Jul 012010

Philip Klotzbach and William Gray, of Colorado State University, have analyzed the atmospheric and oceanic conditions in the Atlantic immediately prior to the 2010 hurricane season. They conclude that this season’s hurricane activity in the Atlantic is likely to be stronger than has been the norm during the past 50 years. They predict that the Atlantic season will see 18 named storms, of which 8 will be classed as tropical storms, 5 as moderate hurricanes (1 or 2 on the Saffir-Simpson scale), and 5 as severe hurricanes (3, 4 or 5 on the Saffir-Simpson scale).

The popular press regularly warns us that on-going global warming will increase the frequency of hurricanes, and their intensity, allegedly due to warmer sea-surface temperatures in the mid-ocean hurricane-spawning areas. Klotzbach and Gray do not believe this. They studied the paths of all severe hurricanes (category 3, 4 or 5) for the fifty years from 1945-1994, dividing this time frame into two 25-year periods (see image).

Tracks of severe Atlantic hurricanes, 1945-1994

Tracks of severe Atlantic hurricanes, 1945-1994. Source: Klotzbach and Gray, 2010. Link to original article at end of this post. Click image to enlarge.

From 1945-1969 was a period of weak global cooling. There were 80 severe hurricanes in this period, some of them taking very erratic paths, with correspondingly dramatic impacts when they struck areas wholly unprepared.

Between 1970 and 1994, the Earth’s temperatures underwent a modest rise (global warming). However, in stark contrast to popular belief, far fewer severe hurricanes occurred during this period (38 in total), and they tended to follow entirely predictable paths.

Clearly the science behind hurricane formation is more complicated than some journalists would have us believe!

Klotzbach and Gray demonstrate the importance of the Thermohaline Circulation (THC) in the Atlantic. The THC is a large-scale circulation in the Atlantic Ocean that is driven by fluctuations in salinity and temperature. The 1945-1969 period coincided with a strong THC, whereas the 1970-1994 period was a time when the THC was weak.

What has happened since 1994? In the fifteen years from 1995-2009 inclusive, the THC was strong, and there were 56 severe Atlantic hurricanes. By comparison, in the preceding fifteen years from 1980-1994, when the THC was weak, only 22 severe hurricanes formed. So it appears that hurricane frequency is not linked to global warming or carbon dioxide (CO2) levels in the atmosphere, but to cyclical changes in the THC.

How accurate are the predictions for the 2010 hurricane season? Only time will tell…

Click here for Klotzbach and Gray’s original article (pdf).

Hurricane warnings in Mexico are the responsibility of the National Meteorological Service (NMS). The NMS also provides an archive of information about past hurricanes.

Hurricanes and other climatological phenomena are analyzed in chapters 4 and 7 of Geo-Mexico: the geography and dynamics of modern Mexico. Buy your copy today, so you have a handy reference guide available whenever you need it.


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