TornadosIs climate change responsible for increasing tornado outbreaks?
Tornadoes and severe thunderstorms kill people and damage property every year. Estimated U.S. insured losses due to severe thunderstorms in the first half of 2016 were $8.5 billion. The largest U.S. impacts of tornadoes result from tornado outbreaks, sequences of tornadoes that occur in close succession. New research shows that the average number of tornadoes during outbreaks—large-scale weather events that can last one to three days and span huge regions—has risen since 1954. But the researchers were not sure why.
Tornadoes and severe thunderstorms kill people and damage property every year. Estimated U.S. insured losses due to severe thunderstorms in the first half of 2016 were $8.5 billion. The largest U.S. impacts of tornadoes result from tornado outbreaks, sequences of tornadoes that occur in close succession. Last spring a research team led by Michael Tippett, associate professor of applied physics and applied mathematics at Columbia Engineering, published a study showing that the average number of tornadoes during outbreaks—large-scale weather events that can last one to three days and span huge regions—has risen since 1954. But the researchers were not sure why.
In a new paper, published today in the journal Science, the researchers looked at increasing trends in the severity of tornado outbreaks, measuring severity by the number of tornadoes per outbreak. They found that these trends are increasing fastest for the most extreme outbreaks. While they saw changes in meteorological quantities that are consistent with these upward trends, the meteorological trends were not the ones expected under climate change.
“This study raises new questions about what climate change will do to severe thunderstorms and what is responsible for recent trends,” says Tippett, who is also a member of the Data Science Institute and the Columbia Initiative on Extreme Weather and Climate. “The fact that we don’t see the presently understood meteorological signature of global warming in changing outbreak statistics leaves two possibilities: Either the recent increases are not due to a warming climate, or a warming climate has implications for tornado activity that we don’t understand. This is an unexpected finding.”
Colombia U notes that the researchers used two data sets generated by the National Oceanic and Atmospheric Administration: one containing tornado reports and the other observation-based estimates of meteorological quantities associated with tornado outbreaks.
“Other researchers have focused on tornado reports without considering the meteorological environments,” said Chiara Lepore, an associate research scientist at Lamont-Doherty Earth Observatory, who is a coauthor of the paper. “The meteorological data provide an independent check on the tornado reports and let us check for what would be expected under climate change.”