Ice Sheets
Ice Mass Change and Ice Sheet Thickness Variations
How fast is the ice being lost in Greenland and Antarctica?
Ice sheets are vast continental-scale masses of glacial ice that cover more than 50,000 km². Today, only two ice sheets exist: the Antarctic Ice Sheet and the Greenland Ice Sheet. Unlike smaller glaciers that are confined by topography, ice sheets form broad dome-shaped structures and flow outward in all directions from their central accumulation areas under their own weight. They can completely bury the underlying landscape, covering mountains, valleys, and plains beneath thousands of metres of ice.
Temporal changes of the volume and mass of ice sheets are sensitive indicators of climate change, and strongly affect the global water cycle, surface energy budget, sea level change, ocean circulation patterns, and hence global climate. A precise monitoring of the behaviors of these ice bodies is essential for improved understanding of the Earth’s system, and interactions between its sub-components. Apart from this scientific motivation, these investigations are also highly relevant to society, since phenomena such as the global sea level rise are largely driven by accelerated melting of the Greenland and Antarctica ice sheets, and could be catastrophic for millions of people in the future.
With observations from dedicated satellite gravity missions (CHAMP, GRACE, GRACE Follow-On, and GOCE), as well as remote sensing techniques from satellites and aircrafts, a precise monitoring of the mass and volume changes of the ice sheets is now possible. The three following methods are currently applied to measure the mass balance and volume changes of these ice bodies:
- comparing net snow accumulation (assessed by atmospheric modeling) with ice discharge to the ocean by ice flow, assessed through measurements of flow velocities by interferometric SAR (InSAR);
Both, the geometric and gravimetric methods require correction for changes in the elevation of rock beneath the ice. This is not necessary for the first method, which however relies on assessing the small difference between two large quantities, each with considerable uncertainty
The results obtained from the three different methods show a high level of agreements for the ice mass and volume changes (The IMBIE team, 2018 and 2020). The mass changes are shown for the Greenland and Antarctic ice sheets (see in top), derived from more than 15 years of GRACE data. In Greenland, the ice masses decrease significantly, particularly at the ice sheet margin. The time series shows a negative trend of ice masses in the order of almost 300 billion tons per year with a pronounced annual signal. The situation is different in Antarctica: There are regions in East Antarctica with an increase of ice masses, whereas the much larger mass loss in West Antarctica (primarily in the Amundsen Bay embayment) leads to an overall decrease of ice masses of about 125 billion tons per year. From 2009, the time series for the mass changes in Antarctica shows an increased negative trend, which is mainly caused by mass loss in West Antarctica. The results do not show a clear annual signal and the estimates are less accurate than those of Greenland, since the required corrections for vertical crustal motions due to glacial isostatic adjustment (GIA) have a larger impact and the GIA models are less accurate (in Antarctica).
Data Sources
Data sets available at the European Space Agency (ESA)
Data sets available at the US National Aeronautics and Space Administration (NASA)
Further Information
