No, We’re Not Calling This “Blowin’ in the Wind”

We just got curious about the relationship between tornadoes and climate change — this is looking like a record-breaking month for twisters — and happily for us, so did WaPo’s Andrew Freedman. So instead of calling a bunch of meteorologists and surveying the literature, we’re going to relay his take, granting that it’s not definitive.

First, tornadoes require a specific recipe to happen: warmth, humidity, a strong jet stream, and wind shear. Add a cold front, and there go the cows.

It’s the jet stream — perhaps caused by La Niña in the Pacific — that’s forcing the issue in the South. The Gulf of Mexico is also running up to 2.5 degrees Celsius above average, providing more evaporated moisture to the brew.

Wait — warm seas? That’s the climate-change smoking gun, isn’t it?

Not necessarily. At least not in this case. Warmth may actually reduce wind shear, removing one of the tornado’s essential ingredients. And, depending on whom you ask, increased warmth may not be sufficient to overcome reduced wind shear until the end of the century.

You still get hellish thunderstorms until then, but not necessarily more tornadoes.

Finally, while April may set a tornado record, the historical record itself is not certain:

While the number of tornadoes recorded in the U.S. has just about doubled during the past 50 years, the number of strong tornadoes (EF2 and above) has actually been decreasing. It may be the case that more tornadoes are being noticed today, given a network of trained storm spotters and a national Doppler radar network, both of which didn’t exist as recently as the early 1980s.

Conclusion? Insufficient evidence. It’s a reasonable question to ask, and a reasonable question to investigate. But until we hear more, we’re not ready to point fingers.

Are La Nina and global warming behind the extreme tornado activity? [WaPo]

Deadly Tornadoes: 245 Killed Across South, Including 162 in Alabama [ABC]