Mass and Height Change
New data until July 2025.
The map and graph show the gain in the mass of ice when there is precipitation, and how much of this mass is lost when snow and ice melt and when icebergs break off from the ice sheet’s major outlet glaciers. The difference in these mass changes over a glaciological year (September-August) is called the total mass balance of the Greenland Ice Sheet.
The map shows the latest changes in mass derived from data from the GRACE and GRACE-FO satellites.
The graph illustrates the month-by-month development in changes of mass measured in gigatonnes, Gt (1 Gt is 1 billion tonnes or 1 km3 of water). The left axis on the graph shows how this ice mass loss corresponds to sea level rise contribution. 100 Gt corresponds to 0.28 mm global sea level rise).
This data shows that most of the loss of ice occurs along the edge of the ice sheet, where independent observations also indicate that the ice is thinning, that the glacier fronts are retreating in fjords and on land, and that there is a greater degree of melting from the surface of the ice.
High on the central region of the ice sheet, however, the GRACE satellites show that there is a small increase in the mass of the ice. Other measurements suggest that this is due to a small increase in precipitation/snowfall.
All changes are given relative to April 2002.
This data are based on DTU Gravitational Mass Balance (Barletta et al. 2020), and it can be seen that during the period 2003-2025, the Greenland Ice Sheet has lost 252 km3 of water per year, corresponding to an annual contribution to the mean increase in sea level of 0.69 mm.
GRACE satellites measure gravitational force
The figures are based on data from the GRACE satellites (jointly operated by NASA and Deutsches Zentrum für Luft- und Raumfahrt, DLR). The gravitational force changes when the amount of ice changes, and this can be measured from the GRACE satellites. Data from the satellites is processed at different centres, which provide monthly models of the Earth’s gravitational field. The method that is used here to derive changes in the amount of ice on the basis of changes in the gravitational force has been developed by researchers at DTU Space and other institutions, and is described in detail in Barletta et al. (2013). The raw GRACE satellite data is carefully processed and validated prior to being released, which explains the delay of several months until the data becomes available.
GRACE (Gravity Recovery And Climate Experiment) and GRACE Follow On (GRACE-FO) are joint NASA-DLR satellite missions. Both GRACE missions consist of twin satellites, which both orbit the Earth at an altitude of around 500 km. The two satellites are separated by a distance of around 220 km. This distance depends on gravity and can be measured very precisely. This information is used to generate monthly, global models of the Earth’s gravitational field.
GRACE was launched in March 2002, and the mission ended in October 2017. GRACE-FO was launched in May 2018. Therefore a gap exists between both missions.
More about the method
As mentioned above, there are several centres that generate the monthly GRACE gravitational fields which are used to estimate changes to ice mass. The data used here is produced by the Center for Space Research, University of Texas.
The GRACE satellites measure the total changes in ice mass – at the present time. A number of these changes occur, however, due to the fact that the mass of the Earth is constantly changing as a sort of delayed consequence of previous changes in the size of the Ice Sheet (similar to the way in which a sofa slowly regains its shape when you stand up). This is known as Glacial Isostatic Adjustment. It should be noted that the changes in mass illustrated here have been corrected for the changes in mass due to Glacial Isostatic Adjustment, with a model developed in Caron et al., 2018.
More information:
The map shows how the Greenland Ice Sheet topography has changed during the three-year period from January 2018 until December 2020. Red areas have thinned while blue areas have thickened. The figure shows the average elevation change per year over the three-year period. It is clearly evident that near many of the large outlet glaciers, the ice sheet has thinned by several metres each year, but we do also see that parts of the ice sheet have thickened due to precipitation during the three years.
The figure shows a clear thinning of a large part of the Greenland ice sheet in the period 2018-2020, and the area of thinning has increased significantly compared to the previous measurement period of 2017-2019. Even highest on the ice sheet we see thinning, which was not seen previously where we mostly found the high thinning rates near the large outlet glaciers .
Radar-based elevation measurements
The elevation change of the Greenland ice sheet are derived from data from the EU Copernicus radar satellite mission Sentinel 3A, which was launched in February 2016. The satellite (almost) repeats the same tracks every month, making the data set well suited for documenting the ongoing changes to the topography in high spatial resolution.
The method that has been applied to obtain the elevation change results is developed at DTU Space and is explained in detail in these publications: Simonsen and Sørensen (2017) and Sørensen et al. (2018)
Sentinel-3A is a so-called radar altimetry mission. The instrument onboard the satellite emits a radar signal, which is reflected on the surface and collected again by the satellite instrument. The height of the surface can then be estimated from the two way travel time of the signal.
There are some challenges associated with using radar altimetry over snow-covered areas, because the signal can penetrate into the top snow, and hence it might not reflect back from the physical surface. This is not a problem though in regions that experience regularly melt, which is the case in the margin zone of the ice sheet.
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