Sea-level rise is one of the most serious consequences of climate change. Since precise satellite measures emerged in the 1990s, the global average sea-level has risen by over three centimeters per decade. A new study led by the Dresden University of Technology (TU Dresden) has recently provided one of the most comprehensive and coherent descriptions of this phenomenon, by analyzing how various factors, including thermal expansion, glacier melting, or changes in land water storage, contribute to sea-level rise.
“Assembling this coherent picture of sea-level and ocean-mass budgets not only required advanced datasets from satellite Earth observation and modelling. It also required the experts from various disciplines to arrive at a common framework,” said study lead author Martin Horwath, a professor of Physical Geodesy at TU Dresden.
“This is the fruit from the continuity in research and development on Earth observation data analysis enabled by the European Space Agency’s Climate Change Initiative [CCI]. The beauty of the results lies in the coherence of all the CCI Essential Climate Variables, which, when well-prepared and assembled, give a precise picture of our climate and its trend. The work doesn’t stop at this impressive milestone, there are still questions to be answered regarding the climate variability and its evolution,” explained Dr. Jérôme Benveniste, a researcher at the European Space Agency.
According to the scientists, about a third of the rise in sea level is caused by thermal expansion: as seawater warms due to climate change, it gradually expands. The other two thirds of the rise are caused by freshwater being added to the ocean, mainly from the melting of the Antarctic and Greenland Ice Sheets, as well as of various glaciers all over the world, but also from water added to the oceans from the land as a result of groundwater storage depletion.
While these results are in line with previous estimations, they gain additional confidence through the extensive data that was gathered and analyzed. However, further improvements in understanding the satellite measurements and the physical processes investigated are necessary. For instance, slow deformations of the solid Earth beneath the ocean can affect satellite measurements. Such effects need to be separated from changes in the ocean itself.
“It is important to be transparent about how results depend on some choices of methodology. For example, our satellite-based numbers on ocean-mass change changed somewhat when we improved the way to account for mass displacements in the solid Earth. More research is needed for the distinction between different processes of mass transports in the Earth system,” concluded study co-author Benjamin Gutknecht from TU Dresden.
The study is published in the journal Earth System Science Data.
Image Credit: ESA