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Wasn’t it just a few short years ago, during the summer of 2005, that headlines were screaming “Hurricanes Growing Fiercer with Global Warming” and “Increase in Major Hurricanes Linked to Warmer Seas”? Now, this hurricane season starts off with “Global Hurricane Activity at Historical Record Lows.”
What gives? Where have all the hurricanes (Atlantic and Eastern Pacific) ‚willy‐willys (Australia), typhoons (Western Pacific), Big Winds (Philippines), blowhards (Michaels), or more generally, tropical cyclones, gone?
Gone to graveyards, every one?
More like they are just being subject to the waxing and waning of the natural forces which promote their development (and also to keep them in check).
The new paper that generated this summer’s “Historical Record Low” headlines was written by Dr. Ryan Maue from the Center for Ocean and Atmosphere Studies at Florida State University and has just been accepted for publication in Geophysical Research Letters.
Maue (rhymes with zowie) analyzed the location and intensity of every tropical cyclone (a warm‐cored low pressure system with sustained wind speed exceeding 39 mph) that has been observed during the period January 1970 through May 2011. For each storm, he calculates the Accumulated Cyclone Energy (or ACE) which is the square of the maximum observed wind speed (reported every six hours) summed over life time of the storm system. The ACE is a reasonable indicator of the cumulative strength of each storm system. The individual storm ACE values can be combined by basin, season, etc. to examine patterns and trends in tropical cyclone activity.
Figure 1 shows the annual ACE values for the Northern and Southern Hemispheres, as well as for the total globe, since 1970. Notice several things. There’s much more activity in the Northern Hemisphere, and there is also more variability here. You can inkle a positive trend in the global ACE in the beginning of Maue’s record from 1970 through the mid‐2000s (the “oughties”) — precisely when the headlines proclaimed that global warming was making hurricanes worse than ever. However, you can also see a declining trend from the early 1990s through the end of the record, and, perhaps, claim that global warming is reducing hurricane activity.
In either case, you’d probably largely be wrong — at least about causation.
Figure 1. The annual ACE index from the Southern Hemisphere (green), Northern Hemisphere (blue), and the entire globe (red), from 1970 through 2010 (from Maue, 2011).
Maue describes this situation in the abstract of his paper: