Scientists detail global-warming impact on U.S.

WASHINGTON — Man-made climate change is already lifting temperatures, increasing rainfall and raising sea levels around the United States — and its effects are on track to get much worse in the coming century, according to a new report released by federal scientists.

The report, "Global Climate Change Impacts in the United States," covers much of the same ground as previous analyses from U.S. and United Nations science panels. It finds that greenhouse-gas emissions are "primarily" responsible for global warming and that rapid action is needed to avert catastrophic shifts in water, heat and natural life.

What's different this time is the report's scope — at 196 pages, the report attempts to present the fullest picture yet of the threats to the United States — and its timing.

It comes out as Congress is considering a mammoth bill that would impose the first national cap on emissions, and then seek to reduce them sharply over the next 41 years.

That bill, supported by President Obama, has spurred some Republicans to say that they are not certain climate change is happening. It has also been criticized, from both sides of the aisle, as a measure that would impose significant costs on energy use and manufacturing.

Though not explicitly a response, today's report says that the evidence of global change is "unequivocal." And, in language stripped of the usual scientific jargon, it sketches out some of the costs of doing nothing to bring down emissions.

"The projected rapid rate and large amount of climate change over this century will challenge the ability of society and natural systems to adapt," the report says.

The report was unveiled at a news conference including John Holdren, Obama's chief science adviser, and Jane Lubchenco, administrator of the National Oceanic and Atmospheric Administration.

Among its findings:

• The average U.S. temperature has risen 2 degrees Fahrenheit over the past 50 years and might rise more rapidly, between 4 and 11 degrees, before 2100. Temperatures will be nearer the upper end of this range if global emissions are not cut.

• Precipitation in the United States has increased an average of about 5 percent over past 50 years. In the future, computer models show that northern areas will become wetter, and southern areas will become drier, especially in the West.

• The heaviest rainstorms are even heavier now, with the amount of rainfall in major storms having increased 20 percent nationwide over the past century. The hardest-hit areas have been the Northeast — where heavy storms are now 67 percent heavier — and the Midwest, with a 31 percent increase.

• Extreme heat waves will also become more common. A temperature reached only once in 20 years until now might be reached every other year or so by the end of the century.

• Sea levels have been rising along most of the U.S. coast over the past 50 years, increasing up to 8 inches in some places. That trend is expected to continue as warmer temperatures melt glaciers and cause the ocean to expand like a wooden door on a hot day.

Some of the worst-hit areas are expected to be along the East Coast, owing to a confluence of rising seas and subsiding land. Seas might rise 2.3 feet near New York City and 2.9 feet in Hampton Roads.

The report can be found online at www.globalchange.gov.