By Doyle Rice, USA TODAY August 5, 2012
Twenty-four summers ago, NASA scientist James Hansen first warned the world about what he called the dangers of global warming.
In front of a Senate panel, he said he was "99% certain" that a recent warming trend was not a natural variation but caused by a buildup of carbon dioxide and other gases in the atmosphere from burning fossil fuels.
Now, a study released this weekend by Hansen, the dean of climate scientists, concludes that the recent heat waves and extreme summers likely were caused by climate change.
"We can state, with a high degree of confidence, that extreme anomalies such as those in Texas and Oklahoma in 2011 and Moscow in 2010 were a consequence of global warming, because their likelihood in the absence of global warming was exceedingly small," Hansen and his NASA co-authors write in the Proceedings of the National Academy of Sciences.
In 2011, Texas and Oklahoma had their hottest summer on record, according to the National Climatic Data Center. The summer of 2010 in much of Russia was the hottest in 130 years of records.
Hansen says the likelihood of such temperatures occurring from the 1950s through the 1980s was rarer than 1 in 300, but now, because of climate change, the odds are closer to 1 in 10.
Atmospheric scientist Clifford Mass of the University of Washington is highly skeptical of Hansen's findings.
"I can't agree with his conclusions," Mass says, saying there is no evidence that the weather patterns that caused the heat waves were associated with global warming. He says the heat waves were due to large-scale, naturally occurring weather patterns, which he says cannot be linked to climate change.
Also, he says that Hansen's study looks back only to the 1950s, ignoring the heat waves of the 1930s, "which dwarf what we have now," Mass says.
He says there is little doubt Earth is warming from a combination of natural and human effects, "but the evidence suggests that the big weather/climate events have little to do with global warming," Mass says.
The NASA study was written before this year's extreme heat and drought in the USA. Through the end of June, the nation was experiencing its hottest year on record, according to the data center. July data will be available this week. For the world as a whole, it has been the 11th warmest through June.
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