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

Vecchi and Knutson introduce their study by stating that "there is currently disagreement within the hurricane/climate community on whether anthropogenic forcing (greenhouse gases, aerosols, ozone depletion, etc.) has caused an increase in Atlantic tropical storm or hurricane frequency," as well, we might add, as storm duration and intensity.

What was done
The authors first derived an estimate of the expected number of North Atlantic tropical cyclones (TCs) that were missed by the observing system in the pre-satellite era (1878-1965), after which they analyzed trends of both reconstructed TC numbers and duration over various time periods and looked at how they may or may not have been related to trends in sea surface temperature (SST) over the main development region (MDR) of North Atlantic TCs.

What was learned
Vecchi and Knutson report that "the estimated trend for 1900-2006 is highly significant (+~4.2 storms century-1)," but they say that this trend "is strongly influenced by a minimum in 1910-30, perhaps artificially enhancing significance," whereas using their base case adjustment for missed TCs leads to an 1878-2006 trend in the number of TCs that is only "weakly positive" and "not statistically significant." In addition, they say that "the trend in average TC duration (1878-2006) is negative and highly significant."

What it means
In the words of the two researchers, "the evidence for a significant increase in Atlantic storm activity over the most recent 125 years is mixed," even though they note that the SST of the MDR "has warmed significantly." What they are left with, then, is the suggestion that "aspects of climate have changed" in such as way as "to make the North Atlantic more favorable to cyclogenesis, while at the same time making the overall environment less favorable to TC maintenance." Consequently, as Vecchi and Knutson see it, "the crucial issue of the response of Atlantic TC behavior to increasing greenhouse gases remains unsettled."

Reviewed 22 October 2008