Monday, December 6News That Matters

Scientists Predict an ‘Above Normal’ Atlantic Hurricane Season

So what are some of those connections?

Thomas Knutson, a climate scientist with the National Oceanic and Atmospheric Administration, has published a series of papers since 2019, including a recent review of research at the site sciencebrief.org that underscores the links with the strongest evidence. Those researchers acknowledged that a warming world is likely fueling more powerful tropical storms and contributing to increased flooding because of rising sea levels. The scientists also stated that rainfall in tropical storms is likely to increase, since a warmer atmosphere can hold more moisture. The team also suggested that the proportion of severe storms has increased, though the overall number of storms worldwide has stayed about the same.

“We’re seeing a rise in the proportion of hurricanes that reach major hurricane status, Category 3 and above,” Dr. Emanuel said. “That’s what we’re unequivocally seeing in the satellite data.”

James Kossin, also with NOAA, has done research lending further support to the idea that hurricanes are getting more powerful. With continued warming, he suggested, “you’ll start to see intensities like you’ve never seen before,” even storms packing 250-mile-per-hour winds. (Major hurricanes, beginning with Category 3, have wind speeds between 111 and 129 miles per hour. A Category 5 storm, currently the most powerful classification, is 157 m.p.h. and above.) “It’s only a matter of time,” he said.

Other research suggests that hurricanes may be weakening more slowly after landfall, increasing their destructive abilities, and that storms are slowing down, lingering as they approach and stretching out the damage over longer time periods.

Between the greater water vapor in the atmosphere and the storm slowdowns, Dr. Kossin said, there has been a 41 percent increase in local rainfall associated with storms that move over land. In addition, he said, the tracks of storms are shifting away from the tropics and are heading farther north, with a subsequent expansion of the range of storm risk.

The area of strongest debate concerns whether climate change has a role in the rising number of hurricanes in the Atlantic. Recent research suggests a strong role for human actions, though not all of those actions are directly related to climate change.

The more conservative faction of scientists attributes much of the rise in storms to natural variability and a cycle of ocean warming and cooling known as the Atlantic Multidecadal Oscillation; NOAA scientists cited the phenomenon as one of the main factors in the rise in last year’s forecast of an active season. Other climate scientists, including Michael Mann of Pennsylvania State University, have cast doubt over whether the oscillation exists at all.