"Picture a baseball player on steroids," Meehl goes on. "This baseball player steps up to the plates and hits a home run. It's impossible to say if he hit that home run because of the steroids, or whether he would have hit it anyway. The drugs just made it more likely."

It's the same with the weather, Meehl says. Greenhouse gasses are the steroids of the climate system. "By adding just a little bit more carbon dioxide to the climate, it makes things a little bit warmer and shifts the odds toward these more extreme events," he says. "What was once a rare event will become less rare.

Peter Miller
 quoting Gerald Meehl from the National Center for Atmospheric Research
Weather Gone Wild 

National Geographic, September 2012, print edition