Last year was one of the hottest on record, even though a major recurring climate pattern was cooling the Earth. But this year, changes to that climate pattern could make things even hotter.
For all of 2022, El Niño Southern Oscillation, or ENSO, was in its cool phase. During this pattern, known as La Niña, strong winds blow warm water on the surface of the Pacific Ocean from South America to Indonesia. As the waters moves westward, cooler waters rise to the surface near the coast of South America, influencing weather around the world and keeping a lid on global average temperatures.
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This La Niña has lasted for three straight years — a rare “triple-dip” that’s only occurred two other times since 1950. But later this year, it looks like the spell might end.
That doesn’t mean we’ll move into an El Niño — which are known for their tendency to boost global temperatures — right away. From the period between February and April, there is a 71 percent chance that the El Niño Southern Oscillation will move into its neutral phase, which means neither La Niña nor El Niño conditions are present, according to the National Weather Service. But this shift could still mean the world gets even hotter.
“When we emerge from La Niña, we’re likely to see it get warmer, unfortunately,” said Max Holmes, president of the Falmouth-based research organization Woodwell Climate Research Center.
By June, El Niño could emerge, according to the latest models from the Australian Bureau of Meteorology. That could heat things up even further, making extreme heat waves, drought, and fires more likely.
2022 brought the longest and most widespread heat wave in world history to China, and a record-shattering heat wave made 160 times more likely by the climate crisis to the United Kingdom. Meanwhile, a heat dome in the United States brought triple-digit temperatures to the Southwest, the Great Plains, and the East Coast — including New England — last year. This coming year, heat could be even more extreme.
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“I shudder to think what the next major El Niño ... will do,” Jennifer Francis, acting deputy director of Woodwell Climate Research Center, said.
The El Niño Southern Oscillation is far from the only factor in how hot a given year will be. There’s always some amount of random variance in weather patterns. And crucially, amid the climate crisis — driven by global greenhouse gas pollution — temperatures are trending higher overall.
“The overall pattern of global temperatures is upward,” said Holmes. “Overall we’re seeing warming.”
For instance, though 2022 wasn’t the single hottest year on record, it was certainly in the top ten — though it’s not yet clear exactly where it will fall on that list — despite the La Niña. And though the hottest year on record, 2016, came during a strong El Niño phase, temperatures in 2020 actually tied that year, even though at that point the current La Niña pattern was beginning. Still, shifts in the El Niño Southern Oscillation can cause temperatures to be around a tenth of a degree Celsius higher.
“In terms of globally-averaged surface temperatures, La Niñas and El Niños have a modest but noticeable effect ... enough so that, within any individual decade, the coldest year will usually be a La Niña and the warmest will be an El Niño, and usually record-setting years are El Niños,” said Matthew Barlow, a professor of climate science at the University of Massachusetts Lowell. “So next year, without a La Niña, would be a bit warmer than it would have otherwise been.
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That means next year has a good chance of being the one of the hottest, or even the hottest, in recorded history.
Scientists have for years been wearily eyeing a global average temperature rise of 1.5 degrees Celsius (2.7 degrees Fahrenheit) above pre-industrial levels. Crossing that benchmark would mean blowing past the more ambitious goals of the Paris Climate Accord and would usher in catastrophic levels of global warming. 2023 could push us closer to it — at least temporarily — especially if an El Niño occurs.
Under the Paris Agreement, crossing the 1.5 degree Celsius mark is measured over a 30-year average, rather than just a single year. But even briefly flitting above that threshold would take us closer to exceeding the limit.
In New England, however, El Niño’s effects are much less clear. In the winter, its influence on the region tends to be “weak and variable,” said Francis, so don’t expect any major shifts. And in the summer, El Niños tend to yield less active Atlantic hurricane seasons, making it less likely that New England will be hit by a tropical storm.
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Dharna Noor can be reached at dharna.noor@globe.com. Follow her on Twitter @dharnanoor.