The world’s oceans continue to absorb heat, and in 2025 this indicator reached record levels in the entire history of observations. According to a major international study published in the journal Advances in Atmospheric Sciences, the oceans absorbed about 23 zettajoules of energy over the year—equivalent to nearly 37 years of global energy consumption at 2023 levels. This increase in heat content intensifies extreme weather events and leads to new climate records.

Record Heat Accumulation

More than 50 scientists from 31 research institutions worldwide participated in the study. For the analysis, independent datasets from leading international scientific centers were combined, including the Institute of Atmospheric Physics of the Chinese Academy of Sciences, Copernicus Marine, NOAA/NCEI, and the CIGAR-RT ocean reanalysis. All sources reached the same conclusion: in 2025, ocean heat content reached its highest level since the beginning of instrumental observations, confirming the ongoing upward trend.

The Ocean’s Role in Climate

The ocean is the planet’s main heat reservoir: over 90% of the additional energy trapped by greenhouse gases is stored in the ocean, not in the atmosphere or on land. Therefore, ocean heat content (OHC) is considered one of the most reliable indicators of long-term climate change, reflecting how much energy Earth has accumulated over time.

Geography and Dynamics of Warming

Ocean warming is uneven. In 2025, about 16% of the world’s ocean area reached record heat content, and around 33% experienced one of the three warmest years on record for their regions. The fastest warming was observed in the tropical oceans, the South Atlantic, the northern Pacific, and the Southern Ocean.

Long-term trends show a steady rise in temperatures: since the 1990s, ocean warming has accelerated, and heat accumulation in the upper 2,000 meters of water has been steadily increasing for several decades. The year 2025 marked the ninth consecutive year of record ocean heat content.

Sea Surface Temperature and Its Consequences

The average sea surface temperature in 2025 ranked third among the warmest years on record, remaining about 0.5°C above the 1981–2010 average. A slight decrease compared to 2023 and 2024 is linked to the transition from El Niño to La Niña conditions in the tropical Pacific.

Sea surface temperature significantly affects global weather: warmer waters increase evaporation and precipitation, making storms more intense and raising the likelihood of extreme weather events. In 2025, this contributed to severe flooding and disruptions in Southeast Asia, prolonged drought in the Middle East, and flooding in Mexico and the northwestern Pacific region.

Impact on the Climate System

As the ocean continues to accumulate heat, the consequences affect the entire climate system. Warmer oceans contribute to sea level rise through thermal expansion, intensify and prolong heatwaves, and make extreme weather events more powerful by adding heat and moisture to the atmosphere. As long as Earth absorbs more energy than it emits, ocean heat content will keep rising, and new records will continue to be set.

Scientific Publications and Symbolism

The study’s results will be included in a special collection on ocean heat dynamics organized by Advances in Atmospheric Sciences. The cover features cartoon images of a sad shrimp and crab—an idea proposed by lead author Lijing Cheng. According to him, the characters are inspired by figures from “Journey to the West,” reimagined not as mighty guardians but as vulnerable creatures whose shells and scales suffer from warming, acidification, and other ocean changes.

The collection will explore various aspects of ocean heat changes, including detailed regional studies of waters near China, the southern Pacific, and the Indian Ocean. As climatologist Kevin Trenberth noted in the foreword, the collection is intended as an ongoing project reflecting the evolution of climate science.

Main Conclusion

Despite advances in scientific knowledge, the main conclusion remains unchanged: the greatest uncertainty in the climate system is how people will respond to these changes. By reducing emissions, preparing for future impacts, and acting together, it is still possible to preserve a climate that is favorable for people and ecosystems.