Copernicus ocean state report warns the seas are changing fast

The world's oceans are warming at what scientists describe as an alarming pace, and a major new assessment says the consequences are arriving faster than the world is prepared to handle. The tenth Copernicus ocean state report, published September 30 by Mercator Ocean International through the European Union's Copernicus Marine Service, draws on more than four decades of data from satellites, buoys and sensors, compiled by more than one hundred international scientists. According to reporting by CNN, the authors call this edition the starkest warning yet about the profound changes sweeping the planet's oceans.

The headline finding is heat. This ocean state report says the global ocean absorbed an additional 23 zettajoules of heat last year, a new record for the ninth year running. A zettajoule is a billion trillion joules, so the scale is hard to picture, and scientists reach for comparisons to make it tangible: that total equals the energy of a dozen Hiroshima-scale explosions going off every second for a full year, or roughly forty times the total energy the world consumed that same year. Oceans now absorb about nine-tenths of the excess heat produced by burning fossil fuels, and the rate of ocean warming has doubled over the past two decades.

On top of that long-term trend sits a monster El Niño, the natural pattern that warms waters along the equator in the Pacific. The ocean state report says it is on track to become the most intense on record, piling more pressure onto marine systems already stretched by warming. The pattern does not drive the long-term trend, the scientists note; it stacks on top of it, adding pressure to an ocean already absorbing record heat. Sea surface temperatures set new record highs in 2023, 2024 and again in 2026, a streak the scientists tie to accelerating heat uptake.

Seas are rising faster, and turning more acidic

The extra heat is pushing seas higher and changing their chemistry. The global mean sea level rose by an average of 3.8 millimetres a year between 1999 and 2025, accelerating to 4.2 millimetres a year across the most recent fourteen-year stretch, the ocean state report states. The ocean has also become roughly 17 percent more acidic since 1985, a shift that threatens shellfish, coral reefs and the food webs around them. That heat drives marine heatwaves and fuels stronger and more destructive storms. It also damages marine life, lifting seas both by melting ice and because warmer water takes up more space.

The damage is already reaching coastal livelihoods. Off Zanzibar, seaweed farmer Fatuma Makame has moved her crop farther from shore because warmer shallow water leaves it vulnerable to poor growth and disease, the Inter Press Service reports. Farming deeper water takes a boat, equipment and new skills, so Makame joined a cooperative, Mwani Zanzibar Mamas, that pooled resources to buy both, and her harvests have since grown larger and more reliable. Her decision is becoming familiar along Zanzibar's coast: move the crop, if they can afford to, or keep planting where it has become harder to grow. The ocean state report's global measurements do not describe the water at any single farm, but Zanzibar's seaweed farmers have contended with warmer water for years.

What scientists say has to happen next

Pierre Bahurel, director-general of Mercator Ocean International, said in a statement that the ocean is transforming before the public's eyes, with warming, rising seas and ecosystem degradation forming interconnected signs of significant and long-term change, and that societies must build permanent capacity to anticipate the transformation. The report's authors point to sustained monitoring, the satellites, buoys and sensors behind decades of continuous data, as the way to spot changes in time to respond. That infrastructure is what makes the report itself possible: decades of observation are the foundation every edition is built on. Without permanent observation capacity, the authors say, the next ocean state report would be flying blind.

The authors say permanent ocean observation lets societies see the next changes coming in time to respond. With a record-strength El Niño bearing down on the hottest oceans ever measured, the next edition of this ocean state report may carry an even starker story. The data, the scientists say, all point the same direction.

Sources: CNN; Inter Press Service