Background
General circulation models of the atmosphere suggest, in the words of the authors, that "an increase in greenhouse gas concentration could significantly warm the planet and create an environment more favorable for severe storms over mid-latitude continental areas."  Hence, many empiricists, as the authors call them, have devoted themselves to looking for evidence of this phenomenon in weather records of the past century or so.

What was done
Balling and Cerveny review the scientific literature to determine what has been learned from United States weather records about severe storms during the modern era of greenhouse gas buildup in the atmosphere, paying particular attention to thunderstorms, hail events, intense precipitation, tornadoes, hurricanes and winter storm activity.

What was learned
The authors report that several scientists have identified an increase in heavy precipitation, but that "in other severe storm categories, the trends are downward."

What it means
The climate models appear to have been correct in one out of the six severe storm categories investigated; but, of course, that means they were wrong in five of the six categories.  Moreover, not only were they wrong in the sense that there were no increases in these phenomena, they were wrong in the sense that there were actually decreases in them.  Consequently, climate model suggestions of increasing storminess in response to global warming appear to be largely 180 degrees out of phase with reality, at least within the confines of the United States and in response to the global warming that helped the planet recover from the global chill of the Little Ice Age.

But wait!  We may have spoken too soon.  In reviewing the paper of Kunkel (2003), we find that although there was a sizable increase in the frequency of extreme precipitation events in the United States since the 1920s and 1930s, the frequencies of the late 1800s and early 1900s were about as high as those of the 1980s and 1990s.  Hence, there has actually been no century-long increase in this extreme type of weather either, leaving the climate models with not a single extreme weather phenomenon that has increased as predicted in frequency or intensity over a period of what is typically described by climate alarmists as "unprecedented" CO2-induced global warming.

Reference
Kunkel, K.E.  2003.  North American trends in extreme precipitation.  Natural Hazards 29: 291-305.
Reviewed 25 June 2003