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Tropical Cyclone Genesis
Nolan, D.S. and Rappin, E.D. 2008. Increased sensitivity of tropical cyclogenesis to wind shear in higher SST environments. Geophysical Research Letters 35: 10.1029/2008GL034147.

What was done
The authors extended the methodology of Nolan et al. (2007) to include a prescribed wind as a function of height that remains approximately constant during the genesis of tropical cyclones in environments of radiative-convective equilibrium that are partially defined by sea surface temperature (SST), which they then employed to explore what happens when SSTs rise.

What was learned
Nolan and Rappin report that "an unexpected result has been obtained, that increasing sea surface temperature does not allow TC genesis to overcome greater shear." In fact, they say that "the opposite trend is found," and that "the new and surprising result of this study is that the effect of shear in suppressing TC genesis actually increases as the SST of the radiative-convective equilibrium environment is increased."

What it means
This new model-based result is eerily analogous to the recent observation-based result of Vecchi and Knutson (2008), who found that as the SST of the main development region of North Atlantic TCs had increased over the past 125 years, certain aspects of climate changed in ways that may have made the North Atlantic, in their words, "more favorable to cyclogenesis, while at the same time making the overall environment less favorable to TC maintenance." Hence, it is doubly interesting that Nolan and Rappin conclude their paper with an intriguing question: "Do these results explain recent general circulation modeling studies predicting fewer tropical cyclones in a global warming world (e.g., Bengtsson et al. 2007)?" It is perhaps too early to say; but it is clearly time to note that even the climate modeling world is not behaving quite the way climate alarmists such as Al Gore and James Hansen would have us believe it is.

Bengtsson, L., Hodges, K.I., Esch, M., Keelyside, N., Kornbluehm, L., Luo, J.-J. and Yamagata, T. 2007. How may tropical cyclones change in a warmer climate? Tellus Series A 59: 531-561.

Nolan, D.S., Rappin, E.D. and Emanuel, K.A. 2007. Tropical cyclogenesis sensitivity to environmental parameters in radiative-convective equilibrium. Quarterly Journal of the Royal Meteorological Society 133: 2085-2107.

Vecchi, G.A. and Knutson, T.R. 2008. On estimates of historical North Atlantic tropical cyclone activity. Journal of Climate 21: 3580-3600.

Reviewed 29 October 2008