Although the year that ended on September 30, 2011 was the driest recorded in Texas since 1985, Hoerling said the extreme absence of moisture resulted from a La Niña cycle event that kept summer tropical storm precipitation from falling on Texas. He acknowledged that the drought has been exacerbated by the extreme summer temperatures. But he said the heat wave "could not have been anticipated" despite the global warming trends. He explained that while the planet has warmed 1 degree Celsius over the past century, Texas has not had a comparable temperature increase, so what happened in 2011 couldn’t have been predicted. "What happened in Texas is uniquely related to variability. Not all places are warming at the same rate," said Hoerling.
Hansen pointed out that his group's study focused only on temperature data, because at this point there isn't enough data to do a comparable analysis of precipitation. But given what is known, he said "there is every reason to believe that the trend toward greater variability, larger anomalies, is true for precipitation as well as temperature."
Temperature greatly influences how much water vapor air can hold, he explained, and "there are multiple indications that moisture falls in more extreme events as the planet warms.
"We can expect that 100-year floods and 500-year floods will be occurring much more frequently than they did in earlier climatology," he said, but "that is not what our paper deals with."
What the paper does focus on, Hansen said, is determining whether extreme weather events like the Texas heat wave can be attributed to climate variability—the natural ups and downs in seasonal temperature—or to the global upward trend in summer temperatures that science now links with climate change.
How this paper will be received remains to be seen. A spokesperson for Senator James Inhofe (R-OK), a leading Congressional climate change skeptic, is already discounting the study because of Hansen’s participation.
"Hansen has lost a lot of credibility ever since he's moved to be more of an activist than a scientist," said Matt Dempsey, communications director for the Senate Environment and Public Works Committee Minority office, which Inhofe leads. "The American people have rejected alarmism on global warming. Global warming has all but gone away on Capitol Hill."
Dempsey also dismissed the IPCC's conclusion, drawn from the work of hundreds of scientists worldwide, that global warming is unequivocal and can be attributed to the increase in greenhouse gasses that are rising due to human activity.
This new paper will likely do little to reconcile the gap between climate scientists and policymakers like Inhofe. But as the political debate continues, government agencies and departments from the U.S. Geological Survey to the Department of Defense are using scientifically observed temperature and climate trends to engage in short- and long-term planning.
At the same time many scientists, including Wuebbles, note that what they've been observing in the way of global warming is now matching what scientific models of climate change have predicted. But to fully understand what's actually happening to the climate—and whether specific events are tied to global changes—we need better ways of analyzing extreme weather events, he said.
Regardless of politics and whether or not it was a result of climate change, Washington, D.C. experienced record-breaking high summer temperatures last year. In fact, July was the capital's hottest month since record-keeping began in 1871.