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D
Leder on Global Environmental Change to
President-Elect George Bush
from the
National Academy of Sciences, the National Academy of
Engineering, and the Institute of Medicine
The Honorable George Bush
The President-Elect of the United States
Old Executive Office Building
Washington, D.C. 20501
Dear Mr. President-Elect:
The problem of global environmental change is now widely
recognized as one of growing urgency that will require re-
sponses by your Administration. Our views on the problem
and possible responses are attached.
Embedded in the diverse manifestations of this problem
gIobal warming, ozone depletion, tropical deforestation, and
acid deposition-are enormous challenges to science and engi-
neering, to your Administration, and to the world community
of nations. in many instances, data and analyses are incomplete
and long-term effects remain indeterminate; in addition, there
are costs to the economy embedded in any decisions made to
address the problem. Yet, even with a continuing background
of uncertainty, it is important to recognize that human activities
are indeed changing the global environment. Prudent courses of
169
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170
APPENDIX D
action need to be initiated now to try to understand and predict
these changes, and to move toward suitable policy responses.
As outlined in the paper that follows, we suggest three
principal actions that your Administration can take against the
possibility that we may be conducting an irreversible experiment
with our planet.
First, the issue of global environmental change must be
made more prominent in the scientific, political, and foreign
policy agendas of the United States. While the issue has been
given more emphasis in the past several months, the need now
is for sustained and systematic attention to economic and envi-
ronmental policies bearing on global change.
Second, a focal point for the deployment of national re-
sources to address the issue needs to be established to coordi-
nate the diverse activities related to the problem. Such activities
under way within the government are often poorly coordinated
and insufficiently focused on the necessary linkages between
scientific understanding and policy options. Further, policies
must be such that they enhance the resiliency, robustness, and
range of options of the affected sectors, from energy production
to agriculture to coastal development.
Third, specific actions should be taken by your Adm~n~stra-
tion to address those aspects of the problem that are reasonably
well understood. Thus, we suggest that you consider the fol-
lowing findings and responses:
.
Both global warming and acid deposition are linked to
heavy reliance on fossil fuels. Therefore, efforts to en-
hance both energy efficiency and conservation should be
strengthened; means for increasing the use of the "clean-
est" fossil fuels, such as natural gas, should be consid-
ered, but In the context of appraising their finite avail-
ability; and alternative non-fossil fuel energy sources,
such as nuclear reactors and solar energy, need to be
reappraised with more emphasis put on their use in a
safe and publicly acceptable manner.
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APPENDIX D
171
The Montreal Protocol is an important first step toward
controlling stratopheric ozone depletion. However, pro-
visions in the Protocol should be called upon to encour-
age deeper reductions in emissions of ozone-destroying
.
.
.
chemicals with a total phaseout of chlorofluorocarbon
products on a reasonable time scale.
Global warming will affect sea levels, agricultural sys-
tems, forestry, and water resources. It is not too soon to
assess possible impacts and responses.
Tropical forests are being cut down at an alarming rate.
Mitigating strategies that consider the economic and
other forces driving this destruction need to be imple-
mented in collaboration with the affected nations.
Improved predictions of the future course of the global
environment require new and innovative approaches to
studying the earth and its environment. A substantial in-
vestment in research and ground- and space-based mon-
itoring activities is needed.
This is a broad agenda, and a challenging one. However,
we believe that it offers a sensible approach to problems that ur-
gently require presidential leadership and whose consequences,
if realized, could be severe for all nations. Leadership by the
United States could be a powerful force for uniting the nations
of the world In a common endeavor vitally Important to all.
FRANK PRESS
President
National Academy
of Sciences
Yours sincerely,
ROBERT M. WHITE
President
National Academy
of Engineering
SAMUEL O. THIER
President
Institute
of Medicine
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172
APPENDIX D
PREFACE
Early in 198S, the Presidents of the National Academies of
Science and Engineering and the Institute of Medicine, with the
concurrence of their Councils, decided on the preparation of
a small number of "White Papers" for the incoming Admin-
istration. The intent was to summarize concisely a few critical
national and global issues to which science and technology were
central, and to suggest presidential options on these issues.
Global environmental change emerged at once as a leading
candidate for such a paper. Concern about man-made changes
in the atmosphere and consequent changes in climate and the
ozone shield has been mounting for more than a decade. A
broader range of issues, including tropical deforestation and
regional degradation in water and air quality, has heightened
public awareness. A major international research program to
build an integrated base of knowledge to address these problems
is taking shape. Thus, an early decision was made to develop
a paper on global environmental change, along with papers on
presidential science advising, the AIDS problem, and national
space policy.
Topical outlines of the principal scientific problems and ele-
ments of the current scientific consensus were prepared with the
aid of the staff and members of various National Research Coun-
ci! groups. These outlines were broadly circulated for comment.
A revised outline, together with an exploratory draft, provided
the basis for a searching discussion by a group of invited senior
scientists at an ad hoc meeting held in Boulder, Colorado, on
Participants in the ad hoc meeting were C. J. Pings, University of Southern Cal-
ifornia (Chairman); James Anderson, Harvard University; Robert Fri. Resources for the
Future; Stephen H. Schneider, National Center for Atmospheric Research; Thomas F.
Malone, St. Joseph College; William Nordhaus, Yale University; Arthur Johnson, Uni-
versity of Pennsylvania; Robert McC. Adams, Smithsonian Institution; Jerry Melillo,
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APPENDIX D
173
August 15-16, 1988. The views elicited in this discussion played
a major role in the subsequent development of the paper by the
Council groups.
The development of the paper was coordinated by John S.
Perry and Ruth S. DeFries of the staff of the NRC Committee on
Global Change and by Norman Metzger of the NRC Executive
Office.
Woods Hole Oceanographic Institution; and Sir Crispin Tickell, United Kingdom Am-
bassador to the United Nations.
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74
APPENDIX D
GLOBAL ENVIRONMENTAL CHANGE
Human activities now match or even surpass nature as an
agent of change in the global environment, as evidenced by a
growing list of seemingly diverse human-induced environmen-
tal changes that have gripped public attention In recent years:
.
rapid changes in the global atmosphere due to fossil fuel
combustion and industrial activities predicted to change
global climate;
. massive ozone depletion over the Antarctic and lesser
decreases over the rest of the globe, both attributed to
emissions of chiorofluorocarbons;
· large-scale destruction of tropical forests for timber, fuel,
conversion to agriculture, and economic development,
with consequent additions to the "greenhouse" effect and
losses in plant and animal species;
damaged lakes in New England, Canada, and Scandi-
navia associated with acid deposition from fossil fuel
combustion.
Although the full long-term implications of these changes
are as yet unclear, there is a growing perception that the future
welfare of human society is to an unknown degree at risk. Our
current scientific understanding amply justifies these concerns, but
also presents opportunities for effective presidential leadership and
action.
Recent events have illustrated the possible social, economic,
and political implications of future global environmental change.
Widespread droughts in the early 1970s set the stage for major
worldwide fluctuations in grain prices. Damage to lakes and
forests has created major political tensions in North America
and Europe. Continued droughts in Africa have stressed the
aid and relief machinery of the developed nations of the north.
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APPENDIX D
175
The inctividual environmental problems that have come to
public attention are intricately and inescapably interlinked, both
scientifically and politically. Scientifically, their resolution re-
quires an understanding of the physical, chemical, and biolog-
ical processes that govern the earth, and of the interaction of
these processes in the entire earth system. Politically, policy
options to address these problems converge on the need for
internationally accepted actions relating to energy, technology,
land use, and economic development. Their implementation
will require U.S. commitment and the development of improved
mechanisms for international collaboration.
Such issues challenge political leadership. The conse-
quences of global changes to indiviclual political constituencies
are probably several clecades away, unclear in nature, but po-
tentially serious. Remeclial and adaptive actions are likely to be
expensive in the short term, whereas their full benefits may be
enjoyed only by future generations. Many possible courses of ac-
tion in policies relating to research, energy, development, and in-
ternational relations involve multiple and interlinked costs and
benefits transcending both national and generational bouncts.
Such problems can only be assessed, and prudent long-term
response policies can only be effectively developecl, at the high-
est political levels. Global change is quintessentially an issue
for leadership at the level of heads of state. The United States,
in your presidential term, is well positioned to play a world
leadership role.
WHAT ACTIONS ARE SUGGESTED?
It is now timely to consider prudent policy actions in three
areas: prevention, adaptation, and research. These actions, which
can only be set in motion by presidential leadership, are dis-
cussed below, followed by synopses of the current scientific un-
derstancting of the components of global environmental change
of current concern.
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76
APPENDIX D
Preventing Global Environmental Change
We are already irrevocably committed to major global
change in the years ahead. The elevated concentrations of green-
house gases produced to date by human activities will persist for
many centuries and will slowly change the climate of the earth,
regardless of our actions. The chIorofluorocarbons (CFCs) that
are depleting the ozone shield have lifetimes on the order of a
century. Complex tropical forest ecosystems have the ability to
regenerate, but this depends on the way they are managed, and
regeneration will occur slowly at best.
While global environmental change cannot be stopped, the
pace of change can be slowed. Put another way, we cannot buy
absolute security against environmental risk, however much we
are willing to pay; but we may be able to reduce environmental
damage and risk markedly by prudent policy actions outlined
below.
Energy Policy
Production of energy from fossil fuels is the root of several
of the agents of global environmental change, notably climatic
change and acid deposition. There has been great concern, and
considerable remedial action, with respect to emissions of sul-
fur and nitrogen compounds from fossil fuel combustion. More-
over, reductions in fossil fuel combustion address the continuing
concerns for regional air quality and acid deposition, the grow-
ing concerns for global climate, and our growing dependency
on foreign energy resources, i.e., petroleum.
To prepare for the possibility that the use of fossil fuels (par-
ticularly coal) may need to be recluced in the years ahead, we
should explore means for reducing energy demand without impeding
economic growth, for example, by using fossil fuels with greater eff~-
ciency, as well as incentives and other means to increase use of the
"cZeanest"fossiZfueZs such as natural gas. However, the finite avail-
ability of natural gas, a premium energy source and valuable
chemical feedstock, also needs to be considered. The potential
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APPENDIX D
177
for energy efficiency gains and fuel-switching is demonstrated
by the responses to the energy price shocks of the early 1970s.
A vigorous research and deveZopment program should give in-
creased emphasis to energy sources that do not produce carbon dioxide.
New technologies for publicly acceptable nuclear reactors-so-
called "safe reactors" should receive attention in an R&D pro-
gram on alternative energy sources. Geothermal, wind, solar,
and other renewable energy sources warrant reexamination to
see if recent progress has improved their economic feasibility as
possible substitutes for fossil fuels in the years ahead.
Actions by the United States alone, while setting a good
example, would in themselves be only marginally effective in
slowing the rate of global carbon dioxide emissions. In the
decades to come, major demands for energy will come from
the developing nations. These nations will have to evaluate the
needs of their own economic progress together with protection
of the global environment. Thus, energy policy issues are likely
to be on the international political agenda.
Policies to Reduce I:ndustriaZ Emissions
The Montreal Protocol to limit emissions of CFCs, signed in
the fall of 1987 by 31 nations including the United States is an
unprecedented example of international cooperation to prevent
global environmental deterioration. The provisions of the Montreal
Protocol comb be called on to urge deeper cuts in the production of
CFCs, to accelerate the timetable for their reduction, and to urge aZZ
countries to sign and enforce the Protocol.
Technology exists to eliminate most of the industrial emis-
sions that cause acid deposition. The use of clean, low-sulfur
coal and combustion and cleaning technologies can significantly
reduce emissions in power plants. However, some emission-
control techniques may be energy-intensive, thus increasing car-
bon dioxide emissions, and may produce solid and liquid waste
products that are difficult to deal with. Thus, policies to con-
trol acid deposition involve trade-offs with measures to address
other environmental problems, and often require international
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178
APPENDIX D
coordination. In any case, there are political and economic com-
ponents in any decision on dealing with acid deposition; and to
date such decisions have been deferred by the past two Admin-
istrations in favor of more research. We believe that the sources
of acid cleposition, the technology to limit emissions, and the as-
sociated costs and political risks are now sufficiently understood
that further deferral in favor of more analysis is unwarranted.
Development Policy
The future course of a number of the global environmen-
tal issues discussed above will be strongly influenced by the
manner in which the economies of the less developed nations
evolve over the next several decades. A nation's impact on its
own environment, and on that of the globe, clearly depends
on its population level, standarcl of living, and the technologies
used to support that standard. Uncontrolled growth of popula-
tions in developing countries seeking better standards of living
with inefficient technologies can only lead to continued damage
to the local anct global environments. Development aid policies
shoul~focus on improving the indigenous scientific and technoZogicaZ
knowledge base and infrastructure of the deveZoping countries as a
foundation for environmentaZZy sustainable economic development to
address these nations' aspirations for a better life. Development aid
decisions should include a consideration of environmental impacts.
Adapting to Global Environmental Change
If we do no more than slow the pace of environmental
change, thus gaining time to deal with its effects, we will have
achieved much. Policy options to enhance our ability to cope
with environmental change should therefore also have high pri-
ority. Because the detailed evolution of the expected changes
cannot at present be predicted, policies should seek to enhance the
resilience, robustness, and range of options of the sectors likely to be
affected. For example, the likelihood of rising sea levels should
clearly be taken explicitly into account in the planning of coastal
development, construction of port facilities, location of waste
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APPENDIX D
179
disposal dumps, and so on. Possible changes in the frequency
and severity of extreme events floods, droughts, and severe
storms- should also be considered. The possibilities for signif-
icant changes in regional hydrology should be considered in
planning for major water-resource projects. Better understand-
ing of the response of crops and natural vegetation to changes
in climate and atmospheric composition is needed. The already
impressive adaptability of agriculture may be further enhanced
by investments in the development of improved crop strains,
the exploitation of new crops, and technology for improving
water utilization.
Options for adaptation are numerous for rich, technologi-
cally advanced nations such as ours, but fewer for poor nations.
It will be in the interests of all to assist the poorer nations in
reducing their vulnerability to environmental change by devel-
oping an effective range of adaptations.
Improving Understanding of Global Environmental Change
We still lack sufficient scientific understanding to predict
confidently the detailed evolution of global and regional change
in the environment. Obtaining this knowledge will require
strong support for research already under way, nationally and in-
ternationally, and support for new long-term programs of interdis-
ciplinary, international research. Monitoring global change will
involve coordinated, long-term observations, both from space
and on the ground. Long-term commitments must be made for
resources that will make uninterrupted observations possible
over the decades to come.
The acquisition of knowledge through research and moni-
toring is expensive, although not nearly as costly as the possi-
ble consequences of ignorance. We are already investing large
resources in the study of the earth, but these efforts require
augmentation and coordination.
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180
Institutional Needs
APPENDIX D
However, current institutions and mechanisms in govern-
ment and in the scientific community both in our country and
in the international communi~need strengthening to assure
a strong scientific program for unclerstanding the global envi-
ronment and developing timely, well-coordinated, and effective
policies. The existing mechanisms for coordination between govern-
ment agencies are not adequate to address the complex scientific and
policy implications of global change.
Mechanisms exist within the federal government that couIct
play a major role in directing the massive and diverse resources
of government on this problem; notably, the interagency Com-
mittee on Earth Sciences of the Federal Coordinating Council on
Science, Engineering, and Technology. However, effective direc-
tion of these governmental resources cannot be achieved solely
by the normal processes of interagency coordination. Even more
complex issues are posed by the need for collaboration between
sovereign nations. Effective leadership and direction in this area
is clearly required. The issue of global environmental change
must have a prominent place on the scientific, political, and
foreign policy agendas of the United States.
PRINCIPAL SCIENTIFIC ISSUES
The policy recommendations suggested above are shaped
by our current understanding of the various aspects of global
environmental change, particularly by the considerable uncer-
tainties in our knowledge. Reducing these uncertainties would
lead to more informed and effective policy decisions.
Climate Change
A central issue in global environmental change is the ef-
fect of changing atmospheric composition on global climate.
The greenhouse effect the trapping of the sun's heat near the
earth's surface by small concentrations of certain gases in the
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APPENDIX D
181
atmosphere has been well understood since the eighteenth cen-
tury and is arguably the most firmly established principle in
atmospheric science. These "greenhouse gases" include water
vapor, carbon dioxide, methane, and the CFCs.
in the nineteenth century, marked growth in carbon dioxide
concentrations began from about 280 parts per million (ppm)
in 1850 to 350 ppm today. This increase can be explained by the
burning of vast quantities of fossil fuels, the massive conversion
of carbon-rich forests to farmland and pasture, and the absorp-
tion of about half of the emitted carbon dioxide in the ocean
Today, fossil fuel use injects about 5 billion tons of carbon into
the atmosphere each year, and deforestation adds at least ~ bil-
lion tons more. As a result, carbon dioxide concentrations are
continuing to increase at about 0.4 percent per year.
Other greenhouse gases are also increasing. Methane, emit-
ted from of! and gas wells, rice paddies, bogs, tundra, and
increasing populations of creatures ranging from cows to ter-
mites, is increasing at over ~ percent per year. The principal
CFCs, despite recent limitations, are still increasing at several
percent per year. Other gases such as nitrous oxide and tropo-
spheric ozone are similarly increasing. The combined effect of
each year's increase in these gases is roughly equal to that of
the carbon dioxide increase alone.
, .
Estimating the influence of continuing increases in green-
house gases on future climate requires quantitative models of
the climate system, as well as predictions of how human ac-
tions will influence future emissions. Based on our current
understanding of natural processes and plausible projections of
population growth, technology, and economic development, it
is expected that before the middle of the next century the com-
bined effect of increases in all greenhouse gases will produce
an impact on the climate roughly equivalent to a doubling of
preindustrial levels of carbon dioxide alone. Numerical models
of the climate system yield estimates of the effect on long-term
global mean temperatures that range between ~ and 5°C (2 to
9°F). The rate of climate change implied by these estimates is as
much as 100 times greater than the average rate of change since
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APPENDIX D
the last glacial period (when global temperatures were about
5°C cooler than today and ice sheets covered our northern tier
of states), and about 10 times greater than the fastest known
sustained climate change during the last 10,000 years.
Recent observations of increased temperatures are consistent
with predicted changes, but we clo not yet know if they actually
confirm that greenhouse warming is indeed in progress. Incli-
vidual disastrous climatic events, such as a dry summer or a
vigorous hurricane season, cannot be attributed to greenhouse
warming.
The expected rapid rate of climate change greatly compli-
cates the task of predicting the changes most important to hu-
man society the timing and regional distribution of changes,
and the frequency and severity of extreme events. Warming
shoulc! lead to worldwide changes in many features of the hy-
clrological cycle, with consequences for soil moisture, river flow,
glacier extent, and the distribution of crop zones. In addition,
there are reasons to expect that warmer ocean temperatures will
lead to more violent tropical storms.
The detailed consequences associated with this expected
warming are still unclear. Complex changes In temperature,
precipitation, soil moisture, and storm patterns could result in
a web of economic impacts.
· Climatic zones and storm tracks may be expected to shift
poleward. Crop zones and natural ecosystems can be
expected to migrate with the changing climate, although
the extent of movement is uncertain. Major shifts could
clearly have far-reaching economic, social, and political
consequences.
Melting of land-borne glaciers and thermal expansion of
sea water are expected to raise global sea levels signifi-
cantly over the next century. Projections of the amount
of rise range from tens of centimeters to as much as 3
meters, with reasonable estimates centering on a ~ meter
rise. Rising sea levels will increase the already trouble-
some rates of coastal erosion and loss of wetlands, while
.
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APPENDIX D
.
.
.
.
183
increased saltwater intrusion would impair water sup-
plies and agriculture in coastal areas.
Warming is expected to be considerably greater in polar
latitudes than in the tropics, and sea ice should diminish.
A navigable Arctic Ocean would have major national
security implications.
Changes in rainfall patterns are likely, and some studies
indicate greater summer dryness in midlatitude conti-
nental regions. Regional changes in water supply and
quality may have significant economic and social conse-
quences.
Adverse climate changes may be difficult to accommo-
date in developing countries, where resources are not
available to adapt to changing conditions. Growing pres-
sures for migration may result.
implications for human health may result from changes
in the range of disease vectors (e.g., insects and rodents)
and in the frequency and intensity of extreme weather
known to influence mortality rates.
There is a disturbing possibility for surprises as the climate
system rapidly changes. The record of the past, notably as
revealed by ice core records, shows that the climate system can
exhibit large and rapid changes in response to slow changes in
natural forcing. Today, humanity is imposing new stresses on
the system, raising the question of possibly triggering climatic
. . .
surprises ~ our own hmes.
Tropical Deforestation
Tropical forests are being rapidly destroyed because of the
pressure of growing local populations for agricultural lanct and
fuel wood supplies, and the strong world markets for tropical
hardwoods and animal products from tropical pastures. Satel-
lite data provide reasonably reliable estimates of the rates of
deforestation; if these rates continue, the planet will be virtually
denuded of tropical forests early in the next century.
This massive change in the earth's vegetation has many
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APPENDIX D
consequences. As noted above, the associated carbon dioxide
release adds about 20 percent to the release from fossil fuel com-
bustion. Other troublesome gases such as nitrogen oxides and
ozone are also produced directly or indirectly from burning to
clear land. Deforestation can also lead to long-term degraciation
of soil fertility, anct is intricately linked to significant changes
in regional hydrology and climate. Perhaps the most serious
long-term impact of tropical deforestation is the loss of plant
and animal species. This loss of genetic resources may rob us
of valuable options for future resources for food, industry, and
health. Many of these changes are irreversible, and the full
range of their long-term consequences is poorly understood.
Stratospheric Ozone Depletion
Ozone is naturally produced in the stratosphere by the inter-
action of sunlight with oxygen. Although present only in small
concentrations, it blocks out highly damaging solar ultraviolet
radiation, and is thus essential to life.
Observed ozone concentrations (a few parts per million) are
maintained by a balance between ozone production and natu-
ral ozone-destroying chain reactions involving extremely small
concentrations of nitrogen, hyclrogen, and chlorine compounds.
The CFCs, synthetic chemicals widely used in industry and con-
sumer products, are known to enter the stratosphere, where they
provide a new primary source of chlorine. This relationship be-
tween surface release of CFCs and global stratospheric ozone
loss was identified in 1974.
The discovery of the Antarctic ozone "hole" the abnor-
mal depletion of ozone over the entire Antarctic continent in the
early Southern Hemisphere spring-was brought to world atten-
tion in 1985. In the last 2 years, ground-based and high-altitude
aircraft experiments have indicated that the ozone depletion is
related to CFC concentrations, and laboratory experiments are
clarifying our understanding of the mechanisms involved.
Small worldwide decreases in total ozone have recently been
detected through careful analysis of surface-based and satellite
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APPENDIX D
185
observations. These changes amount to a few percent, and vary
markedly by latitude and season. Such systematic long-term
declines in ozone are accompanied by large natural seasonal
and interannual variability, which can mask underlying trends.
The best understood implications of stratospheric ozone de-
pletion lie in human health. Changes in total ozone of 5 percent
in the middle latitudes would raise ultraviolet radiation levels
at the surface enough to increase skin cancer incidence by more
than 10 percent. Immunological changes also may result from
ultraviolet exposure. Effects on plants and animals are poorly
understood, although there are grounds for concern. Effects on
food chains in the world ocean, with ultimate effects on fish
harvests, as well as effects on agricultural crops and natural
systems are also likely but have not yet been assessed.
Acid Deposition
Fossil fuel combustion in power plants and in autos pro-
cluces oxides of sulfur and nitrogen, which are converted to
acids in the atmosphere. These compounds are transported in
the atmosphere over long distances and are responsible for re-
duced visibility and increased deposition of acids on the ground
across large regions.
Increased deposition of acids in forester! areas of the north-
eastern United States, Canada, and northern Europe that have
low-alkalinity waters and thin, acid soils has resulted in the
acidification of surface waters, sometimes to the extent that
they no longer can support normal fish populations. The link-
age between fossil fuel combustion and acidification has been
demonstrated.
Acid deposition may be considered as one aspect of a chang-
ing "global chemical climate," with many varied and interTinked
effects. For example, changes in the "chemical climate" have ac-
celerated the corrosion and erosion of buildings and historic
monuments. A serious concern is the possibility that changes in
the deposition of nitrogen and sulfur compounds have signifi-
cant effects on forest productivity. However, the full impact of
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APPENDIX D
acid deposition and other pollutants on forest productivity and
its relationship to the decline of some North American, Cana-
dian, and European forest species is not fully unclerstood, and
the mechanisms of forest damage are not clearly established.
Another aspect of the changing chemical climate is increased
concentrations of ozone at ground level, resulting from reactions
between nitrogen oxides, hydrocarbons, and sunlight. Ground-
leve! ozone increase has also been implicated in human health
problems and significant crop losses. Although the degree of
increase is uncertain, ambient levels of ground-level ozone in the
summertime have been associated in experimental trials with a
loss of growth and altered physiological function of forest trees.
Finally, ozone in the lower atmosphere acts as a greenhouse
gas, and the effects of a changing chemical climate on biological
processes undoubtedly influence the fluxes of other greenhouse
gases as well.
As a final comment, we believe that global environmental
change may well be the most pressing international issue of
the next century. The United States is well positioned to play
a leadership role in coping with and gaining an international
consensus on this difficult issue. Indeed, the United States in the
past has had a major role in examining the problem whether
through the carbon dioxide measurements done on Mauna Loa,
the analysis and development of the experimental evidence for
the relationship of the Antarctic ozone depletion and CFCs,
the substantial contributions of American scientists to creating
mathematical models of climate, or United States leadership on
the Montreal Protocol.
Representative terms from entire chapter:
global environmental
