Study: Winter tornadoes to get more powerful as world warms
Nasty winter tornadoes — like the deadly ones last week that hit five states — are likely to be stronger and stay on the ground longer with a wider swath of destruction in a warming world, a new study shows.
The combination of a longer and wider track with slightly stronger winds means some rare winter tornadoes that are killers now will have nine times more power by the end of the century if carbon dioxide levels continue to rise, according to a study presented Monday at the American Geophysical Union conference.
The preliminary study, which predates the devastating Mayfield, Ky., tornado outbreak, looks at strength and not frequency of big tornadoes as climate change progresses. Not yet peer reviewed, it was presented in poster form as a peek at new research to be published later.
“There is a potential for events in the future that are more intense that would not have been as intense in the current climate,” said study author Jeff Trapp, head of atmospheric sciences at the University of Illinois at Urbana-Champaign. “Bearing in mind that these high-end events are still going to be rare.”
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Trapp took the conditions during two large tornado strikes in 2013 — the Hattiesburg, Miss., tornado that in February of that year injured 82 people with winds of 170 mph and the Moore, Okla., tornado that killed 24 people with winds up to 210 mph in May — and put them into dozens of computer simulations of the worst-case climate change situation by 2100, a scenario that other scientists say is increasingly unlikely.
The worst-case scenario, which the world used to be on track for, would have another 6 degrees (3.3 degrees Celsius) or so of warming between now and the end of the century. Trapp said he will soon run simulations based on a scenario closer to the current trajectory for carbon dioxide emissions of about 3.2 degrees (1.8 degrees Celsius) warming above current levels.
Unusually warm temperatures and a storm system helped create the conditions for the monstrous tornadoes and severe weather in the Midwest and South.
Trapp found big changes for the winter storm: significantly longer and wider tracks and windspeed increases around 14% that added up to the nine-fold increase in power when using a formula that takes wind speed, rotation and size of path into account. Power increased 1.5 times for the spring storm, he said.
Trapp said that’s because there are two key ingredients needed for tornadoes: unstable stormy weather and wind shear. Wind shear, the difference between winds up high and near the ground, is usually stronger in the winter, but there’s not as much stormy weather because it requires warm humid conditions near the ground.
However, as the world warms, there will be more opportunity for instability in the winter, he said.
At least 90 people were feared dead — most of them in Kentucky — after a series of tornadoes tore through the Midwest and Southeast, according to state and local officials.
Three outside scientists said there may be something to the research, but they aren’t yet completely convinced.
“I’m not 100% sold on the technique, but it’s a very interesting approach,” said Harold Brooks, a scientist at the National Severe Storms Laboratory in Norman, Okla. “To me, the really interesting result seems to be the longer tracks for the cool season.”
A single study always raises uncertainty issues, but the results make sense, said Northern Illinois University meteorology professor Victor Gensini: “One of the major components to Friday’s outbreak was the broad and anomalous warm [swath of temperatures that] permitted the storm to last for what will likely be a record-breaking path length.”