2020 was warmest year on record for Earth’s oceans

Ocean waters may have absorbed enough heat to boil 1.3 billion kettles of water

Earth’s oceans are heating up. Warmer waters melt more ice off Greenland and Antarctica, raising sea levels. This warmng also supercharges tropical storms.

NASA/Saskia Madlener

Pandemic stay-at-home orders may have curbed some greenhouse gas emissions last year. But the world continued to warm.

The total amount of heat stored in the upper oceans in 2020 was higher than any other year on record dating back to the 1950s. Researchers reported the findings online January 13 in Advances in Atmospheric Sciences. The three next warmest years on record for the world’s oceans were 2019, 2017 and 2018.

Tracking ocean temperature is important. Warmer waters melt more ice off Greenland and Antarctica. That raises sea levels. Warmer seawater also makes tropical storms stronger.

Kevin Trenberth is a climate scientist who lives in New Zealand. He works for the U.S. National Center for Atmospheric Research. He was part of a team that collected water temperature data from around the globe. They used those data to estimate the total heat energy stored in the upper 2,000 meters (6,500 feet) of Earth’s oceans.

Those upper-ocean waters held 234 sextillion joules more heat energy in 2020 than the annual average from 1981 to 2010. How big is that? It’s 234 followed by 21 zeros. And heat-energy storage was up about 20 sextillion joules from 2019, the team found. The finding suggests that in 2020 alone, the oceans absorbed enough heat to boil some 1.3 billion kettles of water.

But that estimate may be too high, Trenberth warns. So his team crunched the data using a second method. The jump from 2019 to 2020 could be as low as 1 sextillion joules, the team found. That’s still an extra 65 million kettles brought to boil.

a graph showing how much heat Earth's oceans stored from 1959 to 2020
In 2020, Earth’s oceans stored more heat than any other year on record, scientists say. Upper ocean waters contained 234 sextillion joules, more heat energy than the annual average (represented as zero on the y-axis) from 1981 to 2010. T. Tibbitts

Maria Temming is the staff reporter for physical sciences, covering everything from chemistry to computer science and cosmology. She has bachelor's degrees in physics and English, and a master's in science writing.

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