Earth's oceans reached their highest heat levels on record in 2025, absorbing 23 zetta joules of excess energy. This milestone, confirmed by an international team of scientists, underscores the accelerating impact of climate change. The warming trend, building since the 1990s, fuels stronger storms and rising sea levels worldwide.
A collaborative study involving over 50 scientists from 31 institutions across Asia, Europe, and the Americas has revealed that the oceans absorbed more heat in 2025 than in any previous year of modern observations. Published on January 9, 2026, in Advances in Atmospheric Sciences, the research draws on datasets from the Institute of Atmospheric Physics at the Chinese Academy of Sciences, Copernicus Marine, NOAA's National Centers for Environmental Information, and the CIGAR-RT ocean reanalysis. These sources consistently show ocean heat content hitting a new peak, marking the ninth straight year of records.
In 2025, the oceans gained 23 zetta joules—equivalent to roughly 37 years of global primary energy use in 2023, based on about 620 exa joules annually. As Earth's main heat sink, the oceans capture over 90% of the excess energy trapped by greenhouse gases, making their heat content a key indicator of climate change. Warming has intensified since the 1990s, with a slight uptick in the rate for the upper 2,000 meters of the ocean.
The heat buildup is uneven: 16% of the global ocean area set records, while 33% experienced one of their three warmest years. Tropical regions, the South Atlantic, North Pacific, and Southern Ocean saw the most significant increases. Global sea surface temperatures averaged 0.5°C above the 1981-2010 baseline, ranking third warmest overall, influenced by a shift from El Niño to La Niña conditions.
This warming drives broader effects, including thermal expansion that raises sea levels, more intense heatwaves, and amplified storms through added evaporation and moisture. In 2025, it contributed to severe flooding in Southeast Asia, prolonged droughts in the Middle East, and floods in Mexico and the Pacific Northwest.
The study appears in a special collection on ocean heat content, featuring illustrations of distressed marine life. Lijing Cheng, the corresponding author from the Institute of Atmospheric Physics, explained the imagery: "We reimagined them not as mighty guardians, but as vulnerable creatures whose armor—their shells and scales—is under attack by ocean warming, acidification and other ocean environmental changes." As ocean heat rises unabated, the focus shifts to emission reductions and adaptation to mitigate escalating risks.
