Staff Highlights: Prof. Jianli CHEN
Prof. Jianli Chen is a Chair Professor of Space Geodesy and Earth Sciences in the Department of Land Surveying and Geo-Informatics, The Hong Kong Polytechnic University. He graduated from the University of Science and Technology of China in 1986 with a major in Space Physics. He obtained a Master’s degree in Astrometry from the Shanghai Astronomical Observatory, Chinese Academy of Sciences in 1989, and earned a Ph.D. in Geophysics from the University of Texas at Austin, USA in 1998. After having dedicated nearly 30 years of his academic career at the University of Texas in Austin, he joined the Hong Kong Polytechnic University in 2022 through the Strategic Hiring Scheme.
Prof. Chen is a world-renowned expert in space geodesy and its applications in Earth sciences. He has been working on topics related to global climate change and geophysical applications of space geodetic techniques, including satellite gravimetry, satellite altimetry, and other geodetic measurements for over 30 years. He has been extensively involved in data processing, results validation, and geophysical interpretation of the Gravity Recovery and Climate Experiment (GRACE) satellite gravimetry mission, and is a leading science team PI of both the GRACE and GRACE Follow-On missions. He is a fellow of the American Geophysical Union (AGU) and International Association of Geodesy (IAG), and has severed as the chair of the IERS Special Bureau for Hydrology since 2004, and chair/member of numerous other committees in the geodesy community. A crowning distinction of his decorative career was the prestigious 2005 Presidential Early Career Awards for Scientists and Engineers (PECASE), the highest honor bestowed by the United States government on early career scientists and engineers (he was the first PECASE awardee in the geodesy field).
Prof. Chen’s research spans a wide range of topics, including satellite gravimetry, satellite altimetry, processing and application of Global Navigation Satellite System (GNSS) observational data, as well as global sea-level change, terrestrial water storage variations, melting of polar ice sheets and mountain glaciers, Earth rotation, and surface deformation. He has published more than 160 academic papers in top Earth science journals such as Science, Nature, PNAS, Nature Geoscience, Geophysical Research Letters, Journal of Geophysical Research, etc., with over 60 as the first author. He has led more than 20 research projects funded by governmental agencies such as NASA, NSF, NSFC (China), and RGC (Hong Kong), with total funding exceeding HK$63 million.
Prof. Chen’s impact extends beyond the academic fields and across national boundaries, drawing widespread attention from the global media. His research findings have been reported by many major media outlets, including USA Today, BBC News, The Washington Post, Discovery News, National Geographic, the Australian Broadcasting Corporation (ABC), New Scientist, China Daily, People’s Daily, and China Central Television (CCTV), among others. These reports have played a significant role in enhancing public awareness and understanding of Earth’s environment and climate change.
The following is a list of examples of Prof. Chen’s profound contributions in related research fields:
1. The first detection of accelerated melting of the Greenland Ice Sheet (Chen et al., 2006; Science)
Prof. Jianli Chen led a pioneering study published in Science (Chen et al., 2006) to have successfully detected accelerated ice melting of the Greenland ice sheet using early data from the GRACE satellite gravity observations. The melting of the Greenland Ice Sheet is considered as one of the primary contributors to the global sea level rise. However, accurately determining the rate of melting has been extremely challenging.
The launch of the GRACE (Gravity Recovery and Climate Experiment) satellite mission in 2002, jointly sponsored by NASA (United States) and DLR (Germany), has provided a revolutionary tool to precisely monitor mass redistribution within the Earth system - including the melting of polar ice sheets and mountain glaciers. However, the limited spatial resolution and data noise inherent in GRACE satellite gravity observations posed significant challenges in accurately estimating the melting rate of the Greenland Ice Sheet.
Prof. Chen’s team overcame these obstacles by designing a novel data processing method later known as Forward Modeling (FM). Using this method, they successfully corrected the leakage error in GRACE gravity measurements and estimated the melting rate of the Greenland Ice Sheet between April 2002 and November 2005. Their analysis revealed a clear acceleration in melting beginning in the summer of 2004, and that the melting extent had expanded into higher latitudes in the northeastern region of Greenland.
This pioneering research has had a profound impact. By introducing a completely new satellite gravity observational technique, it significantly enhanced people’s understanding of how climate warming affects polar ice sheet melting and contributes to sea level rise. The study was widely reported by over hundreds of media outlets around the world, including USA Today, The Washington Post, BBC News, China Daily, People’s Daily, and China Central Television (CCTV).
2. Accelerated melting of the Antarctic Ice Sheet (Chen et al., 2009; Nature Geoscience)
The Antarctic Ice Sheet is the largest on Earth, covering nearly 14 million square kilometers (km2). If it were to melt completely, the global mean sea levels would rise by more than 60 meters. However, accurately estimating its melting rate is difficult. On one hand, the West and East Antarctic Ice Sheets exhibit markedly different responses to climate change due to differences in elevation and topography. On the other hand, the tremendous scale and remoteness of the Antarctica make field observations scarce, and satellite remote sensing also faces significant limitations. For a long time, it was even unclear whether the Antarctic Ice Sheet as a whole was gaining or losing mass.
Although GRACE satellite gravimetry provided a new approach to quantitatively observe mass changes in the Antarctica, the limited spatial resolution of the GRACE data made it difficult to accurately determine regional glacier mass variations. By applying the innovative Forward Modeling leakage correction method, Prof. Chen’s team was able to overcome the challenge and successfully estimate the melting rates of different regions of the Antarctic Ice Sheet between April 2002 and January 2009 using GRACE satellite gravity observations.
Their analysis revealed that during this nearly 7-year period, the Antarctic Ice Sheet was losing ice at a rate of 190 ± 77 km³ per year (equivalent to 190 billion metric tons of water annually). The majority of this loss, about 132 ± 26 km³ per year, came from coastal glaciers in West Antarctica. Moreover, the melting rate in these areas increased significantly starting in 2006. Another groundbreaking finding was the first detection of notable glacier mass loss in parts of East Antarctica, previously thought to be relatively stable.
This breakthrough studywas published in Nature Geoscience (Chen et al., 2009), and it drew widespread attention from news media around the world as well.
3. Closing the global sea level rise budget (Chen et al., 2013; Nature Geoscience)
Accurate observation and interpretation of global sea level rise are key topics in climate change research. Since the early 21st century, the development of satellite altimetry, satellite gravimetry (GRACE), and the global ocean float network (ARGO) has brought a completely new era for studying sea level change. In theory, after accounting for solid Earth deformation, the observed global sea level change should equal the sum of the ocean mass change (from GRACE) and steric sea level change (from ARGO). However, for a period of time, the altimeter-based global sea level rise rate did not match the sum of mass and steric components, creating what is known as the “sea level budget closure problem”.
Prof. Chen’s team reprocessed the GRACE data using the innovative Forward Modeling method, and found that earlier GRACE solutions had significantly underestimated the ocean mass increase due to inadequate treatment of leakage errors. By systematically reanalyzing satellite altimetry, GRACE gravimetry, and ARGO float observations, they demonstrated that between 2005 and 2011, the observed global sea level rise rate of 2.39 ± 0.48 mm/year was fully consistent with the sum of the GRACE-based ocean mass increase (1.80 ± 0.47 mm/year) and the ARGO-based steric change (0.60 ± 0.27 mm/year), totaling 2.40 ± 0.54 mm/year.
4. Pioneering Global Sea Level Budget Analysis (Chen et al., 1998; GRL)
With the launch of the first modern altimetry satellite TOPEX/Poseidon in the early 1990s, scientists were able to accurately monitor global mean sea level change. However, understanding the mechanisms driving sea level change remained in its infancy. During his Ph.D. studies (1994–1998), Prof. Chen carried out a pioneering analysis of the global sea level change budget closure.
Due to the limited availability of ocean mass and temperature/salinity observations at the time, his early work focused on seasonal changes in the global mean sea level. To address the lack of ocean mass observations, Prof. Chen innovatively proposed using climate model outputs of land water storage and atmospheric water vapor to estimate ocean mass changes through a global water mass balance approach. He also used limited traditional ocean temperature and salinity data from the World Ocean Atlas to calculate potential steric sea level changes, and then compared these with altimetry data from TOPEX/Poseidon. At the seasonal scale, the results from the three methods agreed remarkably well, demonstrating for the first time that global sea level change could be quantitatively explained through budget closure analysis.
5. Global warming shifted the Earth’s rotation pole (Chen et al., 2013; GRL)
With the advancement of modern space geodetic technologies, Earth’s rotation has become one of the most precisely observed geodetic variables. Variations in Earth’s rotation are closely linked to mass redistribution within the Earth system. Accurate measurements of Earth rotation parameters, including Length-of-Day (LOD) and polar motion provide an independent tool for studying global climate change and large-scale mass transport processes.
Length-of-Day reflects changes in the rotational speed of the Earth, while polar motion describes the movement of the Earth’s rotational pole, i.e. the rotational axis’ intersection with the Earth’s surface near the North Pole. Long-term changes in Earth rotation, such as the secular drift of the rotational pole (typically toward the south), are primarily driven by solid Earth processes, including the Post-Glacial Rebound (also-called Glacial Isostatic Adjustment) and plate tectonics. However, seasonal and interannual variations in Earth rotation are mainly caused by mass redistribution within the climate system.
By analyzing long-term polar motion data, Prof. Chen’s team was the first to have detected a shift in the direction of the Earth’s rotational pole drift—from southward to eastward—starting around 2005. Using GRACE satellite gravity data, the team found that this shift was directly linked to accelerated melting of polar ice sheets and rising global sea level driven by global warming.
This major discovery was published in the Geophysical Research Letters (Chen et al., 2013). The study received wide media attention worldwide, including coverage by CBS, New Scientist, Physics Today, Scientific American, Daily Mail, The Guardian, Inverse, Xinhua News Agency, Reference News, and others. Nature published a special commentary as a “Breaking News” item, and both NASA and the U.S. National Science Foundation (NSF) listed the study among their Research Highlights of 2013.
6. Discovery of subglacial lakes in Greenland using GNSS data (Ran et al., 2024; Nature)
The Greenland Ice Sheet is currently the largest single contributor to global sea level rise, with the potential to raise the mean sea level by up to seven meters if completely melted. While scientists have long studied the melt processes of the ice sheet, one crucial question has remained unanswered: how does meltwater storage evolve within the ice sheet throughout the summer melt season?
Prof. Chen and a team of international experts from Hong Kong, mainland China, U.S., Netherlands, Denmark and Belgium, led by Dr. Jiangjun Ran at the Southern University of Science and Technology, used a network of GNSS (Global Navigation Satellite System) stations—called the Greenland GNSS Network—to observe bedrock deformation in response to meltwater loading. These data allowed the researchers, for the first time to detect subglacial lakes and to quantify seasonal meltwater storage processes.
Using continuous GNSS data from 22 stations near outlet glaciers and bedrock from 2009 to 2015, the researchers estimated regional meltwater volume, elastic bedrock deformation, and vertical displacement to understand how meltwater evolves spatially and temporally. GNSS also enabled monitoring of large-scale mass changes in the climate system, such as groundwater depletion and lake storage variations.
Results showed that most meltwater during summer was temporarily stored within the ice sheet, peaking in July and gradually decreasing thereafter. Meltwater induced average bedrock subsidence of about 5 mm, with extreme melt years like 2010 and 2012 causing subsidence up to 12 mm and 14 mm, respectively. The average meltwater residence time was about eight weeks, varying regionally—from about nine weeks in the northeast and west to just 4.5 weeks in the south and southeast.
The study also found that climate models may overestimate runoff or underestimate meltwater retention, and suggested that projected meltwater runoff in warmer years should be adjusted upward by ~20% for more accurate assessments.
This important discovery was published in Nature (Ran et al., 2024) and received widespread media coverage, including Xinhua News Agency, People’s Daily, China Science Daily (front page), ScienceNet.cn, CGTN, and many other major outlets in mainland China and Hong Kong (e.g., Ming Pao, Wen Wei Po, Ta Kung Pao, HK Commercial Daily).
7. Sea level rise and Earth rotation reveal permanent hydrological regime change in the 21st Century (Seo et al., 2025; Science)
Global warming has triggered changes in atmospheric and oceanic temperatures, disrupting terrestrial water cycles and surface water fluxes such as precipitation and evapotranspiration. These processes have led to significant changes in terrestrial water storage (TWS).
In collaboration with international colleagues, Prof. Chen and the team (led by Prof. Ki-Weon Seo at the Seoul National University) have utilised advanced reanalysis datasets and satellite observations, and uncovered a dramatic depletion of terrestrial water storage—particularly soil moisture—across the globe.
Between 2000 and 2002, global soil moisture decreased by about 1,614 Gt (km³)—a loss significantly greater than the roughly 900 Gt of ice mass lost from Greenland during a similar timeframe (2002–2006). From 2003 to 2016, another 1,009 Gt of soil water was lost, and as of 2021, the global soil moisture had not yet recovered to the pre-2000 levels.
To verify this, the team examined independent data from satellite altimetry and Earth rotation observations. They found that between 2000 and 2002, global mean sea level rose by ~4.4 mm, and in the following decade, the Earth’s rotation axis shifted by ~58 cm toward the east. These independent observations support the ERA5 model results, indicating a long-term hydrological shift driven by reduced rainfall and increased evapotranspiration under global warming.
The findings suggest that global soil water depletion is persistent and unlikely to recover under current climate conditions.
This landmark study was recently published in Science (Seo et al., 2025) and has garnered extensive international media attention. Prof. Chen and lead author Prof. Ki-Weon Seo have built a long-term research collaboration, having jointly published over 20 high-impact journal papers in related fields.
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Prof. Chen is currently seeking highly motivated candidates Ph.D. student and for Research Assistant/Associate positions in the field of space geodesy and global climate change. Preferred qualifications include strong interest in space geodesy, geodynamics and global climate change, proficient English communication skills, and good data analysis and programming skills.
The Ph.D. candidates are expected to work on two RGC and NSFC sponsored major projects on global and regional sea level change. Anybody with a major in geodesy, geophysics, or other related Earth science fields is encouraged to apply. Please send your CV (including college transcripts and rankings), a cover letter, and a research statement outlining your Ph.D. research plan (all in PDF format) to Prof. Jianli Chen (jianli.chen@polyu.edu.hk).
