Here's what we know about the effects of climate change on these phenomena.

El Nino and the warmer oceans

In May, the U.S. National Oceanic and Atmospheric Administration (NOAA) predicted a hurricane season in the Atlantic "close to normal."

This prediction was largely based on the existence of the El Nino climate phenomenon. It defuses hurricane formation by increasing vertical wind circulation, which brings down cold air.

Importing this "dry, less energy-charged" air into the heart of a tropical cyclone "prevents it from strengthening," said Allison Wing, a scientist at Florida State University.

But in August, the U.S. agency adjusted its forecast upwards, announcing that the season would be "above normal," based on ocean and atmospheric conditions. The "record surface temperatures in the Atlantic" will probably offset the effects of El Nino, which are unfavorable to hurricanes, she said.

"In terms of forecasting the season, it's a complicated year because we have these two conflicting factors," Wing said.

- More intense storms -

On July 24, a buoy off the southern tip of Florida recorded a temperature of 38.4 degrees, which is more easily associated with a hot tub than the ocean, and which could be a world record.

Hurricane formation requires a specific set of conditions – but when they come together, the warmth of the oceans allows them to generate stronger winds and higher tides.

"You could say that climate change is rolling the dice," Wing adds. "Very different scenarios remain possible for each storm, but the probability of a very intense storm is higher."

Climate change can also increase the amount of rain carried by hurricanes, according to Andrew Kruczkiewicz, a researcher at Columbia University's Institute for Climate and Society Research.

"The warmer the atmosphere, the greater the capacity to absorb water," which can mean more precipitation, he says. Residents who fled inland to escape a hurricane could still face extreme conditions, the expert adds.

Precipitation during Hurricane Ian in September 2022 was boosted by at least 10 percent by climate change, according to recent research.

- Longer hurricane seasons -

Beyond the intensity of storms, it is the season in which they occur that seems to be prolonged.

The period during which ocean surface temperatures favor the formation of tropical storms begins earlier and ends later, according to Michael Mann. This seems to be true in both the Atlantic and the Bay of Bengal.

There is a great deal of work showing that climate change makes hurricanes more dangerous, but its effect on their frequency is less clear, and more research is needed to understand it.

© 2023 AFP