Romain Rouillard / Photo credit: ABDULHAMID HOÅŸBAÅŸ / ANADOLU AGENCY / ANADOLU AGENCY VIA AFP 16:16 pm, June 09, 2023

According to the US National Oceanic and Atmospheric Administration (NOAA), El Niño officially began on Thursday. A climatic phenomenon that could lead to a general rise in temperatures and promote extreme weather events in some parts of the globe.

The climate of the coming months promises some upheavals. And parts of the globe could be particularly affected. In question, the climatic phenomenon El Niño (the little boy in French) which officially began this Thursday, according to the American Oceanic and Atmospheric Administration (NOAA). Many climatologists had indeed predicted its arrival at the end of spring 2023. It could result in a widespread rise in the Earth's surface temperature and the occurrence of several extreme weather events. Explanations.

What is El Niño?

It is a movement of warm waters of the Pacific Ocean from west to east, near the South American coast. "Normally, we will be on an atmospheric circulation regime that blows the trade winds (regular winds of the intertropical regions, editor's note) from east to west," explains Lauriane Batté, climatologist at Météo France.

Forecasters at @NOAA's @NWSCPC announce the arrival of #ElNinohttps://t.co/2pYGBPzLOMpic.twitter.com/swA9gHPjbQ

— National Weather Service (@NWS) June 8, 2023

When an El Niño occurs, these winds tend to weaken, due to rising temperatures in the central Pacific. "The ocean's response to this change in trade winds will reinforce the initial warming," adds Jérôme Vialard, oceanographer and research director at the Institut de recherche pour le développement (IRD). In cases where the El Niño phenomenon is particularly intense, the direction of the trade winds can even reverse and accelerate the movement of warm water to the South American coast, leading to a whole host of disastrous consequences. "But this does not happen systematically," says Jérôme Vialard.

What are the consequences?

They can vary depending on the intensity of the phenomenon. But in general, El Niño translates into increased precipitation in the eastern Pacific. The air rises into the atmosphere due to the high temperature of the water and promotes the formation of clouds, and therefore rain. Conversely, the western Pacific regions - Indonesia or Australia - will experience a more pronounced drying up. Concretely, in case of "super El Niño", torrential rains over the American West and Latin America are not to be excluded. On the other side of the Pacific, this drought combined with high temperatures is a breeding ground for forest fires, for example.

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But that's not all. "In a normal year, trade winds induce upwelling of deep cold waters in the eastern Pacific, which is important for ocean ecosystems because these deep waters are rich in nutrients. During an El Niño, the decrease in trade winds decreases or stops these deep water inflows," adds Jérôme Vialard. As a result, the amount of species present in the waters could be reduced and affect the activity of fishermen.

Why is there talk of widespread warming of the earth's surface?

Last January, the World Meteorological Organization (WMO) indicated that El Niño could make the period 2023-2027 the warmest ever recorded on Earth. But again, it is difficult to see perfectly clear when the phenomenon has just begun.

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If they seem, at first glance, to be confined to the Pacific Ocean, the effects of El Niño will be felt far beyond, given the vastness of the affected area. "When we have an El Niño that affects a large part of the Pacific basin, we reorganize the atmospheric circulation over a good half of the planet," confirms Jérôme Vialard. Nevertheless, most specialists evoke a limited impact in Europe because of its rather remote geographical position.

How long will it last?

Predicting the exact duration of an El Niño is impossible. As a rule, the phenomenon persists between nine and 12 months and occurs every three to nine years. "Most specialists believe that this episode will last until the end of the year," says Lauriane Batté.

When was the last El Niño?

The last El Niño phenomenon occurred between 2015 and 2016. And had also been particularly virulent, the year 2016 having become in the wake the hottest year ever recorded. This sequence then gave way to "La Niña", an opposite phenomenon that materializes by a cooling of the waters of the Pacific and therefore of the global temperature. Beneficial effects for our planet but diminished due to global warming.