The Obama administration is more certain than ever that global warming is changing Americans' daily lives and will worsen conclusions that scientists will detail in a massive federal report.
Once people thought global warming was more in the future and more of an issue in other parts of the world, but the National Climate Assessment will emphasise how the United States is already paying the multibillion-dollar price for man-made climate change, said study co-author Donald Wuebbles, a climate scientist at the University of Illinois.
"We're already seeing extreme weather and it's happening now," Wuebbles said today. "We're seeing more heat waves, particularly in the West and in the South."
This final report to be presented tomorrow is a rewritten and shortened version of a draft that was released in January 2013, with more scientific references, reviews by experts and the public, and a thorough review by the National Academy of Sciences, said Wuebbles and report lead author Gary Yohe of Wesleyan University in Connecticut. There is even stronger evidence than in 2013, Yohe said.
The draft came out just as meteorologists calculated that 2012 was the hottest year on record for the United States, but last year was slightly cooler than the 20th century average. And in the time since the draft report was released, the United States has seen lots of extremes.
Nineteen different state records were set for individual months, such as the hottest January in California this year. And since the draft was released, there's been a dramatic new extreme that a good part of the country is worrying about: California's drought, where a few rural places are in danger of running out of water.
In January 2013, none of California was in either extreme or exceptional drought; now nearly 77 per cent of the state is. It is too early to point directly at the near-record California drought as another sign of global warming, but it fits the pattern, Yohe and Wuebbles said.
