Tornadoes and Global Warming

The Evidence Is Thin. The Consequences Are Real

February 7, 2008 at 12:06PM by Chris Mooney | comment

I want to approach the subject of this post with considerable caution. But at the same time, in the wake of this week's devastating tornado disasters in the South, I know a lot of people are wondering about the matter. So let's see what we can say.

Without a doubt, the tornado outbreak this week was odd. Jeff Masters notes: "What is really unusual about yesterday's Super Tuesday Outbreak is that it occurred in early February. Only one other tornado outbreak in the past century killed so many people so early in the year – the great Warren, Arkansas tornado outbreak of January 3, 1949, which killed 60 people." And Masters goes further:

[The] outbreak was fueled by record warmth over the South. Record high temperatures were recorded in Little Rock, Arkansas (75), Shreveport, LA (78), El Dorado, AR (77), Memphis, TN (75), Jackson, MS (81), and Charleston, SC (79), to name a few locations. A strong cold front associated with a powerful winter storm over the north central U.S. pushed into this warm, unstable air mass, triggering Tuesday's bout of violent weather.

All of this is, of course, suggestive – but we have to be very cautious whenever we're talking about the relationship between climate and weather. First, no individual event can ever be attributed to global climate change.

Moreover, when it comes to tornadoes, last year the definitive source of climate information, the U.N.'s Intergovernmental Panel on Climate Change, explicitly stated that there wasn't enough proof to claim that they had been changing:

There is insufficient evidence to determine whether trends exist in the meridional overturning circulation (MOC) of the global ocean or in small-scale phenomena such as tornadoes, hail, lightning and dust-storms.

That's no surprising conclusion, given how hard it is to get good data on small-scale, short-lived phenomena like tornadoes. For more on that problem, see here.

But just because we can't yet establish firm evidence that tornadoes are changing doesn't mean they aren't. Measurement difficulties cut both ways, and we also have to consider theory – whether we think global warming will change the world in such a way as to produce more or stronger tornadoes, or to change their seasonality, etcetera.

On this front, there is at least one scientific paper that I've come across suggesting theoretical reasons for changes. Scientists at NASA's Goddard Institute for Space Studies found the following:

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.

But, according to the same model, the numbers of severe storms should decline over all, even as the strongest get stronger.

In short, it's a murky area. But for tornadoes as for many weather phenomena, we have to expect that global warming is going to change them in some way or other. And there's little reason to think we are going to much like the nature of those changes.