It is incredible to me that anyone could treat Senator Kerry seriously at this point, but a credulous media seems to be lapping up his accusations that recent tornadoes represent an increase in such storm activity caused by global warming.
I am way too tired of refuting this stuff over and over to repeat the whole post I put up a while ago about tornado frequency, but you can find it here. But here is the short answer for those to tired to click through: Apparent increases in tornado frequency are an artifact of improved technology that can detect more tornadoes. If one corrects for this by looking only at tornadoes of the larger sizes (3-5) that were consistently detectable with 1950's technology, there has actually been a small decreasing trend in tornado strikes in the US.
This is drop-dead obvious to anyone who knows anything about weather. However, since it keeps coming up, the NOAA has an explanation quite similar to mine plastered all over their site.
With increased national doppler radar coverage, increasing population,
and greater attention to tornado reporting, there has been an increase
in the number of tornado reports over the past several decades. This
can create a misleading appearance of an increasing trend in tornado
frequency. To better understand the true variability and trend in
tornado frequency in the US, the total number of strong to violent
tornadoes (F3 to F5 category on the Fujita scale) can be analyzed.
These are the tornadoes that would have likely been reported even
during the decades before Dopplar radar use became widespread and
practices resulted in increasing tornado reports. The bar chart below
indicates there has been little trend in the strongest tornadoes over
the past 55 years.
My daughter when she was 9 years old was able to more accurately portray this fact in a class project than did Mr. Kerry.