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s
Adaptation
The amount of money, labor, and equipment we are willing to expend to
avoid greenhouse warming depends in part on how we view the results of
climate change and how much we are willing to risk possible negative
consequences. Estimating all these outcomes is difficult, however, because
we cannot predict with certainty what changes will occur globally and we
cannot predict at all the effects in a given region. Regardless of what the
changes will be, a necessary first step in determining the proper allocation
of resources is to examine the ability of natural systems and humans to
adapt.
METHODS OF ADAPTATION
Humans, animals, and plants are able to adapt to different climates. Animals
and plants live in the Himalayas and in Death Valley, although not all
species thrive in both. Human adaptability is shown by our living and
working in both Riyadh and Barrow.
Human societies can and do thrive in many different climates, but it is
the rate of climate change as much as its magnitude that could pose a threat.
Disasters caused by severe weather and degradation of the environment
illustrate the kinds of disruptions that could accompany rapid climate change.
There are five alternative human responses: (1) modify the hazard, as by
channeling rivers that are prone to flooding; (2) prevent or limit impacts, as
by building dikes; (3) move or avoid the loss, as by implementing flood
plain zoning; (4) share the loss, as by providing insurance; and (5) bear the
loss, as by losing all or part of a crop. Thus we have a large menu of
potential adaptation options, some of which are best made before an event
and some after.
34
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ADAPTATION
35
Plants and animals will always be found regardless of climatic changes
in the ranges discussed here. The threat to the natural communities of
plants and animals, called ecosystems, from greenhouse warming also comes
from its projected rate of change as much as its magnitude. If the climate
changes as rapidly as some computer models project, the present natural
ecosystems may become fragmented and break up. New communities may
replace them with different mixes of species. Long-lived plants like trees,
for example, might persist. If ill adapted to the new conditions, however,
they would fail to compete and reproduce. Species better fitted to the new
climate would immigrate, sometimes hastened by disturbances of various
kinds. Species well suited to the changing conditions may become more
dominant, or pioneer species that could fill a particular niche may thrive in
the new conditions. Certain ecosystems might vanish if the climate that
currently sustains them disappears or changes its location faster than the
key species are able to migrate.
THE ROLE OF INNOVATION
Much human adaptation involves the invention and diffusion of techno-
logical "hardware" or "software." Examples of technological hardware in-
clude air conditioners that make hot days comfortable and tractors that
cultivate large tracts of land in a few days if spring is late. Software
includes information, rules, and procedures like weather forecasts or insur-
ance restrictions. Knowledge and new procedures are generally indispensable
for adopting new hardware. Major breakthroughs like irrigation usually
consist of innovations in social organization and financing as well as new
machinery.
Many past innovations in hardware and software have helped people
adapt themselves and their activities to climate and variable weather. Food
preservation in warm weather, refrigeration and air conditioning, antifreeze
for all-weather automobile travel, and weather satellites to aid prediction all
help. Such innovations can occur rapidly in comparison to the 40 to 50
years envisioned for the equivalent doubling of atmospheric CO2. For ex-
ample, in 1900 California had little crop production; in 1985 it produced
twice as many dollars of crops as second-place Iowa. Penicillin was discovered
in 1928; by 1945 it was saving thousands of lives.
The question frequently asked is how rapidly inventions can replace ex-
isting equipment and how fast other technology can be supplanted. About
two-thirds of capital stock in most industrialized countries is in machinery,
and one-third is in buildings and other structures. This capital stock turns
over more rapidly than might be expected. Most current office space, for
example, is in buildings built in the last 20 years. In Japan, the average
period for virtually complete replacement of machinery and equipment ranges
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POLICY IMPLICATIONS OF GREENHOUSE WARMING
from about 22 years in textiles to about 10 years in industries like telecom-
munications or electrical machinery. Replacement can be fast in agricul-
ture, too. The estimated lifetime of particular strains for five major crops in
the United States is less than 10 years and is expected to be even shorter in
the future.
As societies have become more affluent, they have reduced their sensi-
tivity to natural phenomena in many ways. Overall, the trend is toward
systems of transportation, communication, and energy production and use
that are less sensitive to climate. Improved technology and social organization
also seem to have lessened the impacts of climate fluctuations on food
supply over the last 100 years. In the time frame over which the effects of
greenhouse warming are felt, more societies may become more robust with
respect to climate change.
ASSESSING IMPACTS AND ADAPTIVE CAPACITY
The data and analyses used in this study to assess impacts and adaptive
capacity are drawn mostly, but not exclusively, from the United States.
Few other countries share the United States' combination of wealth, low
population density, and range of climates. Moreover, the panel recognizes
that our domestic well-being is intimately tied to what happens in other
countries. Major international shifts in trade flows, agricultural production,
energy demand patterns, and more could profoundly affect this country.
But a full analysis of such global interactions remains for future studies.
The assessment of impacts in this study examines separately the sensitiv-
ity of various human and ecologic systems to climate change. Not all
interactions could be assessed, even though the panel recognizes that such
interactions may be relevant. For example, unmanaged natural systems
have important interactions with forestry. Although the assessment of for-
estry considers shifts in ranges of pests and other key species, major alterations
in unmanaged natural systems may contain unforeseen problems for forestry.
The assessment here is an initial appraisal of impacts and adaptive capabilities
of affected human and natural systems in the United States; additional effort
is necessary for a more complete understanding of these issues.
CO2 Fertilization of Green Plants
An increasing atmospheric concentration of CO2 would increase agricul-
tural production by enhancing the use of sunlight and slowing transpiration
in some plants. The overall production of organic material also depends on
other factors such as temperature, moisture, and nutrients. It is difficult to
anticipate the amount of increased organic production accompanying green-
house warming because extrapolation from small-scale laboratory experi
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ADAPTATION
37
meets to whole fields of crops or to complete systems of unmanaged plants
and animals is uncertain. The increases in photosynthesis and slowing of
transpiration, however, would probably be somewhat less than observed in
laboratory experiments. These effects would apply to plants in agriculture,
managed forests, and unmanaged ecosystems.
Agriculture
Changes in average temperature are probably less important for agricul-
tural productivity than changes in precipitation and evaporation. Whether
the projected changes are calculated as precipitation and evaporation or the
resulting changes in crop yields, the different climate scenarios produced by
different general circulation models (GCMs) yield large variations-for agri-
culture. But farming has always been sensitive to the weather, and experi-
ence suggests that farmers adapt quickly, especially in comparison to the
rate at which greenhouse warming would occur. Countries like the United
States, which encompass many climate zones and have active and aggressive
agricultural research and development, would probably be able to adapt
their farming to climatic changes deriving from greenhouse warming. Poorer
countries with less wealth or fewer climate zones may have more difficulty
avoiding problems or taking advantage of better conditions.
Managed Forests and Grasslands
Forests and grasslands each cover more than a quarter of the United
States. Trees have long lifetimes, and are unlikely to adjust rapidly enough
by themselves to accommodate rapid warming. Forests, however, can be
managed to preserve ample forest products. Middle-aged forests are at
most risk if climate changes, since young forests can be replaced cheaply
and older ones are valuable to sustain. The adaptation of valuable forests
by management is possible using methods that are flexible and work in
many climates.
.
Natural Landscape
The natural landscape consists of unmanaged ecosystems that include
many species of animals, plants, and microorganisms harvested as game,
fruit, or drugs. Ecosystems absorb CO2, emit O2, and cleanse air and water.
Ecosystems also emit CO2, CH4, and other hydrocarbons. For a variety of
reasons, the adaptation of natural ecosystems to climate change is more
problematic than that of managed systems like farms or plantation forests.
The principal impacts of climate change are expected to be on plants. Im-
pacts on animals would mostly be indirect, through changes in plant functioning
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POLICY IMPLICATIONS OF GREENHOUSE WARMING
and vegetation dynamics, but significant direct effects of climate change are
possible. Some species of birds appear especially responsive to temperature
and may shift their ranges relatively rapidly. Climate change may make
some species extinct, but the diversity of ecosystems would probably protect
those functions that are carried out by many species. For example, diseases
removed first the chestnut and then the elm from eastern forests, but the
loss of their capacity to absorb CO2 was quickly made up by other species.
Some ecological processes, however, are carried out by only a few species.
Only a few species enhance soil productivity by fixing nitrogen, and the
grazing of a single large species may alter a landscape. If climate change
removed one of these species or encouraged another, even a diverse ecosystem
could be affected. Even small climatic changes resulting from greenhouse
warming would be likely to alter unmanaged ecosystems. The adaptation of
the natural landscape can be helped by moving species when they are in
trouble, providing corridors along which those that can may move, and
intervening to maintain diversity of species in key ecosystems.
Marine and Coastal Environments
Concern about coastal swamps and marshlands comes from their special
ecological value and the fact that they are already under stress from human
development and pollution. Wetlands have persisted in the past despite
slowly changing sea levels. Greenhouse warming could induce sea level
rise, however, faster than new wetlands could form. In addition, human
activity could constrain such movement if wetlands are bounded by dikes,
bulkheads, or other structures. Climate change also could alter upwelling
of deep ocean waters or paths of major currents and thus wind and precipi-
tation patterns. Areas of upwelling are among the biologically most productive
ocean habitats, and such changes could affect fisheries substantially. We
do not understand these phenomena well enough, however, to predict the
ecological consequences of coastal or ocean changes with confidence. At
present, the potential for human intervention to ease adaptation in marine
ecosystems seems limited.
Water Resources
Climate change affects natural seasonal and yearly variations in water
resources by changing precipitation, evaporation, and runoff. The first indications
that the demand for water is exceeding the supply usually come during
drought. Changes in water supply due to greenhouse warming could be
moderated, for example, by storage (in natural aquifers or constructed reservoirs)
or joint operation of water systems. Demand for water can be reduced
through a variety of management techniques, including conservation and
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ADAPTATION
39
price incentives. Constructing dams, canals, and other facilities takes time,
and so such adaptation actions need to be taken well in advance. Actions to
deal with current variability of water supply should help prepare for the
possible consequences of greenhouse warming.
Industry and Energy
Most industrial sectors, including electric power generation, are only
moderately sensitive to climate change. Access to regular water supplies is
the largest single problem. In most sectors, the planning horizon and life-
time of investments is shorter than the rates of change we could expect from
greenhouse warming. In general, industry in the United States will likely
adapt to greenhouse warming without much difficulty.
Tourism and Recreation
Tourism and recreation are more sensitive to climate change than some
other sectors because part of the industry is closely associated with nature.
This part of tourism and recreation will necessarily migrate as the attractive
conditions and areas move. Although specific regions will be adversely or
favorably affected, for a country as large as the United States, the overall
effect will probably be negligible.
Settlements and Coastal Structures
Direct climatic changes of greatest importance to human settlements are
changes in the extremes and seasonal averages of temperature, and in the
geographic and seasonal distributions of rainfall. Although these direct
climatic changes may be important, the secondary effects of greenhouse
warming on the levels of water bodies are much more important. Urban
areas will probably choose to protect existing sites rather than move. Adaptations
can be encouraged by changing building codes and land use planning. A1-
lowances should be made for climate change when long-lived structures or
facilities are constructed or renovated.
Human Health
Humans have successfully adjusted to diverse climates. Human health
could be affected by greenhouse warming because people are sensitive to
climate directly as well as being susceptible to diseases whose carriers, or
"vectors," are sensitive to climate. In the United States, however, the rate
of improvements in health due to better technology and its application should
greatly exceed the threat to health due to climate change. These improve
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POLICY IMPLICATIONS OF GREENHOUSE WARMING
meets would not, of course, result from choices about costs and benefits of
responding to greenhouse warming as such. The health consequences may
be worse in countries with fewer resources.
Migration
Historical evidence suggests that migration over long distances, such as
occurred in the United States during the Dust Bowl period, is not an automatic
response to climate change. Migrations typically follow established routes
and cover relatively short distances. While economic and other stresses
will continue to provide incentives for migrants to move to the United
States or other industrialized countries, there is unlikely to be climate-
driven migration on a scale that could not be managed, at least in the next
two decades. What happens over the course of a decade or two, however,
can set the stage for developments over the longer term. Nevertheless,
taking steps now to prevent future migration would not be justified given
human adaptability to change and uncertainties about which areas would be
affected.
Political Tranquility
Concern about political tranquility stems from fear that the occasional
disaster of today might become persistent tomorrow and that accumulation
of problems may become overwhelming. Countries outside the industrial
world may lack the institutions or resources to manage additional environmental
crises. Difficulties of organizing coordinated, multilateral responses to problems
such as hunger are already evident. Greenhouse warming could aggravate
present economic, political, and social problems, swamping national gov-
ernments and international assistance activities and programs.
SOME IMPORTANT INDICES
The same diversity that illustrates how humanity and nature- adjust to
environmental conditions shows that global averages are inappropriate as
foundations for thinking about impact or adaptation. Because most adapta-
tions are local, their cost cannot be calculated until such factors as future
water supply can be predicted in specific regions. Strategic indices of
greenhouse warming for agencies to monitor and scientists to predict include
the following:
1. Seasonal and yearly variation in regional supplies of water to streams
and soils.
2. Variability of ocean currents, particularly those affecting regional
habitability and coastal life.
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ADAPTATION
4
3. Variation in regional sea level and inshore height of waves.
4. Variability of the timing of such biological events as blooms and
. .
m~grahons.
Since even future global averages are uncertain, we will not soon know
what these four regional indices will indicate and therefore will not be able
to predict local impacts and to design specific adaptations. Nonetheless,
monitoring the local climate, including the water in streams and seasonal
events, is crucial over time and will eventually lay the foundation for de-
signing and selecting these specific adaptations.
EVALUATING ADAPTATION OPTIONS
It is difficult to evaluate adaptation options in the face of uncertainties.
Consider a hypothetical bridge over an estuary as an example. An added
meter of height above sea level might add $100,000 to current construction
costs. If that additional clearance were not included at the time of construc-
tion, and the sea level rose enough to require it after 50 years, the retrofit
raising of the bridge might cost $5 million. Discounted at 6 percent per
year, the present value of that $5 million is $271,000. If we were certain
the sea would rise, we could realize a benefit of $171,000 in this example
by adding the meter of clearance today rather than waiting.
This kind of comparison of current and future investment should be per-
formed when each adaptation option is considered. There are three key
elements in this approach: the probability that the outcome will require
adaptive action, the discount rate, and the time at which future spending
would have to take place. Obviously, reducing our uncertainty about future
climate would justify larger investments in adaptations.
Economical adaptation that lessens sensitivity to climate is desirable.
Developing drought-resistant crops or using water more efficiently should
enable us to deal with weather variability today and position us to cope with
future climate change. Poorer countries may have greater difficulties. They
typically lack money, information, and expertise. Often they are sorely
stressed by current weather extremes, and additional strains accompanying
climate change may make their lot worse. If greenhouse warming improves
their situation, they may have difficulty taking advantage of their good
fortune because of the limits on their capacity to respond.
In general, there are four limits on human responses to greenhouse warming.
One is time. Time is needed for people to adapt in a location to a new
climate, to design and build new infrastructures, or to adapt by moving to a
region where the climate is preferred. Although time is needed to adapt
managed things like farming, the historical evidence suggests that farmers
can respond, especially in developed countries. The second limit is water.
Some uses, like irrigation or cooling, use water in large quantities. Trans
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POLICY IMPLICATIONS OF GREENHOUSE WARMING
porting large quantities of water over great distances is possible but expen-
sive. The third limit, and a common one, is money. Adaptations like furnaces
and air conditioners, sea walls and canals take money. The fourth limit is
techniques and information that are used to make decisions and set priori-
ties.
The recommendations in this report address these areas. It is important
that we incorporate these limitations into our thinking when we imagine the
effects of the climate of 2030 imposed on the people and landscape of that
time.
ADAPTING TO CLIMATE CHANGE
Just as strategic planning requires ranking greenhouse warming with all
the other changes ahead, it also demands sorting human activities and nature
into classes of sensitivity and adaptability to greenhouse warming alone.
Then the more sensitive and serious consequences of greenhouse warming
can be ranked within the whole spectrum of changes, and adaptational responses
can be decided accordingly. The Adaptation Panel developed the classifications
presented in Table 5.1, which are used here to categorize adaptation options
with respect to the United States.
Activities with Low Sensitivity
Fortunately, several human activities have low sensitivity, allowing us to
concentrate on others. Machinery and buildings are renewed faster than the
projected pace of greenhouse warming, and so industry should have little
trouble adapting. In general, the decision-making horizons in industry are
shorter than the time at which most climatic impacts would emerge. Most
industries in countries like the United States can thus be expected to adapt
as the climate changes.
The expected climatic changes are within the range people now experi-
ence where they live and to which those who move usually learn to adapt.
In industrial countries, public health should be less at risk than it is elsewhere.
The pace of improvements in health from better technology and public
measures can and likely will exceed any deterioration from greenhouse
warming. Epidemics from causes already known, failure to control population,
and chemical pollution are more serious threats to health than greenhouse
warming.
Activities That Are Sensitive But Can Be Adapted at a Cost
As the most valuable outdoor human activity, farming would have the
greatest impact on national income due to greenhouse warming. Average
warming would not greatly affect yields, but seasonal variations in precipi
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ADAPTATION
TABLE 5.1 The Sensitivity and Adaptability of Human Activities and
Nature
43
Low Sensitivity
Sensitive, but
Adaptation at
Some Cost
Sensitive,
Adaptation
Problematic
Industry and energy
Health
Farming
Managed forests and
grasslands
Water resources
Tourism and
recreation
Settlements and
coastal structures
Human migration
Political tranquility
Natural landscapes
Marine ecosystems
X
X
X
X
X
X
X
X
X
X
NOTE: Sensitivity can be defined as the degree of change in the subject for each
"unit" of change in climate. The impact (sensitivity times climate change) will thus
be positive or negative depending on the direction of climate change. Many things
can change sensitivity, including intentional adaptations and natural and social sur-
prises, and so classifications might shift over time. For the gradual changes as-
sumed in this study, the panel believes these classifications are justified for the
United States and similar nations.
SOURCE: Chapter 5 of the report of the Adaptation Panel.
ration and evaporation would. Experience shows, however, that farming
must continually adapt to cope with, and even exploit, the stresses and
fickle nature of climate. Adaptations to climate change would be required
in both rich and poor countries to protect crops, substitute new ones, and
protect their foundations of soil and water.
Although less thoroughly managed than farming and growing a crop with
a long life, regeneration and management techniques are available that should
enable needed forest products to be sustained.
Should climate warm, most cities would try to adapt rather than abandon
their sites. Although the adaptation might be costly, the costs would in
most cases be lower than the cost of moving the city. By far the highest
costs would be in coastal cities, where added protection would be needed in
response to storms if the sea rises. Where the coast is thinly settled, protec-
tive zoning or even retreat may be sensible.
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POLICY IMPLICATIONS OF GREENHOUSE WARMING
For the nation as a whole, tourism and recreation seem adaptable to
greenhouse warming at little net cost. Adaptation within a country or a
region, however, may entail switching a function or activity from one geo-
graphical area to another. Some regions may win a new activity, while the
same activity becomes untenable and is lost in another. The gradual changes
foreseen in this study will combine these pluses and minuses, with a likely
small net change for a nation of our size and diversity.
Activities That Are Sensitive with Questionable
Adjustment or Adaptation
In the unmanaged systems of plants and animals that occupy much of our
landscape and oceans, however, the rate of change of some key processes
may be slower than the pace of greenhouse warming, making their future
questionable. Unmanaged ecosystems respond relatively slowly, and hence
their adaptability to greenhouse warming is more questionable than that of
the managed systems of crops on a farm or timber in a plantation.
This slow response comes from the long lives of some of their components,
like trees that last longer than the ones planted for timber. It comes from
the slow and chancy arrival of seed and birds traveling on the wind, in
currents, or along corridors rather than being intentionally transported and
planted by farmers. Response is slow because the replacement of plants
and animals on an acre of wild land or in an estuary can take decades or
centuries and because evolution takes centuries or millennia.
Greenhouse warming would not likely make land barren except at the
arid extremes of existing climates if climate became drier. What is likely are
changes in the composition of ecological communities in favor of those
species that are able to move rapidly and far and the disappearance of some
species that move slowly. Marine plants and animals inhabiting intertidal
regions of rocky shores undoubtedly would be affected by rising sea level.
Coral reefs, which are breeding and feeding areas for many of the world's
tropical fisheries, could suffer because they appear to be particularly sensi-
tive to water temperature changes.
Although the impacts of the whole range of climatic changes on the
functioning of ecosystems cannot be predicted with confidence, the risk of
their happening justifies some of the adaptation strategies recommended in
Chapter 9 and adds to the justification for some of the mitigation strategies.
Cataclysmic Climatic Changes
Large changes in climate have happened in the past. Desperate masses
of people have fled drought or flood in places with marginal farming and
growing population. These disasters occurred before greenhouse gases be
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ADAPTATION
45
gan increasing, and they could occur again. The panel knows of no con-
vincing attempt, however, to compute the probability of cataclysmic changes
such as the stopping of the current that warms Europe. Because the prob-
ability and nature of such unexpected changes are unknown, the panel can-
not project their impacts or devise adaptations to them.
CONCLUSIONS
As discussed in Chapter 3, a rise in global average temperatures in the
next century above those of any period in the last 200,000 years cannot be
excluded. Unfortunately, there currently is no way to reliably determine the
effects of such global changes for particular regions. These changes will
probably be gradual. People in the United States likely will have no more
difficulty adapting to such future changes than to the most severe conditions
in the past, such as the Dust Bowl.* Other countries may have more
*Jessica Mathews, a member of the Synthesis Panel, disagrees with this conclusion
with the following statement. "The analysis does not support the conclusion that
greenhouse warming will be no more demanding than past climatic changes. If the
change is unprecedented in the experience of the human species, how can it be
claimed that people will have no more difficulty adapting to future changes than to
those of the past?
"The reasoning used here is that human economic activities are largely divorced
from nature and that modern technology effectively buffers us from climate. Com-
bined with assumptions of gradual change, no surprises, and an Olympian perspective
on national costs, the result is an unduly sanguine outlook. Even as a portrayal of a
best case scenario (rather than a most likely one), this is a flawed analysis.
"First, it underestimates the extent to which human societies, even affluent ones,
depend on the underpinning of natural systems. While recognizing that the pace of
greenhouse warming will most likely exceed the rate at which species and ecosystems
can adapt, the study does not go on to examine the resulting impacts of severe
ecosystem disruption on human societies.
"Also, the impacts of climate change on economic activities are considered sepa-
rately, sector by sector (farming, industry, transportation, etc). This is understandable
given the great difficulty of analyzing the interactions, but here the compartmental-
ization of impacts in both the natural and economic spheres seems to have led to the
distorted view that people, economic activity, infrastructure, and natural context can
be disassociated. The finding that 'expected climatic changes are within the range
people now experience . . . and to which those who move usually learn to adapt,'
means nothing about adaptation to greenhouse-induced change. The fact that one
can move with ease from Vermont to Miami has nothing to say about the conse-
quences of Vermont acquiring Miami's climate.
"Reasoning from the experience of past adaptations is risky given that in the past
societies could usually expect that climate fifty years hence would be reasonably
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POLICY IMPLICATIONS OF GREENHOUSE WARMING
difficulty, especially poor countries or those with fewer climate zones. Some
natural systems of plants and animals would be stressed beyond sustainability
in their current form, a prospect some people may find unacceptable. The
stronger the concern about these various changes, the greater the motivation
to slow greenhouse warming.
In addition, the panel has not found it possible to rule out or rule in such
major disturbances as sudden and major changes in regional climates, ocean
currents, atmospheric circulations, or other natural or social phenomena. At
present, it is not possible to analyze their likelihood or consequences.
Human societies and natural systems of plants and animals change over
time and react to changing climate just as they react to other forces. It
would be fruitless to try to maintain all human and natural communities in
their current forms. There are actions that can be undertaken now, however,
to help people and natural systems adjust to some of the anticipated impacts
of greenhouse warming. The panel recommends action now (see Chapter 9)
based on gradual climate change. Such action would be more important if
climate change proved to be sudden and unanticipated rather than smooth
and predictable.
like that of the present. This will probably not be the case during a greenhouse
warming, because of the difficulties of forecasting regional impacts, the rate of
expected change, and because we may be operating under conditions with which
mankind has no past experience.
"Finally, it may be strictly accurate that regional 'pluses and minuses' will com-
bine to produce 'small net change for a nation of our size.' But the distribution of
impacts in time and space matters more than this treatment suggests. Costs that are
indisputably enormous (including human suffering) begin to appear deceptively man-
ageable when viewed solely from the perspective of their impacts on a multitrillion
dollar economy. For example, in the case of cities, the study finds that while 'adaptation
might be costly, the costs would in most cases be lower than the cost of moving the
city.' "
Representative terms from entire chapter:
climatic changes
