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Global Warming and Tropical Cyclones
Reference
Vecchi, G.A. and Soden, B.J. 2007. Effect of remote sea surface temperature change on tropical cyclone potential intensity. Nature 450: 1066-1070.

Background
In the words of the authors, "it is often assumed that warmer sea surface temperatures provide a more favorable environment for the development and intensification of tropical cyclones." However, they note that "cyclone genesis and intensity are also affected by the vertical thermodynamic properties of the atmosphere," and this fact complicates the matter to the extent that, as they describe it, "the response of tropical cyclone activity to global warming is widely debated."

What was done
In attempt to discern the ultimate consequence of these two aspects of the issue, Vecchi and Soden used both climate models and observational reconstructions "to explore the relationship between changes in sea surface temperature and tropical cyclone 'potential intensity' -- a measure that provides an upper bound on cyclone intensity and can also reflect the likelihood of cyclone development."

What was learned
The two U.S. researchers find, as they describe it, that "changes in local sea surface temperature are inadequate for characterizing even the sign [our italics] of changes in potential intensity." Instead, they report that "long-term changes in potential intensity are closely related to the regional structure of warming," such that "regions that warm more than the tropical average are characterized by increased potential intensity, and vice versa." Using this relationship to reconstruct changes in potential intensity over the 20th century based on observational reconstructions of sea surface temperature, they further find that "even though tropical Atlantic sea surface temperatures are currently at a historical high, Atlantic potential intensity probably peaked in the 1930s and 1950s," noting that "recent values are near the historical average."

What it means
The ultimate conclusion of the two scientists is that the response of tropical cyclone activity to natural climate variations "may be larger than the response to the more uniform patterns of greenhouse-gas-induced warming," which further suggests, in our estimation, that climate-alarmist attempts to blame any recent imagined increases -- or any near-future real increases -- in either cyclone numbers or intensities on CO2-induced global warming would be wholly unjustified, based on our present state of knowledge.

Reviewed 13 February 2008