TCS Daily

Charley, Frances, Ivan, and Global Warming

By Roy Spencer - September 15, 2004 12:00 AM

This year's active hurricane season is sure to bring out those who point to severe weather events as evidence of global warming. Never mind that the National Hurricane Center has been warning for many years that the U.S. coast has had a long run of relatively good luck, and it's only a matter of time before things change. The 1930's through the 1950's was a particularly bad time for major hurricanes hitting the United States. Well, at least for 2004, things have changed.

Lending to the popular impression that hurricanes are getting worse with time is the very real increase in the cost of hurricane damage in recent decades. It is well know, however, that this is due to the construction of more buildings in hurricane-prone areas. We simply have built more stuff out there to get damaged and destroyed.

A considerable amount of research has been done on the issue of whether there will be more, or worse, hurricanes with global warming. This research, of course, assumes that there will be significant global warming, a view that is debatable. The results of this research have been mixed.

Hurricane formation depends on more factors than just high sea surface temperatures, which are expected to increase with whatever global warming ends up happening. Wind shear (the change in wind speed or direction with height), in particular, needs to be weak for hurricane formation. For instance, with more frequent El Nino's in recent decades we've seen stronger wind shear, and thus fewer hurricanes. The frequency of formation of African easterly waves in the Sahel region south of the Sahara desert is also important, since most hurricanes form from these waves as they travel westward across the tropical Atlantic Ocean. Predicting how wind shear and African wave activity will change years in advance is a little like predicting economic activity years in advance...there are too many variables and uncertainties involved.

What we can be sure of is that there will continue to be some years with many hurricanes, and some with few hurricanes. And in certain years, there will be one state (sorry, Florida) that happens to be particularly unlucky. Some residents will leave the state, having had enough of the hassle and economic loss associated with these storms. I remember in 1980, as mega-hurricane Allen approached south Texas, my father called from there to tell me that privately owned lots on the coast had suddenly become dirt cheap (I was too stupid to buy one). Now, twenty-four years later, that coastline has been built up with hotels, shops, and restaurants. And it hasn't seen a storm like Allen in those twenty four years. Some day, it might well be south Texas' turn for a bit of bad luck.

When a rash of hurricanes occurs, or a gaggle of tornadoes, people like to search for reasons. It helps make being at the mercy of Mother Nature a little less scary. But we forget that unusual weather is, well, usual. I'm afraid science can't yet offer a much better explanation than that.


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