What We Know About Tornadoes and Climate Change
and that parts of the South could experience strong tornadoes on Tuesday, as severe thunderstorms in the lower and mid-Mississippi Valley and other areas produce damaging hail and powerful gusts of wind. Scientists have been able to draw links between a warming planet and hurricanes, heat waves and droughts, attributing the likelihood that climate change played a role in individual isolated events. The same cant be said for tornadoes yet. Even as scientists are discovering trends around tornadoes and their behavior, it remains unclear the role that climate change plays. For a lot of our questions about climate change and tornadoes, the answer is we dont know, said Harold Brooks, a senior research scientist at the National Oceanic and Atmospheric Administrations National Severe Storms Laboratory. We dont see evidence for changes in average annual occurrence or intensity over the last 40 to 60 years. Tornadoes form inside large rotating thunderstorms and the ingredients have to be just right. Tornadoes occur when there is a perfect mix of temperature, moisture profile and wind profile. When the air is unstable, cold air is pushed over warmer humid air, creating an updraft as the warm air rises. When a winds speed or direction changes over a short distance, the air inside the clouds can start to spin. If the air column begins spinning vertically and rotates near the ground, it can intensify the friction on Earths surface, accelerating the air inward, forming a tornado. Like hurricanes and earthquakes, tornadoes are rated on a scale. The Enhanced Fujita, or EF, scale runs from 0 to 5. The National Weather Service warned that storms on Tuesday in parts of the lower Mississippi Valley region and Mid-South could produce tornadoes with an EF rank of at least 3, meaning their gusts could exceed 136 miles per hour. Because its challenging to measure the winds in a tornado directly, surveyors usually evaluate tornadoes by their level of damage to different structures. For instance, they may look to see if the damage is limited to missing roof shingles or whether entire sections of roofs or walls are missing. Based on the level of damage, scientists then reverse-engineer the wind speeds and assign a tornado a rating on the scale. 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 . The overall number of tornadoes annually is holding steady around 1,200. In December 2021, a burst of across central and southern states came at a highly unusual time for the United States. March, with its warmer weather, is typically when tornado activity starts to increase. 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 dont 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 doesnt matter how strong the energy is, he said. If there is all kind of wind shear, but you dont have a storm, you wont 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. A tornados 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 cant capture the phenomenon, Dr. Brooks said. is a reporter covering climate and the environment. is a climate reporter. He joined The Times in 2017 and was part of the team that won the 2021 Pulitzer Prize in public service for coverage of the coronavirus pandemic.