BEIJING (XINHUA) - Last year was the hottest for the world's oceans in recorded human history, according to a study led by an international team of scientists who track the data.

Published on Tuesday (Jan 11) in the journal Advances In Atmospheric Sciences, the study was conducted by 23 researchers from 14 institutes in China, the United States and Italy.

They found that the upper 2,000m in all oceans absorbed a greater amount of heat in 2021 than the previous record set just the year before, equal to 145 times the world electricity generation in 2020.

As more than 90 per cent of the excess heat due to global warming is absorbed by the oceans, ocean heat content is a primary indicator of global warming, said Dr Kevin Trenberth, a scientist with the US National Centre for Atmospheric Research and co-author of the study.

Apart from absorbing heat, the oceans currently absorb 20 per cent to 30 per cent of human carbon dioxide (CO2) emissions, leading to ocean acidification.

However, ocean warming reduced the efficiency of oceanic carbon uptake and left more CO2 in the air, said Dr Cheng Lijing, lead paper author and associate professor at the Institute of Atmospheric Physics (IAP) under the Chinese Academy of Sciences.

"Monitoring and understanding the heat and carbon coupling in the future are important to track climate change mitigation goals," Dr Cheng said, calling for more attention to be paid to the oceans as many countries pledge to achieve carbon neutrality in the coming decades.

"As oceans warm, the water expands and sea level rises. Warmer oceans also supercharge weather systems, creating more powerful storms and hurricanes, as well as increasing precipitation and flood risk," Dr Cheng added.

"The oceans are absorbing most of the heating from human carbon emissions," said Pennsylvania State University professor Michael Mann, an author of the paper.

"Until we reach net-zero emissions, that heating will continue, and we'll continue to break ocean heat content records, as we did this year. Better awareness and understanding of the oceans are a basis for the actions to combat climate change."

Researchers also shared data recorded by China's IAP and the US National Oceanic and Atmospheric Administration in the study, which analysed observations of ocean heat content and its impact dating from the 1950s.