The world’s oceans have absorbed a record amount of heat
This influx of heat is occurring at the same time as sea levels are rising ever more rapidly and ocean acidification continues, reports the British newspaper The Guardian. The amount of heat is equivalent to 40 times the annual global energy consumption
Text by Marika Griehsel
‘The oceans are changing before our very eyes, says Pierre Bahurel, Director-General of Mercator Ocean International, which published the report. Warming, rising sea levels and the deterioration of ecosystems are interlinked signs of significant and long-term changes.´
A record amount of heat – 23 zettajoules – was added to the world’s oceans last year, which has warmed the seawater, raised sea levels and made the environment less habitable, the report shows.
This explosive influx of heat energy – which was almost 40 times greater than all the energy consumed by humankind that year – is occurring at the same time as far-reaching changes are taking place in the deep ocean waters that are vital to life on Earth.
Sea levels have risen by around 3.8 mm per year since 1999, and at a faster rate of 4.2 mm per year between 2012 and 2025, according to the tenth edition of the Copernicus State of the Ocean Report. The report shows that the world’s oceans have become 17 per cent more acidic over the past 40 years.
The oceans have absorbed around one-third of the carbon dioxide emitted by humankind and around 90 per cent of the extra heat that greenhouse gas emissions have trapped within the Earth’s system.
In Europe, where warming is occurring twice as fast as the global average, the Mediterranean and Black Seas have been hit by record-breaking marine heatwaves – with elevated temperatures persisting deep below the surface – and periods of extreme heat lasting for more than a month, the researchers noted.
The researchers found a clear acceleration in sea-level rise in the western Mediterranean, although the eastern part showed uneven increases. The entire sea has warmed by 0.32 °C per decade, according to the report, which has fuelled marine heatwaves, particularly in recent years. One joule, the unit used to measure heat, is the amount of electricity required
The report documented extensive damage to marine life as a result of the heat. Between January 2023 and September 2025, 84 per cent of the world’s coral reefs were subjected to heat stress of a magnitude leading to bleaching. Over the past 30 years, nearly 5 per cent of the oceans have experienced a lasting change in the growth patterns of phytoplankton, the tiny organisms that form the basis of food webs and regulate carbon flows.
In Antarctica, four emperor penguin colonies suffered total reproductive failure in 2022 during periods of record-low sea ice.
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