Every time the weather gets nasty these days, the question of whether global warming is to blame pops up.

It's inevitable. People wonder, politicians bring it up, and scientists have something to say.

But the bottom line is no single storm can be tied to global warming. So while one of the predictions of climate change (based on computer models with assumptions of certain degrees of warming) is that weather will become more severe, only in the future when studies can look back at years worth of data will we all this be proved out, or not.

From The New York Times:
Tornado experts said there was no evidence that the deadly storms were related to global warming or anything other than the clash of contrasting cold and warm air masses that usually precedes such events.

Harold Brooks, a meteorologist at the National Severe Storms Laboratory in Norman, Okla., said there had been a long history of midwinter storms exacting a deadly toll. The most lethal February was in 1971, when tornadoes ripped across Louisiana and Mississippi. According to the laboratory's archives, 134 people died in tornadoes in February that year.
And from the Associated Press:
Meteorologists are quick to say they cannot blame global warming. There is not enough good data over enough years with weather events as small as tornadoes, to draw such conclusions.
Meantime, the signs of global warming are now clearly seen in significant climate shifts that have taken place, not in individual storms.