Globally averaged sea surface temperatures (SSTs) were at record levels between March 2023 and July 2024. Not only were these SSTs record-breaking but they exceeded the previous record of annually averaged SSTs from 2015/16 by 0.25°C. Here, we find that this SST jump was a 1-in-512-year event (1-in-205-year to 1-in-1,185-year event; 95% confidence interval) under the current long-term warming trend based on observation-based synthetic time series. We further used 270 simulations from a wide range of fully coupled climate models to show that these models successfully simulate such global record-shattering SST jumps underlining their usefulness for understanding characteristics, drivers, and consequences of such events. As SSTs revert to the long-term warming trend in all simulated cases, climate models suggest that the record-shattering jump in 2023/24 was an extreme event.

In most model simulations, SSTs return even to pre-jump levels in September of the second year after the jump. Only in models with a high transient climate response to emissions, simulated SSTs revert to the long-term warming trend without returning to pre-jump levels. SSTs have not yet returned to pre-jump levels by August 2025 which may indicate that the real-world climate response to emissions and hence future warming might be larger than expected, or that a potential change in external forcing has happened. A stronger climate response is further supported by a recent study (Vogt et al., 2025) which shows that a bias in climate models towards too little Antarctic sea ice at present is causing too small simulated future atmospheric and ocean warming.

We further show that the jump in SSTs in 2023/24 was likely the start of a global warming hiatus that will develop and continue over the next years. In climate models, the global surface air temperatures in years after such jumps in SSTs do not increase for an average period of 5.7 years. In contrast, the average time period without increasing temperatures after any year is only 2.2 years.

 

Dr Jens Terhaar is an oceanographer and climatologist at the University of Bern, where he leads an SNSF Ambizione project on Arctic Ocean ecosystems. His research spans ocean biogeochemistry, ocean physics, and climate, with a focus on the ocean carbon sink, ocean acidification, and interactions between circulation, marine ecosystems, and climate.

He obtained his PhD in 2019 from the Laboratoire des Sciences du Climat et de l’Environnement and the Université Libre de Bruxelles, and subsequently held research positions in Bern, Paris, and at the Woods Hole Oceanographic Institution before establishing his independent research group in 2023.

His work combines observations and Earth system models to better constrain past and future changes in the ocean. He has contributed to improving estimates of the global and regional ocean carbon sink, primary production, and acidification and to understanding the role of the Arctic and Southern Oceans in the climate system. More recently, his research has focused on large-scale ocean circulation and climate variability, including studies of the Atlantic Meridional Overturning Circulation (AMOC), ocean heat uptake, and the 2023-24 sea surface temperature jump. He developed the Adaptive Emission Reduction Approach (AERA), an algorithm that enables climate models to converge to prescribed temperature targets and allows consistent comparison of climate impacts across stabilization and overshoot scenarios, while also providing realistic emission pathways.

Dr Terhaar is the author of numerous peer-reviewed publications and has contributed to international assessments, including the IPCC and RECCAP2. He is currently part of the author team preparing an assessment report on the AMOC led by JPI Oceans and JPI Climate, and is also active in teaching and supervision in climate and environmental physics. In 2025, he received the European Geosciences Union Outstanding Early Career Scientist Award in Ocean Sciences for his research, teaching, outreach, and efforts to raise awareness of mental health in the geosciences.