Scientists have been able to establish connections between a warming planet and extreme weather events such as hurricanes, heat waves, and droughts, attributing the possibility that climate change may have contributed to these events. However, when it comes to tornadoes, researchers have found it challenging to link them to climate change. Michael Tippett, an associate professor at Columbia University who studies extreme weather, states that tornadoes are the most difficult phenomenon to connect to climate change. While scientists are beginning to uncover patterns in tornado behavior, the extent to which climate change influences tornado activity remains uncertain. 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 as a result of a combination of temperature, moisture profile, and wind profile. These storms occur when unstable air causes cold air to be pushed over warmer, humid air, creating an updraft as the warm air rises. If wind speed or direction changes abruptly over a small area, the air inside the clouds can begin to rotate, leading to the formation of a tornado. Tornadoes can intensify when the air column starts spinning vertically and rotating near the ground, which increases friction on Earth's surface and accelerates the air inward, forming a tornado. They are measured using the Enhanced Fujita (EF) scale, which ranges from 0 to 5. The recent tornado that passed through northeast Arkansas, Tennessee, and western Kentucky was approximately three-quarters of a mile wide with wind speeds reaching between 158 and 206 mph, earning it a minimum EF rating of 3. Due to the difficulty of directly measuring the winds in a tornado, researchers typically assess tornadoes based on the extent of damage to various structures. By examining whether the damage is limited to specific areas or involves entire sections of buildings, scientists can estimate wind speeds and assign a rating to the tornado. According to researchers, there has been a trend in recent years where tornadoes are occurring in clusters and the traditional tornado alley in the Great Plains is seemingly moving towards the east. The annual number of tornadoes remains consistent at around 1,200. Tornadoes in December are uncommon in the United States, as they usually occur in the spring. The tornadoes on Friday may have been caused by high wind shear, which is more common in the winter, and warmer than usual weather. Is climate change responsible for this? The ingredients necessary for tornado formation include warm, moist air near the surface, cool dry air at higher altitudes, and wind shear, which is the change in wind speed or direction. Climate change may impact each of these factors differently. While overall temperature and humidity may increase with a warming climate, wind shear may not. According to Brooks of NOAA, these changes may not all occur in the same direction. If there is not enough wind shear to cause rotation, the strength of the energy in the air becomes irrelevant. The size of a tornado makes it challenging to model, hindering scientists' ability to attribute extreme weather events to climate change. Tornado records are limited compared to other events, possibly due to their localized nature and reliance on eyewitness reports for data collection. This indicates that smaller or unobserved tornadoes might not be documented. ©2021 The New York Times Company.