Tropical Storm Aletta Forms in the Pacific

Kossin, who is also with the National Centers for Environmental Information, found a 20% to 30% slowdown over land areas affected by North Atlantic and North Pacific tropical cyclones, respectively.

First, he noted that over the more than 60-year period of the study, there may be natural, decades-long cycles in the climate system that could affect the steering of storms and have little or nothing to do with global warming. It stated the storm was forecast to maintain shifting out into the Pacific. While this sounds like good news, it isn't: It's not that hurricanes' wind speeds are diminishing, but instead how fast the entire storm moves, a new study reports.

"Still, it's entirely plausible that local rainfall increases could actually be dominated by this slowdown rather than the expected rain-rate increases due to global warming".

And at the same time, a hotter atmosphere can hold more moisture.

In the last 70 years the storms have slowed by ten per cent.

"The poles tend to become disproportionately warmer than the tropics do under global warming", Kossin said.

Hurricanes are slowing down - and leaving behind a lot more damage when they make landfall, according to a new study.

Kossin's work was based on details of nearly 70 years' worth of storms, but he made no attempt to determine what was causing the slowdown.

"Tropical cyclones are just carried along by the wind, so it makes sense", Kossin says.

"What we're seeing nearly certainly reflects both natural and human-caused changes", Kossin said. "At least not yet".

Dr Christina Patricola, from the Climate and Ecosystems Sciences Division at University California, Davis, says the findings raise several questions, especially regarding "stalled" tropical cyclones.

"These trends are nearly certainly increasing local rainfall totals and freshwater flooding, which is associated with very high mortality risk", he said. "And, unfortunately, this signal would point to more freshwater flooding".

  • Joey Payne