Global Warming Has Little Impact In Tropical Storm And Hurricane Numbers, NOAA Reports

"This study adds more support to the consensus finding of the Intergovernmental Panel on Climate Change and other reports that it is likely that hurricanes will gradually become more intense as the climate continues to warm," said Tom Knutson, research meteorologist and lead author of the report. "It's a bit of a mixed picture in the Atlantic, because we're projecting fewer hurricanes overall.” 

The findings are reported in a study by scientists at NOAA's Geophysical Fluid Dynamics Laboratory in Princeton, N.J., scheduled to be published online on May 18 in Nature Geoscience. Knutson’s co-authors are Joseph Sirutis, Stephen Garner, Gabriel Vecchi, and Isaac Held.

The scientists performed hurricane simulations using a new regional model that offers both higher resolution and an improved ability to simulate past observed changes in Atlantic hurricane activity. In a preliminary study published last October in the Bulletin of the American Meteorological Society, the new model was shown to successfully reproduce Atlantic hurricane counts year-by-year from 1980 to 2006, including the observed increasing trend.

In the new study, the model was used to test the influence of greenhouse gas warming on Atlantic hurricane activity through the end of the 21st century. Simulations reveal higher levels of wind shear and other changes, which act to reduce the overall number of hurricanes in the model.

Tropical Atlantic sea surface temperatures have increased over the past century and several studies have reported strong correlations between increasing tropical Atlantic sea surface temperatures and measures of hurricane activity since at least 1950. Although it is widely accepted in the climate change research community that increases in greenhouse gases have caused most of the global warming of the last half century, the link between increasing greenhouse gases and hurricane activity has been a topic of wide debate and of little consensus.

This new study suggests that in the Atlantic basin, global warming from increasing greenhouse gases will have little impact, or perhaps cause some decrease, in tropical storm and hurricane numbers.

“We'll need to keep an eye on upcoming model studies to see how robust the projected increase in wind shear over the Atlantic turns out to be,” said Knutson. 

Large-scale environmental changes in circulation, such as wind shear, as well as possibly moisture, are likely the dominant factors producing the reduced storm frequency. These results support recent research showing that the primary driver of the recent increase in Atlantic hurricane numbers was the warming of the tropical Atlantic relative to the other tropical basins.

These results are also consistent with a number of previous modeling and theoretical studies that have examined the influence of global warming from increasing greenhouse gases on hurricane intensity. An increase in hurricane intensities globally is assessed as "likely" in the Intergovernmental Panel on Climate Change Fourth Assessment Report issued in 2007.