For 100 days straight this summer, the world’s oceans experienced record-breaking heat.
From June 2 through September 10, 2026, average sea-surface temperatures across the global ocean outside the polar regions remained at record highs. On August 22, temperatures reached 21.1°C (69.98°F), the highest daily global average sea-surface temperature recorded in the Copernicus dataset, which dates back to 1979.
Scientists point to human-caused climate change combined with a developing El Niño as major factors behind the extreme temperatures. The ocean absorbs most of the excess heat trapped in Earth’s climate system, making rising ocean temperatures one of the clearest signs of a warming planet.
Even small increases in ocean temperature can have major consequences. Prolonged heat can cause coral bleaching, disrupt marine food webs, force species to move into cooler waters, and threaten fisheries and coastal communities. Warmer oceans also contribute to sea-level rise because seawater expands as it heats.
Marine heatwaves are especially concerning because many ocean species can survive short periods of unusually warm water but struggle when those conditions continue for weeks or months.
One hundred consecutive days of record heat is more than just another temperature record. It shows how quickly conditions in our oceans are changing.
Our oceans regulate Earth’s climate, provide habitats for countless species, and support millions of people who depend on them for food and jobs. Protecting them means reducing the causes of climate change while also protecting coral reefs, wetlands, seagrasses, and other ecosystems that make our coastlines more resilient.
Diya Comar