5.6. North America
North America will experience both positive and negative climate change impacts
(high confidence). Varying impacts on ecosystems and human settlements will
exacerbate subregional differences in climate-sensitive resource production
and vulnerability to extreme events. Opportunities and challenges to adaptation
will arise, frequently involving multiple stresses (Table
TS-12). Some innovative adaptation strategies are being tested as a response
to current climate-related challenges (e.g., water banks), but few cases have
examined how these strategies could be implemented as regional climates continue
to change. Shifting patterns in temperature, precipitation, disease vectors,
and water availability will require adaptive responses—including, for example,
investments in storm protection and water supply infrastructure, as well as
community health services. [15.3.2, 15.4]
| Table TS-12: Climate change adaptation issues in
North American subregions. Some unique issues for certain locations also
are indicated. |
 |
| North American Subregions |
Development Context |
Climate Change Adaptation Options and Challenges |
|
| Most or all subregions |
- Changing commodity markets
- Intensive water resources development over large areas—domestic
and transboundary
- Lengthy entitlement/land claim/treaty agreements—domestic and
transboundary
- Urban expansion
- Transportation expansion |
- Role of water/environmental markets
- Changing design and operations of water and energy systems
- New technology/practices in agriculture and forestry
- Protection of threatened ecosystems or
adaptation to new landscapes
- Increased role for summer (warm weather) tourism
- Risks to water quality from extreme events
- Managing community health for changing risk factors
- Changing roles of public emergency assistance and private insurance |
|
| Arctic border |
- Winter transport system
- Indigenous lifestyles |
- Design for changing permafrost and ice
conditions
- Role of two economies and co-management bodies |
|
| Coastal regions |
- Declines in some commercial marine resources (cod, salmon)
- Intensive coastal zone development |
- Aquaculture, habitat protection, fleet reductions
- Coastal zone planning in high demand areas |
|
| Great Lakes |
- Sensitivity to lake level fluctuations |
- Managing for reduction in mean levels without increased shoreline
encroachment |
|
5.6.1. Communities and Urban Infrastructure
Potential changes in the frequency, severity, and duration of extreme events
are among the most important risks associated with climate change in North America.
Potential impacts of climate change on cities include fewer periods of extreme
winter cold; increased frequency of extreme heat; rising sea levels and risk
of storm surge; and changes in timing, frequency, and severity of flooding associated
with storms and precipitation extremes. These events—particularly increased
heat waves and changes in extreme events—will be accompanied by effects
on health.
Communities can reduce their vulnerability to adverse impacts through investments
in adaptive infrastructure, which can be expensive. Rural, poor, and indigenous
communities may not be able to make such investments. Furthermore, infrastructure
investment decisions are based on a variety of needs beyond climate change,
including population growth and aging of existing systems. [15.2.5]
5.6.2. Water Resources and Aquatic Ecosystems
Figure TS-8: Possible water resources impacts in North America. |
Uncertain changes in precipitation lead to little agreement
regarding changes in total annual runoff across North America. Modeled impacts
of increased temperatures on lake evaporation lead to consistent projections
of reduced lake levels and outflows for the Great Lakes-St. Lawrence system
under most scenarios (medium confidence). Increased incidence of heavy precipitation
events will result in greater sediment and non-point-source pollutant loadings
to watercourses (medium confidence). In addition, in regions where seasonal
snowmelt is an important aspect of the annual hydrologic regime (e.g., California,
Columbia River Basin), warmer temperatures are likely to result in a seasonal
shift in runoff, with a larger proportion of total runoff occurring in winter,
together with possible reductions in summer flows (high confidence). This could
adversely affect the availability and quality of water for instream and out-of-stream
water uses during the summer (medium confidence). Figure TS-8
shows possible impacts. [15.2.1]
Adaptive responses to such seasonal runoff changes include altered management
of artificial storage capacity, increased reliance on coordinated management
of groundwater and surface water supplies, and voluntary water transfers between
various water users. Such actions could reduce the impacts of reduced summer
flows on water users, but it may be difficult or impossible to offset adverse
impacts on many aquatic ecosystems, and it may not be possible to continue to
provide current levels of reliability and quality for all water users. Some
regions (e.g., the western United States) are likely to see increased market
transfers of available water supplies from irrigated agriculture to urban and
other relatively highly valued uses. Such reallocations raise social priority
questions and entail adjustment costs that will depend on the institutions in
place.
5.6.3. Marine Fisheries
Climate-related variations in marine/coastal environments are now recognized
as playing an important role in determining the productivity of several North
American fisheries in the Pacific, North Atlantic, Bering Sea, and Gulf of Mexico
regions. There are complex links between climatic variations and changes in
processes that influence the productivity and spatial distribution of marine
fish populations (high confidence), as well as uncertainties linked to future
commercial fishing patterns. Recent experience with Pacific salmon and Atlantic
cod suggests that sustainable fisheries management will require timely and accurate
scientific information on environmental conditions affecting fish stocks, as
well as institutional and operational flexibility to respond quickly to such
information. [15.2.3.3]
5.6.4. Agriculture
Small to moderate climate change will not imperil food and fiber production
(high confidence). There will be strong regional production effects, with some
areas suffering significant loss of comparative advantage to other regions (medium
confidence). Overall, this results in a small net effect. The agricultural welfare
of consumers and producers would increase with modest warming. However, the
benefit would decline at an increasing rate—possibly becoming a net loss—with
further warming. There is potential for increased drought in the U.S. Great
Plains/Canadian Prairies and opportunities for a limited northward shift in
production areas in Canada.
Increased production from direct physiological effects of CO2, and
farm- and agricultural market-level adjustments (e.g., behavioral, economic,
and institutional) are projected to offset losses. Economic studies that include
farm- and agricultural market-level adjustments indicate that the negative effects
of climate change on agriculture probably have been overestimated by studies
that do not account for these adjustments (medium confidence). However, the
ability of farmers to adapt their input and output choices is difficult to forecast
and will depend on market and institutional signals. [15.2.3.1]
5.6.5. Forests and Protected Areas
Climate change is expected to increase the areal extent and productivity of
forests over the next 50-100 years (medium confidence). However, climate
change is likely to cause changes in the nature and extent of several "disturbance
factors" (e.g., fire, insect outbreaks) (medium confidence). Extreme or
long-term climate change scenarios indicate the possibility of widespread forest
decline (low confidence).
There is strong evidence that climate change can lead to the loss of specific
ecosystem types—such as high alpine areas and specific coastal (e.g., salt
marshes) and inland (e.g., prairie "potholes") wetland types (high confidence).
There is moderate potential for adaptation to prevent these losses by planning
conservation programs to identify and protect particularly threatened ecosystems.
Lands that are managed for timber production are likely to be less susceptible
to climate change than unmanaged forests because of the potential for adaptive
management. [15.2.2]
5.6.6. Human Health
Vector-borne diseases, including malaria and dengue fever, may expand their
ranges in the United States and may develop in Canada. Tick-borne Lyme disease
also may see its range expanded in Canada. However, socioeconomic factors such
as public health measures will play a large role in determining the existence
or extent of such infections. Diseases associated with water may increase with
warming of air and water temperatures, combined with heavy runoff events from
agricultural and urban surfaces. Increased frequency of convective storms could
lead to more cases of thunderstorm-associated asthma. [15.2.4]
5.6.7. Public and Private Insurance Systems
Inflation-corrected catastrophe losses have increased eight-fold in North America
over the past 3 decades (high confidence). The exposures and surpluses of private
insurers (especially property insurers) and reinsurers have been growing, and
weather-related profit losses and insolvencies have been observed. Insured losses
in North America (59% of the global total) are increasing with affluence and
as populations continue to move into vulnerable areas. Insurer vulnerability
to these changes varies considerably by region.
Recent extreme events have led to several responses by insurers, including
increased attention to building codes and disaster preparedness. Insurers' practices
traditionally have been based primarily on historic climatic experience; only
recently have they begun to use models to predict future climate-related losses,
so the potential for surprise is real. Governments play a key role as insurers
or providers of disaster relief, especially in cases in which the private sector
deems risks to be uninsurable. [15.2.7]
