Climate change is the buzz these days, and extreme weather events often get called into service as supposed examples of global warming (or, in the case of cold snaps, reasons to doubt the whole climate-change narrative). Hurricanes are no exception: Katrina's devastating impact in 2005 and the heavy 2008 storm season have both been cited as proof of global warming's existence — or at least as a good reason to worry.
Weather and climate scientists don't back that story up, though. The evidence of global warming is quite strong, and widely accepted (NASA tracks global temperature data). But tropical storm activity doesn't show any upward trend as global temperatures have risen, and hot years don't show any statistical connection to heavy hurricane years either.
2008, for example, happened to be a busy year for hurricanes in the Atlantic Basin, and 8 storms made landfall in the U.S. But that's just the Atlantic. Worldwide, says hurricane expert Jeff Masters on his Weather Underground blog, last year was nothing to write home about. If last year is any indication, global warming appears to mean nothing in terms of global hurricanes.
The Atlantic Basin, however, where storms like 1992's Hurricane Andrew and 2008's Hurricane Ike come from, has its own recognized long-term cycle: two or three decades of heavy activity, followed by 20 or 30 years of slower activity. At the present time, the Atlantic is entering one of its hurricane upswings, the experts say — so global warming or no global warming, we're going to see a lot of hurricanes in the first part of this century, and a lot of hurricane landfalls.
The 2008 Atlantic hurricane season was a big one, Masters notes. And the current trend, probably unrelated to global warming, is for the Atlantic hurricane season to start earlier and last longer. That means coastal builders and remodelers in the United States can't ignore hurricanes — we have to adapt.
Colorado State University forecasters Philip Klotzbach and William Gray release a prediction each winter of the coming year's hurricane activity in the Atlantic Basin. Their 2009 forecast, released in December, calls for an above-average season with 14 named storms and 7 hurricanes. Klotzbach and Gray also include a discussion of the alleged global-warming/hurricane link, noting: "The Atlantic has seen a very large increase in major hurricanes during the 14-year period of 1995-2008 (average 3.9 per year) in comparison to the prior 25-year period of 1970-1994 (average 1.5 per year). This large increase in Atlantic major hurricanes is primarily a result of the multi-decadal increase in the Atlantic Ocean thermohaline circulation (THC) that is not directly related to global sea surface temperatures or CO2 increases."
This map, from Klotsbach and Gray's 2009 hurricane forecast, illustrates that the frequency of severe Atlantic hurricanes has not corresponded to global warming. Major Atlantic hurricane activity was significantly less frequent during the more recent period despite warmer temperatures.
Klotzbach and Gray point out that heavy hurricane years, like the record-setting year 2005, occurred with some regularity in the past, when the planet was cooler: "...six previous seasons had more hurricane days than the 2005 season. These years were 1878, 1893, 1926, 1933, 1950 and 1995. Also, five prior seasons (1893, 1926, 1950, 1961 and 2004) had more major hurricane days. Although the 2005 hurricane season was certainly one of the most active on record, it was not as much of an outlier as many have indicated."
Klotzbach and Gray do expect 10 or 20 years of increased hurricane activity, however. And if global warming is not causing hurricanes, it has been at least theoretically linked to other risk factors — including rising sea levels and an increase in heavy rainstorms and flooding. So any way you look at it, bad weather is something coastal contractors will have to expect in the future — and prepare for now.