Ocean temperatures reached unprecedented heights in 2025, according to groundbreaking research. The seas absorbed an astonishing 23 Zetta Joules of heat last year, a figure equivalent to 37 years of global primary energy consumption at 2023 levels. This staggering amount of heat energy was recorded by an international team of scientists, marking a significant milestone in climate science. The study, published in the prestigious journal Advances in Atmospheric Sciences, is a collaborative effort involving over 50 researchers from 31 institutions worldwide. The oceans, absorbing over 90% of the excess heat trapped by greenhouse gases, are the primary heat reservoir of our climate system. Ocean heat content (OHC), a critical indicator of long-term climate change, reached a record high in 2025, mirroring the previous nine years. The latest assessment, combining data from major international centers and independent research groups, confirms the ongoing ocean heat gain. However, the warming is not uniform, with some regions heating up faster than others. In 2025, approximately 16% of the global ocean area reached a record-high OHC, while 33% ranked among the top three warmest values in their historical records. The tropical, South Atlantic, North Pacific, and Southern Oceans were among the warmest areas. The overall trend shows stronger ocean warming since the 1990s compared to earlier periods. Scientists note a 'fairly steady' increase in upper 2000m OHC in recent decades, with a slight acceleration detected. The global annual mean sea-surface temperature (SST) in 2025 was the third warmest on record, remaining 0.5 °C above the 1981–2010 average. SSTs in 2025 were slightly lower than in 2023 and 2024, primarily due to the transition from El Niño to La Niña in the tropical Pacific. Sea surface temperatures are crucial as they influence weather patterns worldwide. Warmer surfaces enhance evaporation and heavy rains, leading to more intense tropical cyclones and extreme weather events. The research team attributes widespread flooding, droughts, and disruptions in South East Asia, the Middle East, Mexico, and the Pacific Northwest to rising ocean heat. This heat drives global sea-level rise, intensifies heatwaves, and exacerbates extreme weather by increasing atmospheric heat and moisture. As Earth's heat continues to rise, scientists predict that ocean heat content will keep increasing, setting new records. The study's findings will be published in a special collection on Ocean Heat Content Changes, organized by the journal Advances in Atmospheric Sciences. The cover art, featuring a sad shrimp and crab, was inspired by Professor Lijing Cheng's suggestion, drawing from the classic tale of 'shrimp soldiers and crab generals' guarding an underwater palace. Cheng explains that the characters symbolize vulnerable creatures under threat from ocean warming, acidification, and environmental changes. He emphasizes that human actions are the biggest climate uncertainty, and collective efforts to reduce emissions and prepare for changes are essential to safeguarding a sustainable future for humanity.
