Researchers around the world are closely following the arrival of La Niña, expected between September and October 2024, given that it will follow one of the most intense El Niño events, with record average global temperatures and unprecedented warming of the ocean surface beyond the Pacific Rim.
La Niña is associated with lower surface temperatures in the equatorial Pacific and changes in weather conditions in several regions of the world. But experts are uncertain about what the phenomenon will look like this year.
“Climate models had predicted that we would have a strong El Niño in 2023, with an increase in temperatures of the waters of the equatorial Pacific and the average global temperature of up to 1.3 degrees Celsius. [°C] above the average of the pre-industrial period,” he told SciDev.Net “However, it was a much more dramatic scenario,” said climatologist Carlos Nobre of the Institute for Advanced Studies at the University of São Paulo (USP) in Brazil.
Across much of the Atlantic basin, surface temperatures in 2023 were up to 2°C above the 1971-2000 baseline. In waters off South Africa, Japan and the Netherlands, the anomaly reached 3°C or more, according to the U.S. National Oceanic and Atmospheric Administration (NOAA).
According to data from the European Union’s Copernicus Climate Change Service, between July 2023 and June 2024, the average temperature of the planet – driven by El Niño – was at least 1.5 °C higher than the average of the pre-industrial period. “The Earth has never been so hot,” Nobre added.
Evolution of thermal anomalies on the planet. Image credit: Berkeley Earthunder license Creative Commons CC BY-NC 4.0 Deed.
Scientists still don’t know what caused this heat spike in 2023. “Greenhouse gas levels continued to rise, but the additional load from 2022 could account for an additional warming of only 0.02°C,” the climatologist said. “The 2023 temperature anomaly revealed an unprecedented knowledge gap, perhaps for the first time since about 40 years ago.”
From Lima, Peru, physical oceanographer Antonio Salvá warned that 2024 could also reach temperature records. According to what he told SciDev.NetJune was the warmest month since temperature records began in 1850 and the global average temperature from July 2023 to June 2024 reached +1.68 °C above the average measured from 1850 to 1900.
For physicist Paulo Artaxo, from the USP Physics Institute, global warming could be changing atmospheric dynamics, compromising the ability of climate models to accurately predict climate behavior. “This makes it more difficult to know exactly how the next La Niña will behave, what its intensity and effects will be,” he told SciDev.Net. “We are in uncertain territory.”
“We expect a moderate La Niña, but given the temperature anomaly of the past year, predictions about the phenomenon in 2024 may not be sufficiently accurate.”
Carlos Nobre, climatologist at the Institute for Advanced Studies at the University of São Paulo (USP), in Brazil
“Many climate models have not considered the impact that global warming may have. In long forecast periods, 10, 20, 30 years, it is clear how global warming is affecting the prediction models. In short-term models, for two or three months, this impact obviously does not appear. I think that these models will need to be adjusted to this situation of global warming,” said Salvá, a senior professor at the Faculty of Oceanography, Fisheries and Food Sciences at the Federico Villarreal National University in Lima.
During La Niña years, the east-west trade winds in the tropics intensify and push warm surface waters from the Tropical Pacific of the Americas towards Oceania, causing colder, deeper eastern waters to rise to the surface near the equatorial coasts of South America. This creates a mass of colder waters along the equator in the central and eastern Pacific, which often changes weather conditions in several regions of the world, including Latin America.
In Colombia, for example, rainfall is above average, becoming more intense and potentially causing flooding, while rainfall is reduced in the northern half of Argentina and in Chile, Peru, Paraguay, Ecuador and Uruguay. In Brazil, the phenomenon usually triggers heavier rainfall in the North and Northeast regions. Severe droughts are observed in the South. In the Southeast and Center-West, the effects are more unpredictable, with possible droughts, floods and storms.
“We expect a moderate La Niña, but given the temperature anomaly of the past year, predictions about the phenomenon in 2024 may not be sufficiently accurate,” Nobre said.
The phenomenon usually lasts between 9 and 12 months, but can sometimes extend up to three years. “It is difficult to predict its duration when it has not yet been fully established and especially because we do not know what has changed in terms of its dynamics with El Niño,” said Artaxo.
For Madeleine Renom, a meteorologist at the Faculty of Sciences in Uruguay, everything indicates that La Niña will be moderate, but its duration or real intensity cannot yet be predicted. Regarding its effects, she told SciDev.Net Uruguay is experiencing a few months of rainfall deficit (July and August), so the arrival of La Niña, usually associated with less rain between October and December, may accentuate the conditions of low water availability.
“Global warming is altering the climate as we know it and that leads to marches and countermarches: if it is going to happen [La Niña]or it will take a while, if it will be a moderate event, the only thing that is certain is that global warming will continue,” said Salvá. He estimates that, although there is a cooling of the waters in the Central Pacific, “it is not really La Niña as it is defined” and that, if it occurs, it will be a moderate event.
But meteorologist Micael Amore Cecchini, from the Department of Atmospheric Sciences at the Institute of Astronomy, Geophysics and Atmospheric Sciences at IAG-USP, pointed out SciDev.Net that there is also a 50 or 60 percent chance that La Niña will lose strength between February and May 2025.
This article was produced by the Latin America edition of SciDev.Net
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