Ocean Running a Fever: Marine Heatwaves Triple Since 1990s

The ocean is running a fever. In 2025, the number of days of marine heatwaves—long periods when the sea becomes abnormally and dangerously warm—was more than triple what it was in the early 1990s. These are not abstract statistics. A severe and persistent marine heatwave bleaches coral reefs. It strips away kelp forests that shelter young fish. It empties fishing grounds. If such heatwaves occur frequently, they can push entire ecosystems past the point of recovery. Nearly every indicator of climate change is flashing red. But we still hold the tools to bring the planet back into balance. Karina Von Schuckmann is an IGCC author and senior adviser of Mercator Ocean International.