The Pacific Ocean is like a bathtub where warm water is sometimes turned on. When the water heats up more than usual, it's called El Niño. The warm patch can end up near the coast of South America, bringing floods to Peru and Ecuador. Or it can sit in the middle of the ocean, bringing drought to India. Previously, you could only tell what kind of El Niño it would be a month before it started. Too late to prepare.
Scientists have found a simple indicator that is visible a year in advance. In December, they look at water temperatures in two places: the western Pacific and its center. If the west is warmer than the center, the warm patch will most likely appear near South America the following year. If the west is colder than the center, the patch will be in the middle of the ocean. It's like a seesaw: whichever way it tips in December, that's the way it will swing a year later.
Why does this work? Probably because of westerly wind bursts, which move warm water differently depending on where it has already accumulated. But even without fully understanding the mechanism, the method can be used right now: farmers, water services, and emergency responders will be able to prepare for floods or droughts a year in advance, not just a month. And then the Pacific will no longer be a surprise.
In October 2022, the temperature difference was +1.6°C, pointing to a likely EP El Niño if one began in 2023. And indeed, the 2023–2024 event was classified as eastern Pacific.
In Kim Stanley Robinson's novel 'Forty Signs of Rain', climate scientists try to predict abrupt climate changes, and the accuracy of long-term forecasts becomes a matter of life and death. This work on an early precursor for El Niño type resonates with that theme: a small but reliable gain in lead time can change how we prepare for a disaster.