The United Nations weather agency forecast on Tuesday a moderate or possibly strong El Nino that could drive up global temperatures and increase the risk of extreme weather until at least November.
El Nino is a periodic warming of sea surface temperatures in the central and eastern Pacific Ocean, which typically lasts between nine and 12 months, according to the World Meteorological Organization.
The World Meteorological Organization said there is an 80 per cent chance that an El Nino event develops between June and August, and a 90 per cent chance it will last until at least November. The statement is the clearest signal yet of the likelihood.
The El Nino phenomenon naturally occurs every two to seven years, when weakening trade winds result in warmer waters in the eastern Pacific. The result tends to be higher global temperatures, and disrupted rainfall - meaning drought in some regions, heavy rains in others. It also affects hurricane formation.
“We need to prepare for a potentially strong El Nino event - which will exacerbate drought and heavy rainfall and increase the risk of heatwaves both on land and in the ocean," said WMO Secretary-General Celeste Saulo.
The weather pattern is known to disrupt regional climates, potentially bringing warmer temperatures across the globe, while increasing rainfall to southern South America, the southern United States, parts of the Horn of Africa and central Asia. It can also cause drought in Australia, central America, Indonesia, and sections of southern Asia, and lead to the formation of hurricanes in the central and eastern Pacific Ocean, the WMO said.
The most recent El Nino, in 2023 to 24, contributed to making 2024 the hottest year on record, Saulo added.
'The risks are enormous'
Each El Nino is different, and its effects vary around the world - making it hard to predict how this one will behave.
Typically, regions including southern South America and parts of Central Asia get more rain in an El Nino, while Central America and Australia dry out. The phenomenon also intensifies heatwaves, including in regions far from the Pacific, such as Europe.
These effects can have disastrous consequences for food production, industries and human life.
In April to May 2024, floods in Rio Grande do Sul in Brazil killed more than 180 people and displaced 600,000. Scientists said both climate change and El Nino strengthened the rains that triggered the disaster.
Francisco Aquino, head of the University of Rio Grande do Sul's climate centre, said a strong El Nino this year risked causing a similar disaster.
"When you have an El Nino over what climate change already brought, the risks are enormous," Aquino told Reuters. "A strong El Nino can lead to the exact same scenario we saw then, because the world keeps getting warmer, and the temperature in the ocean keeps rising."
Climate change is also compounding the impact of El Ninos in southern Africa. There, the weather pattern reduces rainfall during the rainy season, limiting hydropower generation and cutting crop yields.
"Climate change will make that below-normal rainfall more intense, so it will last longer or have less rainfall... and that, of course, will affect agriculture, especially the rain-fed farmers in the region," said Izidine Pinto, a Senior Climate Researcher at the Netherlands Meteorological Institute.
Antonio Navarra, head of Italy's Euro-Mediterranean Center on Climate Change, said stronger Pacific cyclones were another impact governments should prepare for.
"Because the water in the Pacific will be much warmer, there will be a much more favourable environment for the formation of tropical cyclones.... El Nino will input an enormous amount of energy into the system, so everything will be more intense," he said.
Some scientists said the destruction likely from this year's El Nino could provide a foretaste of extremes that will become the norm in around five years' time even without an El Nino.
"It does give a window into the future," said Forster.
Theodore Keeping, Research Associate at Imperial College London, said El Nino's impact on atmospheric circulation means it affects weather patterns in a way that a warmer climate alone would not - but broadly speaking, it can offer a flavour of future climate change.
"You're able to kind of sample weather conditions that you would otherwise in a neutral El Nino only expect to see in a warmer climate," he said.
The risks include heat-related illness and disease
“Extreme heat alone is already one of the deadliest climate hazards we face, and an El Nino event could intensify the threat,” said Saulo. The risks include more heat-related illness, a wider spread of vector-borne diseases and increased pressure on food and water systems.
“Communities that were already struggling will be pushed farther beyond their limits,” she said.
A shift has been observed in the Equatorial Pacific, with sea surface temperatures rising rapidly from late April to mid-May, suggesting El Nino conditions were developing, the WMO said. The agency said it has observed unusually warm subsurface conditions across the tropical Pacific with temperatures exceeding 6 degrees Celsius above average, creating a reservoir of heat that is driving surface warming.
Some national weather agencies have forecast the strongest El Nino, in a decade, warning of hotter, drier weather across Asia in the second half of 2026 that is likely to damage crops and food supplies as farmers already struggle with fertiliser shortages and costly fuel caused by the Iran war. However, the WMO said currently there was still uncertainty about the strength of El Nino as some models are not predicting a strong El Nino.
“The world must treat it as the urgent climate warning it is. El Nino conditions will pour fuel on the fire of a warming world,” said UN Secretary-General António Guterres, urging a shift away from fossil fuels towards renewable energy.
While there is no evidence that climate change increases the frequency or intensity of El Nino patterns, it can make associated impacts such as extreme heatwaves and heavy rainfall worse, according to the WMO.