The devastating string of tornadoes, droughts, wildfires and floods that hit the United States this spring marks 2011 as one of the most extreme years on record, according to a new federal analysis.
Just shy of the halfway mark, 2011 has seen eight $1-billion-plus disasters, with total damages from wild weather at more than $32 billion, according to the National Oceanic and Atmospheric Administration. Agency officials said that total could grow significantly, since they expect this year’s North Atlantic hurricane season, which began June 1, will be an active one.
Overall, NOAA experts said extreme weather events have grown more frequent in the United States since 1980. Part of that shift is due to climate change, said Tom Karl, director of the agency’s National Climatic Data Center.
"Extremes of precipitation are generally increasing because the planet is actually warming and more water is evaporating from the oceans,” he said. “This extra water vapor in the atmosphere then enables rain and snow events to become more extensive and intense than they might otherwise be.”
But for some kinds of extreme weather, teasing out a contribution from climate change is more difficult.
The second half of April brought a swarm of tornadoes that leveled parts of the Midwest, including the twister that killed 151 people in Joplin, Mo. So far, 2011 has seen the sixth-highest number of tornado deaths on record, prompting many people to wonder whether climate change has played a role. So far, scientists say there’s no good evidence for or against a climate change influence on tornado behavior.
Meanwhile, computer models predict that droughts — like those that have scorched large swaths of Texas, New Mexico and Arizona this year — will become stronger and more frequent as climate change continues. But because patterns of drought vary widely from decade to decade, that makes it “very difficult and unlikely that we’re going to be able to discern a human fingerprint, if there is one, on the drought record in the foreseeable future,” Karl said.