The warmth of the world’s oceans hit a record. Again. A new analysis, published Tuesday in the journal Advances in Atmospheric Sciencesshowed that oceans contained the most heat energy in 2021 since measurements began six decades ago — accelerating at a rate only possible because of human-emitted greenhouse gases.

Since the late 1980s, Earth’s oceans warmed at a rate eight times faster than the preceding decades.

“When you have this long-term upward trend, you’re getting records broken almost every year and it’s this monotonous increase,” said John Abraham, a co-author of the study and a professor at the University of St. Thomas in Minnesota. “We’ve built up so much greenhouse gas that the oceans have begun to take in an increasing amount of heat compared to what they previously were.”

The team analyzed data from a worldwide network of buoys in seven ocean basins. Overall, it found that the upper 2,000 meters of Earth’s oceans absorbed more than 227 excess zettajoules of energy compared with the 1981-2010 average. Last year broke the previous record set in 2020 by at least 14 zettajoules.

Additionally, the team found that ocean waters have been steadily warming since 1958, with each decade warmer than the last. Warming significantly increased in the 1980s. Over recent decades, portions of the Atlantic Ocean, Pacific Ocean and Indian Ocean have warmed the most.

Through climate model experiments, the researchers showed that the warming pattern since 1979 was mainly attributed to increased anthropogenic greenhouse gas concentrations. The longer-term trends brought on by human activity are also overpowering short-term climate fluctuations, such as La Niña and El Niño, which can have regional effects.

“Ocean stores more than 90% of the Earth’s net heat gain due to greenhouse gases, thus ocean warming is a fundamental indicator of the climate change,” Lijing Cheng, lead author and associate professor at the Chinese Academy of Sciences, wrote in an email. “The record ocean warming in 2021 is strong evidence that global warming continues.”

The map shows the ocean heat content anomaly in 2021 relative to the 1981-2010 baseline. (Cheng, et al. (2021))

The 2021 record isn’t surprising, said ocean researcher Linda Rasmussen, who was not involved in the study. Mainly, Rasmussen said, because the major driver of ocean warming has not changed.