Climate change is expected to increase the areal extent and productivity of forests over the next 50-100 years (medium confidence). Extreme and/or long-term climate change scenarios indicate the possibility of widespread decline (low confidence).
Climate change is likely to cause changes in the nature and extent of several "disturbance factors" (e.g., fire, insect outbreaks) (medium confidence). Of particular interest in North America are changes in fire regimes, including an earlier start to the fire season, and significant increases in the area experiencing high to extreme fire danger. The long-term effects of fire will depend heavily on changes in human fire management activities, which are uncertain, especially in remote boreal forests.
There is a strong need for a long-term comprehensive system to monitor forest "health" and disturbance regimes over regional scales that can function as an early warning system for climate change effects on forests.
Climate change can lead to 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.
Food production is projected to benefit from a warmer climate, but there probably will be strong regional effects, with some areas in North America suffering significant loss of comparative advantage to other regions (high confidence). 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 (high confidence). Crop yield studies for the United States and Canada have indicated a wide range of impacts. Modeled yield results that include direct physiological effects of carbon dioxide (CO2), with sufficient water and nutrients, are substantially different from those that do not account for such effects. Economic studies that include farm- and agricultural market-level adjustments (e.g., behavioral, economic, and institutional) 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 will depend on market and institutional signals, which may be partially influenced by climate change.
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. However, when the possibility of replanting with incorrect species is considered, economic impacts could become negative.
Increased interest in agricultural sinks for carbon sequestration includes proposed use of reduced-tillage practices in North America. Negative consequences may include increased use of pesticides, reduced yields, and increased risk for farmers (medium confidence). Potential benefits include reduced input costs, increased soil moisture, and reduced soil erosion (high confidence).
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