Oceans Absorbed Record 23 Zettajoules in 2025: A Planet on Overheat

The planet's largest thermostat is breaking. On January 9, 2026, a global team of researchers revealed that the world's oceans absorbed more heat in 2025 than any year since modern records began. It marks the eighth consecutive year that ocean heat content has shattered previous records, underscoring the relentless progression of climate change.

The Massive Scale of 2025 Ocean Heat Content Record

According to the study published in Advances in Atmospheric Science, the oceans took in an additional 23 zettajoules of heat in 2025. To put that in perspective, 2024 saw an increase of 16 zettajoules. John Abraham, a professor at the University of St. Thomas and co-author of the paper, noted that the warming in 2025 is the energetic equivalent of 12 Hiroshima bombs exploding in the ocean every second of the year.

Why Sea Surface Temps Don't Tell the Whole Story

While global surface temperatures are what people feel directly, they can be misleading due to phenomena like El Niño or La Niña. In fact, sea surface temperatures in 2025 were slightly lower than in 2024. However, the heat content—the total energy stored throughout the water column—continues to climb. The ocean acts as a massive heat sink, absorbing over 90 percent of the excess warming trapped in our atmosphere.

Modern Oceanography: Sensors and Mammals

The researchers utilized a combination of mathematical models and a vast array of data sources. A cornerstone of this data is the Argo float network, which consists of more than 3,500 robotic buoys. In a fascinating twist of technology, scientists also attached instruments to marine mammals that dive under polar ice, allowing for temperature measurements in regions inaccessible to robots.