Powerful Hurricanes Intensify More Rapidly Today Than 30 Years Ago Due Largely to a Natural Climate Phenomenon

The team found that the biggest factor explaining the increasingly rapid intensification is the AMO. The result comes in part from analyses using 16 separate climate models to isolate the impact from global warming.

“This was a surprise, that the AMO seems to be a bigger influence in rapid intensification than other factors, including overall warming,” said Balaguru, the first author of the paper.

The AMO governs how the temperature of the waters in the North Atlantic cycles between warmer and cooler, with each period typically lasting a decade or more. The cycling occurs for reasons scientists don’t completely understand, but it has broad effects on the environment. For example, it plays a big part in determining the heat content of the oceans, an important factor powering hurricanes.

The AMO has generally been “positive” — causing warmer waters — since the late 1990s.

Balaguru noted that while rapid intensification historically has occurred more often in the western Atlantic, that’s not where the team found the increasing strength of the last 30 years. Rather, the phenomenon is strengthening more in the central and eastern Atlantic, especially to the east of the islands of the Lesser Antilles, which includes the Virgin Islands and Saint Kitts. That’s the same area where the AMO creates warmer waters and boosts ocean heat content, in the central and eastern Atlantic.

That’s exactly the alley where hurricanes Irma, Jose and Maria powered up rapidly last year. It’s a proving ground of sorts where many of the most powerful hurricanes strengthen dramatically.

Balaguru notes that teasing out the effects of the AMO from broader effects of global warming was beyond the scope of the current study but is a focus for scientists.

The work was supported by the Department of Energy’s Office of Science.