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Global Warming and Vertical Wind Shear: Effects on Hurricane Intensity
Vecchi, G.A. and Soden, B.J. 2007. Increased tropical Atlantic wind shear in model projections of global warming. Geophysical Research Letters 34: 10.1029/2006GL028905.

What was done
Noting the existence of the "intense scientific debate" that is currently raging over the impact of global warming on hurricane intensity, as well as the need to resolve this important issue, the authors "explore 21st Century projected changes in VS [vertical wind shear] over the tropical Atlantic and its ties to the Pacific Walker circulation, using a suite of coupled ocean-atmosphere models forced by emissions Scenario A1B (atmospheric CO2 stabilization at 720 ppm by year 2100) for the Intergovernmental Panel on Climate Change 4th Assessment Report (IPCC-AR4)," where VS is defined as "the magnitude of the vector difference between monthly-mean winds at 850 hPa and 200 hPa," and where "changes are computed between two 20-year periods: 2001-2020 and 2081-2100."

What was learned
Vecchi and Soden report that the 18-model ensemble-mean projected change in VS over the 21st Century is "a prominent increase in VS over the topical Atlantic and East Pacific (10°N-25°N)." Noting that "the relative amplitude of the shear increase in these models is comparable to or larger than model-projected changes in other large-scale parameters related to tropical cyclone activity," they state that the projected changes "would not [our italics] suggest a strong anthropogenic increase in tropical Atlantic or Pacific hurricane activity during the 21st Century," and that "in addition to impacting cyclogenesis, the increase in SER [shear enhancement region] shear could act to inhibit the intensification of tropical cyclones as they traverse from the MDR [main development region] to the Caribbean and North America."

What it means
In addition to the growing body of empirical evidence that indicates global warming has little to no impact on the intensity of hurricanes (Donnelly and Woodruff, 2007; Nyberg et al., 2007), there is now considerable up-to-date model-based evidence for the same conclusion; yet climate alarmists such as Al Gore continue to proclaim just the opposite. Why they are doing so would thus appear to be the next major question that needs answering.

Donnelly, J.P. and Woodruff, J.D. 2007. Intense hurricane activity over the past 5,000 years controlled by El Niņo and the West African Monsoon. Nature 447: 465-468.

Nyberg, J., Malmgren, B.A., Winter, A., Jury, M.R., Kilbourne, K.H. and Quinn, T.M. 2007. Low Atlantic hurricane activity in the 1970s and 1980s compared to the past 270 years. Nature 447: 698-701.

Reviewed 11 July 2007