"Extreme [weather] anomalies" such as the deadly European heat wave of 2003, Moscow heat wave of 2010, and Texas-Oklahoma drought of 2011 are becoming more common as a direct consequence of climate change, says a new peer-reviewed study. Human activities - mainly the burning of fossil fuels - have made extreme weather events more frequent and severe, according to the paper.
"Perception of Climate Change," published Aug. 6 online in the Proceedings of the National Academy of Sciences by James Hansen, director of NASA's Goddard Institute for Space Studies, states that "while average global temperature has been steadily rising due to a warming climate, the extremes are actually becoming much more frequent and more intense worldwide."
According to a National Academy of Sciences summary of the research, Hansen looked at summer surface temperature anomalies during a "base period" between 1951 and 1980, and compared it to more recent years.
"Their findings revealed that extremely hot summers... occurred much more frequently in the past several years than during the base period, when they were practically absent," the summary states. "These extremely hot summers have affected an estimated 10% of global land area in recent years, compared with less than 1% of the Earth's surface during the base period."
"This is not some scientific theory. We are now experiencing scientific fact," Hansen told the Associated Press in an interview. "These weather events are not simply an example of what climate change could bring. They are caused by climate change. The odds that natural variability created these extremes are minuscule, vanishingly small... [T]he extremes of unusually cool and, even more, the extremes of unusually hot are being altered so they are becoming both more common and more severe."
Claudia Tebaldi, a scientist with a nonprofit organization called Climate Central, said she felt that the paper was "on solid ground in asserting a greater overall likelihood of heat waves as a consequence of global warming," but Hansen's attribution of specific heat waves to climate change was "not backed by persuasive evidence."
Martin P. Hoerling, a researcher with the National Oceanic and Atmospheric Administration who studies the causes of weather extremes, said in a statement to the New York Times that Hansen's paper "confuses drought, caused primarily by a lack of rainfall, with heat waves."
"This isn't a serious science paper," Hoerling said. "It's mainly about perception, as indicated by the paper's title. Perception is not a science."
Hansen is one of NASA's principal climate scientists and the primary custodian of its records of the earth's temperature. He was among the first scientists to warn about climate change and its potential effects during a 1988 Senate hearing. He is also an activist who "marches in protests to demand new government policies on energy and climate," according to the New York Times. In 2011, he was arrested alongside other activists outside the White House at a demonstration against the proposed Keystone XL oil sands pipeline.
Associated Press, "Study by ‘Global Warming Godfather’: Texas Drought, Europe Heat Waves Are Climate Change," washingtonpost.com, Aug. 4, 2012
Neela Banerjee, "Extreme Summer Heat Linked to Climate Change, Scientists Say," latimes.com, Aug. 6, 2012
John M. Broder, "How to Parse Climate Change and Extreme Weather?," green.blogs.nytimes.com, Aug. 7, 2012
Ben Geman, "New Study Ties Heat Waves to Climate Change," thehill.com, Aug. 5, 2012
Justin Gillis, "Study Finds More of Earth Is Hotter and Says Global Warming Is at Work," nytimes.com, Aug. 6, 2012
James E. Hansen, "Climate Change Is Here - And Worse Than We Thought," washingtonpost.com, Aug. 3, 2012
James E. Hansen, "Perception of Climate Change," Proceedings of the National Academy of Sciences, Aug. 6, 2012
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