Climate change made 2020's hurricanes wetter

A new study finds clear evidence of what scientists have been warning of due to global warming: Atlantic hurricanes are producing more rainfall and becoming more intense.

Why it matters: The study, published in Nature Communications, examines the 30 named storms that occurred during the record 2020 Atlantic hurricane season.

• The findings show human activities, such as burning fossil fuels for energy, are making tropical cyclones more destructive.
• Water, not wind, causes the most fatalities from hurricanes.

Driving the news: The findings show that warmer sea and air temperatures led to a 10% uptick in three-hourly storm rainfall rates when measured across the full 2020 season, as well as a 5% increase in extreme three-day rainfall totals.

Zoom in: When looking only at those storms that reached hurricane intensity, the study found that extreme three-hourly rainfall rates and three-day rainfall totals went up by 11% and 8%, respectively.

Context: The atmosphere can hold about 7% more moisture for every 1°C of warming.

• Yet for a season in which ocean temperatures were 0.4°C to 0.9°C above average, the result was even greater rainfall than this key rule of physics would suggest.
• This points to a subtle uptick in storm intensity, study co-author Michael Wehner of the Lawrence Berkeley National Laboratory, told Axios in an interview.

How it works: The study used computer models to simulate 2020's storms both with and without the influence of human-caused climate change.

What they're saying: According to Wehner, the rainfall findings are an "indirect measure of the intensity of the 2020 season."

• "Even though we don't detect it in Saffir-Simpson [Scale] measures of wind speed, the storms are a little more intense. And so the more intense the storm, the more efficient it is at raining out," Wehner said.

The big picture: Jim Kossin, a scientist at The Climate Service, described hurricanes as "water vapor vacuum cleaners."

• He told Axios via email that the study points to the possibility of simultaneous changes in storms' inner workings along with the increased availability of water vapor, both of which may be related to climate change.
• The study is unique in that it examines an entire hurricane season across an ocean basin and finds a human-driven signal in storm characteristics. Previous studies had focused on attributing aspects of individual storms, such as 2017's Hurricane Harvey.

Yes, but: Kerry Emanuel of MIT, who like Kossin was not involved in the new study, told Axios its findings are limited by looking only at rainfall.