Key facts
- A record 23 zettajoules of heat was absorbed by the world's seas last year.
- Ocean waters are hotter, higher, and less hospitable due to heat absorption.
- Sea level rise has accelerated to 4.2mm per year between 2012 and 2025.
- The global ocean has become 17% more acidic in the last 40 years.
- Marine heatwaves have plagued the Mediterranean and Black Seas.
- 84% of the world's coral reefs experienced bleaching-level heat stress from January 2023 to September 2025.
A record 23 zettajoules of heat was absorbed by the world's oceans last year, contributing to significant changes in ocean temperature, sea level, and acidity, according to the 10th edition of the Copernicus ocean state report. This addition of thermal energy is nearly 40 times greater than all the energy humanity used in the same year.
Sea levels have risen by approximately 3.8mm per year since 1999, with a faster rate of 4.2mm per year observed between 2012 and 2025. The global ocean has also become 17% more acidic over the past four decades. Oceans have absorbed about one-third of human-emitted carbon dioxide and approximately 90% of the excess heat trapped by greenhouse gas pollution.
Pierre Bahurel, director general of Mercator Ocean International, which published the report, stated that the ocean is undergoing significant and long-term transformation, evidenced by warming, rising seas, and ecosystem degradation. In Europe, which is warming twice as fast as the global average, the Mediterranean and Black Seas have experienced record marine heatwaves that persist deep below the surface and last for over a month. The Mediterranean Sea has warmed by 0.32C per decade, exacerbating marine heatwaves.
Separate Copernicus research found that extreme heat and air pollution subjected over one-third of the global population to dangerous levels of ground-level ozone pollution in the first eight months of 2026. This phenomenon, known as the 'ozone-climate penalty,' results from chemical changes due to heat and sunlight. Florian Pappenberger, director-general of the European Centre for Medium-Range Weather Forecasts, highlighted that air pollution transcends borders, with wildfire smoke, ozone, and dust traveling thousands of kilometers and affecting communities far from their origin.