The 55 scientists who contributed to the report published Friday in the journal Advances in Atmospheric Sciences warn that continued trends are increasing extreme weather, sea level rise and the instability of marine ecosystems. He says the main reason for this is clearly increasing greenhouse gas emissions.
We are already seeing the devastating effects of ocean warming on communities around the world, particularly through stronger storms and more severe flooding. Researchers point to several deadly events in 2025, including unprecedented monsoon rains that killed more than 1,300 people across Southeast Asia and flash flooding in central Texas that killed at least 138 people — including 27 young summer campers and counselors.
“In the long term, consistent with projections from state-of-the-art climate models, global [ocean heat content] “Records are expected to continue to be broken until net-zero greenhouse gas emissions are achieved,” the authors write.
reach boiling point
Earth’s oceans act as its primary thermal energy sink, absorbing 90% of the excess heat trapped by greenhouse gases in the atmosphere. Ocean thermal conditions therefore play an important role in modulating global and regional climate impacts, primarily through increases in atmospheric moisture and energy availability, which promote hurricane intensity.
To calculate how much heat the world’s oceans absorb in 2025, researchers measured temperature fluctuations in the upper 6,500 feet (2,000 meters) of the global ocean. They found that the amount of ocean heat lost was about 23 zettajoules greater than at the end of 2024, making 2025 the hottest year on record in terms of OHC.
About 14% of the global ocean area reached its warmest on record last year, particularly in the Southern Ocean, the tropical and South Atlantic Ocean, the Mediterranean Sea, and the northern Indian Ocean. Nearly one-third of the global ocean area ranked among its top three warmest years on record, and more than half ranked among its five warmest years. According to the researchers, this underlines the widespread and cumulative nature of ocean warming.
no end to the trend
That extra thermal energy is supercharging storms, but it’s also accelerating the already rapid melting of glaciers and sea ice. In 2025, Arctic sea ice extent reached its lowest annual maximum since satellite observations began, while Antarctic sea ice extent fell to its third lowest annual maximum.
According to the researchers, year-by-year observations also show that both the Greenland and Antarctic ice sheets reached record-low mass levels, and the new studies show that parts of them have passed critical climate tipping points. These findings indicate a continued long-term contribution to global sea-level rise.
The warming of the oceans also poses a deadly threat to coral reefs. When seawater temperatures exceed the thermal tolerance limits of these delicate organisms, they expel the symbiotic algae that provide them with nutrients and energy, resulting in bleaching.
According to NOAA, the world is currently in the midst of the fourth global coral bleaching event, with bleaching-level heat stress affecting approximately 84% of the world’s coral reef area by January 2023. Large-scale coral bleaching has been documented in at least 83 countries and territories.
Researchers don’t expect this nine-year streak of record-breaking ocean temperature rise to end any time soon. Unless the world achieves net-zero carbon emissions, global ocean heat content will continue to increase.
We’re nowhere close to reaching that goal, but rapid emissions cuts can still limit future impacts. To better understand and prepare for these impacts, the authors emphasize the importance of strengthening ocean monitoring and uncovering the mechanisms behind ocean heat redistribution. These efforts will help communities around the world adapt and build resilience to the new climate reality.
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