ST. PAUL (AP) -- A federal study ordered by Congress in 1990 projects average temperatures in the Midwest will rise 5 to 10 degrees Fahrenheit in the 21st century.
The change will bring about lower lake and river levels, more exotic pests, fewer opportunities for winter activities, and higher crop yields, resulting in lower consumer prices.
Released by the Clinton administration Monday, the report was prepared by representatives of government, universities, industry and private groups. A six-page section of the 145-page summary, based on computer models and historical data, deals with the Midwest.
Many scientists have concluded that a buildup in heat-trapping gases such as carbon dioxide already has contributed to a 1-degree increase in the past century.
If warming trends continue, increased temperatures will place greater stress on urban areas, which typically are warmer than surrounding rural areas, the study found. With minimum temperatures expected to increase slightly more than the overall average, there will be less relief at night during heat waves. During those hot periods, unhealthy air pollutants also are trapped nearer the surface.
Winters will be milder, providing fewer opportunities for skiing, snowmobiling and ice fishing.
Farmers will have a longer growing season, giving them more chances to plant a second crop after the first is harvested. More carbon dioxide will make plants grow faster and contribute to higher yields. Consumers will pay lower prices, cutting deeper into farmers' margins.
Precipitation will increase, but because of rising temperatures and other meteorological factors, evaporation also will be greater, leading to deficits in soil moisture, lower lake and river levels, and more drought-like conditions.
''An increase in demand for water across the region at the same time as net flows decrease is of particular concern,'' the report said. ''There is a possibility of increased national and international tension related to increased pressure for water diversions from the (Great) Lakes as demands for water increase.''
With warmer water, there will be a shift from cold-water fish such as trout to warmer-water species such as bass, and the environment will be more susceptible to invasions by non-native species.
Lakes will be hurt in other ways, too. Heavy rains will lead to more runoff of nutrients from fertilizer, which, combined with higher water temperatures, will spur algae growth, depleting oxygen for other living things.
Higher temperatures and increased evaporation, meanwhile, will reduce forest acreage and make forests more susceptible to pests, diseases and fire.
''What people see so far is going to pale in comparison to what their grandchildren are going to experience 100 years from now,'' said J. Drake Hamilton, policy coordinator for Minnesotans for an Energy-Efficient Economy, a St. Paul-based nonprofit organization. ''As a rational society, we need to plan for the change that we know is inevitable.''
On the Net:
The federal report, prepared by the U.S. Global Change Research Program, can be found at http://www.nacc.usgcrp.gov/.
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