s total forest and woodland
acreage has been reduced by about 15% since
1850, primarily to accommodate the expansion
of cultivated lands. It is generally estimated
that approximately 11 million hectares (Mha)
of tropical forests are currently lost each year,
while only 1.1 Mha are reforested per year.
Generally, temperate and boreal forests appear
to be in equilibrium. Estimates of net
emissions of CO 2 to the atmosphere due to
changes in land use (deforestation,
reforestation, logging, and changes in
agricultural area) in 1980 range from
approximately 10-30% of annual
anthropogenic CO 2
atmosphere.
Reversing deforestation offers one of
the most attractive policy responses to
potential climate change. Although a vast
area of land would have to be involved to
make a significant contribution to reducing net
CO 2 emissions, preliminary estimates suggest
that the cost of absorbed or conserved carbon
could be low in comparison to other options,
at least initially. How rapidly reforestation
costs would increase as lands with increasingly
high productivity in other uses were
transferred to forest use is not well
understood. The areas of land that would be
feasible and economic to transfer to forest use
are also not well defined. Furthermore, a
reforestation strategy could offer a stream of
valuable ecological and economic benefits in
addition to reducing CO 2 concentrations, such
as production of forest products, maintenance
of biodiversity, watershed protection, nonpoint
pollution reduction, and recreation. Devising
successful forestry programs presents unique
challenges to scientists and policymakers
because of the vast and heterogeneous
landscape, uncertain ownership, lack of data,
and the need for more research and field trials.
Investments that would be small by the
standards of the energy industry, however,
could make an enormous impact on forestry.
In the Stabilizing Policy scenarios it is
assumed that by 2000 the biosphere is
transfortned from a source to a sink for
carbon. A combination of policies succeed in
stopping deforestation by 2025, while up to
one billion hectares of land is reforested by
2100 (some of this land is devoted to biomass
energy plantations as discussed above). This
assumed area of reforestation could exceed the
area of the United States. Whether or not
this much land could be made available on a
global basis for reforestation, given the needs
for uses for subsistence and commercial
agriculture, has not been determined.
Reforestation accounts for almost one-fifth of
the decrease in warming by 2050 in the RCWP
versus the RCW scenarios.
Agriculture, Landfills, and Cement
Domestic animals, rice cultivation, and
use of nitrogenous fertilizers are significant
emissions to the
35
-------
Policy Options for Stabilizing Global Climate
sources of greenhou e gases. Methane is
produced as a by-product of digestive
processes in herbivores, particularly ruminants
(e.g., cattle, dairy cows, sheep, buffalo, and
goats). Globally, domestic animals
(predominantly cattle) are responsible for
about 15% of total methane etmssions. The
gas is also produced by anaerobic decom-
position in flooded rice fields and escapes to
the atmosphere largely by transport through
the rice plants. The amount of CH 4 released
to the atmosphere is a complex function of
rice species, number and duration of harvests,
temperature, irrigation practices, crop residue
management, and fertilizer use. Rice fields are
estimated to contribute approximately 10-30%
of the global emissions. Nitrous oxide is
released through microbial processes in soils,
both Lhroàgh denitrification and nitriflcation.
The use of nitrogenous fertilizer enhances
N 2 0 emissions since some of the applied N is
converted to N 2 0 and released to the
atmosphere. The amount of N 2 0 released
varies a great deal depending on rainfall,
temperature, the type of fertilizer applied,
mode of application, and soil conditions. A
preliminary estimate suggests that this source
produces 1-20% of global N 2 0 emissions.
Future research and technological
changes could reduce agricultural emirsions.
In the policy scenarios we do not assume
changes in the demand for agricultural
commodities, but rather changes in production
systems that could reduce greenhouse gas
emissions per unit of product. Although the
impact of specific approaches cannot be
quantified at present, a number of techniques,
such as feed additives for cattle, changes in
water management in rice production, and
fertilizer coatings, have been identified for
reducing methane and nitrous oxide emissions
from agricultural sources. The extent to which
these options are implemented depends on
further research and demonstrations. For
simplicity we have assumed that methane
emissions per unit of rice, meat, and milk
production decrease by 0.5% per year
(emissions from animals not used in
commercial meat or milk production are
assumed to be constant). Emissions of nitrous
oxide per unit of nitrogen fertilizer appliedare
also assumed to decrease by 0.5% per year for
each fertilizer type. In addition, we assume
that after 2000 there is a shift away from those
types of fertilizers with the highest emissions.
Under these assumptions agricultural
emissions are substantially lowered in the
policy scenarios relative to the No Response
scenarios, although absolute emissions do not
decline.
Landfills represent a potentially
controllable source of methane. Waste
disposal in landfills and open dumps generates
methane when decomposition of the organic
material becomes anaerobic; approximately
80% of urban solid wastes is currently
disposed in one of these ways. Most of the
decomposition in landifils and some of the
decomposition in open pits is anaerobic.
Annual methane emissions from landifils and
open pits represent about 10% of total
methane emissions.
Landfilling can be expected to increase
dramatically in developing countries as
population growth, urbanization, and
economic growth all imply increased disposal
of municipal solid waste. The result is a three
and fivefold increase in methane emissions
from landfills in the SCW and RCW scenarios,
respectively. The Stabilizing Policy scenarios
assume that gas recovery systems, recycling,
and waste reduction policies will be adopted,
resulting in roughly constant global emissions
from landfills.
Carbon dioxide is emitted in the
calcining phase of the cement-making process
when calcium carbonate (CaCO 3 ) is converted
to lime (CaO). For every ton of cement
produced 0.14 tons of carbon are emitted as
CO 2 from this reaction. World cement
production increased from 130 million tons in
1950 to about one billion tons currently.
Thus, current CO 2 emissions from calcining
are 0.14 billion tons of carbon (0.14 Pg C), or
more than 2% of total CO 2 emissions. In the
Stabilizing Policy scenarios, advanced materials
are assumed to reduce the demand for cement
relative to the No Response scenarios, but
emissions still grow significantly.
Reduced emissions from agriculture,
landfills, and cement manufacture account for
12% of the reduced warming in the RCWP in
2050 relative to the RCW scenario.
36
-------
Executive Summary
A WIDE RANGE OF POLICY
CHOICES FOR THE SHORT
AND LONG TERM
The prospect of global climate change
presents policymakers with a unique challenge.
The scale of the problem is unprecedented in
both space and time. Many choices are
available and the consequences of these
choices will be profound.
A wide range of policy choices is
available for reducing greenhouse gas
emissions. There is an important distinction
between short-term and long-term policy
options. In the short term, the most effective
means of reducing emissions is through
strategies that rely on pricing and regulation.
There is a wide range of potential policy
choices that may make sense despite the
scientific and economic uncertainties. In the
long term, policies to increase research and
development of new technologies, to enhance
markets through information programs and
other means, and other actions making it
possible to achieve world-wide economic
growth while limiting emissions growth will be
essential for long-term effects on the climate
change problem.
• The most direct means of allowing
markets to incorporate the risk of climate
change is to ensure that the prices of fossil
fuels and other sources of greenhouse gases
reflect their full social costs. It may be
necessaiy to impose emission fees on these
sources according to their relative contribution
to global warming in order to accomplish this
goal. Unfortunately, the costs and benefits of
global warming are not fully known, and,
therefore, the fees that would correspond to
charging full social costs can not now be
determined. Better information would be
needed as a basis for establishing levels of fees.
Fees would also raise revenues that could
finance other programs or offset other taxes.
The degree to which such fees are accepted
will vary among countries, but acceptability
would be enhanced if fees were equitably
structured. The impact of fees on the global
economy would depend on the size of the fees,
how they were phased in, and how the
revenues were used, among other factors. The
effectiveness of fees in reducing world-wide
greenhouse gas emissions would depend on the
degree to which they are applied consistently
throughout the world and therefore avoid
encouraging emissions-intensive activities to
relocate to low fee areas. These issues require
additional analysis.
Regulatory programs would be a
necessary complement if pricing strategies
were not effective or had undesirable impacts.
In the U.S., greenhouse gas emissions are
influenced by existing federal regulatory
programs to control air pollution, increase
energy efficiency, and recycle solid waste.
Reducing greenhouse gas emissions could be
incorporated into the goals of these programs.
New programs could focus directly on reducing
greenhouse gas emissions through
requirements such as emissions offsets (e.g.,
tree planting), performance standards, or
marketable permits. Different kinds of
regulatory approaches would have different
degrees of efficiency and costs, differences in
treating greenhouse gases in a comprehensive
fashion, and differences in how they permit
those regulated to make cost-optimal
decisions. A full understanding of these
differences and of the inherent advantages of
using automatic market mechanisms to
encourage environmentally sound behavior is
needed, particularly with respect to regulatory
approaches in countries with limited
experience in market-oriented environmental
regulation. Regulatory approaches, like other
policies, would also have to deal with the need
to avoid encouraging emissions-intensive
activities to relocate to areas of less stringent
regulation.
• State and local government policies in
such areas as utility regulation, building codes,
waste management, transportation planning,
and urban forestry could make an important
contribution to reducing greenhouse gas
emissions.
• Voluntary private efforts to reduce
greenhouse gas emissions have already
provided significant precedents for wider
action and could play a larger role in the
future.
• Over the long term, other policies will
be needed to reduce emissions and can
complement pricing and regulatory strategies.
37
-------
Policy Options for Stabilizing Global Climate
Other policy options include redirecting
research and development priorities in favor of
technologies that could reduce greenhouse gas
emissions, implementing information programs
to enhance awareness of the problems and
solutions, and making selective use of
government procurement to promote markets
for technological alternatives.
• The United States is implementing a
number of actions (described above) that can
be justified because they produce benefits that
are not subject to the uncertainties associated
with climate change. Further study will most
likely identify additional actions that fall into
that category. At some point it may be
desirable to consider actiOns that can not be
justified by their non-climate benefits, but
must depend for justification on the benefits
from reducing the degree of climate change.
It will be important, at that time, to have a
full understanding of the economic, social, and
other implications of such actions so that
decisions despite the uncertainties will be
based on The best information that can be
developed. Some of the types of action that
will need to be considered and some of the
questions that will need to be addressed are
discussed throughout this report.
• A number of other countries have made
public commitments to take actions to reduce
their greenhouse gas emissions by similar or
greater proportions. While such actions will
somewhat delay the increasing concentrations
of greenhouse gases, the problem of achieving
economic growth and improved well-being in
the developing world while avoiding or
limiting the emissions increases from such
growth remains a key, unsolved problem.
Several studies have been conducted
that identify the wide range of policy choices
that are available for reducing emissions. For
example, see A Compendium of Options for
Government Policy to Encourage Private Sector
Responses to Potential Climate Change (U.S.
DOE, 1989), the National Energy Strategy
(NES) which is currently under development
by the U.S. DOE and other agencies within
the Federal government, and Box 3 (which is
an illustrative analysis based on preliminary
estimates of the impacts of the policies
discussed in Box 3).
The Timing of Policy Responses
The costs and benefits of actions taken
to reduce greenhouse gas emissions are
difficult to evaluate because of the many
uncertainties associated with estimates of the
magnitude, timing, and consequences of global
climate change, as well as the difficulty of
assessing the net social costs of strategies that
involve widespread and long-term shifts in
technological development. Given this
situation it may be prudent to delay some
costly actions to reduce greenhouse gas
concentrations until the magnitude of the
problem and the costs of responses are better
established. The potential benefits of delay,
however, must be balanced against the
potential increased risks.
The models indicate that delaying the
policy response to the greenhouse gas
buildup would substantially increase the
global commitment to future warming. For
this reason, the U.S. is taking a number of
policy actions (described earlier) that will
produce a substantial response to the
greenhouse gas buildup, particularly actions
that can be justified for reasons not subject to
the scientific and economic uncertainties about
climate change. Analytical efforts to date have
not been able to determine the appropriate
level of trade-off between accepting additional
costs associated with additional climate change
and incurring additional costs to avoid that
additional climate change. The Stabilizing
Policy cases and the Rapid Reduction case
both assume that immediate action is taken to
begin reducing the rate of greenhouse gas
buildup. The impact of delay was investigated
by assuming that industrialized countries do
not respond until 2010 and that developing
countries wait until 2025. Once action is
initiated, policies are assumed to be
implemented at roughly the same rates as in
the Stabilizing Policy cases. The result would
be a significant increase in global warming (see
Figure 11): the equilibrium warming
commitment in 2050 would increase by about
40-50% relative to the scenarios that assume
policy implementation beginning in 1990. It is
clear that many nations are already taking or
publicly committed to taking actions that are
not reflected in this scenario. For example,
the U.S. has committed to a number of policy
38
-------
Executive Summary
Box 3. Illustrative Analysis of Current US. Policy Initiatives
Several policy initiatives are currently under discussion or have been approved that could
reduce the U S contribution to greenhouse gas emissions These initiatives cover a wide range
of activities that emit different types of greenhouse gases Several examples of these initiatives
include: (1) a recently-proposed reforestation program to plant one billion trees per year that
would sequester carbon as the trees matured; (2) a total phaseout of the major CFCs and
related chemicals that deplete the stratospheric ozone layer, (3) new landfill regulations that
would restrict the amount of CH 4 emissions from decomposing wastes, and (4) several
initiatives that would reduce the amount of energy consumed and thereby reduce CO 2
emissions, including revisions to the Clean Air Act to control acid rain and develop less
polluting transportation fuels and proposals by the U S DOE to adopt more efficient appliance
standards, improve lighting in Federal and commercial buildings, promote state least-cost utility
planning, obtain U S HUD adoption of U S DOE binldmg standards, and expand use of
hydroelectnc power and the transfer of photovoltaic technology
These specific pøhcy initiatives are used here as examples of the types of emission
reduction policies that can be justified for reasons other than climate change The options
included are those for which estimates of emissions were readily available Many other
potential options exist which have not been systematically evaluated. As an illustration of the
potential for reducing emissions, however, we have combined the emission reductions from all
of the initiatives mentioned above Into a single estimate using the concept of Global Warming
Potentials (GWP) discussed in Box 1 and the Addendum to Chapter II to convert the emission
reductions estimated from each initiative to a CO 2 equivalent basis (expressed as carbon) The
impact of these proposed initiatives on estimated U S greenhouse gas emissions is summarized
in the figure below, which indicates that this illustratwe package of proposed initiatives could
reduce total U S greenhouse gas emissions about 13% below projected levels for the year 2000
to a level about 7% lower than estimated 1987 emissions on a C0 2 -equivalent basis If only
CO 2 emissions are considered however, the percentage reduction is substantially less - about
4% below projected 2000 emissions Estimated reductions when only CO 2 is considered are
much lower than reductions that consider all gases on a CO 2 equivalent basis because the
largest source of emission reductions - CFCs as a result of the London Amendments to the
Montreal Protocol and 1990 Clean Air Act Amendments - is not included For a complete
discussion of these results, see the Addendum to Chapter VII
U.S. GREENHOUSE GAS EMISSIONS
(Carbon-Equivalent Basis)
3.0 CFCs
20 CO
E I21NOx
O5
Co 2
0
1987 Baseline 2000 BaselIne 2000 with Policy
EmIssions Emissions Options Package
39
-------
Policy Options for Stabilizing Global Climate
FIGURE 11
INCREASE IN REALIZED WARMING
DUE TO GLOBAL DELAY IN POLICY OPTIONS
(Based on 3.0 Degree Sensitivity)
Slowly Changing World
5
4
3
2
Rapidly Changing World
1555 2000 2028 2080
Year
Yw
Figure 11. Assumes that industrialized countries delay action until 2010 and that developing countries
delay action until 2025. Once action is initiated, policies are assumed to be implemented at roughly
the same rate as in the Stabilizing Policy cases.
5
4
3
2
3
a
S
0
a
S
S
S
a
0
2075 2100
0
1558 2000 2025 2050 2075 2100
40
-------
Executive Summary
measures that will mitigate emissions.
Although this delay scenario clearly does not
correspond to currently planned actions, the
basic point illustrated is still valid.
Policy development and imple-
mentation can be a lengthy process,
particularly at the international level. Any
decision to respond to the greenhouse gas
buildup cannot be fully translated immediately
into action. Roughly a decade was required
for the process that led to international
agreement to reduce emissions of CFCs,
embodied in the Montreal Protocol, and it will
take another decade to implement the agreed-
upon reductions. Agreements to reduce other
greenhouse gas emissions could take much
longer to achieve and implement.
The development of technologies to
reduce greenhouse gas emissions will take
many years. The majority of emissions are
associated with activities that are fundamental
to the global economy (transportation, heating
and cooling of buildings, industrial production,
land clearing, etc.); thus, reducing emissions by
curtailing these activities would be highly
disruptive and undesirable. While this report
has identified a large menu of promising
technologies that can meet our needs for
goods and services while generating much
lower emissions of greenhouse gases, many
require additional research and development
to become economically competitive. The
time required to bring innovative technologies
to market is unpredictable, but the process
usually takes many years. And once a
technology is cost-effective, it may take years
before it achieves a large market share and
decades more for the existing capital stock to
be replaced. Depending on the sector, it may
take 20-50 years or more to substantially alter
the technological base of industrial societies,
and the cost of reducing emissions could rise
dramatically as the time allowed for achieving
these reductions is decreased. While the rate
of change in rapidly developing countries can
be higher and may be influenced by
government policies, once industrial
infrastructure is built, it will be many years
before it is replaced.
The Need for an International
Response
If limiting U.S. and global emissions
of greenhouse gases is desired, government
action will be necessaly. Throughout the
world, market prices of energy from fossil
fuels, products made with CFCs, forest and
agricultural products, and other commodities
responsible for greenhouse gas emissions do
not reflect the risks of climate change. As a
result, increases in population and economic
activity will cause emissions to grow in the
absence of countervailing government policies.
The risk of substantial warming is
unavoidable if developing countries do not
participate in stabilizing strategies.
Increasing the availability of energy services is
a high priority for developing countries
attempting to meet basic human needs.
Increased energy use in developing countries
could lead to dramatic increases in greenhouse
gas emissions unless stabilizing policies are
adopted. The share of greenhouse gas
emissions arising from developing countries
(weighted by their estimated impact on global
warming) increases from about 40% currently
to 50% by 2025 and almost 60% by 2100 in
the RCW scenario; the developing countries’
contribution to greenhouse gas emissions also
rises to about 50% in the SCW (see Figure
12). We examined the implications for global
warming if industrialized countries adopted
climate stabilizing policies without the
participation of developing countries.
Assuming that policies adopted in
industrialized countries have some impact even
in developing countries that do not participate
in an international agreement, equilibrium
warming commitment in 2050 is about 40%
higher than in the Stabilizing Policy cases (see
Figure 13). This implies that action by
industrialized countries on their own can
significantly slow the rate and magnitude of
climate change, but that without the
participation of the developing countries, the
risk of substantial global warming is
unavoidable. Even if developing countries
participate, the degree to which it will be
possible, at any point in time, to avoid
41
-------
Policy Options for Stabilizing Global Climate
80
FIGURE 12
SHARE OF GREENHOUSE GAS EMISSIONS BY REGION *
Scw
100 .... .
r -.-.
20
0
100
SO
20
0
100
SO
20
0
1088 2000
2028 2080
V..,
2078 2100
100
80
So
40
20
0
100
20
0
100
80
20
Scwp
0th.,
D.v.ioping
CP Asia
USSR &
CP Europ.
* See Appendix B for further discussion of these scenarios.
42
OECD
Unit.d Stat.s
Oth.r
Dsv.ioping
CP Asia
USSR &
CP Europ.
OECD
Unitid Stst.s
Oth.r
D .v.Ioping
CP Asia
USSR &
CP Europ.
OECD
U&t.d Stat..
RCW
RCWP
U
.
> SO
C
.
U
40
S
.
C
.
9
40
S
C
0
.
40
80
So
40
RCWA
RCWR
.
So
40
2028 2080
Y r
-------
Executive Summary
FIGURE 13
INCREASE IN REALIZED WARMING
WHEN DEVELOPING COUNTRIES DO NOT PARTICIPATE
(Based on 3.0 Degree Sensitivity)
Slowly Changing World
5
4
3
2
I
Rapidly Changing World
1985 2000 2025 2060 2075 2100
Year
Figure 13. Assumes that industrialized countries follow the Stabilizing Policies scenarios while
developing countries follow the No Response scenarios, except that there is some transfer of low-
emissions technology to developing countries despite their failure to adopt stabilizing policies.
S
4
3
2
0
0
C)
0
0
0
I-
S
0
scw
SCWP with
No Participation
by D.v.ioping
Countri..
0
0
1995 2000 2025 2080 2076 2100
Y•ar
43
-------
Policy Options for Stabilizing Global Climate
emissions increases in developing countries
that would otherwise accompany economic
growth is unknown.
Although most of the costs and
benefits of responding to climate change
cannot be quantified at this time, some
potential actions would have other benefits.
Benefits could include reductions in
conventional pollutants, increased energy
security, and reductions in the balance of
payments deficit, as well as reduced risk of
warming. Similarly, reversing deforestation
has a wide range of benefits, including
maintenance of biological diversity, reduction
in soil erosion and reservoir siltation, and
local climatic amelioration. The phaseout of
production of CFCs, halons, carbon
tetrachloride, and methyl chloroform under
the Montreal Protocol will be most significant
in reducing the risk of stratospheric ozone
depletion and will also make an important
contribution to reducing the risk of climate
change. The U.S. is taking, or is committed to
taking, a number of other actions that have
benefits other than those related to climate
change. In total, these U.S. actions are
estimated to have significant effects on U.S.
emissions of greenhouse gases. Some of the
options discussed here, such as reduced
agricultural emissions, improved biomass
production, and heavy reliance on photo-
voltaic , would require further research and
development to ensure their availability.
Relatively small investments in such research
could yield important payoffs.
NOTES
1. Estimates of equilibrium warming
commitments greater than 6°C represent
extrapolations beyond the range tested in most
climate models, and this warming may not be
fully realized because the strength of some
positive feedback mechanisms may decline as
the Earth warms. These estimates are
represented by >6°C.
REFERENCES
Conway, T.J., P. Tans, L.S. Waterman, K.W.
Thoning, KA Masarie, and R.H. Gammon.
1988. Atmospheric carbon dioxide
measurements in the remote global
troposphere. 1981 - 1984. Tellus 40:81-115.
Hansen, J., I. Fung, A. L.acis, D. Rind, S.
Lebedeff, R. Ruedy, and G. Russell. 1988.
Global climate changes as forecast by Goddard
Institute of Space Studies Three-Dimensional
Model. Journal of Geophysical Research
93:9341-9364.
Hansen, J., A Lacis, D. Rind, G. Russell, P.
Stone, I. Fung, R. Ruedy, and J. Lerner. 1984.
Analysis of feedback mechanisms. In Hansen,
J., and T. Takahashi, eds. Climate Processes
and Climate Sensitivity. Geophysical
Monograph 29, Maurice Ewing Volume 5.
American Geophysical Union, Washington,
D.C. 130-163.
IPCC (Intergovernmental Panel on Climate
Change). 1990. Scientific Assessment of
Climate Change. Draft Report of Working
Group I. April 30.
Keeling, C.D. 1983. The global carbon cycle:
What we know and could know from
atmospheric, biospheric, and oceanic
observations. In Proceedings of the CO 2
Research Conference: Carbon Dioxide, Science
and Consensus. March 19-23, 1982, Berkeley
Springs, West Virginia. DOE CONF-820970,
U.S. DOE, Washington, D.C. 11.3-11.62.
Komhyr, W.D., R.H. Gammon, T.B. Harris,
L.S. Waterman, TJ. Conway, W.R. Taylor, and
K.W. Thoning. 1985. Global atmospheric CO 2
distribution and variations from 1968-1982
NOAAJGMCC CO 2 flask sample data. Journal
of Geophysical Research 90:5567-5596.
Lashof, D. 1989. The dynamic greenhouse:
feedback processes that may influence future
concentrations of atmospheric trace gases and
climate change. Climatic Change 14:213-242.
44
-------
Executive Summary
NOAA (National Oceanographic and
Atmospheric Administration). 1987.
Geophysical Monitoring for Climatic Change
No. 15, Summary Report 1986. Schnell, R.C.,
ed. U.S. Department of Commerce, NOAA
Environmental Research Laboratories,
Boulder. 155 pp.
Ramanathan, V., R.J. Cicerone, H.B. Singh,
and J.T. Kiehi. 1985. Trace gas trends and
their potential role in climate change. Journal
of Geophysical Research 90:5547-5566.
Rouy, R.M. 1987. A look at 1983 CO 2
emissions from fossil fuels (with preliminaiy
data for 1984). Tellus 398:203-208.
Siegenthaler, U. 1983. Uptake of excess CO 2
by an outcrop-diffusion model of the ocean.
Journal of Geophysical Research 88:3599-3608.
Smith, J. and D. Tirpak, eds. 1989. The
Potential Effects of Global Climate Change on
the United States. U.S. Environmental
Protection Agency, Washington, D.C.
U.S. DOE (U.S. Department of Energy). 1989.
A Compendium of Options for Governmental
Policy to Encourage Private Sector Responses to
Potential Climate Change, Report to the
Congress of the United States. U.S. DOE/EH-
0102, Washington, D.C.
45
------- |