Global ocean surface temperatures reach record 21.1 degrees Celsius in August

New temperature record set in August

The global average sea surface temperature outside polar regions reached 21.1 degrees Celsius (70 degrees Fahrenheit) on Friday, 21 August 2026, and Saturday, 22 August 2026, according to measurements published by the European Union's Copernicus Climate Change Service. The new measurement narrowly surpassed the prior record of 21.09 degrees Celsius recorded on three separate days in March 2024. The data derives from measurements taken 10 metres below the surface by a network of buoys, ships, and satellites.

Scientists noted the uncharacteristic timing of the peak. Worldwide sea surface temperatures typically reach their annual high point in March or April, coinciding with the end of summer in the Southern Hemisphere, which contains the majority of the planet's ocean area. Setting an all-time record in August deviates from typical seasonal cycles.

This is yet another sign of our climate system under strain and the ocean under immense pressure.

Drivers of ocean warming

The ocean heating results from a combination of long-term human-caused climate change and an intensifying El Nino event in the Pacific Ocean. Fossil fuel combustion from coal, oil, and gas has contributed 0.8 degrees Celsius (1.4 degrees Fahrenheit) of direct warming to the oceans over several decades. Oceans absorb more than 90% of the excess heat trapped by greenhouse gases.

On top of this baseline, the current El Nino is pushing warm water across the central and eastern tropical Pacific. Forecasters expect the phenomenon to strengthen further until its peak between November and January, with elevated temperatures potentially persisting into 2027.

El Niño is adding heat to the system, but it is doing so on top of decades of human-driven warming.

Marine heatwaves and weather disruptions

According to data from the National Oceanic and Atmospheric Administration, marine heatwaves currently cover 42% of the world's oceans. In the Pacific Ocean, marine heatwaves occupy an area equal to nine times the size of the contiguous United States. Dr Samantha Burgess noted that the global number of marine heatwave days has more than tripled since the early 1990s.

Warm waters alter weather patterns globally by adding moisture and thermal energy to the atmosphere. The current conditions have contributed to Hurricane Lala near Hawaii, heavy rainfall in the United States, and sustained summer heat in Europe. In the Southern Hemisphere and Asia, the El Nino pattern has brought reduced monsoon rainfall to India, wildfires to Indonesia, and elevated bushfire risks to Australia.

An ocean this warm destabilizes weather patterns and threatens food security, economic prosperity and marine life. A warmer ocean is not our friend.

Broader environmental consequences

Higher water temperatures lower the oxygen-carrying capacity of seawater and increase ocean acidity, creating severe stress for fisheries and marine ecosystems. In coastal regions, warm seas prevent night-time cooling by eliminating cool sea breezes during heatwaves. Warmer water also expands in volume, accelerating sea level rise and increasing coastal flood threats.

University of Ottawa professor Ryan Katz-Rosene noted that sediment core records indicate ocean temperatures may now exceed any levels seen during the 12,000-year Holocene period, reaching levels last observed during the interglacial era roughly 125,000 years ago. Hotter oceans also absorb carbon dioxide less efficiently, reducing their ability to buffer future emissions.