Extreme Weather Flooding the Midwest Looks a Lot Like Climate Change

As global temperatures rise and the oceans warm, what used to be 500-year floods are now happening more frequently.

Devastating storms still roiling much of the American Midwest have dumped record levels of rain over the past week and caused flash flooding that has killed at least 10 people, inundated towns and highways, and forced hundreds of people to evacuate their homes.  Parts of Missouri, Illinois, Indiana, Arkansas and Louisiana received 10 to 15 inches of rain in the past seven days, according to the National Weather Service, resulting in record crests of numerous rivers across the central United States.

Extreme storms like these have become more common as global temperatures have risen and the oceans have warmed.  Some have the clear fingerprints of man-made climate change.

"Of course there is a climate change connection, because the oceans and sea surface temperatures are higher now because of climate change, and in general that adds 5 to 10 percent to the precipitation," Kevin Trenberth, a climate scientist with the National Center for Atmospheric Research, said.  "There have been many so-called 500-year floods along the Mississippi about every five to 10 years since 1993."    

Scientists won't know the extent to which climate change played a role in these storms unless they do an attribution study.  Such analyses determine how much the rise in trapped greenhouse gases increased the odds of a single event happening.  Increasingly, scientists have tried to do these studies far more quickly to spread accurate information about how climate change is affecting us today and improve longer-term forecasts and warnings.

An attribution study of last August's deadly Louisiana's storms—classified as a 1,000-year storm in the worst-hit areas and a 500-year storm in others—found that human-caused climate warming increased the chances of the torrential rains by at least 40 percent.

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