Skip to content

Richard Muller: Does Global Warming Weaken Tornadoes?

|
Richard A Muller, The New York Times

Yes, you read that correctly. Despite the recent spate of deadly twisters, including those that tore through the Midwest over the weekend, the scientific evidence shows that strong to violent tornadoes have actually been decreasing for the past 58 years, and it is possible that the explanation lies with global warming.

That is certainly not the popular impression. Senator Barbara Boxer, Democrat of California, commented in May on the powerful tornadoes that had just hit Oklahoma. “This is climate change,” she said, adding: “You’re going to have terrible storms. You’re going to have tornadoes.” Commenting around the same time, Michael E. Mann, a prominent climatologist, was only slightly more cautious. He said, “If you’re a betting person — or the insurance or reinsurance industry, for that matter — you’d probably go with a prediction of greater frequency and intensity of tornadoes as a result of human-caused climate change.”

But the evidence shows the opposite.

I am not talking about global warming per se, which I am convinced is real and caused by man-made emissions of greenhouse gases. But not everything attributed to global warming has a scientific basis. […]

The NOAA chart shows that the number of these storms has been significantly decreasing over the past 58 years, from over 50 per year in the first half to under 40 per year in the second. The statistical significance of this decrease is extremely high: well above 99 percent confidence.

How can this be? What about all the recent horrible tornadoes? What about the fact that a tornado in Oklahoma in May set a width record of 2.6 miles?

It is wise to be cautious about the panic that sets in when a storm kills a large number of people. People search for reasons to believe the storms are worse than in the past, even if the numbers contradict them. Victims naturally wish to explain why loved ones died and they look for a villain — and they can find one in global warming.

But global warming does not obviously lead to increased or more violent tornadoes. It is possible, for instance, that the increased energy brought by the higher temperatures of global warming is less significant than global warming’s reduction in the north-south temperature difference (the poles warm more than the Equator). The latter could reduce the kind of hot-cold weather fronts that generate severe storms. The current climate models are simply unable to make a clear prediction, and reduced tornadoes from global warming are just as plausible as increased ones.

One thing is clear, however: The number of severe tornadoes has gone down. That is not a scientific hypothesis, but a scientific conclusion based on observation. Regardless of the limitations of climate theory, we can take some comfort in that fact.

Full comment