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America’s Changed Climate

Federal Report: National Climate Assessment finds widespread drought, sea-level rise, intensifying storms

by Jeff Johnson
May 9, 2014 | A version of this story appeared in Volume 92, Issue 19

Credit: Shutterstock
Climate change is expected to bring more intense rainfall because of a warming atmosphere.
People walk in a rain storm.
Credit: Shutterstock
Climate change is expected to bring more intense rainfall because of a warming atmosphere.

Measurable changes in the U.S. climate are already occurring because of anthropogenic greenhouse gas emissions, and all regions of the country are being affected, according to a report released last week by a committee of leading U.S. scientists at a White House briefing. The U.S. National Climate Assessment states that climate-related changes will accelerate through the century.

Prior editions of this assessment were published in 2000 and 2009, but the difference between those reports and the latest one is that the observed impacts are clearer and more extreme, says Jerry M. Melillo, distinguished scientist at the Marine Biological Laboratory in Woods Hole, Mass., and chair of the advisory committee that prepared the assessment. The new report also “digs deeper” into climate-change effects in the U.S., he notes, particularly looking at regional impacts as well as overall cumulative changes.

“For decades we have been collecting the dots about climate change,” Melillo says. “Now we have connected those dots.”

The report increases sea rise estimates, adds Thomas R. Karl, director of the National Oceanic & Atmospheric Administration’s National Climatic Data Center.

“Back in 2000, we projected a 10- to 17-inch increase in sea level by 2100; now we estimate it to be between 12 and 48 inches,” Karl says. The rise is driven by some 350 billion tons of ice sheets that have melted over the past 10 years, he says.

Sea-level rise, with its impact on coastal cities such as Miami; Norfolk, Va.; and Portsmouth, N.H., is one of three areas of greatest climate concern singled out by Melillo and Karl. The other two are persistent drought in the southwestern U.S., with the increasing likelihood of prolonged fire seasons, and extreme and intense precipitation events, which show a 70% increase in recent years in the northeastern U.S.

The report’s findings underscore the need to take action to cut greenhouse gas emissions and reduce the environmental threats of climate change, the two scientists stress. The report lends support to President Barack Obama’s announcement last June that he intends to take action through executive orders and regulations to reduce greenhouse gas emissions as well as mitigate the worst impacts of a changing climate.

The path ahead, however, will be difficult. After publication of the climate assessment, a flood of criticism came from fossil-fuel industries and their allies in Congress.

One of them is Lamar S. Smith (R-Texas), chairman of the House of Representatives Committee on Science, Space & Technology. Smith calls the report a “political document intended to frighten Americans” with “little science to support any connection between climate change and more frequent or extreme storms.” The President, Smith adds, is stretching the truth to “drum up support for more costly and unnecessary regulations and subsidies.”



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