For some reason some members of the scientific community are pushing hard through the media to allege a direct connection between the Florida hurricanes of 2004 and human-caused climate change, so we’re going to revisit the topic (yet) again. Examples include here and here and here and here and here). This organized effort seems quite odd to me for two reasons:

1) There is a strong scientific consensus that if greenhouse gas emissions have an effect on hurricanes, these effects will be quite small as compared to the observed variability in hurricane frequencies and intensities. (See the primer below.)

2) There is overwhelming evidence that the most significant factor in trends in and projections of the damages associated with hurricane impacts is societal vulnerability to those impacts. (See this post and this post.)

One obvious reason for a group of scientists to invoke via the media a connection between this year’s storms and climate change is part of a strategy of political advocacy in support of greenhouse gas reductions. If the issue was simply scientific, then I’d assume that the scientists would just battle their differences out on the pages of peer-reviewed journals, far from the public eye. But the great irony here is that those who invoke the modulation of future hurricanes as a justification for changes to energy policies to mitigate climate change are their own worst political enemy. Not only do they provide a great opening for criticism of their reasoning and science, they are advocating a policy that simply won’t be effective. There are much, much better ways to deal with the threat of hurricanes than with energy policies. There are also much, much better ways to justify climate mitigation policies than with hurricanes.

Last week my colleague and occasional collaborator Chris Landsea, one of the world’s foremost experts on hurricanes, put together the following short primer on hurricanes and climate change, and I’ve shared it here with his permission:

Hurricanes and Global Warming
Chris Landsea (chris.landsea@noaa.gov)
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There are no known scientific studies that show a conclusive physical link between global warming and observed hurricane frequency and intensity. Whatever suggested changes in hurricane activity that might result from global warming in the future are quite small in comparison to the large natural variability of hurricanes, typhoons and tropical cyclones. For example, the latest GFDL global warming study suggested about a 5% increase in the winds of hurricanes 80 years in the future. This contrasts with the more than doubling that occur now in numbers of major hurricanes between active and quiet decades in the Atlantic basin.

If global warming is influencing hurricane activity, then we should be seeing a global change in the number and strength of these storms. Yet there is no evidence of a global increase in the strength and frequency of hurricanes, typhoons, and tropical cyclones over the past several years.

Beginning in 1995, there has been an increase in the frequency and intensity of hurricanes in the Atlantic basin. However, this increase is very likely a manifestation of a natural multi-decadal cycle of Atlantic hurricane activity that has been occurring likely for the last few hundred years. For example, relatively few Atlantic major hurricanes were observed in the 70s, 80s and early 90s, but there was considerable activity during the 40s, 50s and early 60s. Also, the period from 1944 to 1950 was particularly infamous for Florida – with 11 hurricanes hitting the state during those years.

Total U.S. direct damages from Atlantic hurricanes this year will be on the order of $30 billion, making it about equal to the most damaging year on record – 1992 with the landfall of Hurricane Andrew. However, such increased destruction from hurricanes is to be expected because of the massive development and population increases along the U.S. coastline and in countries throughout the Caribbean and Central America. There is no need to invoke global warming to understand both the 10 years of active hurricane seasons and the destruction that occurred both in Florida and in Haiti this season. The former is due to natural cycles driven by the Atlantic Ocean and the latter is due to societal changes, not due to global warming.