Deep Ocean Warming Identified as Key Driver of Rising Sea Levels

Scientists have uncovered a critical factor contributing to the mysterious rise in global sea levels: heat absorption occurring deep within the ocean. A study published in *Earth’s Future* reveals that warming in ocean layers below 2,000 meters plays a significant role in accelerating sea level rise. This discovery fills a major gap in understanding the factors driving recent changes in global mean sea level (GMSL).

For years, researchers have tracked contributors to sea level rise, including melting ice sheets, glacier loss, and thermal expansion of seawater. However, an unexplained discrepancy emerged around 2016: observed sea levels were rising faster than models could account for. Now, deep ocean warming appears to be the missing piece. According to the research, this phenomenon likely contributes nearly 0.4 millimeters annually to sea level rise between 2005 and 2022, accounting for almost ten percent of the total increase during that period.

The study, led by Anny Cazenave of the Laboratory of Space Geophysical and Oceanographic Studies in France, used a reanalysis method called CIGAR to estimate deep ocean conditions. This approach combined satellite data, including ocean mass measurements from the GRACE program, with advanced computer models. The findings highlight that while surface and upper ocean layers are well-documented as heat reservoirs, deeper waters also absorb significant amounts of energy, driving sea level expansion and rise.

This discovery underscores the importance of understanding deep ocean dynamics, which remain less studied due to limitations in data collection tools like Argo floats, which only measure up to 2,000 meters. The research not only improves models for projecting future sea level changes but also raises new questions about the broader impacts of deep ocean warming on global climate systems.