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Hurricane Intensity vs. Temperature
Free, M., Bister, M. and Emanuel, K.  2004.  Potential intensity of tropical cyclones: Comparison of results from radiosonde and reanalysis data.  Journal of Climate 17: 1722-1727.

Free et al. note that "increases in hurricane intensity are expected to result from increases in sea surface temperature and decreases in tropopause-level temperature accompanying greenhouse warming (Emanuel, 1987; Henderson-Sellers et al., 1998; Knutson et al., 1998)," but that "because the predicted increase in intensity for doubled CO2 is only 5%-20%, changes over the past 50 years would likely be less than 2% -- too small to be detected easily."  In addition, they say that "studies of observed frequencies and maximum intensities of tropical cyclones show no consistent upward trend (Landsea et al., 1996; Henderson-Sellers et al., 1998; Solow and Moore, 2002)."  In point of fact, many of the studies of the subject that we have reviewed and archived under the general heading of Hurricanes in our Subject Index have actually found hurricane frequencies and intensities to decline as temperatures rise.

What was done
In an application of the old saw that "if at first you don't succeed, try, try again," Free et al. do just that, looking, however, not for increases in actual hurricane intensity, but for increases in potential hurricane intensity, because, as they put it, "changes in potential intensity (PI) can be estimated from thermodynamic principles as shown in Emanuel (1986, 1995) given a record of SSTs [sea surface temperatures] and profiles of atmospheric temperature and humidity."  This they thus do, using radiosonde and SST data from 14 island radiosonde stations in the tropical Atlantic and Pacific Oceans, after which they compare their results with those of Bister and Emanuel (2002) at grid points near the selected stations.

What was learned
In the words of the authors, "our results show no significant trend in potential intensity from 1980 to 1995 and no consistent trend from 1975 to 1995."  What is more, they report that between 1975 and 1980, "while SSTs rose, PI decreased, illustrating the hazards of predicting changes in hurricane intensity from projected SST changes alone."

What it means
Making any prediction is hazardous, especially with respect to climate and its effects on extreme weather phenomena; and as Free et al. have demonstrated once again, the case for increasing hurricane intensities in a warming world is not only not to be found in actual hurricane intensity data, it is not to be found in potential intensity data either.  It would thus appear that the only places where this scenario has found a home are the vivid imaginations of the world's climate alarmists and Hollywood movie producers.

Bister, M. and Emanuel, K.  2002.  Low frequency variability of tropical cyclone potential intensity. 1. Interannual to interdecadal variability.  Journal of Geophysical Research 107: 10.1029/2001JD000776.

Emanuel, K.A.  1986.  An air-sea interaction theory for tropical cyclones. Part I: Steady-state maintenance.  Journal of the Atmospheric Sciences 43: 585-604.

Emanuel, K.A.  1987.  The dependence of hurricane intensity on climate.  Nature 326: 483-485.

Emanuel, K.A.  1995.  Sensitivity of tropical cyclones to surface exchange coefficients and a revised steady-state model incorporating eye dynamics.  Journal of the Atmospheric Sciences 52: 3969-3976.

Henderson-Sellers, A. et al.  1998.  Tropical cyclones and global climate change: A post-IPCC assessment.  Bulletin of the American Meteorological Society 79: 19-38.

Knutson, T., Tuleya, R. and Kurihara, Y.  1998.  Simulated increase of hurricane intensities in a CO2-warmed climate.  Science 279: 1018-1020.

Landsea, C., Nicholls, N., Gray, W. and Avila, L.  1996.  Downward trends in the frequency of intense Atlantic hurricanes during the past five decades.  Geophysical Research Letters 23: 1697-1700.

Solow, A.R. and Moore, L.J.  2002.  Testing for trend in North Atlantic hurricane activity, 1900-98.  Journal of Climate 15: 3111-3114.

Reviewed 4 August 2004