Record-shattering jump in sea surface temperatures in 2023/24 was unlikely but not unexpected

Globally averaged sea surface temperatures were at record levels between March 2023 and July 2024. Not only were these temperatures record-breaking but they exceeded the previous record of annually averaged SSTs from 2015/16 by 0.25°C. The nearly global extent and the magnitude of this jump prompted questions about how exceptional this event was, whether climate models can represent such record-shattering jumps in surface ocean temperatures, and if global warming has accelerated. Here, we show that the sea surface temperature jump in 2023/24 that broke the old record by 0.25°C was a 1-in-512-year event under the current long-term warming trend (1-in-205-year to 1-in-1,185-year event; 95% confidence interval) based on observation-based synthetic timeseries. Without global warming, such a large jump in sea surface temperatures would have been impossible. We further used 270 simulations from a wide range of fully coupled climate models to show that these models successfully simulate such record-shattering jumps in global sea surface temperatures. The ability of these models to simulate such jumps underlines the models’ usefulness of these models for understanding characteristics, drivers, and consequences of such events. Moreover, the sea surface temperatures in the simulated jumps stop to be record-breaking between May and October in the year after temperatures started to be record-breaking. Similarly, observed sea surface temperatures also stopped to be record-breaking in July 2024, the year after the jump started. Furthermore, sea surface temperatures return to the long-term warming trend in all cases in the years following the jump. Thus, climate model simulations suggest that the record-shattering jump in surface ocean temperatures in 2023/24 was an extreme event after which surface ocean temperatures are expected to revert to the expected long-term warming trend.