Figure 2.1 Average Surface Air Temperature and CO2 Concentrations Since 1880

emissions from human activity are unequivocally warming the planet’s climate. Further, the IPCC report finds that — even with a stabilization of GHG concentrations at current levels — the impact of climate change will lead to potential irreversible impacts.5

The IPCC projects that global temperatures will rise 1.1 to 6.4°C by 2100, and global sea level will rise 18 to 59cm. This warming will have many impacts: on ecosystems, food production, coastlines, human settlements, health, and water availability. Impacts from the changing climate will vary across the globe, and even within North America climate change will have different effects on differ ent regions.

Some of the major impacts projected by the IPCC for North America include: Coastal communities and habitats will be

increasingly stressed by climate change impacts interacting with development and pollution. Population growth and the rising value of infrastructure in coastal areas increase vulnerability to climate variability and climate change, with losses projected to increase as the intensity of tropical storms increases. Current adaptation efforts are uneven, and readiness for increased exposure is low.

There is high confidence that many semiarid areas of the western United States will suffer a decrease in water resources due to climate change. Warming in the western mountain states is projected to cause decreased snow pack, more winter flooding, and reduced summer flows in rivers and streams, exacerbating competition for over-allocated water resources. The extent of drought-affected areas is projected to expand.

Figure 2.1 Average Surface Air Temperature and CO2 Concentrations Since 1880

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Global Temperature Anomaly (°C) (bars)

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-0.6 1880 1900 1920 1940 1960 1980 2000 400

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Concentration (ppmv) (curve) CO 2

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5 Intergovernmental Panel on Climate Change (IPCC), 2007. Fourth Assessment Report, Climate Change 2007: Synthesis Report. Valencia, Spain.

Disturbances from pests, diseases, and fire are projected to have increasing impacts on forests, with an extended period of high fire risk, and large increases in area burned. This will be most pronounced in western states.

In the early decades of this century, moderate climate change is projected to increase aggregate yields of rain-fed agriculture by five to twenty percent, but with important variability among regions. Major challenges are projected for crops that are grown near the warm end of their suitable range or that depend on irrigation from highly utilized water resources.

Cities that currently experience heat waves are expected to be further chal lenged by an increased number, intensity, and duration of heat waves during the course of the century, with the potential for adverse health impacts. Elderly populations are most at risk.

In the Arctic region, the main projected

“In the Arctic region, the main projected biophysical effect is the reduction in thickness and extent of glaciers, ice sheets, and sea ice.”

biophysical effect is the reduction in thickness and extent of glaciers, ice sheets, and sea ice. Some detrimental impacts to society include those on infrastructure, as well as on traditional indigenous ways of life. Potential beneficial impacts include reduced heating costs and more navigable northern sea routes.

The report also highlighted some specific impacts that are likely to affect trans portation in the United States:

Warmer winters will likely reduce delays,

improve ground and air transporta tion reliability, and decrease the need for winter road maintenance;

Increased coastal and riverine flooding and landslides will very likely result in negative impacts on transportation;

Reduced water depth in the Great Lakes would lead to the need for “light loading,” resulting in adverse economic impacts;