Global ocean surface temperatures reached a record 21.10°C on 22 August 2026, the highest reading in the ERA5 dataset, which extends back to 1979, according to a report published by karmactive.com on 25 August 2026. Marine heatwaves were by that point affecting approximately 42% of the global ocean surface area, with temperatures running 0.67 to 0.95°C above baseline averages across affected regions.
Scientists linked the intensifying heat to strengthening El Niño conditions, with forecasters putting the probability of a very strong El Niño event at greater than 90% for the Northern Hemisphere autumn and winter of 2026-27. Along the west coast of the Americas, including California, waters ran roughly 1.7 to 2.2°C above normal, while tropical coral reefs faced persistent thermal stress and recurring bleaching events, conditions that compound year on year as reefs struggle to recover between heat episodes.
The August figures did not emerge in isolation. Weeks earlier, the European Union’s Copernicus Marine Service had already flagged a rapidly intensifying marine heatwave, setting out a trajectory that the ERA5-based data would later confirm had continued to worsen through the northern summer.
A summer of compounding ocean heat
Copernicus reported on 1 July 2026 that approximately 82% of the global ocean had experienced marine heatwave conditions by the end of June, with the Mediterranean among the worst affected at 98%, four-fifths of that area registering strong, severe, or extreme heat levels. In the tropical Pacific, average temperatures for January to June reached 26.91°C, matching the record set during the major El Niño event of 2016. Copernicus also identified hotspots in the central North Atlantic and in upwelling regions off Chile and California, zones that typically support some of the world’s most productive fisheries.
Read together, the two reports, one drawing on Copernicus data through June and the other on ERA5 data through August, describe an ocean heatwave that did not plateau over the northern summer but continued to intensify, expanding its reach by late August.
Stakes for fisheries and coastal food security
For fishing communities and coastal economies across the Global South, sustained marine heat carries direct consequences. Warmer waters alter where fish stocks migrate, stress the coral reef systems that sustain reef fisheries, and intensify the kind of upwelling disruptions already observed off Chile and California, both significant fishing grounds.
With a very strong El Niño now considered more likely than not for the coming autumn and winter, the conditions behind this year’s record ocean temperatures show little sign of easing in the near term, leaving fisheries and coastal food systems in the tropics and subtropics exposed to a longer stretch of thermal stress than usual.
