An international team of 54 scientists from 7 countries led by Lijing Cheng from the Institute of Atmospheric Physics at the Chinese Academy of Sciences was able to show that the temperatures of the oceans in 2024 reached a new high – as well regarding the sea surface temperatures as the deeper water temperatures.

“Our paper provides an up-to-date summary of global ocean temperature data, which robustly shows that 2024 confirmed the long-term trend and again set new temperature records at the sea surface and in the deep ocean. The effect of natural fluctuations such as El Niño, which normally results in a temporary cooling of the oceans, was relatively small this year,” explains co-author Michael Mayer from the Department of Meteorology and Geophysics at the University of Vienna, who was involved in the scientific interpretation of the results regarding the role of different drivers of ocean temperatures, in particular the influence of El Niño.

Ocean as critical part of the Earth’s climate

A hotter ocean directly affects our lives on land, argue the authors, as the ocean is a critical part of the Earth’s climate – most of the excess heat from global warming is stored in the ocean (90%) and the ocean covers 70% of the Earth’s surface. Because of this, the ocean dictates our weather patterns by transferring heat and moisture into the atmosphere. The ocean also controls how fast climate change happens.

Results from three international teams who collaborated on this project were consistent – the ocean is warming, and 2024 was a record. This referred not only to the surface temperature, but also to the upper 2000 meters of ocean waters. From 2023 to 2024, the global upper 2000 m ocean heat content increase is 16 zettajoules (1021 Joules), ~140 times the world’s total electricity generation in 2023; and it rose steadily over the past five years despite the La Niña and El Niño cycles.

Staggering rise in surface temperatures since late 1950s

The ocean surface temperature is also setting records. The surface temperature refers to temperatures just at the surface, where the ocean waters and atmosphere commute. Surface temperatures are important because they dictate how fast heat and moisture (humidity) can transfer from the ocean to the air and thus affect weather. The rise in surface temperatures since the late 1950s has been staggering.

The changes are not uniform; regional variations can be substantial. The Atlantic is warming along with the Mediterranean Sea, and across the mid-latitude Southern Ocean. While parts of the Northern Pacific Ocean have warmed very rapidly, other areas (the tropical region) have not, mostly due to the La Niña/El Niño cycle in that area. The heat has even accumulated near both the North and South Poles.

"Water vapor is a powerful greenhouse gas"

“The main way the ocean continues to influence the climate is through accompanying increases in water vapor in the atmosphere that leads to the damaging increases in extremes in the hydrological cycle.  Water vapor is also a powerful greenhouse gas and increased heating leads to drying and risk of drought and wildfire.  But it also fuels storms of all sorts and leads to risk of flooding. That includes hurricanes and typhoons,” says Kevin Trenberth, a senior scientist at National Center for Atmospheric Research, USA.

For example, over the past 12 months, 104 countries have recorded their hottest temperatures ever. Droughts, heat waves, floods, and wildfires have impacted Africa, Southern Asia, the Philippines, Brazil, Europe, the USA, Chile, and the Great Barrier Reef, as just but a few examples. Since 1980 for example, climate disasters have cost the USA nearly $3 trillion.

"Measuring oceanic heat content is the best way to quantify the accumulating effect of anthropogenic climate change, and it will also be an effective way to monitor the efficiency of eventual global emission reductions," says Mayer from the University of Vienna. If there continues to be a failure to take action to slow climate change, the disruption, unprecedented change and its implications, costs and loss and damages will continue to increase.

Publication: Cheng, L., Abraham, J., Trenberth, K.E. et al. Record High Temperatures in the Ocean in 2024. Adv. Atmos. Sci. (2025). https://doi.org/10.1007/s00376-025-4541-3