Frost episode: without global warming, "the plantations would have had to resist"

An episode of frost affected many crops this week in France.

Temperatures fell, in some places, below 0 degrees at a rate not seen since 1947 for one month of April.

Thierry Castel, associate researcher in the climatology team of the Biogeoscience * laboratory and teacher at Agrosup Dijon, answers our questions on this worrying phenomenon.

To discover

• A lead to explain the rare thromboses linked to the AstraZeneca vaccine

LE FIGARO.

- How to explain this cold in April, when we talk all the time about global warming?

Thierry CASTEL.

It is, however, well linked.

The temperature differences are reduced between the polar zone and the mid-latitudes.

This leads to modulating the undulations of the “jet” (very fast winds located in the North Atlantic, which play an important role in atmospheric circulation, Editor's note).

Because of this, we face more cold air sinks and hot air rises.

For example, while in February 2017 we had temperatures in France well above the seasonal averages, it snowed in Libya.

It will get worse.

Read also: At the bedside of the vineyards, a nightmare of fire and ice

Can we say that the plantations are more affected than before by this phenomenon of frost?

It is in reality the vulnerability of plants to frost that is increased, and not the cold episodes which would be more intense.

Let me explain: normally at this time of year, the plantations should have been able to withstand temperatures of -6 or -7 degrees.

But because of global warming that we have known for 30 years, the buds are now arriving earlier.

Once they have started to open, this is a phase where the plants are extremely sensitive to frost.

Even if it is not very cold, it is enough to cause significant damage.

We can clearly see this phenomenon in the vines, it is clear.

What can farmers do?

In the Chablisien, the winegrowers sprinkle them: they water the vines to create an external layer of water.

It is the latter which will freeze and not the bud.

On the Côte de Nuits and Côte de Beaune, they try to mix the cold air close to the ground with higher air which is warmer.

Or they burn straw.

Global warming is on track and therefore the consequences of this type are real issues in the medium and long term.

Farmers are already realizing this.

* University of Burgundy