El Niño is here — how bad will it be?

El Niño is here — how bad will it be?

Floods are more likely in some regions during an El Niño phase.Credit: Elias Agustin/EPA/Shutterstock

Hot on the heels of a three-year La Niña global weather pattern, the planet seems to be headed into what could be a strong El Niño event with worldwide consequences.

This El Niño might turn out to be a moderate one. But some scientists fear it could be powerful, and meteorologists and emergency-preparedness officials are bracing for potential floods and droughts, and the possibility that planetary temperatures could reach record highs. The World Health Organization has warned that the new El Niño could stoke the spread of mosquito-borne diseases such as Zika and chikungunya. Already an El Niño pattern of warm ocean waters has been implicated in Peru’s severe outbreak of the viral disease dengue.

Creeping warmth

During an El Niño event, which repeats around every two to seven years, trade winds slacken above the tropical Pacific Ocean, allowing warmer waters to travel east across the equatorial Pacific.

The US National Oceanographic and Atmospheric Administration (NOAA) declared on 8 June that an El Niño had arrived and was expected to strengthen gradually in the coming months. Other meteorological agencies have not yet officially declared an El Niño, because they rely on different indices to define its start — but many have said it should soon get under way. Australia’s Bureau of Meteorology, for instance, issued an alert on 6 June that El Niño is likely to develop.

El Niño conditions arose just a few months after its opposite pattern, La Niña, waned in the early months of 2023. “It was a quick transition,” says Emily Becker, a climate scientist at the University of Miami in Florida. “But this is not uncommon when La Niña is followed by El Niño.” That La Niña lasted for a rare three years.

So far the nascent El Niño seems on track to be a moderate to strong event, on the basis of how much warming has been observed in the waters of the east-central tropical Pacific. “I think this one is going to be pretty big,” says Mickey Glantz, a social scientist at the University of Colorado Boulder who studies the impacts of El Niño.

El Niño warms some regions of the planet more than usual. That means that the growing El Niño, if it becomes severe enough, could also help to push global temperatures to record or near-record highs in 2024. The hottest year on record was 2016, thanks in part to a powerful El Niño.

Drought here, flooding there

Meanwhile, officials are preparing for a range of impacts, including drought in Australia and parts of southeast Asia, plus increased rainfall in regions such as the Horn of Africa and Central Asia. Heavy rains can flood farmland, reducing production, whereas drought causes crops to suffer. In Indonesia, which is likely to experience drier conditions than normal, the government recently signed an agreement with India to be able to import rice in an emergency.

Even in its infancy, this El Niño is affecting human health. El Niño-like conditions off the coasts of Peru and Ecuador brought torrential rains to the region earlier this year. The resulting floods, combined with rains from a tropical cyclone in March, allowed more mosquitoes to breed and transmit viral diseases including dengue. In Peru, more than 150 people have died in this year’s dengue outbreak.

That’s not all because of El Niño: many factors, including lack of mosquito control, can affect the magnitude of an outbreak. “It’s not just about that one health problem,” says Ivan Ramírez, a geographer at the University of Colorado Denver. “It’s that that one health problem is part of a broader context.” Multiple infectious-disease outbreaks can combine with recurrent hazards from El Niño to create a complex situation for public-health experts to manage, he says.

Assaf Anyamba, a geographer at Oak Ridge National Laboratory in Tennessee, has his eye this year on cases of diseases such as dengue and chikungunya in southeast Asia, where El Niño’s impacts can be particularly strong. He is also watching eastern Africa, where El Niños are associated with outbreaks of Rift Valley fever and other disease. During the last big El Niño, in 2015–16, Anyamba and his colleagues chronicled disease outbreaks around the globe in areas that were most affected by it1. “The whole idea is that El Niño amplifies or depresses conditions in different locations,” he says.

All of these impacts are playing out against the backdrop of a warming planet. “Whether or not this El Niño is a strong one, a warmer atmosphere can exacerbate many of the effects,” says Nandini Ramesh, a climate scientist at the Australia national research organization CSIRO in Sydney. “Heatwaves, wildfires or tropical cyclones, for example, are all more intense and damaging in a warming world.”

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