A sudden spate of tornadoes in Texas on Tuesday destroyed an estimated 650 homes. Seventeen people were injured, though thankfully no fatalities have been reported. (If you’re feeling charitable, the American Red Cross is accepting donations to assist the in the relief effort.)
As severe weather events often do, the series of tornadoes set off a round of speculation by pundits eager to attribute them to global warming – or climate change, as one CNN weatherman made sure to label it:
ALEXANDRA STEELE: The same area’s in place for severe weather in terms of maybe some hail and very gusty winds tomorrow. It’s just not progressive.
CAROL COSTELLO: Such a strange spring.
STEELE: It really is. That’s kind of the climate change we are seeing. Extremes are ruling the roost and what we are seeing, more become the norm.
COSTELLO: It makes me afraid for what next spring will bring. It might be unnaturally cold.
STEELE: Because that’s not it–this global warming is really kind of a misnomer. Global climate change—so the colds are colder and warms are warmer, and the severes more severe.
Steele’s label choice notwithstanding, the National Oceanic and Atmospheric Administration prefers the “global warming” tag, and is adamant that it has at best an unknown impact on tornado occurence. NOAA writes in its tornado FAQ (emphasis added):
Does ”global warming” cause tornadoes? No. Thunderstorms do. The harder question may be, “Will climate change influence tornado occurrence?” The best answer is: We don’t know. According to the National Science and Technology Council’s Scientific Assessment on Climate Change, “Trends in other extreme weather events that occur at small spatial scales–such as tornadoes, hail, lightning, and dust storms–cannot be determined at the present time due to insufficient evidence.” This is because tornadoes are short-fused weather, on the time scale of seconds and minutes, and a space scale of fractions of a mile across. In contrast, climate trends take many years, decades, or millennia, spanning vast areas of the globe. The numerous unknowns dwell in the vast gap between those time and space scales. Climate models cannot resolve tornadoes or individual thunderstorms. They can indicate broad-scale shifts in three of the four favorable ingredients for severe thunderstorms (moisture, instability and wind shear), but as any severe weather forecaster can attest, having some favorable factors in place doesn’t guarantee tornadoes. Our physical understanding indicates mixed signals–some ingredients may increase (instability), while others may decrease (shear), in a warmer world. The other key ingredient (storm-scale lift), and to varying extents moisture, instability and shear, depend mostly on day-to-day patterns, and often, even minute-to-minute local weather. Finally, tornado recordkeeping itself also has been prone to many errors and uncertainties, doesn’t exist for most of the world, and even in the U. S., only covers several decades in detailed form.