Like a year marked by repeated heat waves, 2022 ended with a very mild winter in Europe.
And 2023 starts in the same vein.
In France, the thermometer thus displayed, Thursday, January 12, for the third consecutive week, temperatures 3 to 4 degrees above normal for the season, according to Météo France.
As a symbol of this continuity between the year that is ending and the one that is starting, several temperature records were broken on December 31 and January 1.
In France, the mercury reached 18.6 ° C in Strasbourg, in the Bas-Rhin, or even 24 ° C in Dax, in the Landes – unheard of.
Same observation in Germany, Luxembourg or Poland.
In Warsaw, the thermometer thus posted 18.9 ° C, far from the previous record dating from 1993 with 13.8 ° C.
“Since December 18, and certainly until the end of January, we have been experiencing a winter heat wave, also called a false spring”, explains Davide Faranda, climatologist at the Pierre-Simon Laplace Institute and at the CNRS.
A "frequent" phenomenon, according to the specialist, but "exceptional this year in terms of intensity and duration".
If the idea of leaving the sweaters in the closet can be tempting for those who fear the harshness of winter, "this false spring upsets the balance of ecosystems, with consequences on agriculture and more broadly, on biodiversity" , warns Serge Zaka, agroclimatologist and administrator of the Infoclimat association.
And to sneer: "We tend to focus on summer heat waves because the effects on the economy and human health are immediate and obvious. But we must look beyond the tip of our nose: the winter weather is just as important to the planet."
More vulnerable plants
First, this "false spring" can disrupt the development of plants.
For good reason, all plant species synchronize their stages of development with the seasons and to determine whether they are in summer or winter, they use either the length of the day or the temperature as a benchmark.
"So when the mercury panics abnormally, the plants of the second category no longer know where they are", summarizes Serge Zaka.
"For wheat, for example, which is especially sensitive to light, heat waves have little impact," he illustrates.
"Conversely, fruit trees, in particular apricot trees, hazelnut trees or even apple trees are in the front line."
"To sum up, when the mercury rises, it's as if these plants received the signal that spring is starting," he continues.
They then begin to bud, that is to say that their buds begin to hatch even if it is several weeks in advance.
"This will make them very fragile in the face of the return of the cold and particularly vulnerable to episodes of frost", continues Serge Zaka.
A threat that farmers know well: in 2021, a strong episode of frost after a period of mild winter weather caused more than 4 billion euros in damage to French vineyards and orchards.
For several years now, the wine-growing and arboreal sectors have therefore been trying to adapt.
"But unlike in the summer when you can stagger the plantations or irrigate against drought, when faced with the cold, the range of solutions is more limited", deplores Serge Zaka.
>> To read also: Forgotten grape varieties, new practices: the French vineyard adapts to global warming
“Some try to diversify the plant species to extend the flowering period as much as possible and thus save part of their production from frost,” he explains.
"But faced with the economic costs that this generates, the majority opts rather for short-term solutions, with tools to fight against freezing such as heating wires."
In addition to this increased vulnerability of plants to temperature variations, this "false spring" also promotes the survival of parasites and fungi, potential spreaders of diseases in crops.
"Normally, the latter have difficulty surviving the cold, and precisely, the frost. If the weather is mild, they can survive, continue to lay eggs and proliferate in the spring", explains Serge Zaka again.
A shift in biological cycles
"Beyond the agricultural world, all ecosystems can be weakened", continues Wilfried Thuillier, research director at the Alpine Ecology Laboratory in Grenoble.
"Because the biological cycles of insects and animals are also strongly linked to the alternation of the seasons. Abnormal variations in temperature can therefore modify their behavior with consequences for their habitat."
There are many examples of these vicious circles.
The migration of certain birds may be delayed, leading to increased pressure on their environment of origin.
Pollinating insects, such as bees, can appear too early, before the plants flower - yet they need them to survive.
Other species, conversely, can proliferate by taking advantage of the temporary sweetness.
In Belgium, also subject to this period of winter heat, salamanders, newts, frogs or even hedgehogs, which normally hibernate in winter, have thus already been seen, warns Arnaud Laudelout, biologist at the Association for the Defense of Natagora nature with the RTBF.
"These animals come out of hibernation because of the temperatures that are too mild. The problem is that they are unable to feed themselves because their prey is scarce," he notes.
"Our ecosystems are increasingly tired"
"For the moment, this winter of 2022 is not yet dramatic", however nuance Serge Zaka, who wants to be resolutely optimistic.
"If the temperatures finally return to normal for the season, the consequences of this heat wave may be limited."
The real concern, agree to say the specialists interviewed by France 24, does not hold so much in this winter which does not arrive but in the recurrence of extreme meteorological events.
"If this episode was an exception, it wouldn't matter. Mild winters and late frosts have always existed and have always been part of the hazards to which farmers are subject," recalls Serge Zaka.
"But before, it happened exceptionally. Now, it's the same story every year."
“In this year 2022 alone, plants, like insects and animals, had to endure late spring frost, repeated heat waves, drought and now this winter heat”, continues Wilfried Thuillier.
"Each time, it's as if we were dealing an additional blow to our ecosystems, which are increasingly tired. It's really this effect of repetition that puts them at risk."
"And this is all the more worrying as these extreme weather phenomena are set to accelerate further under the effect of climate change", warns Davide Feranda.
“While summer heat waves will increase, winters like this will become the norm by 2050. And there will be even hotter ones,” he continues.
“We are entering a non-winter phase in Europe. This does not mean that there will be no more cold spells, but the number of warmer than average days will continue to increase”.
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