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5
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.
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Representative terms from entire chapter:
climatic changes
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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
technological "hardware" or "software." Examples of technological
hardware include 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 insurance 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 example, 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 existing 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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from about 22 years in textiles to about 10 years in industries
like telecommunications or electrical machinery. Replacement can be
fast in agriculture, 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
sensitivity 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
sensitivity 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 forestry 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 agricultural 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 greenhouse warming because extrapolation from
small-scale laboratory experiments
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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
agricultural 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
agriculture. But farming has always been sensitive to the weather,
and experience 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. Impacts on
animals would mostly be indirect, through changes in plant
functioning
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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 precipitation 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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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 lifetime 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.
Allowances 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 improvements
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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
governments 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 adaptations 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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3. Variation in regional sea level and inshore height of
waves.
4. Variability of the timing of such biological events as
blooms and migrations.
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 designing 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 construction, 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 performed 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. Transporting
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large quantities of water over great distances is possible but
expensive. 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 priorities.
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 (see Part Four) 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
experience 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 precipitation
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TABLE 5.1 The Sensitivity and Adaptability of Human
Activities and Nature
Low Sensitivity
Sensitive, but Adaptation at Some Cost
Sensitive, Adaptation Problematic
Industry and energy
X
Health
X
Farming
X
Managed forests and grasslands
X
Water resources
X
Tourism and recreation
X
Settlements and coastal structures
X
Human migration
X
Political tranquility
X
Natural landscapes
X
Marine ecosystems
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 surprises, and so classifications might shift
over time. For the gradual changes assumed in this study, the
Adaptation Panel believes these classifications are justified for
the United States and Similar nations.
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, protective zoning or even
retreat may be sensible.
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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 geographical 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 sensitive 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 began
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increasing, and they could occur again. The panel knows of no
convincing attempt, however, to compute the probability of
cataclysmic changes such as the stopping of the current that warms
Europe. Because the probability and nature of such unexpected
changes are unknown, the panel cannot 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
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.
*See dissenting statement by panel member
Jessica Mathews at the end of Part One.
