Taking the Lid Off

If you put a lid on a pot of boiling water, most of the heat stays inside the pot. But when you take the lid off, a lot of heat escapes, warming the air around the pot.

The same thing has been happening in the Pacific Ocean. For several years, La Niña acted as a lid, trapping a lot of heat in the ocean. Then El Niño came along and took the lid off. That released huge amounts of heat into the atmosphere, helping to produce the hottest year ever recorded.

From 2020 to 2023, there was a sequence of La Niñas-periods of especially cool surface waters in the eastern Pacific. They trapped the heat in the deeper ocean. The La Niñas were followed by a moderately strong El Niño-especially warm surface waters. That took the lid off the trapped heat.

Research has shown that, from July 2023 through June 2024, the average global temperature was about two-thirds of a degree Fahrenheit higher than during the previous 12 months. That’s the largest single-year jump seen so far. Almost all of that rise was driven by the higher ocean surface temperatures produced by the transition from three years of La Niña to El Niño.

Not all oceans contributed equally to the increase. Most of the heat came from tropical regions. The tropical Pacific Ocean, the Indian Ocean, and the tropical North Atlantic Ocean accounted for 80 percent of the bump. In all, they contributed about half a degree Fahrenheit to the average temperature around the entire planet.

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