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Global Tropical Cyclone Activity
Reference
Maue, R.N. 2011. Recent historically low global tropical cyclone activity. Geophysical Research Letters 38: 10.1029/2011GL047711.

Background
Climate alarmists have long contended that tropical cyclone (TC) activity -- in terms of frequency, intensity and their interaction -- tends to rise with an increase in sea surface temperature. But is this claim correct?

What was done
In the latest study to broach this question, Maue (2011) obtained global TC life cycle data from the IBTrACS database of Knapp et al. (2010), which contains six-hourly best-track positions and intensity estimates for the period 1970-2010, from which he calculated the accumulated cyclone energy (ACE) metric (Bell et al., 2000), which is analogous to the power dissipation index (PDI) used by Emanuel (2005) in his attempt to convince the world of the truth of the climate-alarmist claim.

What was learned
The U.S. researcher from Florida State University reports that "in the pentad since 2006, Northern Hemisphere and global tropical cyclone ACE has decreased dramatically to the lowest levels since the late 1970s," and he also finds that "the global frequency of tropical cyclones has reached a historical low." Some details of note include the fact that "a total of 69 TCs were counted during calendar year 2010, the fewest observed in the past 40 years with reliable frequency data," as well as the fact that over that same four-decade period, "12-month running-sums of the number of global TCs of at least tropical storm force has averaged 87," while "the minimum number of 64 TCs was recently tallied through May 2011."

What it means
In view of the fact that "there is no significant linear trend in the frequency of global TCs," in agreement with the analysis of Wang et al. (2010), plus the fact that the earth is experiencing "this current period of record inactivity," as Maue describes the situation in the final six words of his paper, it would appear that the long-held climate-alarmist contention that global warming increases the frequency and intensity of tropical storms is simply not true.

References
Bell, G.D., Halpert, M.S., Schnell, R.C., Higgins, R.W., Lawrimore, J., Kousky, V.E., Tinker, R., Thiaw, W., Chelliah, M. and Artusa, A. 2000. Climate assessment for 1999. Bulletin of the American Meteorology Society 81: S1-S50.

Emanuel, K. 2005. Increasing destructiveness of tropical cyclones over the past 30 years. Nature 436: 686-688.

Knapp, K.R., Kruk, M.C., Levinson, D.H., Diamond, H.J. and Neumann, C.J. 2010. The International Best Track Archive for Climate Stewardship (IBTrACS): Unifying tropical cyclone best track data. Bulletin of the American Meteorological Society 91: 363-376.

Wang, B., Yang, Y., Ding, Q.-H., Murakami, H. and Huang, F. 2010. Climate control of the global tropical storm days (1965-2008). Geophysical Research Letters 37: 10.1029/2010GL042487.

Reviewed 14 September 2011