Could Dust Weaken Hurricanes?

The Atlantic hurricane season starts Saturday, and some scientists will try something new this year to unravel the extremely complex mosaic that creates storms of varying intensities. Is it possible, the scientists are asking, that dust storms in Africa might weaken those Atlantic storms before they reach the eastern seaboard?

For several years now, scientists have had evidence that dust from storms across the vast expanse of the Sahara Desert drifts out over the Atlantic where it reflects some solar radiation back into space, thus cooling the ocean waters that fuel hurricanes. Cooler waters should mean fewer, or less intense, storms, according to recent studies.

Amato Evan of the University of Wisconsin-Madison's Cooperative Institute for Meteorological Satellite Studies is hoping that this year could tell something about the effect of Africa's dust storms on Atlantic hurricanes. His computer model indicates a moderate level of dust storm activity for Africa this year, thus a moderate impact on Atlantic storms. It may take more extreme years to answer the question, but at least this is a start.

This year, he said, the amount of cooling will be only about average. But in February Evan came out with a startling claim. At least one third of the recent increase in Atlantic Ocean temperatures is due to a decrease in dust storms, he said. If he's right, dust could play a very important role in determining the strength of hurricanes.

Evan has compiled data from records covering more than a quarter of a century and found a distinct correlation between the amount of dust in the atmosphere and the severity of storms. Low dust years correlate with higher ocean temperatures leading to higher severity. The record-breaking year of 2005 had below-average dust over the Atlantic, very warm sea surface temperatures, and an unprecedented four hurricanes that reached category 5, the highest classification.

So was it the dust that made the difference? It should be pointed out that correlation does not prove causation, so the fact that there was less dust does not prove that dust was related to hurricanes.

It's safe to say that many scientists believe that even if dust contributed significantly, it probably wasn't a major player. One scientist noted that El Nino and La Nina events are likely much more dominant. Dust also tends to dry out the air, and dry air should diminish hurricanes, not intensify them. So there is likely to be much debate over this for several years.

The early predictions for this year's hurricane season are a little worrisome. Ocean temperatures are already one to two degrees higher than average off the coast of Africa this year, according to Phil Klotzbach of Colorado State University, so the storm season could be robust. In the section of the ocean where hurricanes most often spawn, temperatures were higher than they have been in all but three years since 1950.

So Klotzbach's team has predicted 15 named storms, including eight hurricanes. Half should be category 3 or higher, and there is a 70 percent chance that at least one will hit the U.S. coast.

But predicting the weather remains one of the great challenges of modern science. Weather forecasting is so complex, and subject to so many random variables, that it spawned a whole new field of science, called chaos. In other words, there's so many poorly understood things going on that we can't be sure what the heck is going to happen.

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