NASA scientists have developed a new climate model that indicates that the most violent severe storms and tornadoes may become more common as Earth's climate warms.  
 
...The study found that continents warm more than oceans and that the altitude at which lightning forms rises to a level where the storms are usually more vigorous.  
 
These effects combine to cause more of the continental storms that form in the warmer climate to resemble the strongest storms we currently experience.