Global warming won’t lead to an increase in Atlantic Basin hurricanes, and, in fact, it may lead to fewer tropical storms and hurricanes, scientists with the National Oceanic and Atmospheric Administration (NOAA) have determined.

In a paper published on-line by Nature Geoscience, the NOAA scientists explained how they simulated Atlantic hurricane activity in 21st century conditions — during periods of an expected rise in greenhouse gas (GHG) emissions. The simulations indicated 27% fewer tropical storms and 18% fewer hurricanes. The strongest hurricanes had slightly higher wind speeds.

“This does not support the idea that we’ve already seen a large positive trend in hurricane activity emerging from greenhouse gases,” said NOAA meteorologist Tom Knutson, who was lead author for the paper. “In fact, it points in the other direction.”

Even though there were fewer storms and hurricanes with higher GHG emissions, “at the same time, near-storm rainfall rates increase substantially,” said Knutson. “Our results do not support the notion of large increasing trends in either tropical storm or hurricane frequency driven by increases in atmospheric greenhouse gas concentrations.”

Tropical storms are said to form when the sea surface temperatures reach around 80 degrees. Under that theory, warmer temperatures — likely under some global warming conditions — would lead to more storms that would last longer. However, the NOAA study found that wasn’t necessarily the case.

“The response of Atlantic tropical cyclones to increased greenhouse gases depends on more than the warming Atlantic Ocean,” said NOAA scientist and co-author Gabriel Vecchi. “In our experiments, the reduction in Atlantic storms seems to be, at least partly, related to a projected increase in wind shear in the tropical Atlantic as we look out into the 21st century.”

Computer models are not certain, the authors noted. In the past storm simulations relied on one of the climate models used by the Intergovernmental Panel on Climate Change (IPCC) to forecast future global temperatures. However, the IPCC models each have various wind shear calculations over the Atlantic, so each result is different. Knutson’s study used an average of all of the IPCC models, which generally would lead to a better forecast.

The NOAA study parallels a review by the National Hurricane Center’s Christopher Landsea, a science and operations officer. Landsea, formerly of NOAA, does not believe that global warming has a strong influence on hurricanes, and has written that “global warming might be enhancing hurricane winds, but only by 1% or 2%.” He has argued that the apparent increase in Atlantic storms is only because of today’s better meteorological tools. Taking into account the improved monitoring, Landsea argues that the number of storms in the Atlantic is “on par” with previous busy storm periods in the basin.

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