[Illustrations, footnotes and references available in PDF version]
We have visited this topic repeatedly over the past five years (e.g., here and here), and here we go again given the latest news. Every self-respecting presentation about global warming includes a claim that hurricanes are becoming more intense, and if you don’t believe it, you will be treated to images of the Katrina disaster as the final proof. Gore’s film clearly makes the case that burning fossil fuel equals higher levels of atmospheric carbon dioxide concentration which equals higher atmospheric and oceanic temperatures. He claims in the film and during every stop on his global circuit that the warmer sea surface in the tropics clearly means more intense hurricanes and BANG … the Katrina horrors are unveiled. It seems to work every time, and despite a lot of research that suggests the relationship is not so clear, people have bought the intense hurricane pillar of the global warming scare. If you suggest that there is some debate on the subject, you will undoubtedly be told that the climate deniers are few in number, well financed from industry, and discredited by scientists the world over.
Many would argue that Nature is the leading scientific journal in the world, and over the years, Nature has been an ally of the global warming crusade. A recent article in Nature begins with the sentence “The response of tropical cyclone activity to global warming is widely debated.” That sentence alone hints that the article may be somewhat atypical of Nature, since actual acknowledgement of the “d” word is greatly frowned upon by the crusaders. The second sentence states “It is often assumed that warmer sea surface temperatures provide a more favourable environment for the development and intensification of tropical cyclones, but cyclone genesis and intensity are also affected by the vertical thermodynamic properties of the atmosphere.” Once again, we get the hint that this presumed link between warmer oceans and more intense hurricanes may be more complicated than we’ve (or, rather, you’ve) been led to believe by the likes of Gore. We have been telling you this has been the case for several years.
The authors of the latest piece are Gabriel Vecchi and Brian Soden of the NOAA’s Geophysical Fluid Dynamics Laboratory in New Jersey and the University of Miami, and the work was funded by both NOAA and NASA (no evidence of industry funding whatsoever). Basically, they note that higher sea surface temperatures (SSTs) in the vicinity of a hurricane could, in fact, increase the potential intensity (or, PI, how strong a storm could get if everything fell perfectly into place) of the storm. They state “With all other factors being equal, a local warming of SST would act to destabilize the overlying atmosphere and increase PI. However, remote SST changes can also influence PI through their influence on upper atmospheric temperatures. In the tropical free troposphere, where the Coriolis force is weak, temperature gradients are small and, on timescales longer than a few months, upper tropospheric temperature anomalies are determined by changes in the tropical-mean SST. Thus, local PI in the tropics is influenced by both local and remote SST changes.” Basically, local SST warming can destabilize the atmosphere and increase the intensity of the hurricanes, but widespread SST warming alters the temperature structure of the higher levels of the atmosphere, which in turn cancel or even reverse the potential intensity of the events.
To say the least, including the effect of more distant SSTs really changes the outcome. Vecchi and Soden used three different, but highly correlated SST datasets and calculated the potential intensity of tropical storms for the North Indian Ocean, the western tropical Pacific Ocean, and the tropical Atlantic Ocean (see figure below). In their own words, they note “All three SST data sets indicate substantial warming in the three regions over the twentieth century. In the Atlantic sector, SSTs have been at unprecedented levels since the late 1990s, yet the tropical Atlantic PI is at near-average levels for that period, and had its highest levels during the middle of the twentieth century.
The only long-term increase in PI has been in the Indian Ocean, and recent Pacific PI has been lower than the long-term mean (the decrease arising abruptly in the 1970s).” Furthermore, they state “The combined influence of local and remote SST changes on PI can be seen clearly in the Atlantic basin. Atlantic PI began to decrease in the mid-1950s, even though local SST was not changing substantially (PI decreases by 0.6–0.7 °C from the 1950s to the 1980s, while local SST decreases by only 0.1–0.2 °C). This reduction in PI was not dominated by a local SST decrease, but by the rapid warming elsewhere in the tropics (much of it in the Indian Ocean).”
OK, so there hasn’t been any great increase in potential intensity of tropical cyclones over the long run, despite what the global warming advocates would lead you to believe. Well, you could suggest that like everything else, the disaster will reveal itself a decade or so from now. Unfortunately for such optimists (or are they pessimists?), Vecchi and Soden calculated PI for the next 150 years, and as seen below, SSTs are expected to rise, but in the North Indian Ocean and the tropical Atlantic Ocean, there should be no rise whatsoever in potential intensity of hurricanes.
Let’s all wait and see if the global warming crowd (or the media) embraces these results – of course they won’t and of course they will continue to scream that hurricanes are becoming more intense and will become even more intense in the decades to come. The results published in Nature by Vecchi and Soden will be nothing more than inconvenient trash to be swept under the rug of truth!
Vecchi, G.A. and B.J. Soden. 2007. Effect of remote sea surface temperature change on tropical cyclone potential intensity. Nature, 450, 1066-1071.
Source: World Climate Report