World's oceans were warmest on record, again, in 2021: study

For the sixth straight year, the world’s oceans were warmer in 2021 than at any time before, according to a new study.

Researchers found that in 2021 the upper 2,000 metres of the oceans absorbed 14 more zettajoules than in 2020. For context, the annual global energy consumption by humans is estimated to be half a zettajoule. A zettajoule is equal to one joule, a unit of energy, plus 21 zeros.

"The ocean heat content is relentlessly increasing globally, and this is a primary indicator of human-induced climate change," Kevin Trenberth, distinguished scholar at the U.S. National Center for Atmospheric Research and co-author of the study, said in a news release. "In this most recent report, we updated observations of the ocean through 2021, while also revisiting and reprocessing earlier data."

The study, published Tuesday in the peer-reviewed Advances in Atmospheric Sciences, summarizes data from the Institute of Atmospheric Physics at the Chinese Academy of Sciences and the National Centers for Environmental Information of the U.S. National Oceanic and Atmospheric Administration.

The research looked into the role of natural weather variations, such as the warming and cooling phases El Nino and La Nina, which greatly affect regional temperature changes. In spite of these phenomena, analyses indicated significant ocean warming across the globe since the 1950s.