Published online 21 January 2010 | Nature | doi:10.1038/news.2010.24


Most powerful hurricanes on the rise

Global warming could lead to fewer but more-intense storms.

HurricaneFewer, more powerful hurricanes in future?NASA

The number of major Atlantic hurricanes per year may almost double by the end of the century in response to global warming, according to a new study.

A team of hurricane researchers suggests that damage from a larger number of very strong — Category 4 and 5 — hurricanes is likely to outweigh a projected decline in less-intense storms1.

In 2008, a group led by Thomas Knutson of the National Oceanic and Atmospheric Administration (NOAA) Geophysical Fluid Dynamics Laboratory (GFDL) in Princeton, New Jersey, projected a marked reduction in the overall number of tropical storms and hurricanes in the western North Atlantic Ocean2.

That result, based on a simulation of Atlantic hurricane activity in a warming world, came as a surprise. Seeking an explanation, the team hypothesized that the western Atlantic Ocean might become less favourable for storms if rising sea surface temperatures further south attract storms from the Gulf of Mexico and adjacent regions.

However, at a resolution of about 18 kilometres, the models that the team used for their initial simulation were too coarse to resolve individual storm systems.

When they repeated their efforts with a model with much higher resolution, the scientists found a shift in the distribution of storms. The finer-grained simulation confirmed the decline in the overall number of storms, but it also showed an 80% increase in the frequency of the most intense storms — Category 4 (210–249 kilometres per hour) and Category 5 (faster than 250 kilometres per hour).

Storm force

The study, led by Morris Bender, an atmospheric scientists at the GFDL, used the same 18 global climate models as the previous study, along with four other models, to simulate sea surface temperatures and Atlantic storm activity under an Intergovernmental Panel on Climate Change moderate-future-emissions scenario for the twenty-first century. They then zoomed in on any storms, generating a more detailed picture of them with a hurricane model used by NOAA's National Weather Service, and oberved their behaviour over five simulated days.

Hurricane projectionsClick for a larger version.Geophysical Fluid Dynamics Laboratory/NOAA

"Downscaling the models revealed details such as hurricanes' rain-bands, vertical motion and eye-wall structure," says Bender. "We think that increased vertical wind shear in a warmer climate will prevent many storms from growing to hurricane force. But in small sub-regions of the Atlantic the effect may not come to bear, and storms tracking across those spots are likely to get more intense."

"This is important because, for example in the United States, 80% of the damage is done by storms of Category 3 and higher," says Kerry Emanuel, a hurricane researcher at the Massachusetts Institute of Technology in Cambridge.

Modelling uncertainty

Wind shear — spatial change in wind direction and speed — is predicted to get stronger in a warmer planet and inhibit the cyclonic rotation of winds, an effect that some scientists think might outweigh the effect of rising sea temperatures.

The projection that there will be fewer but more intense Atlantic hurricanes is in agreement with results of other groups that have used high-resolution climate models to study hurricane activity.


Emanuel, for example, has focused on the amount of energy that storms release to project changes in hurricane activity. Some of the models he used projected a large increase in hurricane power in the Atlantic3, consistent with the most recent findings by the GFDL team.

But Knutson adds a note of caution. One of the four other models the team used for their simulations shows a decrease in all hurricane categories — which he says must still be considered a plausible solution.

"What gives us confidence is that our models do reproduce historical observations very well," he says. "But we're still dealing with a problem that has a lot of inherent uncertainty." 

  • References

    1. Bender, M. A. et al. Science 327, 454-458 (2010). | Article | ChemPort |
    2. Knutson, T. R., Sirutis, J. J., Garner, S. T., Vecchi, G. A. & Held, I. M. Nature Geosci. 1, 359-364 (2008). | Article | ChemPort |
    3. Emanuel, K., Sundararajan, R. & Williams, J. Bull. Am. Meteorol. Soc. 89, 347-367 (2008). | Article
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