Nearly 100 people died in tornadoes that swept the central eastern United States in mid-December. About 30 tornadoes traveled more than 350 kilometers, from Arkansas to Kentucky. This distance makes it a major event, rarely noticed. “This is not an unexpected event, but we can consider it unusual,” notes Robert Vautard, a climate scientist at the National Center for Scientific Research and director of the Pierre-Simon Laplace Institute. Its origin is due to the great atmospheric instability that prevailed at the beginning of December. In question, a cold front encounters a mass of humid and abnormally hot season air coming from the Gulf of Mexico.

But should climate change be blamed for the disaster? No study has yet made it possible to establish a link between climate change and hurricanes, unlike other extreme weather events. In general, the impact of climate change on hurricanes is not well understood. Some changes have been noted, according to the latest IPCC inventory: When a storm occurs that generates hurricanes, they are more numerous. But the number of hurricane days is declining: the result is a stagnating annual number of hurricanes. Another note: tornadoes are usually grouped in Tornado Alley in the central United States, and are now concentrated in the east.

normal variability. “We cannot determine whether these trends are related to climate change or natural variability,” adds Robert Vattard. It would take at least fifty years of hurricane recording to answer this question, but the first data goes back about 30 years. Elsewhere in the world, particularly in Europe, the number of hurricanes is so few that changes are difficult to detect and strong observations are not made.

Another way to study the impact of climate: climate models that simulate the future. Here again, scientists are relatively helpless. The best climate models make calculations over areas of at least one square kilometer…not accurate enough to simulate hurricanes, which are much smaller.

Otherwise, scientists are still using it to simulate the future. They monitor the occurrence of certain weather conditions, the ones that lead to the birth of hurricanes. These are, for example, certain types of storms that are known to generate tornadoes. Going forward, in the United States, models show that it is likely (but not certain) that the season for these storms will lengthen. It is also likely that it occurs in the north and east. “Even if simulated environmental conditions were favorable for these storms, this does not mean that there will be hurricanes,” explains Robert Vautard. The birth of hurricanes also depends on specific conditions in the clouds, which are not simulated at all in climate models. » Does climate change affect hurricanes? Only when climate models are able to simulate hurricanes, and the data is sufficient, will climate scientists answer us.