Will our summers and winters experience additional heatstroke in 2023 and 2024? The question worries the small world of climatologists. Of the two major climate events that affect global temperatures, La Niña tends to cool the planet. However, after three years of activity, it is losing power, the World Meteorological Organization (WMO) warned in early March, and must give way to its “hot” equivalent of El Niño.
The exact date of his return is still under discussion. The chances of seeing impacts between June and August next year will be just over one in two, according to the WMO. “We are in a period where it is very difficult to predict its evolution. It is possible that he will return after the summer, but I do not put my hand on it yet, ”said Jérôme Vialard, director of research at the Institute for Research and Development (IRD).
Despite these inaccuracies, the imminent reappearance of the phenomenon is beyond doubt. “It’s a natural cycle with a constant seasonality: we go from La Niña to El Niño, then to La Niña, and so on. Neutral conditions between them can last for several months,” explains Paloma Trascasa Castro, a doctoral student in the field of environmental sciences. environment. climate (Barcelona Supercomputing Center and University of Leeds).
WMO monitoring, even indefinitely, is important for the countries most sensitive to these climate fluctuations. Because El Niño, which lasts from 9 to 12 months and is characterized by warming of the surface waters of the equatorial Pacific Ocean, combined with changes in the atmosphere, has its share of consequences. In Australia, South Africa and Southeast Asia, droughts tend to become more severe; conversely, heavy rainfall can occur in the western United States, East Africa, and South America.
“The frequency of intense El Niño may increase”
And in Europe? “The effects are much weaker,” the IRD researcher rages. Other natural and climatic phenomena compete and greatly weaken its influence in our latitudes. “In the case of a very strong El Niño, we tend to see a rotten summer, very rainy at home,” the climatologist cautiously puts forward. The effects, on the other hand, will be more noticeable in winter, during its peak, between December and February – hence its name, “child” in Spanish, a reference to Jesus, resulting from the experience of Peruvian sinners. watching the peak of this phenomenon at Christmas. “We would see a milder winter in southern Europe with more rainfall,” Paloma Trascasa Castro details. “Especially in Spain, the Mediterranean region and southern France. It will be colder and drier in northern Europe. But the effects may change.” a lot from one El Niño to another.”
Experts cannot yet accurately predict its intensity. But the WMO is already warning: “There is an increased chance of seeing the hottest year on record.” If, according to Jérôme Vialard, La Niña is considered a “planetary conditioner”, then El Niño does the opposite. “During these years, the temperature of the planet’s surface rises,” confirms Eric Gilliardi, director of research at CNRS and an expert on this phenomenon. 2016 was a good example.
Problem: This effect is superimposed on global warming. The latter has also made the “cooling” effect of La Niña much less noticeable over the past eight years, which remain among the hottest on record. “Natural climate variability no longer ‘masks’ global warming because it’s happening faster than we thought,” agrees Paloma Traskasa Castro. Therefore, the doctoral student believes that in 2024 it will be possible to “temporarily” exceed the famous threshold of 1.5°C compared to the pre-industrial era. “Unlikely”, judge for your part Jerome Vialard: “In 2020, the so-called neutral year, we were at around 1.2 ° C, and the effect of El Niño on the average temperature of the planet is l from 0.1 to 0, 2. °C”. But that doesn’t stop part of the scientific community from seeing the targets set out in the 2015 Paris Agreement as unattainable, given the trajectory of our CO2 emissions.
In the long term, climatologists are also wondering about the possible impact of global warming on the phenomenon itself. “The frequency of intense El Niño [NDLR : comme ceux de 1997-1998 ou 2015-2016] may increase,” says Eric Gilliardi cautiously. But studies have not yet confirmed this.