Researchers at The Hong Kong Polytechnic University have analyzed 30 years of data to show that global sea levels have risen by about 90 millimeters since 1993, with melting land ice now driving most of the increase. The study, using satellite laser ranging, indicates an average rise of 3.3 millimeters per year, a rate that is speeding up. Ocean mass from ice melt accounts for over 60 percent of the rise since 2005.
Rising global mean sea level serves as a key indicator of planetary warming. A team from The Hong Kong Polytechnic University, led by Prof. Jianli Chen and Dr. Yufeng Nie, has created the first direct 30-year record of changes in global ocean mass from 1993 to 2022. This record, based on satellite laser ranging data, highlights the growing role of added water mass in elevating sea levels.
Sea level rise stems from two main processes: the thermal expansion of seawater as it absorbs heat and the influx of water from melting land ice. The study found that global sea level increased at an average of 3.3 millimeters annually over the period, with the pace accelerating. Between 1993 and 2022, the total rise reached approximately 90 millimeters, of which roughly 60 percent resulted from ocean mass gains, particularly since 2005.
The primary contributor to this mass increase is accelerated melting of land ice, with losses from Greenland and mountain glaciers making up more than 80 percent of the added ocean water. The researchers overcame technical limitations of satellite laser ranging—such as limited satellites and resolution—through innovative forward modeling that enhanced spatial detail by accounting for ocean-land boundaries.
Prof. Jianli Chen stated, "In recent decades, climate warming has led to accelerated land ice loss, which has played an increasingly dominant role in driving global sea-level rise. Our research enables the direct quantification of global ocean mass increase and provides a comprehensive assessment of its long-term impact on sea-level budget. This offers crucial data for validating coupled climate models used to project future sea-level rise scenarios."
Dr. Yufeng Nie noted, "The research showed that the ocean mass changes derived from SLR analysis align well with the total sea level changes observed by satellite altimeters, after accounting for the effect of ocean thermal expansion. This demonstrates that the traditional SLR technique can now serve as a novel and powerful tool for long-term climate change studies."
The findings appear in the Proceedings of the National Academy of Sciences.