Copernicus Ocean State Report finds ocean warming rate has doubled in 20 years

The world's oceans are warming at an accelerating pace, with knock-on effects for sea levels, marine heatwaves, sea ice and coastal communities, according to the 10th Copernicus Ocean State Report, published on September 30, 2026. The report was produced by Mercator Ocean International with contributions from 125 scientists and is funded by the European Commission.

CNN, reporting on the release, said the rate of ocean warming has doubled over the past 20 years and that sea surface temperatures reached record highs in 2023, 2024 and 2026.

Record heat uptake

According to the Copernicus press release, the ocean absorbed an additional 23 zettajoules of heat in 2025, roughly 40 times the energy the whole world consumed that year. CNN put the same figure in other terms: the equivalent of 12 Hiroshima bombs detonating every second for a year. Global oceans absorb roughly 90 percent of the excess heat produced by burning fossil fuels, CNN reported.

The report draws on more than four decades of satellite, buoy and other sensor data.

Rising and more acidic seas

Global mean sea level rose by 3.8 millimeters per year (plus or minus 0.3) between 1999 and 2025, and the rate accelerated to 4.2 millimeters per year between 2012 and 2025, according to Copernicus. The ocean became about 17 percent more acidic between 1985 and 2025.

Small island developing states are especially exposed. The report finds that 65 percent of their combined Exclusive Economic Zone area has seen accelerating sea level rise since 1999, and nearly 28 percent contains vulnerable or critically endangered coral reefs.

Extremes and the Arctic

The report documents a series of regional extremes in 2024. Marine heatwaves in the Mediterranean and Black Seas pushed temperatures more than 4.6°C above average, with some lasting more than 30 days, CNN reported. Storm Louis sent waves of more than eight meters onto Spain's Atlantic coast, and north-easterly winds caused a record 153 centimeter drop in sea level in the Bothnian Bay.

In the Arctic, sea surface temperatures have risen 4.2°C over the past four decades, and monthly average sea ice has shrunk by roughly 190,000 square miles per decade from 1979 to 2025, about the area of Spain, according to CNN. The Barents Sea has lost 70 percent of its sea ice extent since 1982, the Copernicus release says.

What the scientists said

"The ocean is transforming before our eyes: warming, rising seas and ecosystem degradation are interconnected signs of significant and long-term change," said Pierre Bahurel, Director General of Mercator Ocean International.

Karina von Schuckmann, who directs the report, said: "It provides a growing scientific record of an ocean under intensifying pressure."

Andrius Kubilius, the European Commissioner for Defence and Space, said: "These changes demand stronger knowledge, international cooperation and action."

Why it matters

The ocean absorbs most of the extra heat trapped by greenhouse gases, so its heat content is one of the clearest measures of how fast the climate system is changing. The report's findings, faster warming, accelerating sea level rise and increasing acidity, point to growing pressure on fisheries, coral reefs and low-lying coasts, with small island states among the most exposed.

Sources

This article was drafted with AI assistance and checked against the sources above. Company claims are reported as claims. Cover image is AI-generated.