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GFDL Study Suggests Doubling of Category 4 and 5 Hurricanes this Century

A team of scientists from NOAA’s Geophysical Fluid Dynamics Laboratory (GFDL) used a unique downscaling approach to model hurricane activity through the end of the 21st century, and their results produce nearly a doubling of the frequency of category 4 and 5 storms.

Most climate models are incapable of reproducing the strongest hurricanes (category 3 or higher), so GFDL scientists used a unique three-step approach. They began by creating an average climate change projection based on 18 global climate models, and then fed this projection into a regional model with much higher resolution to simulate entire hurricane seasons. Finally, they used GFDL’s operational hurricane prediction model to re-simulate each storm generated by the regional model--but at a still higher resolution--so that the very intense (category 4 and 5) hurricanes could be simulated.

These results are based on projections of a substantial warming of the tropical Atlantic hurricane regions over the 21st century due to an increase in greenhouse gases. The projections used on a standard future emission scenario from the Intergovernmental Panel on Climate Change (IPCC).

In these experiments, the models showed a decrease in the total number of hurricanes by the end of this century, yet still produced nearly a doubling of category 4 and 5 hurricanes. The largest increase in intense hurricanes was seen in the Western Atlantic region (between 20°N and 40°N).

Category 4 and 5 hurricanes making landfall account for approximately 48% of all hurricane damage in the U.S., despite accounting for only 6% of the total number of hurricanes that make landfall. The authors estimate about a 30% increase in potential damage from the combined effect of fewer hurricanes overall and more very intense hurricanes.

The authors conclude that the increase in intense hurricanes may not be evident until late in the 21st century, because of year-to-year variations in storm activity and multi-decadal fluctuations that are known to exist in the Atlantic. Persistent change can only be detected using many decades of recorded observations, to look for trends that emerge over the long-term.

This study was published in the January 22nd issue of Science. Authors are Morris Bender (GFDL), Thomas Knutson (GFDL), Robert Tuleya (Old Dominion University), Joseph Sirutis (GFDL), Gabriel Vecchi (GFDL), Stephen Garner (GFDL) and Isaac Held (GFDL). More information about this research is available here.