The possibility of a record-strength El Niño climate pattern this year is raising alarm among climate scientists, who are watching Pacific Ocean temperatures closely. Even a weaker El Niño on top of human-driven global warming could have sweeping consequences for the climate, ranging from coral reef bleaching in Australia to flooding in East Africa, and also cost the global economy trillions of dollars.
“We have enough climate madness going on elsewhere without adding an El Niño to it,” says at the University of Colorado Boulder.
El Niño, which occurs when sea surface temperatures in the eastern tropical Pacific Ocean rise 0.5°C above the long term average, arrived around two months earlier than usual in May, following an unusual streak of three La Niña years. Historically, this cycle of surface temperatures – known as the El Niño Southern Oscillation (ENSO) – shifts between the warm El Niño state and the cool La Niña state every two to seven years, with neutral years in between.
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In the years since the last strong El Niño in 2015-16, the Pacific has accumulated record amounts of heat, both from global warming and from natural oscillations in the ocean, says at the US National Oceanic and Atmospheric Administration (NOAA). The switch to El Niño means much of that heat comes pouring back out into the atmosphere. “The lid is off on the ocean,” he says.
All that heat has already begun to have some influence on global weather, with predictions that it could make 2024 the first year global average temperatures surpass 1.5°C of warming. But the new El Niño is still relatively weak. The extent of its influence, and the severity of the consequences for every continent, largely depends on how much stronger it gets.
According to the latest from NOAA, there is a greater than 90 per cent chance that this El Niño continues through to February next year. Its strength remains more uncertain, but at NOAA says there is a greater than 50 per cent chance it will be in the “upper echelon of strong category”, and a 20 per cent chance it will rival the powerful El Niños of 1997-98 and 2015-16. “We could be in record territory,” says Rosencrans.
The specific outcome depends on how high the sea surface temperature gets in the tropical Pacific Ocean, as well as how closely the atmosphere responds to that warming. “ENSO is like a dance between the ocean and the atmosphere,” says McPhaden. “Both partners need to be dancing to the same tune.”
Generally, warmer waters weaken the easterly trade winds, which leads to more warming in the ocean. But despite the record amount of heat stored in the ocean, the winds haven’t slowed much yet, says McPhaden. “There are lots of things that can dither that signal,” he says.
Counterintuitively, one possible reason for El Niño’s sluggish development so far might be due to climate change. DiNezio thinks warm waters in the western Pacific could be offsetting the impact of warmer eastern waters on the trade winds.
Whatever the cause, the longer it takes El Niño to strengthen, the less likely it is that it will reach historic strength this year. We should know by September, says Rosencrans. “There’s not a lot of months left for this event to grow into a monster,” says DiNezio.
While a strong event could be disastrous, even a relatively weak El Niño risks creating more extreme weather, says McPhaden. Due to human-driven global warming, “what might be a heavy El Niño rain now becomes an extreme El Niño rain,” he says. The same is true of drought and heat.
El Niño could also have consequences for ecosystems, such as causing coral bleaching in the Great Barrier Reef due to warmer waters. The Amazon is another worry. at Yale University is concerned drought conditions driven by El Niño on top of climate change and deforestation could make for an especially bad fire season there. “Scientists have been ringing the bell for months,” he says.
That said, El Niño can have beneficial effects. For instance, it could bring much-needed rain to the Horn of Africa, where 32 million people have been made food insecure by crop failures due to an unprecedented drought and years of conflict, says at the UN Food and Agriculture Organization. But too much rain could mean flooding, and to other parts of East Africa.
Overall, the coming El Niño is likely to have a negative impact, says at Dartmouth College in New Hampshire. He and his colleagues have found the economic impacts of the climate pattern can be staggering, especially in poorer countries in the tropics. They estimate the very strong El Niño of 1997-98 cost the global economy $5.7 trillion at the time.
Depending on how much carbon dioxide we continue to emit, Callahan’s team says the impacts of El Niño in the 21st century could cause as much as a 5 per cent reduction in global economic output. With global warming in the mix, the potential consequences of an El Niño of any strength are much more volatile, warns Callahan.
