The development of a comprehensive Doppler weather radar system helped overcome many observation gaps by the 1990s, but modern technology can’t make up for the limited records of the past. This makes it harder to find trends in tornado data than in temperature data, said Michael Tippett, a professor of applied mathematics at Columbia University.
However, Dr. Tippett and his colleagues have published research on tornado outbreaks — tornadoes that occur in a bunch — and they did find a trend. “Those bunches are getting bigger,” said Dr. Tippett.
Though it’s not possible to quantify to what degree, if any, climate change played a role in the tornadoes in New York and Massachusetts, researchers have some inkling into how climate change will affect tornadoes more broadly.
They don’t yet have the historical data or computing power to simulate tornadoes themselves. But they can simulate the broader, changing climate to see how it will affect the underlying conditions that create thunderstorms, which set the stage for tornadoes.
Researchers know that there are two ingredients that fuel severe storms that could spawn tornadoes: potential energy in the air and wind currents, or wind shear. The rising levels of greenhouse gases in the air add more energy to the climate system, Dr. Diffenbaugh said. There’s less consensus on how climate change will affect wind shear, though a 2013 study on the thunderstorm conditions that form tornadoes found that the impact was negligible.
Over all, “We do have strong evidence that at the large scale that global warming is likely to increase the atmospheric environments that create the kind of severe thunderstorm that produces tornadoes,” Dr. Diffenbaugh said.
When scientists run climate models assuming global average temperatures of one degree Celsius (two degrees Fahrenheit) higher than preindustrial levels — where the Earth currently stands — some show an uptick in tornado frequency, but others do not. That disagreement, however, fades away at two degrees Celsius of warming, the threshold that the Paris climate agreement is intended to avoid. All the models agree that the frequency of tornadoes will increase by that point.
And climate change may already be affecting tornadoes, Dr. Diffenbaugh said. “It’s just that we can’t distinguish the signal from the noise,” he said.
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