Record sea surface temperature jump in 2023-2024 unlikely but not unexpected

Global ocean surface temperatures were at record levels for more than a year from April 2023 onwards, exceeding the previous record in 2015-2016 by 0.25 °C on average between April 2023 and March 2024¹. The nearly global extent and unprecedented intensity of this event prompted questions about how exceptional it was and whether climate models can represent such record-shattering jumps in surface ocean temperatures². Here we construct observation-based synthetic time series to show that a jump in global sea surface temperatures that breaks the previous record by at least 0.25 °C is 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). Without a global warming trend, such an event would have been practically impossible. Using 270 simulations from a wide range of fully coupled climate models, we show that these models successfully simulate such record-shattering jumps in global ocean surface temperatures, underpinning the models' usefulness in understanding the characteristics, drivers and consequences of such events. These model simulations suggest that the record-shattering jump in surface ocean temperatures in 2023-2024 was an extreme event after which surface ocean temperatures are expected to revert to the expected long-term warming trend.