Researchers have found correlations between a warming planet and severe weather events like hurricanes, heat waves, and droughts, suggesting that climate change may have played a part in these occurrences. However, the connection between tornadoes and climate change remains elusive. Despite ongoing studies on tornado trends and behavior, the role of climate change in tornado activity remains uncertain. According to Michael Tippett, an associate professor at Columbia University, tornadoes are the most challenging weather phenomenon to link to climate change. Harold Brooks, a senior research scientist at the National Severe Storms Laboratory, acknowledges that many questions regarding the relationship between climate change and tornadoes remain unanswered. Tornadoes are created within large rotating thunderstorms when there is a combination of specific temperature, moisture, and wind conditions. This occurs when unstable air causes cold air to move over warmer, humid air, creating an updraft as the warm air rises. If the wind changes speed or direction rapidly within the clouds, the air can begin to spin, leading to the formation of a tornado. Tornadoes, like hurricanes and earthquakes, are measured on a scale called the Enhanced Fujita (EF) scale, which ranges from 0 to 5. The tornado that moved through northeast Arkansas, Tennessee, and western Kentucky recently was believed to be around three-quarters of a mile wide with wind speeds reaching between 158 and 206 mph, classifying it as at least an EF3. Because directly measuring the winds in a tornado is difficult, surveyors typically assess tornadoes based on the extent of damage to various structures. This can include determining if the damage is limited to missing roof shingles or if entire sections of roofs or walls are missing. Scientists then use this information to estimate wind speeds and assign a rating to the tornado. Researchers have noted a trend of tornadoes occurring in clusters in recent years, with the traditional tornado alley in the Great Plains seemingly shifting eastward. The total amount of tornadoes each year remains consistent at approximately 1,200. Tornadoes in December in the United States are uncommon as they usually happen in the spring. The tornadoes on Friday could have been a result of high wind shear, which typically peaks in the winter, and warmer than usual weather. The question is raised whether climate change is the reason for this. The elements that lead to tornado formation consist of warm, moist air near the surface, cool dry air at higher altitudes, and wind shear, which involves changes in wind speed and direction. The impact of climate change on these factors may vary, with some affected differently than others. According to Brooks from NOAA, as the Earth heats up and the climate shifts, these elements may not all change in the same way. While temperature and humidity levels, which provide energy to the atmosphere, may increase with a warming climate, wind shear may not. Brooks explains that without sufficient wind shear to create rotation, the strength of the energy present becomes irrelevant. The size of a tornado makes it difficult to model, hindering scientists' ability to attribute extreme weather events to climate change. Tornado records are sparse compared to other events, possibly due to their localized nature and reliance on eyewitness reports for data collection. This indicates that smaller or unnoticed tornadoes might not be officially recorded. ©2021 The New York Times Company.