Ocean hits record warmth of 21.1°C, sparking alarm for marine life and humans

Over the weekend the world’s oceans warmed to a record 21.1 °C, according to Copernicus, narrowly beating the previous high set in March 2024. Samantha Burgess of Copernicus said the extreme temperature results from a still-growing El Niño combined with long-term warming from fossil-fuel emissions. Scientists such as Jane Lubchenco, Boris Worm and John Bruno warned that hotter water becomes more acidic, holds less oxygen and fuels more intense storms, while also endangering coral reefs and expanding jellyfish blooms.

The heat threatens the planet’s largest fishery, the Peruvian anchovy catch, and could cascade through marine food webs, affecting seabirds and human nutrition. Unusually, the record was set in August rather than the typical March-April peak, and temperatures are expected to rise further as El Niño peaks between November and January. Former NOAA chief Rick Spinrad stressed that the ocean functions as Earth’s thermostat, making these records a clear signal of escalating challenges for societies worldwide.