GFDL - Geophysical Fluid Dynamics Laboratory

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

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
(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.