Report gives sobering view of warming's impact on US

Because the Northeast has an extensive seacoast (New York State alone, observes the report, has more than $2.3 trillion in insured coastal property), the sea-level rise associated with climate change poses a major risk: the kind of coastal flood that inundates New York City once a century, for example, will happen ten times as often. 

SOUTHEAST

Like many regions, the Southeast will experience both more intense downpours - in large part because of more water evaporating from warmer oceans - and longer periods of drought. Already in the Southeast, average autumn precipitation is up 30 percent since 1901, while areas experiencing moderate to severe spring and summer drought have expanded 12 to 14 percent since the mid-1970s.

Without major cutbacks in greenhouse-gas emissions, add about 10 degrees to the average summer day in Atlanta or Birmingham and you'll have a pretty good idea what's in store by 2100. In the 1960s and 1970s, north Florida experienced about 60 days a year with temperatures above 90 degrees; by the end of this century, that number could be 165 days, and in the southern part of the state, it could be more than 180 days.

The Southeast is especially prone to hurricanes, which are expected to get more powerful (but not necessarily more frequent) by century's end. By itself, that would inevitably cause more destruction, but the threat will be made worse by rising sea levels.

MIDWEST AND GREAT PLAINS

In the Midwest - a region far from the moderating influence of oceans - heat waves have been more frequent in recent decades. Heavy downpours now come twice as often as they did a century ago. If emissions aren't curbed, heat waves like the one that struck in 1995 - during which temperatures nearly reached 100 degrees and 700 people died - are likely to occur about three times a year. One possible silver lining: The region's frigid winters will moderate.

Warmer summers - and shorter winters with less ice cover - will also cause more evaporation from the Great Lakes. As a result, average lake levels could drop by up to two feet by 2100, disturbing both natural shoreline ecosystems and the lakeshores' industrial and tourist infrastructure. Shallower Great Lakes will also force ships to carry lighter cargoes - which means shipping costs will go up.

In the crucially important agricultural sector, a longer growing season will be a good thing, but the combination of heat waves and floods, plus potential invasions by heat-loving insects and weeds, could erase any such benefits. These pests would threaten not just crops, but livestock and forests as well. To think about the change in climate conditions, imagine that by 2100 the state of Illinois will have a climate similar to the Texas Gulf Coast.

While rainfall is likely to increase in parts of North Dakota and Montana, it will probably decrease in already-dry West Texas, Oklahoma, and eastern Colorado. The region's population is currently using underground aquifers for irrigation and drinking water at an unsustainable rate. Stresses on water supply, along with higher temperatures in summer, will have a detrimental impact on cattle ranching and on crops such as wheat, corn, hay, barley, and cotton. 

SOUTHWEST

In the past 30 years alone, temperatures in the Southwest - already the hottest part of the US - have averaged 1.5 degrees F higher than the 1960 to 1979 baseline. And thanks to southern California and cities like Phoenix, the region has a large and growing population, which places increasing demands on the region's water resources. Meanwhile, California's Central Valley, whose climate is very dry, uses massive irrigation to create one of the most productive areas of cropland in the nation.