Last year, global ocean temperatures recorded the highest levels in observational history. Scientists analyzed that unprecedented heat accumulation occurred not only at the surface but also in waters as deep as 2,000 meters.
An international research team, including the Institute of Atmospheric Physics at the Chinese Academy of Sciences, announced the results of their analysis of global ocean temperatures on Dec. 10 (local time). The research findings were published in the international academic journal "Advances in Atmospheric Sciences."
The oceans, which cover 70% of the Earth's surface, store 90% of the excess heat generated by global warming. They play a critical role in the global climate system. The oceans also transfer heat and moisture to the atmosphere, influencing weather patterns and regulating the pace of climate change. John Abraham, a professor at the University of St. Thomas and a co-author of the study, emphasized that "to understand climate change, we must look at the oceans," indicating the importance of ocean data.
According to the analysis by an international research team consisting of 54 scientists from seven countries, ocean heat content last year increased by a record high of 16 ZJ (zetajoules, a unit of energy), which is equivalent to about 140 times the global electricity production in 2023. Ocean heat content refers to the heat stored from the ocean surface down to depths of 2,000 meters.
Michael Mann, a professor at the University of Pennsylvania, explained that "ocean heat content has steadily increased by 15 to 20 ZJ over the past five years, unaffected by El Niño and La Niña cycles." El Niño refers to the phenomenon of warming sea surface temperatures in the eastern Pacific, while La Niña refers to its opposite, characterized by cooling sea surface temperatures in the eastern Pacific.
Along with ocean heat content, sea surface temperatures also reached record levels. Sea surface temperature refers to the temperature of the surface where seawater and the atmosphere interact. Since the late 1950s, surface temperatures have risen rapidly, increasing by 0.6 degrees compared to the average from 1981 to 2010. Warmer surface temperatures in the oceans lead to increased heat and moisture being transferred to the atmosphere, causing extreme climate events.
The researchers noted that changes in ocean temperatures showed significant regional variability. Particularly, the North Pacific, Atlantic, and Mediterranean regions were warming rapidly. In these areas, the increase of moisture in the atmosphere, which acts as a greenhouse gas, led to rising temperatures, resulting in extreme events such as droughts, wildfires, storms, floods, hurricanes, and typhoons.
The researchers noted that "in the past 12 months, 104 countries have set record high temperatures, and droughts, floods, heatwaves, and wildfires have occurred in Africa, Asia, and the United States, with the U.S. suffering approximately $3 trillion (about 4,378 trillion won) in losses due to climate disasters since 1980."
They added, "The heat of the oceans is the best indicator to monitor climate change, and the oceans are the "Fasoo" of global warming. If methods to mitigate climate change are not implemented, unprecedented changes and damages will continue to increase."
Reference materials
Advances in Atmospheric Sciences (2025), DOI: https://doi.org/10.1007/s00376-025-4541-3