Brussels: The world’s oceans absorbed a record 23 zettajoules of heat last year as rising sea levels, acidification and marine heatwaves continued to alter ocean conditions.
The figure is almost 40 times the total energy used by humanity during the year. The findings come from the 10th edition of the Copernicus Ocean State Report, which tracks major changes across the world’s oceans and European seas. The report provides a broad assessment of the ocean’s changing physical and environmental conditions.
Sea levels have risen by about 3.8 mm per year since 1999. The rate increased to 4.2 mm per year between 2012 and 2025. Ocean acidity also increased significantly, with the global ocean becoming 17 percent more acidic over the past 40 years.
Oceans absorbed about 90 percent of the additional heat trapped in the Earth’s climate system by greenhouse gas pollution. The seas also taken in about one-third of the carbon dioxide released by human activity. A zettajoule is equal to 1 billion trillion joules.
The changes was particularly visible in European waters. The Mediterranean and Black Seas experiences record marine heatwaves. High temperatures also extended deep below the surface. The Mediterranean warms by 0.32C per decade, while parts of the region recorded marine heatwaves lasting more than a month.
Scientists also documented growing damage to marine ecosystems. Between January 2023 and September 2025, 84 percent of the world’s coral reefs experienced heat stress at levels associated with bleaching. Almost 5 percent of the ocean also recorded persistent changes in phytoplankton growth patterns over the past 30 years.
Antarctica also faced serious consequences as well. Four emperor penguin colonies recorded complete breeding failures in 2022 during periods of exceptionally low sea ice. The wider climate picture also included worsening air-quality risks.
The Copernicus research found that more than one-third of the global population was exposed to dangerous levels of ground-level ozone during 2026. Only 5 percent of the world’s population experienced ozone levels considered good under World Health Organization guidelines during the first 8 months of the year.
The findings underline the growing links between ocean warming, climate change and environmental health. Copernicus continues to monitor these changes through observations, modelling and long-term ocean indicators.
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