After the latest Tornado series, the US environmental agency should not only clarify this question
US President Joe Biden has instructed the EPA, the national environmental agency, to investigate what role climate change could have played in the devastating cyclones in the Midwest and Southeast. It is known that “everything becomes more intense when the climate warms up,” said Biden. However, he cannot say exactly what influence this had on this tornado series.
There have been tornado events in US history with similar or even worse effects. In 1925, the so-called three-state tornado in Illinois, Indiana and Missouri killed around 700 people, and in 2011 a hurricane in Missouri killed more than 160 people.
What is unusual this time is that the cyclones occurred in late autumn. The US tornado season usually runs from March to June. Then the conditions in the atmosphere are most likely such that they can arise. In fact, the five tornadoes with the highest casualty rates to date have all occurred during this period.
The current disaster could mark a new trend. Weather expert: inside, namely, do not rule out that hurricanes will also form more frequently in autumn or winter in the future, because climate change can also cause warm air masses to form and make them possible. Professor Victor Gensini of Northern Illinois University said, “One word: remarkable. It was really a kind of late spring in the middle of December. “
This time, in any case, the conditions for violent tornadoes were there. Warm and cold air masses hit each other with force, triggered by a large temperature difference between the southeast of the country with over 25 degrees Celsius and the north with below zero, for example in Minnesota. In addition, there were significant wind shearings, i.e. sudden, sharp changes in the direction and speed of the winds in higher and lower layers of air. Experts believe that the La Niña climate phenomenon that has dominated the world since autumn could also have played a role.
A clear tendency towards an increase in extreme tornadoes has not yet been identified exactly in the USA, but it may also be a consequence of the fact that they are difficult to record systematically. From a physical point of view, there are two opposing tendencies. Warmer air, which absorbs more moisture than colder air, drives hurricanes. But the warming can also cause the wind shear to decrease. The two phenomena could cancel each other out. It was found, however, that the usual “tornado route” in the US is shifting further east, away from the Kansas-Oklahoma region and into the states in which the current tornadoes occurred – into the regions around the Mississippi Valley.
In any case, the national coordination office for disaster relief of the USA (FEMA) urges us to prepare for stronger storm events. Their highest federal official for emergency management, Jeanne Criswell, said that these strong storms are the “new normal” in the age of climate change. “The effects of climate change are the crisis of our generation.”
