Global ocean surface temperature hits new all-time high, EU monitor says

The world's oceans have reached a new milestone in warmth. Data from the European Union's Copernicus Climate Change Service (C3S) shows the daily global average sea surface temperature climbed to 21.1 degrees Celsius on August 22, edging past the previous all-time high of 21.09°C recorded in March 2024.

What makes this record particularly striking is its timing. Ocean temperatures typically peak in March or April, following the austral summer. The previous highest reading for an August was 20.98°C, set in 2023. This year's August figure has already blown past that mark, underscoring the unusual warmth persisting across the world's seas.

C3S noted that global sea surface temperatures have remained at historically elevated levels throughout 2026, with several months registering record or near-record values. The agency pointed to a developing El Nino in the tropical Pacific as a contributing factor, adding heat to an ocean already warmed by decades of human-induced climate change.

The World Meteorological Organization expects El Nino to intensify in the coming months, and C3S seasonal forecasts suggest the event could strengthen to levels not seen in decades.

Samantha Burgess, strategic lead for climate at the European Centre for Medium-Range Weather Forecasts, described the record as "another clear signal of an ocean under growing stress." She warned that rising ocean temperatures heighten risks to marine ecosystems and coastal communities, noting that the number of marine heatwave days globally has more than tripled since the early 1990s.

Long-term ocean warming also contributes to sea-level rise through thermal expansion and increases the likelihood and intensity of marine heatwaves. These conditions put pressure on sensitive ecosystems such as coral reefs and seagrass meadows, as well as on fisheries and aquaculture that depend on stable ocean conditions.