Overview

• Global average sea-surface temperatures hit a record 21°C in spring 2024, with Copernicus data showing ocean warming has accelerated since the 1960s.
• Marine heatwaves were unusually intense and persistent in 2023–24, with parts of the Atlantic experiencing more than 300 heatwave days in 2023.
• The Baltic is warming more than three times the global rate and the North Sea about twice as fast, while Germany’s BSH reported up to +1.5°C above average in the southwest Baltic this summer.
• The Mediterranean saw its longest recorded heatwave from May 2022 to early 2023, enabling invasive Atlantic blue crabs and beard fireworms that devastated mussel stocks in Italy’s Po Delta and disrupted Sicilian fisheries.
• Sea level has risen nearly 23 cm since 1901 as ice losses continue, ocean acidification and plastic pollution intensify, scientists urge rapid emissions cuts, and a UN high-seas treaty will enter into force in January 2026 to help establish protected areas.