Record levels of heat were absorbed last year by Earth’s seas, which have been warming year-on-year for the past decade

“Astounding” ocean temperatures in 2023 supercharged “freak” weather around the world as the climate crisis continued to intensify, new data has revealed.

The oceans absorb 90% of the heat trapped by the carbon emissions from the burning of fossil fuels, making it the clearest indicator of global heating. Record levels of heat were taken up by the oceans in 2023, scientists said, and the data showed that for the past decade the oceans have been hotter every year than the year before.

The heat also led to record levels of stratification in the oceans, where warm water ponding on the surface reduces the mixing with deeper waters. This cuts the amount of oxygen in the oceans, threatening marine life, and also reduces the amount of carbon dioxide and heat the seas can take up in the future.

Reliable ocean temperature measurements stretch back to 1940 but it is likely the oceans are now at their hottest for 1,000 years and heating faster than at any time in the past 2,000 years.