Is there a link between global warming and Hurricane Katrina?

Is there a link between global warming and Hurricane Katrina?

The day after Hurricane Katrina came ashore, one of the main links at CNN.com said something like "Is Global Warming to Blame?"

They're not the only ones to ask. A Google search for "Katrina Global Warming" yields more than 1.5 million hits. The issue even stirred something of a diplomatic row after German Environment Minister Juergen Trittin made comments to the effect that given the Administration's position on global warming, the U.S. shouldn't be surprised at events like Katrina.

The potential contribution of global warming to the number and magnitude of extreme weather events has been a topic of discussion and debate for years. The fact that damage costs of extreme events have increased markedly in recent decades doesn't mean much, since we've tended to put more and more houses, and bigger houses, in the paths of such events.

The basic link between global warming and hurricanes is not particularly complicated. We know that warm ocean waters drive hurricanes, and that ocean temperatures are expected to increase with global warming. Given that, how will hurricane patterns be affected? And can Hurricane Katrina be attributed to global warming?

The latest research suggests that the number of hurricanes may not change significantly as a result of global warming and increased ocean temperatures, but that their severity will increase. RealClimate.org, a Web site put together by climate scientists, does a great job of explaining how to interpret this fact in the context of specific events like Hurricane Katrina: "Imagine constructing a set of dice where sixes occur twice as often as normal. But if you were to roll a six using these dice, you could not blame it specifically on the fact that the dice had been loaded. Half of the sixes would have occurred anyway, even with normal dice. Loading the dice simply doubled the odds. In the same manner, while we cannot draw firm conclusions about one single hurricane, we can draw some conclusions about hurricanes more generally. In particular, the available scientific evidence indicates that it is likely that global warming will make -- and possibly already is making - those hurricanes that form more destructive than they otherwise would have been."

Last week, new research was released that seems to provide a corroborating analysis from the historical record. Researchers from the Georgia Institute of Technology and the National Center for Atmospheric Research studied the number, duration and intensity of cyclonic storms from 1970 to 2004. They found that the 1970s saw a worldwide average of about ten Category 4 and 5 storms per year. Since 1990, however, the percentage of such storms out of the total number of storms has almost doubled.

If you want to look deeper into the question of hurricanes and climate change, I urge you to visit RealClimate.org. Participating scientists posted a comprehensive review of this issue on September 2, 2005, complete with links to additional data and analysis. There is a particularly interesting graph showing a projection of how the distribution of hurricane strength may shift. There have been almost 200 follow-up postings from other scientists and non-scientists alike. This is the best climate science site around.

-----
Dr. Mark C. Trexler has more than 25 years of energy and environmental experience, and has focused on global climate change since joining the World Resources Institute in 1988. He is now president of Trexler Climate + Energy Services, which provides strategic, market, and project services to clients around the world.

Got a question for our climate expert? Email [email protected].