This year's weak or missing La Nina may indicate an accelerated timeline for climate change.
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As 2023 came to a close, scientists had hoped that a stretch of record heat that emerged across the planet might finally begin to subside this year. It seemed likely that temporary conditions, including an El Niño climate pattern that has always been known to boost average global temperatures, would give way to let Earth cool down.
That didn’t happen.
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that’s because El Niño is quickly replaced with La Niña. Under this pattern, the same strip of Pacific waters become colder than normal, creating a larger cooling effect on the planet. But La Niña hasn’t materialized as scientists predicted it would, either.
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The year 2023 is the current warmest year on record at 1.48 degrees Celsius above the preindustrial average. However, 2024 is expected to be at least
1.55 degrees, breaking the record set the year before. Last year’s record was further above the expected track of global warming than scientists had ever seen, by a margin of more than three tenths of a degree. This year, that margin is expected to be even larger.
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Compared to past years when El Niño has faded, the current conditions are unlike any seen before.
A look at sea surface temperatures following three major El Niño years — 2024, 1998 and 1983 — reveal that a La Niña-like pattern was evident in all three years, with a patch of cooler than average conditions emerging in the equatorial Pacific Ocean.
But in 2024, the patch was narrow, unimpressive and dwarfed by warmer than average seas that cover most of the planet, including parts of every ocean basin.
Known as marine heat waves, these expansive blobs of unusual oceanic heat are typically defined as seas being much warmer than average, in the highest 10 percent of historical observations, across a wide area for a prolonged period. Strong to severe marine heat waves are occurring in the Atlantic, much of the Pacific, the western and eastern Indian Ocean, and in the Mediterranean Sea.
In October, ocean temperatures at that high threshold
covered more than a third of the planet. On the other end, less than 1 percent of the planet had ocean temperatures in the lowest 10 percent of historical values.
Warm and cold ocean temperature extremes should more closely offset each other. But what’s happening is a clear demonstration that oceans, where heat accumulates fastest, are absorbing most of Earth’s energy imbalance. Warm extremes are greatly exceeding cold ones.
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“Is this just a blip, or is this actually an acceleration of the warming?” Gettelman said. “That’s the thing everyone is trying to understand right now.”
How big these changes are partly depends on how much warming occurs in the year ahead. But that is unclear because the cooling that usually follows El Niño still hasn’t arrived.
It’s possible that normal planetary variations are playing a bigger role than scientists expect and that temperatures could soon begin to drop, said Hausfather, who also works for the payments company Stripe.
Even without the cooling influence of a La Niña, a stretch under neutral conditions, with neither a La Niña nor an El Niño, should mean some decline in global average temperatures, he said.
At the same time, if this year’s unusual planetary warmth doesn’t slow down into 2025, there would be nothing to prevent the next El Niño from sending global temperatures soaring — the starting point for the next El Niño would be that much higher. Whether that happens later in 2025 remains to be seen.
But the lack of clarity isn’t a promising sign when some of
the most plausible explanations allow for the most extreme global warming scenarios, Hausfather said.
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