More storms predicted

In discussing the most likely effects of a warming climate shift, tropical storms have been a weak link. The thermomechanics controlling formation and evolution of tropical cyclonic storms – hurricanes and typhoons – are ridiculously complicated. Predictions are very hard to make, and require loads of data that take decades to gather…. but there’s no way to rush the weather.

Tropical storms are formed ultimately by temperature differences between the tropics and the higher latitudes. A warming Earth would see most of its temperature gains happen at the poles, diminishing the tropics-to-poles thermal gradient… so, fewer storms? But shouldn’t a warmer world have more raw heat energy and water vapor in its atmosphere, fueling more powerful storms? To a great extent the jury has been out on this important point. The frequency and strength of severe storms does appear to be increasing, but the signal to noise ratio is fairly low in the data so far.

A new paper (well it came out a few days ago, but I’m still catching up) provides some evidence to help resolve the argument of what, exactly, global warming will do to tropical storms. The authors used satellite data tracking the formation of thunderheads – where storms start – around the world, and found that warmer temperatures drive the formation of more thunderheads. All else being equal, a higher ambient air temperature creates more thunderheads, each of which can potentially seed a larger storm system.

For every 1 degree Celsius increase in average sea-surface temperature, the team noted a 45 percent increase in how frequently deep convective clouds appeared. Other studies show that Earth’s average temperature is now rising about 0.13 degrees Celsius per decade, says Aumann. So, if that temperature rise continues, the tropics will see the frequency of strong storms rise about 6 percent each decade.

The authors’ model predicts that more storms will occur in a warmer world, which means more chances for small storms to grow into big storms. Double the number of storms total, and you double statistically the number of Category 5 hurricanes. It remains to be seen whether the distribution of weak versus strong storms changes in other ways, and for other reasons, but in the meantime studies like this one are very helpful in figuring out what to expect as global warming proceeds.

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~ by Planetologist on December 27, 2008.

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