The high cost of an El Niño in 2023 (2023)

Over the coming months, a vast body of warm water will slosh slowly across the tropical Pacific Ocean in the direction of South America. As it does so, it will trigger the start of a climate phenomenon that will bring dramatic shifts in weather patterns around the world.

Climate scientists are now warning there is now a 90% chance of an El Niño weather pattern taking hold through the end of this year and the first months of 2024. And they are warning it could be a strong one.

If that turns out to be the case, then the impacts could be significant. Scientists have already warned that with rising emissions and a strong El Niño there is a 66% chance the world will break through a key 1.5C global warming limit at least one year between now and 2027. But it could also bring damaging extreme weather such as heavy rainfall and flooding to communities in the US and elsewhere this winter.

"We're projecting an above 90% probability that there will be El Niño conditions through the winter," says David DeWitt, director of the US National Oceanic and Atmospheric Administration's Climate Prediction Center. "There's an 80% probability that we're going to be in El Niño in July."

The effects of this could also reverberate for some time to come – a recent study by researchers at Dartmouth College, Hanover, New Hampshire, estimates that an El Niño starting in 2023 could cost the global economy as much as $3.4tn (£2.7tn) over the following five years. And they say that following two previous very strong El Niño events in 1982-83 and 1997-98, the US gross domestic product was 3% lower half a decade later than it otherwise would have been. If an event of a similar magnitude was to happen today, it could cost the US economy $699bn (£565bn), they calculated.

El Nino: How does it affect global weather?

It is worth noting that coastal tropical countries such as Peru and Indonesia, however, suffered a 10% drop in GDP following the same El Niño events, the researchers say. They project that global economic losses will amount to $84 trillion (£68 trillion) this century as climate change increases the frequency and strength of El Niño events.

"El Niño is not simply a shock from which an economy immediately recovers. Our study shows that economic productivity in the wake of El Niño is depressed for a much longer time than simply the year after the event," says Justin Mankin, co-author of the study and assistant professor of geography at Dartmouth College.

"When we talk about an El Niño here in the United States, it means that the types of impacts that we'll see, floods and landslides, aren't typically insured against by most households and businesses," says Mankin. In California, for example, 98% of homeowners don't have flood insurance.

Other economic impacts in the US could include infrastructure damage from flooding, which would lead to supply chain disruption, and poor harvests caused by floods or drought, says Mankin.

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But should people in the US be bracing themselves for a particularly miserable winter this year if there is an arrival of El Niño? Not necessarily. While El Niño can bring intense periods of extreme weather to North America, it doesn't always do so.

During El Niño, winds that usually push warmer water in the Pacific Ocean towards its west side weaken, allowing the warmer water to drift back towards the east and spread out over a larger area of the ocean. This leads to more moisture-rich air above the warmer ocean that alters the circulation of air in the atmosphere around the world. In North America, this typically causes Canada and the northern US to have a warmer, drier winter than normal while the southern states and Gulf coast tend to get wetter conditions, says DeWitt.

What are El Niño and La Niña?

"El Niño tends to enhance the probability of above normal precipitation for the southern third of the US," says DeWitt. El Niño also typically reduces the number of hurricanes in the Atlantic Ocean, but can lead tomore hurricanes to the Pacific coast of the US. But all these effects largely depend on the strength of the El Niño that is driving them.

Southern states in the US are the most likely to experience severe impacts, including heavy rainfall and potential flash flooding, DeWitt warns. This would come after several years ofdrought following three consecutive La Niña seasons.

"Frequently what happens [during El Niño] is that when the rain comes, it comes very fast. That can causemudslides in Californiaand in other places where there have been wildfires, which can be quite devastating," says DeWitt. This is because scorched earth is able to retain less water, which can lead to dangerous runoff. The strongEl Niño events of 1997-98and 2015-16, for example, brought flooding andmudslides to California. The 1997-98 event was also associated with other unusual extreme events elsewhere in the country, such as severe ice storms in New England and deadly tornadoes in Florida.

An El Niño event in 1998 led to severe flooding in California (Credit: John Mabanglo / Getty Images)

But the changes in weather patterns brought by El Niño also brings other problems. Infectious diseases can become more prevalent in areas where conditions favour the insects and other pests that spread them. One study of the 2015-2016 El Niño event found that disease outbreaks became between 2.5%-28% more intense. There were increases in cases of West Nile virus, spread by mosquitoes, in California, while New Mexico, Arizona, Colorado, Utah and Texas also saw increase outbreaks of hantavirus pulmonary syndrome, which is mainly spread by rodents. There were even increases in the number of human cases of plague – if still only a handful of cases – in the western and southwestern states of the US.

During El Niño a lot of heat and moisture is transported from the tropics towards the poles. "When you increase the moisture at higher latitudes, it traps more thermal infrared radiation which leads to warming. This is what we call the greenhouse effect," says DeWitt.

Even a temporary breach of the 1.5C threshold due to rising emissions and this year's El Niño, as predicted by the World Meteorological Organization, could lead to widespread human suffering worldwide. According to a recent study by the University of Exeter in the UK, limiting long-term global warming to 1.5C could save billions of people from exposure to dangerous heat (average temperature of 29C or higher).

Current policies are projected to lead to 2.7C of warming globally by the end of the century, which could leave two billion people exposed to dangerous levels of heat worldwide, the authors say. Limiting warming to 1.5C would mean five times fewer people live in dangerous heat and would help prevent climate-related migration and detrimental health outcomes, including pregnancy loss and impaired brain function, says Tim Lenton, co-author of the study and director of the Global Systems Institute at the University of Exeter.

There are concerns that as carbon emissions continue to rise, future El Niño events might tip global temperatures above the 1.5C threshold more and more often.

"Every 0.1C really matters," says Lenton. "Every 0.1C of warming we can avoid, by our calculation, is saving 140 million people from exposure to unprecedented heat and the harms that could come with it."

"It's saving hundreds of millions of people from harm and that should be a huge incentive to work harder to get to zero emissions."

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