On 30 September 2026, the Copernicus Marine Service released the 10th edition of the Ocean State Report (OSR10). It examined long-term changes in the global ocean, including ocean warming, sea-level rise, marine heatwaves, biodiversity, and changes in marine ecosystems. It also highlighted record marine heatwave activity in the Mediterranean, with 2024 recording the highest number of marine heatwave days in the past two decades.
The Copernicus Marine Service is the marine component of the European Union’s Copernicus Earth Observation Programme, implemented by Mercator Ocean International in France. It provides free, science-based information on the global ocean and European regional seas, covering ocean temperature, sea level, currents, sea ice, marine ecosystems, and other indicators to support monitoring, research, policy and decision-making.
1. Consistently changing ocean
Across its 10 editions, the Ocean State Report has progressively documented long-term changes in the global ocean and European regional seas, using observations, satellite data, and ocean models. The recurring effects are ocean warming, rising sea levels, changing sea ice, acidification, and increasing extreme events such as marine heatwaves. The significance of OSR10 is not only what happened in the latest year but also how the evidence accumulated over the decade shows that ocean change is persistent and interconnected with ecosystems, societies, and economies.
2. Ocean warming is accelerating; marine ecosystems are being reshaped
The report finds that the global ocean continues to warm, with 2025 recording a record in ocean heat content. For example, at a regional level the Mediterranean Sea-surface temperature increased at an average rate of 0.032 degree Celsius per year between 1982 and 2024, while the 2024 annual mean temperature was 1.23 degrees Celsius above the 1982–2024 average. The Eastern Mediterranean experienced an even higher warming rate of 0.034 degrees Celsius per year.
The report says that the changes in temperature can alter species distribution, marine biological cycles, and ecosystem conditions, while increasing exposure to extreme events. The report, therefore, presents sustained ocean warming as a long-term transformation with implications extending from marine ecosystems to coastal communities and maritime activities.
3. Marine heatwaves are increasing; more pressure on the European seas
The report records a significant increase in marine heatwave activity in European regional seas. In the Mediterranean, 2024 recorded more marine heatwave days than any other year during the previous two decades. The Mediterranean experienced 214 marine heatwave days in 2024, compared with 153 days in 2023. The Eastern Mediterranean recorded 244 days under the same method, with some locations experiencing marine heatwaves for up to 350 days.
The report highlights that marine heatwaves create cumulative thermal stress for marine systems and can intensify the effects of long-term ocean warming. They can also affect fisheries, aquaculture, and tourism, making marine heatwaves an environmental as well as socioeconomic concern for coastal regions.
4. Arctic changes are accelerating; environmental and coastal risks are widening
The report identifies the polar oceans as among the most rapidly changing components of the climate system. It notes that the polar oceans cover around 20 per cent of the global ocean surface but have a disproportionate influence on the Earth system because they absorb and store large amounts of heat and carbon and influence global ocean circulation. OSR10 documents amplified warming, sea-ice loss and compound changes affecting Arctic coastal environments.
The report highlights that changes in the polar ocean can influence climate, sea level, and weather beyond the high latitudes, while simultaneously affecting Arctic ecosystems and communities. The report, therefore, connects physical changes in the Arctic with wider environmental and societal consequences and emphasises the need for coordinated responses involving climate, biodiversity and ocean governance.
5. Coastal communities are facing growing and uneven risks from ocean change
The report highlights that changing ocean conditions are creating growing and uneven risks for coastal communities worldwide. Rising sea levels increase the exposure of coastal populations to coastal flooding, erosion and other hazards, while ocean warming and acidification place additional pressure on marine ecosystems that support livelihoods and food security.
The impacts are particularly significant in Small Island Developing States (SIDS), coral reef regions and polar areas, where communities often have a strong dependence on marine resources while facing high exposure to environmental change. In coral reef regions, changes in ocean temperature and increasing acidification can affect reef ecosystems and the services they provide to coastal populations. For SIDS, rising sea levels pose concerns for low-lying coastal areas, settlements, and livelihoods. In polar regions, changes in sea ice and ocean conditions can affect ecosystems and communities dependent on marine resources.
The report presents ocean change as a community-level concern, with risks distributed unevenly across regions. It highlights the importance of understanding local vulnerabilities and strengthening responses that connect ocean, climate, ecosystem and coastal governance.
6. Ocean monitoring is strengthening climate adaptation and decision-making
The report highlights the growing importance of continuous ocean observation, forecasting, and marine information services. By combining satellite observations, in-situ measurements, ocean modelling and long-term datasets, Copernicus Marine provides information on ocean temperature, sea level, currents, sea ice and marine ecosystems. These observations help identify both gradual changes and extreme events across the global ocean and European regional seas.
The report highlights that ocean observation is increasingly becoming a tool for governance and climate adaptation rather than remaining only a scientific exercise. Timely and accessible ocean information can support early-warning systems, coastal planning, fisheries management, maritime activities, and disaster preparedness. Therefore, the report underlines the importance of sustained monitoring and translating scientific ocean data into usable information for governments, communities, and maritime sectors as ocean-related risks intensify.
