The climate pattern known as El Niño is heading for the exit, after a year when it helped drive global temperatures to new records. Forecasters at the National Oceanic and Atmospheric Administration (NOAA) say conditions will likely switch to a La Niña pattern by the end of the summer.
El Niño is marked by warmer than normal ocean temperatures in the Eastern Pacific, where large amounts of heat are released to the atmosphere. It's why El Niño years are typically hotter than average. Paired with the warming caused by heat-trapping gasses from burning fossil fuels, 2023 ranked as the hottest year recorded.
Scientists say it's a stark warning that the combination of climate change and El Niño could set the stage for even worse heat waves, floods and droughts in the future.
"It wasn't surprising that 2023 was the warmest year on record," says Tom DiLiberto, climate scientist at NOAA. "What was surprising was just how high temperatures got and how much they smashed the records by."
The El Niño and La Niña patterns, which are natural fluctuations, also affect rainfall around the globe. In the Southwestern U.S., El Niño years are typically wetter, while La Niña years are drier, exacerbating drought conditions.
"What it ends up doing is shifting where the jet stream sets up across the mid-latitudes where we live," DiLiberto says. "The jet stream acts like this storm highway and if you change where the jet stream goes, you change where the storms go."
The current shift to La Niña could make the Atlantic hurricane season worse this year. Ocean temperatures are already warm there, which can help fuel the growth of storms. La Niña also typically acts like a "supporting character" by reducing the wind shear in the atmosphere. Less wind shear makes it easier for hurricanes to strengthen.
The departure of El Niño doesn't mean 2024 will necessarily end the recent streak of record-breaking temperatures, with the last eight years having been the hottest on record.
"Even while we shift into La Niña, we don't see the impacts of that on global temperatures until later in the year," DiLiberto says. "We should expect 2024 to probably be in the top five of warmest years on record."
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