The extreme global ocean warming of 2023-2024 had a return period of 512 years, but it does not indicate an acceleration of global warming.
The record-breaking global ocean warming observed between 2023 and 2024 was truly exceptional. However, despite the extreme temperature anomalies, this does not necessarily mean that global warming is accelerating, as some recent studies have suggested. That’s the conclusion of a study published on March 12, 2025, in Nature by researchers from the University of Bern and Sorbonne University.
The extraordinary surge in ocean temperatures
Between April 2023 and March 2024, global sea surface temperatures reached unprecedented levels, surpassing the previous 2015-2016 record by an average of 0.25°C—a significant margin in ocean temperature dynamics.
To grasp the magnitude of this event, it’s useful to compare it to past records. Before 2023, the largest increases were 0.16°C in 2015-2016, 0.14°C in 1997-1998, and 0.09°C in 2009-2010. The North Atlantic experienced the most extreme warming, exceeding its previous record by 0.42°C.
A detailed statistical analysis estimated that an event of this scale has a return period of 512 years under current global warming conditions. More significantly, without ongoing climate change, such a temperature jump would have been virtually impossible.
An anomaly, not an acceleration
Exceptional? Yes. Unpredictable? No. The study argues that while this level of ocean warming is extreme, it does not indicate an acceleration of global warming. Instead, researchers describe it as an extreme event after which ocean temperatures should return to their long-term warming trend.
In fact, data shows that since mid-July 2024, global ocean temperatures are no longer at record levels, though they remain warmer than in any year prior to the 2023 surge. This suggests that the event was a temporary anomaly rather than a shift to a new baseline.
Using 270 simulations across multiple climate models, researchers demonstrated that these models successfully replicated the record-breaking warming of 2023-2024, even though it falls at the extreme end of the possible range.
