For the sixth year in a row, the ocean’s heat content is record-breaking.

Researchers write that in the magazine Advances in Atmospheric Sciences. They are based on data from Chinese and American research institutes that have been monitoring and analyzing the heat content of the oceans (see box below) since the 1950s.

Heat content of the oceans
The earth is warming. And nowhere is that felt more clearly than in the oceans. “More than 90 percent of the heat from global warming is stored in the oceans,” said study researcher Lijing Cheng. “And that causes warming of the oceans.” Scientists have been keeping a close eye on ocean warming for decades by taking temperature measurements in the upper water layer (up to about 2000 meters deep), because the lion’s share of the heat is absorbed at the surface. The total amount of heat that the oceans absorb is called the heat content of the oceans and expressed in zettajoules.

Not so long ago – in 2020 – the top 2000 meters of the oceans worldwide recorded the highest temperature since 1955. In that year, the oceans absorbed 20 zettajoules. That amount of heat is comparable to the heat released when 630 billion hair dryers blow 24 hours a day for a year. But that 2020 record didn’t last long. Because the most recent data now show that the oceans will absorb another 14 zettajoules in 2021 than in 2020. “The heat content of the oceans continues to increase worldwide,” said researcher Kevin Trenberth.

Climate change

And that can only be explained in one way: by anthropogenic – or man-induced – climate change. Because while natural variations – such as La Niña and El Niño – can also leave their mark on the temperature and heat content of an ocean, they cannot possibly explain the significant ocean warming that researchers worldwide and for years in a row have seen. “Our study shows that ocean warming is the result of human-related changes in atmospheric composition,” Cheng said.

Effects

And that enormous absorption of heat will not affect the oceans. “As the ocean warms, the water expands and sea levels rise. And warmer oceans also generate more powerful storms and hurricanes.” In addition, heat waves occur more frequently in the sea, which have far-reaching consequences for the organisms that live in the ocean waters.

In addition, there is also a feedback process, in which the warming of the ocean as a result of climate change also influences climate change itself. “In addition to heat, the ocean currently absorbs 20 to 30 percent of our CO2 emissions,” Cheng said. “But ocean warming is making the ocean less efficient at absorbing carbon and leaving more carbon dioxide in the atmosphere.” It is another good reason for scientists to closely monitor the warming of the oceans and to clarify the link between that warming and carbon absorption. Because only in this way can they better predict how the atmosphere and oceans and therefore also our climate will respond to our future (reduced) emissions. “Until we get to net zero emissions, warming will continue and oceans’ heat content will continue to break records,” said researcher Michael Mann. “We need to be more aware of the oceans and understand them better to tackle climate change.”

2021 was hot
The news that the heat content of the oceans has reached a new record comes a day after the news that 2021 was the fifth warmest year on record. The global average temperature in 2021 was 1.1-1.2 degrees Celsius higher than in the pre-industrial period between 1850 and 1900. Now that the figures for 2021 are known and processed, it appears that the 7 warmest years ever measured also included the 7 most recent years.