

The whole study ties together the many different process using GRACE data from a pair of satellites that by measuring changes in Earth’s gravitational field can measure changes in the total mass of the ice sheet and also displayed on the polar portal. Although GRACE ended in 2016, the team is looking forward to extending the record with the new GRACE-Follow On (GRACE-FO) mission when it becomes available. “We have calculated via two independent techniques that the Greenland ice sheet lost on average 255 ± 15 km3 of ice every year between 2003 and 2016” said DTU scientist Valentina Barletta. “That’s just a bit less than 1mm of sea level per year over the period where we have observations but we also see quite a lot of variability from one year to the next which we really need to understand, so it’s important to keep an eye on this”.



As well as straightforward monitoring, the ESA CCI team have used the observations to better understand the changes they have observed. “By combining GRACE data with climate model output we can assess how much of the ice is being lost by surface melt and how much by ocean processes like icebergs and ocean melt” said Ruth Mottram. “What we have also done in this latest paper is to break this down into regions on the ice sheet. There are some areas where the ocean interface is much more important and other areas where getting the surface processes right is more important.” She continues. “There are also some areas where we see models need to be improved.”



The satellite data in this latest study is used to test how well climate models work in Greenland. One of the final outcomes of the paper shows that although huge strides in understanding the ice sheet and the climate have been made over the last 30 years, ground observations are still vital. “One of the areas we discuss is in southern Greenland where the models and satellite observations don’t seem to agree very well” said Ruth Mottram “fortunately our colleagues at GEUS who were also part of this study have very useful data from their promice weather stations that we could use to identify and correct the problems with the model output. We also identified areas in this study where we need a lot more direct observations from both satellite and ground observations to help better understand the processes we want to model with both climate and ice sheet models. The really important point though is we have a long-term and consistent set of observations. This means we can now quickly identify anomalies and assess how the ice sheet is changing in really fine detail”.



More details are available in the open access scientific article:



Mottram, R.; B. Simonsen, S.; Høyer Svendsen, S.; Barletta, V.R.; Sandberg Sørensen, L.; Nagler, T.; Wuite, J.; Groh, A.; Horwath, M.; Rosier, J.; Solgaard, A.; Hvidberg, C.S.; Forsberg, R. An Integrated View of Greenland Ice Sheet Mass Changes Based on Models and Satellite Observations. Remote Sens. 2019, 11, 1407.



doi.org/10.3390/rs11121407



This work was carried out by the ESA Climate change initiative for the Greenland ice sheet funded via ESA-ESRIN contract number 4000104815/11/I-NB and in the framework of the Sea Level Budget Closure CCI Project funded via ESA-ESRIN contract number 4000119910/17/I-NB. HIRHAM5 regional climate model simulations were carried out by R.M. as part of the ice2ice project, a European Research Council project under the European Community’s Seventh Framework Programme (FP7/ 2007-2013)/ ERC grant agreement 610055.