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Recent Heat Waves Caused by Global Warming, Hansen Says

The record heat wave and drought tormenting much of the U.S. is part of a “new extreme category” of weather that is most likely the result of global warming, a top U.S. government climate scientist said.

Abnormal weather episodes were so rare from 1951 to 1980 that events such as the drought in Texas last year and heat wave in Russia in 2010 can only be explained as the effects of the increasing accumulation of carbon dioxide in the atmosphere, according to research published today. If carbon emissions continue unchecked, such events will become routine, with more extremes common within 50 years.

“You would not have these extremes without global warming,” James Hansen, the top climate-change scientist at the U.S. National Aeronautics and Space Administration and the main author of the paper, said today in an interview.

Hansen was one of the first scientists to identify threats from climate change, and to advocate for action to counter carbon-dioxide emissions. He testified to Congress in 1988 that global warming had begun, and last year was arrested during a protest in front of the White House against the proposed Keystone XL pipeline. He urged President Barack Obama to reject the permit for the project, saying that tapping the Canadian oil sands would be “game over” for the Earth’s climate.

The paper by Hansen and two co-authors was published today in the peer-reviewed Proceedings of the National Academy of Sciences. It was written before record heat and drought across the U.S. Still, Hansen said the drought and heat fits the pattern identified in the research paper.

Record Heat

January through June in the U.S. this year was the warmest on record, with the average temperatures 4.5 degrees higher than the 20th-century average and 28 states from Texas and Oklahoma to Vermont and Massachusetts posting record warmth, the National Weather Service said. Oregon and Washington were the only states considered near normal, the agency said.

Drought and heat struck at least six states last year, and in Texas and Oklahoma are blamed for losses as high as $10 billion in crops, livestock and timber, according to the U.S. National Oceanic and Atmospheric Administration in a report.

The 2010 drought and heat wave in Russia destroyed 13 million hectares (32.1 million acres) of crops, Prime Minister Vladimir Putin said in March 2011.

‘Weather Anomalies’

Hansen wrote the paper on extreme weather with Makiko Sato, also of NASA and the Columbia University’s Earth Institute, and Reto Ruedy, of Arlington, Virginia-based Trinnovim LLC, which provides support for U.S. agencies such as NASA.

They looked for examples of “weather anomalies,” defined as three standard deviations away from normal based on a statistical history. From 2006 to 2011, areas meeting the criteria covered about 4 percent to 13 percent of the Earth. Those types of extremes were basically nonexistent in the period studied from 1951 to 1980, they said.

The researchers chose a period of cool weather, and if they had picked a longer period that included the 1930s Dust Bowl and Texas heat waves of the 1950s, would not have found such extremes now, said John Christy, director of the Earth System Science Center at the University of Alabama in Huntsville.

“Once you pick an earlier period, these extremes look less anomalous,” Christy said in an interview.

Hansen countered that if they had compared recent years with data for the previous 10,000 years, it would have found similar, and maybe even stronger, results showing the effects of climate change.

Those three 20th century decades are “a very good period within the range of climates that existed” in history, he said.

Even as he linked recent weather to climate change, Hansen warned that these associations can be limited in terms of affecting public opinion.

“The public takes the anomalies in the most recent season as to their notion of what the climate trend has been,” he said. If next winter is mild or cold, “they will think there isn’t any trend” of warming, he said.

To contact the reporter on this story: Mark Drajem in Washington at mdrajem@bloomberg.net

To contact the editor responsible for this story: Steve Geimann at sgeimann@bloomberg.net

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