AMS Dispatch: Numbers Game

[Tracks of the record 28 named storms of the 2005 Atlantic hurricane season.]

Something of a subtle shift may be happening in the ongoing hurricane-global warming debate. This was very much on display yesterday in San Antonio during a panel that featured Greg Holland, director of the Mesoscale and Microscale Meteorology Division of the National Center for Atmospheric Research, and Chris Landsea, science and operations officer for the National Hurricane Center.

A year ago, this debate--spurred by two papers in Nature (PDF) and Science (PDF)--centrally focused on the question of whether hurricanes had intensified globally. Holland, a longtime hurricane specialist, was a co-author on the Science paper, which said that the number and proportion of Category 4 and 5 storms had increased up dramatically over the past several decades, but did not strongly attribute this trend to global warming (although it was hard to miss that implication).

More recently, though, Holland and his co-author Peter Webster of Georgia Tech have gone further and, in a new paper (PDF), asserted that in the Atlantic, an increase in tropical cyclone numbers over the past 100 years is indeed being caused by global warming's heating of the tropical ocean. As the paper puts it: "It is concluded that the overall trend in SSTs and tropical cyclone and hurricane numbers is substantially influenced by greenhouse warming." The paper further argues that although the proportion of major to minor hurricanes has not changed in the Atlantic, there are more of the strongest storms just because there are more storms in total.

With this new focus on storm numbers in the Atlantic, though, we are quickly drawn into yet another confusing and at times even disorienting data dispute. Holland spent most of his talk yesterday defending the data he was using to show that Atlantic storm numbers had indeed shot upward in response to a warming of the ocean basin. The trend, Holland argued, is "robust to all known potential problems with the data base"--which in this case is the so-called HURDAT database maintained by the National Hurricane Center. But Landsea contested that, arguing that weak storms, storms forming far out at sea and never striking land, and short-lived storms were probably not detected as well in earlier periods, without the use of satellites in particular. He drew a big laugh when he showed a slide depicting a group of cavemen--with his own face superimposed atop one of their shoulders--to emphasize just how primitive previous means of detecting storms had been.

"I'm the caveman that put that database together," said Landsea.

What's happening here is that the hurricane-global warming debate, which has been raging for some time now, is forcing scientists to slice and dice the data in new ways--to pick it up, spin it around, and look at it from a variety of angles; to take it, shake it, try to figure out what it's really saying. It can be confusing and even frustrating at times for non-scientists, who just want to know what's going on out there, to watch this process occur. But remember: Each year will bring more storms in the Atlantic, which means better, uncontested data (because no one thinks we miss any storms these days). This, combined with the considerable scientific energy now being brought to bear on studying the old data, means these kinks will eventually be worked out.

In the mean time, we can start protecting and readying ourselves--and there's no such thing as over-preparing. It really depends on whether or not there is a prolongation of El Nino conditions, but at least according to the early forecasts, it's going to be a busy year out there in the Atlantic in 2007....