Copernicus report details accelerating ocean changes

A new Copernicus assessment says the world’s oceans absorbed about 23 zettajoules of heat in 2025, roughly 40 times the energy used globally that year, as warming, rising seas and ecosystem shifts continue. The tenth annual Copernicus Ocean State Report, produced by Mercator Ocean International with contributions from more than 100 scientists, draws on more than four decades of observations to describe changes across the ocean. The report estimates that global mean sea level rose about 3.8 millimeters per year from 1999 to 2025, accelerating to about 4.2 millimeters annually from 2012 to 2025. It also says 84% of the world’s coral reefs experienced bleaching-level heat stress between January 2023 and September 2025. The report estimates ocean acidity has increased about 17%, although the supplied accounts describe different baselines for that figure, so its precise time period is unclear. The assessment describes the ocean as a major absorber of excess heat in the climate system. It says the pace of ocean warming has doubled over the past two decades, while sea surface temperatures reached records in 2023, 2024 and 2025.