There have been increasing numbers of measured tornadoes in the past 60 years, and may be even more in the future. Meteorologists chalk this up to better detection. But climatologists believe that we’re going to see more and worse severe storms and tornadoes in the U.S. in coming years thanks to climate change.
Two studies from 2007 point to a warmer future that could "bring the USA a dramatic increase in the frequency of weather conditions that feed severe thunderstorms and tornadoes by the end of the 21st century." The first, a study published in the Proceedings of the National Academy of Sciences, says that the some locations will see twice as many days per year that favor severe thunderstorms.
"The densely populated regions of the South and East, including New York City and Atlanta, could be especially hard-hit," reports study lead author Jeff Trapp of Purdue University.
A second study from the Goddard Institute for Space Studies in New York says that "the strongest severe storms and tornadoes are likely to happen more often and be stronger."
However, there are other forces at work, such as reduced wind shear (or side to side movement of air) in a warmer climate, that could have the opposite effect on tornado frequency. So basically, climate change could lead to more tornadoes, or possibly to fewer tornadoes.
The problem, it seems, is that climate models simply aren't detailed enough to model features as small as tornadoes. Only in the past two years have global climate models attained a high enough resolution to simulate hurricanes, which are much larger.