The 2005 Hurricane season was the most active and destructive in recorded history. The devastation from hurricanes like Katrina, Rita, and Wilma was powerful evidence that man-made global warming had triggered an onslaught of unforeseen consequences — at least, that was the way the media tended to portray it. Maybe I am wrong, but I think the current focus on global warming in this country would be much weaker had those hurricanes not hit landfall, or had they hit Mexico instead of the U.S.
The scientific community, however, never argued a strong link between global warming and hurricanes. At the Sixth International Workshop on Tropical Cyclones held by the World Meteorological Organization in November of 2006, the participants came to the following conclusions:
Consensus statements by the workshop participants
1. Though there is evidence both for and against the existence of a detectable anthropogenic signal in the tropical cyclone climate record to date, no firm conclusion can be made on this point.
2. No individual tropical cyclone can be directly attributed to climate change.
3. The recent increase in societal impact from tropical cyclones has been largely caused by rising concentrations of population and infrastructure in coastal regions.
4. Tropical cyclone wind-speed monitoring has changed dramatically over the last few decades leading to difficulties in determining accurate trends.
5. There is an observed multi-decadal variability of tropical cyclones in some regions whose causes, whether natural, anthropogenic or a combination, are currently being debated. This variability makes detecting any long-term trends in tropical cyclone activity difficult.
6. It is likely that some increase in tropical cyclone peak wind-speed and rainfall will occur if the climate continues to warm. Model studies and theory project a 3-5% increase in wind-speed per degree Celsius increase of tropical sea surface temperatures.
7. There is an inconsistency between the small changes in wind-speed projected by theory and modeling versus large changes reported by some observational studies.
8. Although recent climate model simulations project a decrease or no change in global tropical cyclone numbers in a warmer climate there is low confidence in this projection. In addition, it is unknown how tropical cyclone tracks or areas of impact will change in the future.
9. Large regional variations exist in methods used to monitor tropical cyclones. Also, most regions have no measurements by instrumented aircraft. These significant limitations will continue to make detection of trends difficult.
10. If the projected rise in sea level due to global warming occurs, then the vulnerability to tropical cyclone storm surge flooding would increase.
In general, I am not a fan of science by consensus. It is interesting, however, that you can get a bunch of scientists to basically agree that they don’t even know whether global warming will cause hurricanes to increase or decrease. The conclusion is especially surprising because no one ever wants to look like they don’t know the answers, and because scientists who work on hurricanes have strong incentives to convince everyone else of the important of their research. This statement clearly avoids that latter temptation.
Recently, a new study was released that flies in the face of the scientific consensus. Researchers Greg Holland and Peter Webster make the claim that global warming has nearly doubled the number of hurricanes over the last century. Reading between the lines of the various media reports on this study, I don’t think Holland and Webster have convinced many climatologists; in the four or five articles I read, there wasn’t a single endorsement from another scientist. One researcher actually came out and called it “sloppy science” in this Miami Herald report.
Also, could the timing of the article’s release be any worse? Two months into what was supposed to be a very active season, with 7-10 hurricanes predicted, so far not a single hurricane has appeared. By this time in 2005, there had already been three hurricanes. The biggest losers in all of this are the reporters — just think how much fun they could have had with this study had a hurricane been about to make landfall on the U.S. coastline.