The world’s oceans have absorbed record heat for the 9th year in a row

It would take about 365 million Hiroshima-sized atomic bombs to release the amount of energy absorbed by the world’s oceans as additional heat in 2025. The figure comes from the latest Global Ocean Heat Content report, which reveals record marine warming for the ninth consecutive year.

The 55 scientists who contributed to the report, published Friday in the journal Advances in atmospheric sciencewarn that this continuing trend is exacerbating extreme weather, sea level rise and the destabilization of marine ecosystems. According to them, the main factor is unequivocally the increase in greenhouse gas emissions.

We are already seeing the catastrophic effects of marine warming on communities around the world, including through stronger storms and more severe flooding. Researchers point to a series of deadly events in 2025, from unprecedented monsoon rains that killed more than 1,300 people in Southeast Asia to flash floods that killed at least 138 people, including 27 young summer campers and counselors, in 2025. Central Texas.

“In the long term, in accordance with the projections of the most modern climate models, [ocean heat content] is expected to continue breaking records until net greenhouse gas emissions are zero,” the authors write.

Reaching a boiling point

Earth’s oceans are the primary sink of thermal energy, absorbing 90% of the excess heat trapped by greenhouse gases in the atmosphere. The thermal state of the ocean therefore plays an important role in regulating global and regional climate impacts, primarily through increases in atmospheric humidity and energy availability, which fuel storm intensification.

To calculate how much heat the world’s oceans would absorb in 2025, the researchers measured temperature fluctuations in the upper 2,000 meters of the global ocean. They found that the heat content of the oceans was about 23 zettajoules higher than it was at the end of 2024, making 2025 the hottest year on record in terms of OHC.

About 14% of the world’s ocean area reached its warmest state on record last year, particularly in the Southern Ocean, the tropical and southern Atlantic Ocean, the Mediterranean Sea and the northern Indian Ocean. About a third of the world’s ocean area is among the three warmest years on record, and more than half among the five warmest years. This highlights the pervasive and accumulated nature of ocean heat gain, the researchers say.

The trend never ends

This additional thermal energy is supercharged stormsbut it also speeds up the already rapid melting of glaciers and ice floes. In 2025, Arctic sea ice extent reached its lowest annual maximum since satellite observation began, while Antarctic sea ice extent fell to its third lowest annual maximum.

Observations since the start of the year also show that the Greenland and Antarctic ice sheets have reached record mass levels, and new studies suggest that parts of them have crossed critical climate tipping points, researchers say. These results indicate a continued long-term contribution to global sea level rise.

Ocean warming poses a problem deadly threat to coral reefs Also. When seawater temperatures exceed the thermal tolerance threshold of these fragile organisms, they expel the symbiotic algae that provide them with nutrients and energy, leading to bleaching.

The world is currently in the midst of its fourth global coral bleaching event, according to NOAAwith bleaching-related heat stress affecting approximately 84% of the world’s coral reef area since January 2023. Mass coral bleaching has been documented in at least 83 countries and territories.

Researchers don’t expect this nine-year streak of record-breaking marine warming to end anytime soon. Until the world reaches net zero carbon emissions, the global heat content of the oceans will continue to increase.

We are far from reaching this goalbut rapid emissions reductions can still limit future impacts. To better understand and prepare for these impacts, the authors emphasize the importance of strengthening ocean monitoring and discovering the mechanisms behind the redistribution of ocean heat. These efforts will help communities around the world adapt to a new climate reality and build resilience.