Why we still don’t fully understand the tornado-climate change relationship

Why we still don’t fully understand the tornado-climate change relationship

Natural disasters like heat waves, fires, and floods are growing more dangerous because of climate change, but the effect a warming world has on tornadoes is complicated and inconclusive.

There’s been a recorded increase in the overall number of observed tornadoes since 1950, according to National Oceanic and Atmospheric Administration data, but experts say that’s largely a result of better technology such as Doppler radar. There’s been no observed increase in the frequency of major tornadoes over time.

But given the pervasive influence of global warming on the atmosphere, it’s unavoidable that climate change would impact tornadoes too, says Victor Gensini, an extreme weather expert at Northern Illinois University.

“Instead of asking: ‘Did climate change cause this tornado?’ It’s better to operate under the assumption that climate change did play a role,” he says. “Start from the premise that every extreme event is being affected by climate change.”

How tornadoes form

To understand how climate change could impact tornadoes, it helps to understand how warm, humid air flowing beneath cool, dry air creates the unstable atmospheric conditions in which they form.

As warm air rises into cooler air, wind shear—a sudden change in the wind’s speed or direction—can spin this upward-moving air like a top, creating a tornado.

(Learn more about tornadoes.)

As the climate warms, it’s heating the atmosphere and creating more energy to power tornadoes. Large December tornadoes are rare because December tends to be cool—but in December 2021, a rare tornado hit western Kentucky, killing 74 people.

Changing winds

How climate change will alter the winds that bring tornadoes to life is still unclear.

Warmer conditions actually may be diminishing the wind shear that spins up tornadoes; the Arctic is warming more quickly than lower latitudes, which may be weakening the strength of jet stream winds and the resulting wind shear.

“It’s anybody’s guess how that’s going to play out,” says Jeff Masters, a meteorologist at Yale Climate Connections.

When conditions are ripe for a tornado, however, more heat will mean “you can have bigger outbreaks because there’s more energy” stored up, Master says. That means more tornadoes could spin out of storms. One study published in 2016 found that, since 1954, single storms were producing more tornadoes.

Research on tornadoes is challenging because small tornadoes have been historically more difficult to observe, making it challenging to conclusively say how they have changed.

More storms in the southeast 

One study published in 2018 looked at tornado observations since 1979 and observed a shift in tornado locations, from slightly west of the Mississippi River to east of the river, in more populated states like Kentucky and Arkansas.

“We think it might be climate change. But it might also be natural variability,” says Gensini, an author on the study. “We stepped on the scale, and we know we gained 15 pounds, but we don’t know if it’s poor diet or lack of exercise.”

However even a slight geographic shift could have major consequences if storms become more common in more densely populated parts of the country. A tornado striking a cornfield is less dangerous than one tearing through a subdivision.

“The scary part of this is, in the Southeast [there are] an increasing number of manufactured homes,” says Stephen Strader, a geographer studying extreme weather risk at Villanova University. “The odds are stacked against us [there].”

Overall, Americans have made great progress in protecting ourselves against tornadoes: When population increase is taken into account, the tornado fatality rate has declined dramatically over the past century, in large part because of improved weather forecasting and warning systems.

But how we build our communities has a major impact on how much death and destruction they cause in future.

Strader notes one simple solution: “We could save countless lives if we improved how mobile homes are anchored to the ground.”

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