The El Niño climate pattern in the Pacific Ocean is coming to an end after boosting record temperatures and extreme weather across the planet over the past year. But it is uncertain how soon a transition to a cooler La Niña will bring respite from the heat.
“La Niña should stop that streak of record-breaking temperatures,” says at the University of Colorado Boulder. “If it doesn’t, are our models wrong? Are we underestimating global warming?”
El Niño conditions are characterised by above-average sea surface temperatures in parts of the tropical Pacific. These waters usually oscillate between a warm El Niño temperature pattern, neutral conditions and a cool La Niña every two to seven years, a cycle that is one of the strongest factors influencing the global climate. El Niño is associated with hotter average temperatures and a distinctive pattern of weather conditions in much of the world.
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The current El Niño first appeared in June 2023, following a rare three-year-long La Niña. Temperatures in the Pacific Ocean are now expected to return to neutral conditions within the next month, according to the from the US National Oceanic and Atmospheric Administration (NOAA). Cool La Niña conditions are then very likely to appear between June and September.
“You can already see [La Niña] emerging,” says Dinezio. “You can see it there in the Pacific right now.”
Early last year, researchers were alarmed that the developing El Niño might reach historic strength, comparable to the powerful ones of 2015-2016 or 1997-1998. A very strong event could have an outsized influence on weather around the world.
What emerged was a strong El Niño – the temperature anomaly in the Pacific reached 2°C above average at its peak – but not a record-breaking one. However, combined with background global warming from human-caused climate change and other factors, the outcomes of this year’s El Niño were unprecedented.
The heat pouring out of the Pacific helped make global average temperatures in 2023 the hottest on record, with shocking heat anomalies on land and in the oceans. Each of the past 11 months since El Niño emerged has also been the hottest of that month on record, according to NOAA.
Many of the regions that normally see weather influenced by El Niño also saw those effects amplified by background warming. For instance, drought and heat drove intense fire seasons in South America and Indonesia. In Central America, low water levels linked to El Niño created a traffic jam in the Panama Canal, disrupting global trade. Heavy precipitation caused flooding from California to Afghanistan.
Not all these effects were entirely negative. In the Horn of Africa, for instance, the rain helped ease a drought that has contributed to near-famine conditions in the region.
But the overall damages of this El Niño will probably be significant and last for years, says at Stanford University in California. Past El Niño periods have been linked to trillions of dollars in damages and persistent economic losses, especially in poor countries in the tropics. “This was an El Niño superimposed on global warming in a way we have never seen before,” says Callahan. “A lot of the global impacts we saw, it’s still hard to disentangle.”
Even as a usual pattern of El Niño’s influence emerged, other places saw extreme weather that fell outside the norm. For instance, the Mediterranean isn’t sensitive to El Niño, but last September, it saw torrential rain that led to a catastrophic dam collapse in Libya. And ocean temperatures in the Atlantic reached record high temperatures even before El Niño developed.
Dinezio says this suggests the impact of background warming on the climate may be growing to match the influence of the El Niño cycle for the first time. “Last year, those two had equivalent influence,” they say. There is some these forces were actually working against each other in certain locations.
The rapid shift to La Niña conditions, which is not unusual following a strong El Niño event, could help moderate global average temperatures – although this won’t happen immediately. “There’s still going to be a lag in the climate system, and certainly in the global oceans,” says at NOAA. Historically, the year after El Niño develops is hotter, and 2024 is still expected to break 2023’s heat record.
But the end of El Niño will help researchers understand how much of the past year’s heat can be attributed to its influence, as opposed to background global warming or factors such as the 2022 eruption of Hunga Tonga-Hunga Ha’apai. This could help resolve an ongoing debate among researchers about whether 2023’s off-the-charts temperatures suggest climate change is accelerating faster than models projected.
“A clear answer from La Niña should help us tease that out,” says Dinezio. “Is there something off or not?”
