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Monitoring Arctic Glaciers and IceCaps from Space

Final Report Summary - MAGICS (Monitoring Arctic Glaciers and IceCaps from Space)

Sea level change is one of the major challenges for the next century. Historically, ice loss from mountain glaciers and ice caps (MGIC) has been the single largest contributor to the ~2 mm/yr sea level rise over the last century and 50% of this contribution has come from the Arctic. The contribution of the Arctic MGIC to sea level rise is estimated to have more than doubled, from approximately 0.27 mm/yr (1961-1992) to 0.64 mm/yr in recent years, which is comparable to the contribution of the much larger ice sheets of Antarctica and Greenland. There is, however, a large uncertainty associated with these estimates. Direct observations of glaciers are sparse, both in space and in time, because of the labour intensive nature and are biased toward glaciers systems in accessible, mostly maritime, climate conditions.

The MAGICS (Monitoring Arctic Glaciers and Ice Caps from Space) aims to provide time-evolving estimates of the mass balance of the Arctic MGIC, based on combination of complementary remote-sensing observations. This has the potential to greatly improve our insights of their response to climate changes and their contribution to sea level rise and will help to close the envelope of the present day sea level rise budget and serve as an important validation tool for the development of dynamical ice sheet and glacier components which are currently poorly represented in globally coupled climate models. In the MAGICS project, the emphasis lies on the combination of two complementary satellite approaches: GRACE gravimetry and ICESat/Cryosat-2 altimetry.

The outgoing phase of the fellowship was spent at the University of Colorado at Boulder. The first part of the project has been dedicated to optimizing and improving the GRACE gravity data. In previous work, the fellow had developed a method to estimate the mass balance of the Greenland Ice Sheet from the GRACE data. This method has now expanded to retrieve the mass balance of all major glaciated areas of the Earth. The GRACE data has been compared to the ICESat data, where available, and the results have been incorporated in a study published in Science.

The GRACE gravity data has a rather low resolution of about 300 km. Therefore, only a coarse (yet accurate) picture of the changes of the Arctic MGIC can be obtained from this data. To identify individual glaciers and ice caps, which have a typical size of 10 to 100 kilometers, one needs to revert to satellite altimetry, which provides observations of changes in the surface elevation of the ice fields at a resolution of a few kilometers. The second part of the project therefore focused on processing, preparing and interpreting altimetry data from the ICESat and Cryosat missions. Although the fellow was familiar with the use of satellite altimetry over the oceans, the application to glaciated regions was new. In order to get acquainted with the data and processing methods, the fellow has visited the Glaciology group at the Scripps Institute of Oceanography, who are heavily involved in the ICESat mission. The software necessary to process the data has been written by the fellow and was bench-marked by comparison with results from earlier studies.

In the second and third year of the project, a method was developed to extract ice surface elevation changes from the new European Space Agency Cryosat-2 mission. Due to the innovative nature of this mission and the specific characteristics of the Arctic mountain glaciers and ice caps, existing techniques cannot be directly applied to the Cryosat-2 observations. The method developed for the MAGICS project delivers surface elevation rates at a higher resolution and accuracy than existing algorithms. In study published in Science, these Cryosat-2 observations revealed that a region of the Antarctic Ice Sheet, it was shown that the previously stable glaciers in the Bellingshausen Coast region suddenly started to shed ice into the ocean starting in 2009 at rate of about 55 cubic km each year. This makes the region one of the largest contributors to sea-level rise in Antarctica.

Beside anthropogenic warming, ice sheets and glaciers are affected by many natural processes, such as multi-year fluctuations in the atmosphere (for example, shifting pressure systems in the North Atlantic, or El Niño and La Niña events) and slow changes in ocean currents. To average out the effect of such natural fluctuations, a sufficiently long observation period is required. In a study published in Nature Geoscience, a team lead by the fellow showed that the ice loss detected by the GRACE satellites is larger than what we would expect to see just from natural fluctuations, but the speed-up of ice loss over the last years is not. The study suggest that another ten years of satellite observations is needed to do so for Greenland. As a result, extrapolation of the current contribution to sea-level rise of the ice sheets to 2100 may be too high or low by as much as 35 cm.

In the final stage of the MAGICS project, the ice mass changes of the Arctic MGICs obtained from the gravimetry and altimetry observations were compared to one another. A very good agreement was found between the two independent methods, giving a high rate of confidence in the results. It was found that the contribution of the Arctic glaciers to sea level rise has slightly increased over the last five years (2010-2014) compared to the first part of this century (2003-2009). Furthermore, the altimetry data produced by the MAGICS project have resulted in a fourfold increase in coverage, thereby providing observations of the Arctic MGICs with an unprecedented level of detail.

The Marie Curie Fellowship provided the fellow the opportunity to become an established expert in the field of satellite altimetry, also reflected in the invitations to present his work at international conferences and institutions, and being awarded the European Geosciences Union's 2016 Arne Richter Award for Outstanding Young Scientists.

The results of the MAGICS project were presented at international conferences, institutions and workshops and were published in high-quality journals. Since the start of the fellowship, the fellow has (co-)authored 18 peer-reviewed publications, including 4 in the top journals Science and Nature Geoscience. Furthermore, the fellow has (co-)written press releases for the most important articles published during the project. These press releases were successfully picked up by the popular media and reports of the fellow's work have appeared in major newspapers, magazines and received world-wide coverage on national radio and television stations (e.g. The Guardian, Der Spiegel, El Pais, BBC Radio, Al Jazeera, ...). Other dissemination activities include participation in the Researchers' Night organized by the University of Bristol, promoting the Marie Curie program to students and mentoring master and phd students on the use of Cryosat-2 data.