Hurricane season is here again, and the good people at the National Hurricane Center are predicting a 70% chance of more activity than normal this year. I'm predicting a greater than 99.9% probability that this season's windbags will be conflated with global warming.
We can look forward to another year of numbing hurricane hype. Tropical cyclones (the generic for hurricanes, typhoons, willi-willies, etc…) are the sexiest weather beasts on TV, with seductive eyes surrounded by towering cumulonimbi. A category 3 (out of 5) storm within a week's distance from the East Coast commands 24/7 attention from The Weather Channel and at least 50% of CNN's time. Given that storms get this close (or closer) a couple of times every year, the coverage seems a bit out of proportion.
It's part of our culture. Hurricanes became media stars when Dan Rather, a cub reporter from Houston, convinced CBS headquarters in 1961 to add 15 minutes to the (then) 15 minutes of network news featuring — surprise — him, braving the Galveston Seawall while big, bad Hurricane Carla languorously eyed the Texas Coast. While there's still debate about whether Carla may have actually been more powerful than 2005's legendary Katrina, it is certainly true that she made Dan a rather big man.
So this year is supposed to be another big one. The planetary surface temperature is warmer than it was back in Carla's day. Aren't these two things related?
Hurricanes long since graduated from being singular weather events to becoming climatic signposts. After all, it seems pretty logical that they should be enhanced by global warming, as the thermal source that they convert to destructive kinetic energy is the heat of the ocean, which should go up with the surface temperature.
Tropical cyclones are a bit more complicated than "warmer ocean in, bigger hurricane out". For months on end, the vast majority of the earth's tropical oceans sport surface temperatures above 80°F, the threshold required for their formation. Given this massive amount of suitable ocean surface, why are there so few hurricanes? And why would warming of a degree or two really change this?
Under global warming, it turns out that the threshold temperature goes up too. A report published last November in Nature Geoscience found a rise of about 0.5 degrees in that temperature in recent decades paralleling the observed rise in tropical ocean surface temperatures. Everything else being equal (which never occurs), this would mean no increase in hurricane frequency and intensity.
For over a decade, federal climatologist Kevin Trenberth has claimed that global warming will increase the frequency and strength of El Niño, the large periodic warming of the tropical Pacific. One of the few sure things about hurricane climatology is that Los Niños destroy Atlantic storms as they unfavorably shift the winds aloft.
The global warming-hurricane war has been raging in the scientific literature for over a decade. One of the major battles is over the quality of historical data, and whether or not hurricane statistics are being inflated by nonclimatic forces.
A few years ago I began to notice that cloud blobs of decidedly unseductive proportions began to be named as tropical cyclones.
While I've published some papers in the scientific literature on hurricanes and climate change, I never figured how to test that surmise. To my surprise, two weeks ago, my hypothesis was tested in a paper in Journal of Geophysical Research, and it appears to be supportable. The paper shows that there has been no increase whatsoever in the number of Atlantic storms that last more than 48 hours. There has been a major increase in the number of short-lived storms; i.e. ones which the Hurricane Center wouldn't have named decades ago.
On reason is because we have learned that even relatively weak tropical storms can produce extreme floods. People began to pay attention to this in 1979, when tropical storm Claudette drowned Alvin, in southeast Texas, under 45 inches of rain. In 1994, weak tropical storm Alberto killed 33 in the southeast, largely a result of over two feet of rain. Tropical storm Allison, in 2001, dropped 40 inches, again in southeast Texas.
While slightly warmer oceans should slightly enhance rainfall from tropical cyclones, all the refereed research out there indicates that such an effect won't be detectable for decades, in part a result of the obviously great variability that exists in rainfall from these storms.
So we can go back and forth on whether or not hurricanes are getting worse because of global warming. But while we debate, nature adjudicates.
Ryan Maue at Florida State University has been tracking hurricane power over the years. That's the square of the maximum wind speed summed over the lifetime of each storm. His results tell you everything you need to know:
Maue's hurricane power index shows that current values are near the lowest ever measured, both in our hemisphere (black dots) and globally (blue dots), and exhibit no overall trend, effectively blowing any linkage between recent storms and global warming out of the water.
Both globally and in our hemisphere, total hurricane power is at or near the lowest it has ever been measured. So much for Hurricane hype.