120

Large Impacts in Some Places

he impacts of climate change will be significant for Americans. The nature and

intensity of impacts will depend on the location,activity,time period,and geographic scale considered. For the nation as a whole,direct economic impacts are

likely to be modest. However,the range of both beneficial and harmful impacts

grows wider as the focus shifts to smaller regions,individual communities,and specific activities or resources. For example,while wheat yields are likely to increase

at the national level,yields in western Kansas,a key US breadbasket region,are projected to decrease substantially under the Canadian climate model scenario. For

resources and activities that are not generally assigned an economic value (such as

natural ecosystems),substantial disruptions are likely.

Multiple-stresses Context

hile Americans are concerned about climate change and its impacts,they do

not think about these issues in isolation. Rather they consider climate

change impacts in the context of many other stresses,including land-use change,

consumption of resources, fire,and air and water pollution. This finding has profound implications for the design of research programs and information systems at

the national, regional,and local levels. A true partnership must be forged between

the natural and social sciences to more adequately conduct assessments and seek

solutions that address multiple stresses.

Urban Areas

rban areas provide a good example of the need to address climate change

impacts in the context of other stresses. Although large urban areas were not

formally addressed as a sector, they did emerge as an issue in most regions. This is

clearly important because a large fraction of the US population lives in urban areas,

and an even larger fraction will live in them in the future. The compounding influence of future rises in temperature due to global warming, along with increases in

temperature due to local urban heat island effects,makes cities more vulnerable to

higher temperatures than would be expected due to global warming alone.

Existing stresses in urban areas include crime,traffic congestion,compromised air

and water quality, and disruptions of personal and business life due to decaying

infrastructure. Climate change is likely to amplify some of these stresses,although

all the interactions are not well understood.

CONCLUSIONS

T

W

Positive impacts will

possibly be associated with climate

changes such as

warmer winters in the

North, more precipitation in the Southwest,

and longer growing

seasons in parts of

the nation where agriculture and forestry

are important. 

The warmer conditions associated with

longer growing seasons in many parts of

the country are likely

to lead to increased

pest and disease

problems for agriculture and forestry.

U
Impact, Adaptation, and 

Vulnerability

s the Assessment teams considered the negative impacts of climate change for regions,sectors,and

other issues of concern,they also

considered potential adaptation

strategies. When considered together,

negative impacts along with possible

adaptations to these impacts define

vulnerability. As a formula,this can

be expressed as vulnerability equals

negative impact minus adaptation.

Thus,in cases where teams identified

a negative impact of climate change,

but could not identify adaptations

that would reduce or neutralize the

impact,vulnerability was considered

to be high. A general sense emerged

that American society would likely be

able to adapt to most of the impacts

of climate change on human systems

but that the particular strategies and

costs were not known.

Widespread Water Concerns

prime example of the need for

and importance of adaptive

responses is in the area of water

resources. Water is an issue in every

region,but the nature of the vulnerabilities varies,with different nuances

in each. Drought is an important

concern in every region. Snowpack

changes are especially important in

the West, Pacific Northwest,and

Alaska. Reasons for the concerns

about water include increased threats

to personal safety, further reduction

in potable water supplies,more frequent disruptions to transportation,

greater damage to infrastructure,further degradation of animal habitat,

and increased competition for water

currently allocated to agriculture.

The table below illustrates some of

the key concerns related to water in

each region.

Health, an Area of Uncertainty

ealth outcomes in response to

climate change are highly

uncertain. Currently available information suggests that a range of health

impacts is possible. At present, much

of the US population is protected

against adverse health outcomes associated with weather and/or climate,

although certain demographic and

geographic populations are at greater

risk. Adaptation,primarily through

the maintenance and improvement of

public health systems and their

responsiveness to changing climate

conditions and to identified vulnerable subpopulations should help to

protect the US population from

adverse health outcomes of projected

climate change. The costs,benefits,

and availability of resources for such

adaptation need to be considered,

and further research into key knowledge gaps on the relationships

between climate/weather and health

is needed.

Vulnerable Ecosystems

any US ecosystems,including

wetlands, forests, grasslands,

rivers,and lakes, face possibly disruptive climate changes. Of everything

examined in this Assessment,ecosystems appear to be the most vulnerable to the projected rate and magnitude of climate change,in part

because the available adaptation

options are very limited. This is

important because,in addition to

their inherent value,they also supply

Americans with vital goods and services,including food, wood,air and

water purification,and protection of

coastal lands. Ecosystems around the

nation are likely to be affected,from

the forests of the Northeast to the

coral reefs of the islands in the

Caribbean and the Pacific.

121

Floods

X

X

X

X

X

X

X

Droughts

X

X

X

X

X

X

X

X

Snowpack/

Snowcover

X

X

X

X

X

X

Groundwater

X

X

X

X

X

X

Lake, river, and

reservoir levels

X

X

X

X

Quality

X

X

X

X

X

X

Region

Northeast

Southeast

Midwest

Great Plains

West

Northwest

Alaska

Islands

WATER ISSUES

This table identifies some of the key regional concerns about water. Many of these issues were raised

and discussed by stakeholders during regional workshops and other Assessment meetings held

between 1997 and 2000.

A

H

M

A
122

Agriculture and Forestry Likely to Benefit in the Near Term

n agriculture and forestry, there are likely to be benefits due to climate change

and rising CO2levels at the national scale and in the short term under the scenarios analyzed here. At the regional scale and in the longer term,there is much

more uncertainty. It must be emphasized that the projected increases in agricultural

and forest productivity depend on the particular climate scenarios and assumed

CO2fertilization effects analyzed in this Assessment. If, for example, climate change

resulted in hotter and drier conditions than projected by these scenarios,both agricultural and forest productivity could possibly decline.

Potential for Surprises

ome of the greatest concerns emerge not from the most likely future outcomes

but rather from possible "surprises." Due to the complexity of Earth systems,it

is possible that climate change will evolve quite differently from what we expect.

Abrupt or unexpected changes pose great challenges to our ability to adapt and can

thus increase our vulnerability to significant impacts.

A Vision for the Future

uch more information is needed about all of these issues in order to determine appropriate national and local response strategies. The regional and

national discussion on climate change that provided a foundation for this first

Assessment should continue and be enhanced. This national discourse involved

thousands of Americans:farmers, ranchers,engineers,scientists,business people,

local government officials,and a wide variety of others. This unique level of stakeholder involvement has been essential to this process,and will be a vital aspect of

its continuation. The value of such involvement includes helping scientists understand what information stakeholders want and need. In addition,the problem-solving abilities of stakeholders have been key to identifying potential adaptation strategies and will be important to analyzing such strategies in future phases of the

assessment.

The next phase of the assessment should begin immediately and include additional

issues of regional and national importance including urban areas,transportation,and

energy. The process should be supported through a public-private partnership.

Scenarios that explicitly include an international context should guide future assessments. An integrated approach that assesses climate impacts in the context of other

stresses is also important. Finally,the next assessment should undertake a more

complete analysis of adaptation. In the current Assessment,the adaptation analysis

was done in a very preliminary way, and it did not consider feasibility, effectiveness,

costs,and side effects. Future assessments should provide ongoing insights and

information that can be of direct use to the American public in preparing for and

adapting to climate change.

The following section offers suggestions about new approaches, new knowledge,

and new capabilities that would improve future assessments and thus provide

more effective guidance for responding to the challenges posed by climate

change.

CONCLUSIONS

M

S

I

This national discourse

involved thousands of

Americans: farmers,

ranchers, engineers,

scientists, business

people, local government officials, and a

wide variety of others.

This unique level of

stakeholder involvement

has been essential to

this process, and will be

a vital aspect of its continuation. The value of

such involvement

includes helping scientists understand what

information stakeholders want and need.
123

Forests

Semi-arid and Arid

Ecosystem Type

Impacts

Changes in tree species composition and 

alteration of animal habitat

Displacement of forests by open woodlands and 

grasslands under a warmer climate in which 

soils are drier

Displacement of grasslands by open woodlands and forests under a wetter climate

Increase in success of non-native invasive

plant species

Loss of alpine meadows as their species are displaced by lower-elevation species

Changes in plant community composition and

alteration of animal habitat

Loss of northern tundra as trees migrate poleward

Increase in woody species and loss of desert 

species under wetter climate

Loss of prairie potholes with more frequent

drought conditions

Habitat changes in rivers and lakes as amount and

timing of runoff changes and water temperatures

rise

Loss of coastal wetlands as sea level rises and

coastal development prevents landward migration

Loss of barrier islands as sea-level rise prevents

landward migration

Changes in quantity and quality of freshwater

delivery to estuaries and bays alter plant and 

animal habitat

Loss of coral reefs as water temperature increases

X X X X X X X

X

X

X X X X

X X X X

X

X

X

X

X X X X X X

X X X X X

X X

X X X X X X

X X

Changes in ice location and duration alter

marine mammal habitat

Grasslands

Tundra

Coastal & Marine

Freshwater

ECOSYSTEMS

VULNERABILITY

The table below gives a partial list of

potential impacts for major ecosystem

types in various regions of the US.

While the impacts are often stated in

terms of what is likely to happen to

plant communities, it is important to recognize that plant-community changes

will also affect animal habitat.

X

Ecosystem

Forests

Freshwater

Systems

Grasslands

Coastal 

Systems

Agroecosystems

Goods

timber, fuelwood, food

(such as honey, mushrooms, and fruits)

drinking and irrigation

water, fish, hydroelectricity

livestock (food, game,

hides, fiber), water, genetic

resources

fish, shellfish, salt, seaweeds, genetic resources

food, fiber, crop genetic

resources

Services

purify air and water, generate soil, absorb carbon, moderate

weather extremes and impacts, and provide wildlife habitat and

recreation

control water flow, dilute and carry away wastes, and provide

wildlife habitat, transportation corridors, and recreation

purify air and water, maintain biodiversity, and provide wildlife

habitat, employment, aesthetic beauty, and recreation

buffer coastlines from storm impacts, maintain biodiversity,

dilute and treat wastes, and provide harbors and transportation

routes, wildlife habitat, employment, beauty, and recreation

build soil organic matter, absorb carbon, provide employment,

and provide habitat for birds, pollinators, and soil organisms

NE SE MW GP WE PNW AK IS