In a recent story on global warming, ABC claimed that tornado frequency this year is running nearly twice that of last year and that this can be linked to global warming. (HT Maggies Farm) Now, I would have tended to argue that year-over-year variations are probably not related to multi-decadal climate trends, but if ABC wants to so argue, I will go with it.
The only problem is that the first five months of 2008 have been the coolest since 1993 and has run well below the average temperature for the period from 1978-1990. This while 2007 was one of the warmer Jan-May periods in recent memory. In fact, average US temperatures were about a degree Celsius cooler in 2008 than in 2007:
UAH MSU temperature for USA (average anomaly)
Jan-May 2007: .668 C
Jan-Apr 2008: -.228 C
Difference: .896 C
So, if one wants to posit that tornado variation in 2008 is a result of a long-term climate trend rather than natural variability, then one must assume that global cooling causes tornadoes to increase, and that in fact global warming would benefit mankind by decreasing tornado frequency.
The whole history of the global warming causes tornadoes claim is one of grossly bad science, most famously including Al Gore’s claim in that movie of his. I debunked that claim here, demonstrating that the increase in measured tornadoes is a function solely of better measurement, not more tornadoes, something the NOAA has been careful to state as well.