As I write this, Hurricane Wilma is setting the all-time record low in the Atlantic Basin for barometric pressure, besting 1988's Hurricane Gilbert. Wilma is also the 21st tropical cyclone this season, tying the 1933 record for number of storms. To climatologists, that 1933 record was like Babe Ruth's 714 home runs — something that would never be broken. But 2005 has come along, just as Hank Aaron did. Neither Aaron nor Ruth was juiced. But has the performance of 2005 hurricanes been enhanced by global warming?
Just a year ago, two of my scientific colleagues made headlines by running a computer model showing that, by 2080, hurricanes would increase in maximum wind speed by 6 percent and precipitation rate by 18 percent. In the model, 55 percent of the intensity variation of hurricanes was related to warming sea-surface temperatures.
Rather than use a computer model, I checked the actual relationship between sea temperatures and hurricane intensity in recent decades — a period of global warming. In reality (as opposed to the virtual reality of the computer), only 10 percent of storm-to-storm variation in intensity is related to sea surface temperatures. Ninety percent is due to other factors, such as El Niño, (a warm current of water). Some of these factors are actually less favorable to hurricanes in a warmer world.
Almost all severe hurricanes must experience water of 82 degrees sometime in their life cycle. Oddly enough, there is no relationship between more intense hurricanes and ocean surface temperature once this threshold is reached.
Georgia Tech's Peter Webster, using data back to 1970, released a paper arguing that hurricane severity has increased. Had he looked at reliable hurricane-hunter aircraft data over the Atlantic back to 1945, he would have discovered that the proportion of severe storms was exactly the same in the 1940s and 1950s as it is now.