Why the bad weather is expected to be more violent and more regular

Meteorological disturbances have become more numerous and more intense in recent years, in France as in the rest of the world. A trend that can be explained and that could be confirmed, or even worsen in the future.

“With climate change, we must prepare for increasingly frequent “difficult episodes,” warned Prime Minister Michel Barnier on Friday, October 18, at the end of a “Cévennes episode that hit France with a force not seen in 40 years. “We must get used to and arm ourselves to face” these intense storms, added the same day the Minister of Ecological Transition and Climate, Agnès Pannier-Runacher on BFMTV. Speeches that are worrying, but confirmed by recent meteorological phenomena.

The storms that brought down the equivalent of one to six months of rain in some departments in just two days, between October 16 and 18, are a new manifestation of meteorological risks. Storm Kirk that hit France or Hurricane Milton that swept through Florida just a week earlier also attested to the tendency for meteorological phenomena to gain in intensity. “We can say that [the last] Cévennes episode presents accumulations of more than double what was predicted in some places. We can see a concrete effect of global warming there,” indicated Régis Crépet, meteorologist for La Chaine Météo.

Global warming is indeed responsible for the intensification of bad weather, agrees climatologist Valérie Masson-Delmotte, who explains to the Parisienthat “the atmosphere can hold 7% more humidity per degree of warming”. More humidity means more precipitation and therefore risks of flooding and consequent flooding. A reality observed in 2024 with a very rainy spring and a very wet September which brought more rain than the average annual precipitation in several French territories. In Nice, in the Alpes-Maritimes, for example, 850 mm of cumulative rainfall has been measured since the beginning of 2024, when the annual norm is 791 mm.

Heavy rainfall that eventually causes more regular and severe flooding. “Intensified extreme rainfall increases the frequency and magnitude of runoff flooding, as rainfall intensity exceeds the capacity of natural and artificial drainage systems”, i.e. the ability of the soil to absorb water, which are less and less absorbent due to concreting, explains Valérie Masson-Delmotte.

The continuation of global warming will therefore logically lead to meteorological phenomena similar to recent bad weather, or even more intense and more regular. Because beyond disturbances such as the Cévennes or Mediterranean episodes, these are depressions, storms and hurricanes that can end up forming more often due to global warming, particularly due to the warming of the oceans. When the ocean water is warmer, it releases more water vapor which feeds and sometimes reinforces the bad weather. Problem: the temperature of the oceans has remained at a higher level than usual in 2024.

But the warming of the oceans and more generally global warming will only be able to stop or at least slow down with sufficient actions advocated by scientists, including the IPCC. The group of specialists assures that a significant reduction in greenhouse gas emissions could help slow climate change. However, the objectives set by national and international policies during the various COPs are either not respected or are not sufficiently important.