What happened
A new Ocean State Report found that the world’s seas and oceans took in 23 zettajoules of heat during the period assessed, the highest level recorded. This volume is estimated at roughly 40 times humanity’s total annual energy consumption.
The report describes a zettajoule as one billion trillion joules. A joule is the energy needed to operate a one-watt device for one second.
Ocean conditions are changing alongside the heat gain. Since 1999, global sea level has risen by about 3.8 mm a year. The rate increased to 4.2 mm a year over 2012–2025. The report also says global oceans have become 17% more acidic over the past 40 years.
In Europe, the Mediterranean and Black Sea experienced record marine heatwaves. The report says these seas are warming at twice the global rate, with heat reaching below the surface and some extreme events lasting longer than a month. Across the Mediterranean, temperatures have risen by 0.32°C per decade.
Why it matters
The findings are relevant to coastal decision-makers and businesses in Türkiye and the EU because the Mediterranean and Black Sea are among the regions identified as warming rapidly. Higher sea levels and warmer coastal waters are occurring alongside damage to marine ecosystems and more frequent heatwaves over the sea.
The material does not set out new legal obligations, costs or compliance deadlines. It does, however, point to physical risks affecting coastlines and marine environments, including the interaction between sea-level rise and extreme weather that can erode Mediterranean shores.
Background
Oceans have absorbed about one-third of the carbon dioxide released by human activity and around 90% of the additional heat retained in the Earth system by greenhouse-gas pollution, according to the report.
Marine impacts are already visible. Between January 2023 and September 2025, 84% of coral reefs worldwide experienced heat stress at levels associated with bleaching. Over the past 30 years, around 5% of the ocean has seen lasting changes in phytoplankton growth patterns. In Antarctica, breeding failed completely in four emperor penguin colonies during record-low sea-ice conditions in 2022.
