Not related to climate change but rather natural variability according to NOAA and other meterologists.
[url]http//www.physorg.com/news/2011-04-tornadoes-climate.html[/url]
"If you look at the past 60 years of data, the number of tornadoes is increasing significantly, but it's agreed upon by the tornado community that it's not a real increase," said Grady Dixon, assistant professor of meteorology and climatology at Mississippi State University.
"It's having to do with better (weather tracking) technology, more population, the fact that the population is better educated and more aware. So we're seeing them more often," Dixon said.
But he said it would be "a terrible mistake" to relate the up-tick to climate change.
However, the stronger-than-usual tornadoes affecting the southern states were actually predicted from examining the planet's climatological patterns, specifically those related to the La Nina phenomenon.
"We knew it was going to be a big tornado year," he said. But the key to that tip-off was unrelated to climate change: "It is related to the natural fluctuations of the planet."
http://www.foxnews.com/politics/2011/04/28/noaa-scientist-rejects-global-warming-link-tornadoes/Greg Carbin, the warning coordination meteorologist at NOAA’s Storm Prediction Center in Norman, Oklahoma, said warming trends do create more of the fuel that tornadoes require, such as moisture, but that they also deprive tornadoes of another essential ingredient: wind shear.
“We know we have a warming going on,” Carbin told Fox News in an interview Thursday, but added: “There really is no scientific consensus or connection [between global warming and tornadic activity]….Jumping from a large-scale event like global warming to relatively small-scale events like tornadoes is a huge leap across a variety of scales.”
and although the number of measured tornados of any size seems to be increasing (due to improved measuring techniques as noted above) the actual intensity of individual tornados is decreasing.
http://lwf.ncdc.noaa.gov/img/climate/research/tornado/tornadotrend.jpg