Hurricane Irene (which seemed more like Tropical Storm Irene from Virginia Beach to New York City) has prompted the usual rhetoric from the usual suspects about global warming making these storms worse. Too bad there is no evidence for this whatsoever on a global scale.
Ryan Maue, at Florida State University, tracks global tropical cyclone energy back to 1970, which is the time at which adequate data on hurricane winds became available. His “Accumulated Cyclone Energy” (ACE) index peaked in the mid 1990’s and in recent years has been at or near the lowest point ever recorded. His most recent refereed paper, in press at Geophysical Research Letters, is called “Recent Historically Low Global Tropical Cyclone Activity.” Enough said?
However, there is an interesting trend in Atlantic hurricane activity. The Department of Commerce’s National Hurricane Center (NHC) is naming tropical storms that they clearly would have ignored in previous years. This year we have had ten (the latest is “Jose”, which currently looks weak in satellite imagery), and I doubt that seven of these would have made the grade years ago. In fact, I have written to NHC’s Chris Landsea (with whom I have authored refereed papers on hurricanes) about this, and he agrees that NHC is naming systems that they would have previously ignored or missed. Frankly, some of our recent “tropical storms” have pitiful presentations, looking more like small clusters of thunderstorms than the familiar pinwheels of nascent hurricanes. A recent paper in Journal of Geophysical Research, by Princeton’s Gabriele Villarini, noted the contamination of the Atlantic hurricane data by what he called “shorties.”
Why NHC is doing this, and why they kept Hurricane Irene’s “category” (one through five) high despite acknowledging that hurricane hunter aircraft were having trouble finding enough wind, has more to do with risk aversion than any putative conspiracy to toe the politically correct line on global warming. The result is that ships at sea are “warned” of brisk winds and high seas that might have previously surprised them, and that politicians and emergency management officials can justify massive evacuation orders. This used to be known as covering one’s posterior. Now NHC sometimes calls it “the course of least regret.”
It is also a dangerous practice. People who endure the endless torture of a hurricane evacuation from barrier islands like the North Carolina Outer Banks from storms that cause little damage may be reluctant to leave when the next – big and real – one shows up.