Have tornadoes changed over the years?
Researchers say that in recent years tornadoes seem to be occurring in greater “clusters,” and that the region known as tornado alley in the Great Plains, where most tornadoes occur, appears to be shifting eastward. The overall number of tornadoes annually is holding steady around 1,200.
December’s killer tornadoes were highly unusual for the United States. March, with its warmer weather, is typically when tornado activity starts to increase.
Is climate change the cause?
The ingredients that give rise to tornadoes include warm, moist air at ground level; cool dry air higher up; and wind shear, which is the change in wind speed or direction. Each of these factors may be affected differently by climate change.
As the planet warms and the climate changes, “we don’t think they are all going to go in the same direction,” said Dr. Brooks of NOAA. For instance, overall temperature and humidity, which provide energy in the air, may rise with a warming climate, but wind shear may not.
“If there is not enough shear to make something rotate, it doesn’t matter how strong the energy is.” he said. “If there is all kind of wind shear, but you don’t have a storm, you won’t get a tornado, either.”
Although we know that climate change may be playing a role in making some storms more powerful, the complexity of tornadoes means that it is hard to extend that connection with certainty, especially for an individual event.
Scale is everything
A tornado’s relatively small size also makes it harder to model, the primary tool that scientists use when attributing extreme weather events to climate change. “We are working at such small scales that the model you would use to do the attribution studies just can’t capture the phenomenon,” Dr. Brooks said.
Raymond Zhong contributed reporting.