Hurricane Ian: impact of climate change


Climate change added at least 10% more rain to Hurricane Ian, according to a study prepared immediately after the storm.

Thursday’s research, which is not peer-reviewed, compared peak precipitation rates during the actual storm to about 20 different computer scenarios from a model featuring characteristics of Hurricane Ian hitting the Sunshine State in a world without human-caused climate change.

“The real storm was 10% wetter than the storm that might have been,” said Lawrence Berkeley National Lab climatologist Michael Wehner, co-author of the study.

Forecasters predicted that Ian will have dropped up to 61 centimeters of rain in parts of Florida by the time it stops.

Wehner and Kevin Reed, an atmospheric scientist at Stony Brook University, published a study in Nature Communications earlier this year on 2020 hurricanes and found that during their wettest three-hour periods, they were more than 10% wetter than in a world without heat-trapping greenhouse gases. Wehner and Reed applied the same scientifically accepted attribution technique to Hurricane Ian.

According to a long-standing physical rule, for each additional degree Celsius (1.8 degrees Fahrenheit) of heat, the air in the atmosphere can hold 7% more water. This week the Gulf of Mexico was 0.8 degrees warmer than normal, which should have meant about 5% more rain. The reality turned out to be even worse. The flash study found that the hurricane brought double the fall, or 10% more rain.

Ten percent might not sound like a lot, but 10 percent of 20 inches (50 centimeters) is two inches (five centimeters), which is a lot of rain, especially on top of the 20 inches that’s already fallen, Reed said.

Other studies have observed the same feedback mechanisms of stronger storms in warmer weather, said Princeton University atmospheric scientist Gabriel Vecchi, who was not part of the study.

MIT hurricane researcher Kerry Emanuel said that in general, a warmer world makes for rainier storms. But he said he was uncomfortable drawing conclusions about individual storms.

“This activity over very, very heavy rain is something we expected to see because of climate change,” he said. “We will see more storms like Ian.”

Princeton’s Vecchi said in an email that if the world were to recover from the disasters “we need to plan for wetter storms in the future because global warming is not going to go away.”