The average temperature on the surface of the world's oceans has reached a record for a single day: on Saturday 22 August, 21.1 degrees Celsius was recorded. This figure surpasses the reading from March 2024, when the previous all-time high of 21.09 degrees Celsius was reached, according to the European climate monitoring service Copernicus.

A record driven by climate change and El Niño

A similar figure had already been flagged back in April. And the data from the National Oceanic and Atmospheric Administration (Noaa) appeared consistent: the US agency had reported 21.12 degrees Celsius, just below the absolute record of 21.16 degrees. The figure is 0.57 degrees above the 1991–2020 average for the period.

The rise in ocean temperatures is being driven by the combined effect of climate change and El Niño, the cyclical phenomenon consisting of the warming of the equatorial portion of the Pacific Ocean, which this year is manifesting with exceptional intensity. What is also unusual, is the timing: Copernicus points out that "ocean temperature peaks normally occur in March and April" — that is, at the end of the summer period in the Northern Hemisphere, where the largest ocean masses are found.

"Oceans under growing stress"

"This record is another clear signal of an ocean under growing stress," commented Samantha Burgess, Head of Climate Strategy at Ecmwf. "El Niño is adding heat to the system, but it is doing so against a backdrop already shaped by decades of human-caused warming. As ocean temperatures continue to rise, so do the risks for marine ecosystems and coastal communities. The consequences are already visible: the number of marine heatwave days globally has more than tripled since the early 1990s."

For this reason, as reported by Climate Home News, ahead of the next United Nations world climate conference — Cop31, to be held in November in Turkey — a sizeable group of countries has called for ocean protection measures to be incorporated into the decisions to be taken at the summit. The call came from a number of European Union member states, African countries, South American nations and small island states.

The call for a roadmap ahead of Cop31 in Turkey

Turkey and Australia, which will share the co-presidency of Cop31, have given the green light to work on a "voluntary ocean roadmap", described as "a concise action plan". At the same time, a group of more than 150 world-renowned scientists has called, ahead of the conference, for "ocean-related priorities to be integrated into negotiating texts on mitigation, adaptation and finance". They also stressed the need for "a clear political declaration and finance outcomes" on ocean-based climate solutions at the World Leaders Summit — a two-day event held during the Cop at which heads of state deliver speeches outlining their positions on climate.