Human-driven climate change is to blame for extreme heat and drought seen in the US, Europe and other regions in recent years, a top NASA scientist has said.
James Hansen, who directs the NASA Goddard Institute for Space Studies, added in a Washington Post editorial that even his "grim" predictions of a warming future, delivered before the US Senate in 1988, were too "optimistic."
"I have a confession to make: I was too optimistic," Hansen wrote.
"My projections about increasing global temperature have been proved true. But I failed to fully explore how quickly that average rise would drive an increase in extreme weather."
Hansen co-wrote an analysis of the past six decades of global temperatures, published in the Proceedings of the National Academy of Sciences, that revealed a "stunning increase in the frequency of extremely hot summers."
Hansen blamed climate change for last year's drought in Texas and Oklahoma, the 2010 heat wave in Russia and the 2003 European heat wave that led to tens of thousands of deaths.
The same was likely true for "the extremely hot summer the United States is suffering through right now," he said, Agence France-Presse reported.
The past year through June 2012 in the continental US was the hottest since modern record-keeping started in 1895, according to the National Oceanic and Atmospheric Administration (NOAA).
Hansen told The Associated Press in an interview that the world was now experiencing scientific fact which, he said, had "deeply troubling ramifications for not only our future but also for our present."
His analysis was based not on models or predictions, "but actual observations of weather events and temperatures that have happened."
The peer-reviewed study showed global temperature had steadily risen due to a warming climate, about 1.5 degrees Fahrenheit in the past century, leading to more frequent extreme events.
According to AFP, the study echoed the findings of research released last month that climbing greenhouse gas emissions boosted the odds of severe droughts, floods and heat waves in 2011.
Experts cited by the AP said they didn't expect Hansen's study to change any minds.
While he is respected by other climate scientists, he is also an activist who had agitated for action to curb greenhouse gases.
Meanwhile, a former skeptic of global warming, University of California Berkeley professor Richard Muller, last week made a very public turnaround, saying that a close look at the data had convinced him that his beliefs were unfounded.
"Call me a converted skeptic," Muller, wrote in an op-ed in The New York Times.
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