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No evidence global warming spawned twister

By Elizabeth Landau, CNN
May 22, 2013 -- Updated 1713 GMT (0113 HKT)
CNN iReporter Brenton Leete took this photo of the tornado on the ground in Moore, Oklahoma, on Monday.
CNN iReporter Brenton Leete took this photo of the tornado on the ground in Moore, Oklahoma, on Monday.
STORY HIGHLIGHTS
  • Expert: Moore tornado likely would have happened regardless of global warming
  • Science has stronger support for connection between climate change and drought, heat wave
  • More research and discussion is needed about future warming and storms

(CNN) -- Yes, climate change is happening. But it's hard to say that the tornado that ripped through Moore, Oklahoma -- or any given tornado, for that matter -- was influenced by climate change.

Scientific research has not made a clear connection between tornadoes and climate change, said J. Marshall Shepherd, climate change expert and professor at the University of Georgia.

There is currently a much better understanding of how climate change increases the risks of droughts, heat waves and precipitation, he said. There are also indications that changing patterns may influence the intensity of hurricanes. But as far as tornadoes: There's just not a lot of information.

As far as the Moore tornado, "This tornadic storm, in my view, probably would have happened irrespective of whether there's climate change or not," Shepherd said. "The question is: Are we increasing the risk and probability of more extreme events in general as our climate differs?"

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More research and discussion is needed about future warming and the environments that might produce storms, he said.

Trends in tornado occurrence over the last 50 years do not appear to have changed in conjunction with more greenhouse gases in the atmosphere and patterns of rising temperatures, Shepherd said.

Beyond the climate change question, meteorologists don't know a lot about why some thunderstorms produce tornadoes and not others. According to the National Oceanic and Atmospheric Administration, only about 1% of thunderstorms generate tornadoes. However, tornado prediction is advancing and evolving.

Weather, says Shepherd, is like mood -- it changes all the time. The deeper underlying forces we call "climate" are like personality. Greenhouse gases building up in our ocean atmosphere system, from human activity, influence that personality -- which is much harder to undo.

To put it a different way, a driver who is sober has a certain risk of getting into an accident, said Patrick Kinney, the study's senior author and director of the Columbia Climate and Health Program at Columbia University's Mailman School of Public Health. The risk goes up with a couple of drinks. Similarly, as humans pump more greenhouse gas into the atmosphere, that raises the likelihood of extreme weather events.

"Greenhouse gases are kind of like the alcohol in the system of the climate," Kinney said.

Climate change will mean more heat deaths

Earlier this month, scientists measured for the first time an average carbon dioxide concentration of 400 parts per million at Mauna Loa Observatory in Hawaii, representing a new peak for this iconic monitoring station.

More space and science news from CNN Light Years

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