Trouble is brewing in the sea. The Pacific Ocean has transitioned away from La Niña conditions, when a long band of cold water forms off the coast of South America, and is barreling toward its counterpart: an El Niño, when a warm band emerges instead. Scientists expect El Niño to arrive in the next few months, with a 55 percent chance of it being a particularly strong event. This shift could help raise global temperatures above 1.5 degrees Celsius, the Paris Agreement’s warming threshold, and will influence weather all over the world, potentially causing significant droughts in some places while boosting extreme rainfall in others.
The economic consequences, researchers report today, could be a $3 trillion hemorrhage over the next several years, with low-income tropical countries getting hit especially hard. Writing in the journal Science, they determined that the El Niños of 1982-83 and 1997-98 led to worldwide losses of $4.1 trillion and $5.7 trillion, respectively, which dragged on for more than five years after the climatic events had dissipated. By the end of this century, the cumulative bill for El Niños could come to $84 trillion. “There's an economic legacy of El Niño in GDP [gross domestic product] growth,” says Christopher Callahan, an Earth system scientist at Dartmouth College who coauthored the paper. “That primarily occurs in the countries in the tropics that are strongly affected by El Niño. But this effect is quite large.”
The paper adds to a growing body of research that climate change and increasingly extreme weather are going to be extraordinarily expensive, especially for developing economies. “For optimal climate policy, adaptation, and questions of climate justice, we need to know what the social and economic costs of climate change are,” says Leonie Wenz of the Potsdam Institute for Climate Impact Research, who studies climate economics but wasn’t involved in the new paper. “We find more and more evidence that the costs of warming are substantial and way bigger than previously thought and commonly assumed.”
As El Niño waters warm in the Pacific, tropical countries bear the bulk of the knock-on effects. Peru in particular tends to suffer heavy rainfall during an El Niño, which damages infrastructure and waterlogs crops. Normally, upwelling off of Peru’s coast brings up nutrients that feed fisheries, but that churning begins to slow during El Niño. In addition, marine heatwaves kill off fish, snatching away a source of income. “So you get the loss of fishing off the coast of Peru during these events, you get infrastructure being flooded, you get extreme heat,” says Callahan. “All these things sort of stack on top of one another.”
But farther to the east, El Niño can have the opposite effect, kicking off severe drought in the Amazon rainforest, which is already devastated by human development and burning. A drought could help push parts of the Amazon closer to a tipping point at which they will transform from rainforest into grassland—an ecological point of no return. The loss of trees will imperil species and lessen the Amazon’s ability to sequester carbon.
The other side of the Pacific could face drought as well. “You're going to be dry in Indonesia and Australia, and that drought can have really significant economic impacts,” says Callahan. “In the 1998 El Niño, famously, you had these massive wildfires across a lot of Southeast Asia, especially Indonesia. The drought there, combined with the overall warmer temperatures, lead to the conditions set up for huge wildfires.” Because Indonesia is home to expanses of carbon-rich peat, which is notoriously difficult to extinguish once it starts burning, wildfires there could significantly raise carbon emissions and accelerate climate change.