World's oceans absorbed record 23 zettajoules of heat last year
What's the story
The world's oceans absorbed a staggering 23 zettajoules of heat in 2025, a new report has revealed. This is nearly 40 times the total energy consumed by humanity in that year. The report highlights how this massive influx of thermal energy is contributing to rising sea levels and ocean acidification, among other changes.
Climate impact
Ocean acidification and sea level rise
The report, published by Mercator Ocean International, notes that the global ocean has become 17% more acidic over the last four decades.
It also highlights a clear acceleration in sea level rise since 1999, with an annual increase of about 3.8mm.
Between 2012 and 2025, this rate accelerated to an even faster pace of about 4.2mm per year.
Carbon sink
The ocean is transforming before our eyes
The report also highlights the oceans' role as a major carbon sink, absorbing about one-third of the carbon dioxide emitted by humans.
It adds that they have taken in nearly 90% of the additional heat trapped by greenhouse gas pollution in Earth's system.
"The ocean is transforming before our eyes," said Pierre Bahurel, Director General of Mercator Ocean International.
Regional impact
Europe heating twice as fast as global average
The report mentions Europe which is heating twice as fast as the global average.
The Mediterranean and Black Seas have been hit by record-breaking marine heatwaves with temperatures lasting for over a month.
The entire sea has warmed by 0.32 degree Celsius per decade, fueling marine heatwaves especially in recent years.
Biodiversity threat
Impact on marine life
The report also shows the impact of rising temperatures on marine life.
Between January 2023 and September 2025, a staggering 84% of the world's coral reefs experienced bleaching-level heat stress.
Over the last three decades, nearly 5% of ocean waters have witnessed a persistent shift in phytoplankton growth patterns, tiny organisms that form the basis of food webs and carbon cycling.