%0 Journal Article %J Science Advances %D 2019 %T Contribution of the Greenland Ice Sheet to sea level over the next millennium %A Aschwanden, Andy %A Fahnestock, Mark A. %A Truffer, Martin %A Brinkerhoff, Douglas J. %A Hock, Regine %A Khroulev, Constantine %A Mottram, Ruth %A Khan, S. Abbas %X The Greenland Ice Sheet holds 7.2 m of sea level equivalent and in recent decades, rising temperatures have led to accelerated mass loss. Current ice margin recession is led by the retreat of outlet glaciers, large rivers of ice ending in narrow fjords that drain the interior. We pair an outlet glacier–resolving ice sheet model with a comprehensive uncertainty quantification to estimate Greenland's contribution to sea level over the next millennium. We find that Greenland could contribute 5 to 33 cm to sea level by 2100, with discharge from outlet glaciers contributing 8 to 45% of total mass loss. Our analysis shows that uncertainties in projecting mass loss are dominated by uncertainties in climate scenarios and surface processes, whereas uncertainties in calving and frontal melt play a minor role. We project that Greenland will very likely become ice free within a millennium without substantial reductions in greenhouse gas emissions. %B Science Advances %V 5 %P eaav9396 %8 jun %G eng %U http://advances.sciencemag.org/lookup/doi/10.1126/sciadv.aav9396 %R 10.1126/sciadv.aav9396 %0 Journal Article %J The Cryosphere %D 2018 %T Design and results of the ice sheet model initialisation experiments initMIP-Greenland: an ISMIP6 intercomparison %A Goelzer, Heiko %A Nowicki, Sophie %A Edwards, Tamsin %A Beckley, Matthew %A Abe-Ouchi, Ayako %A Aschwanden, Andy %A Calov, Reinhard %A Gagliardini, Olivier %A Gillet-Chaulet, Fabien %A Golledge, Nicholas R. %A Gregory, Jonathan %A Greve, Ralf %A Humbert, Angelika %A Huybrechts, Philippe %A Kennedy, Joseph H. %A Larour, Eric %A Lipscomb, William H. %A Le clec'h, Sébastien %A Lee, Victoria %A Morlighem, Mathieu %A Pattyn, Frank %A Payne, Antony J. %A Rodehacke, Christian %A Rückamp, Martin %A Saito, Fuyuki %A Schlegel, Nicole %A Seroussi, Helene %A Shepherd, Andrew %A Sun, Sainan %A van de Wal, Roderik %A Ziemen, Florian A. %X Abstract. Earlier large-scale Greenland ice sheet sea-level projections (e.g. those run during the ice2sea and SeaRISE initiatives) have shown that ice sheet initial conditions have a large effect on the projections and give rise to important uncertainties. The goal of this initMIP-Greenland intercomparison exercise is to compare, evaluate, and improve the initialisation techniques used in the ice sheet modelling community and to estimate the associated uncertainties in modelled mass changes. initMIP-Greenland is the first in a series of ice sheet model intercomparison activities within ISMIP6 (the Ice Sheet Model Intercomparison Project for CMIP6), which is the primary activity within the Coupled Model Intercomparison Project Phase 6 (CMIP6) focusing on the ice sheets. Two experiments for the large-scale Greenland ice sheet have been designed to allow intercomparison between participating models of (1) the initial present-day state of the ice sheet and (2) the response in two idealised forward experiments. The forward experiments serve to evaluate the initialisation in terms of model drift (forward run without additional forcing) and in response to a large perturbation (prescribed surface mass balance anomaly); they should not be interpreted as sea-level projections. We present and discuss results that highlight the diversity of data sets, boundary conditions, and initialisation techniques used in the community to generate initial states of the Greenland ice sheet. We find good agreement across the ensemble for the dynamic response to surface mass balance changes in areas where the simulated ice sheets overlap but differences arising from the initial size of the ice sheet. The model drift in the control experiment is reduced for models that participated in earlier intercomparison exercises. %B The Cryosphere %V 12 %P 1433–1460 %8 apr %G eng %U https://www.the-cryosphere.net/12/1433/2018/ %R 10.5194/tc-12-1433-2018 %0 Journal Article %J Frontiers in Earth Science %D 2018 %T Modeling Winter Precipitation Over the Juneau Icefield, Alaska, Using a Linear Model of Orographic Precipitation %A Roth, Aurora %A Hock, Regine %A Schuler, Thomas V. %A Bieniek, Peter A. %A Pelto, Mauri %A Aschwanden, Andy %K Alaska %K downscaling %K glacier mass balance %K Juneau Icefield %K Modeling %K orographic precipitation %K snow accumulation %B Frontiers in Earth Science %V 6 %P 1–19 %8 mar %G eng %U http://journal.frontiersin.org/article/10.3389/feart.2018.00020/full %R 10.3389/feart.2018.00020 %0 Journal Article %D 2017 %T Sediment transport drives tidewater glacier periodicity %A Brinkerhoff, Douglas %A Truffer, Martin %A Aschwanden, Andy %X Most of Earth’s glaciers are retreating, but some tidewater glaciers are advancing despite increasing temperatures and contrary to their neighbors. This can be explained by the coupling of ice and sediment dynamics: a shoal forms at the glacier terminus, reducing ice discharge and causing advance towards an unstable configuration followed by abrupt retreat, in a process known as the tidewater glacier cycle. Here we use a numerical model calibrated with observations to show that interactions between ice flow, glacial erosion, and sediment transport drive these cycles, which occur independent of climate variations. Water availability controls cycle period and amplitude, and enhanced melt from future warming could trigger advance even in glaciers that are steady or retreating, complicating interpretations of glacier response to climate change. The resulting shifts in sediment and meltwater delivery from changes in glacier configuration may impact interpretations of marine sediments, fjord geochemistry, and marine ecosystems. %V 8 %P 90 %8 2017/07/21 %@ 2041-1723 %G eng %U https://doi.org/10.1038/s41467-017-00095-5 %N 1 %! Nature Communications %0 Journal Article %J Frontiers in Earth Science %D 2016 %T Bayesian Inference of Subglacial Topography Using Mass Conservation %A Brinkerhoff, Douglas J %A Aschwanden, Andy %A Truffer, Martin %X We develop a Bayesian model for estimating ice thickness given sparse observations coupled with estimates of surface mass balance, surface elevation change, and surface velocity. These fields are related through mass conservation. We use the Metropolis-Hastings algorithm to sample from the posterior probability distribution of ice thickness for three cases: a synthetic mountain glacier, ̈ Storglaci aren, and Jakobshavn Isbræ. Use of continuity in interpolation improves thickness estimates where relative velocity and surface mass balance errors are small, a condition difficult to maintain in regions of slow flow and surface mass balance near zero. Estimates of thickness uncertainty depend sensitively on spatial correlation. When this structure is known, we suggest a thickness measurement spacing of one to two times the correlation length to take best advantage of continuity based interpolation techniques. To determine ideal measurement spacing, the structure of spatial correlation must be better quantified. %B Frontiers in Earth Science %V 4 %P 1–27 %8 feb %G eng %U http://journal.frontiersin.org/article/10.3389/feart.2016.00008 %R 10.3389/feart.2016.00008 %0 Journal Article %J Nature Communications %D 2016 %T Complex Greenland outlet glacier flow captured %A Aschwanden, Andy %A Fahnestock, Mark A %A Truffer, Martin %B Nature Communications %V 7 %P 10524 %8 feb %G eng %U http://www.nature.com/doifinder/10.1038/ncomms10524 %R 10.1038/ncomms10524 %0 Journal Article %J Science Advances %D 2016 %T Geodetic measurements reveal similarities between post-Last Glacial Maximum and present-day mass loss from the Greenland ice sheet %A Khan, Shfaqat A %A Sasgen, Ingo %A Bevis, Michael %A van Dam, T. %A Bamber, Jonathan L %A Wahr, John %A Willis, Michael %A Kjaer, K. H. %A Wouters, Bert %A Helm, Veit %A Csatho, Beata %A Fleming, Kevin %A Bjork, A. A. %A Aschwanden, Andy %A Knudsen, Per %A Munneke, Peter Kuipers %B Science Advances %V 2 %P e1600931–e1600931 %8 sep %G eng %U http://advances.sciencemag.org/cgi/doi/10.1126/sciadv.1600931 %R 10.1126/sciadv.1600931 %0 Journal Article %J Journal of Glaciology %D 2016 %T Modeling the evolution of the Juneau Icefield between 1971 and 2100 using the Parallel Ice Sheet Model (PISM) %A Ziemen, Florian A %A Hock, Regine %A Aschwanden, Andy %A Khroulev, Constantine %A Kienholz, Christian %A MELKONIAN, ANDREW %A ZHANG, JING %B Journal of Glaciology %V 62 %P 199–214 %G eng %0 Journal Article %J The Cryosphere %D 2016 %T Modelled glacier dynamics over the last quarter of a century at Jakobshavn Isbræ %A Muresan, Ioana S. %A Khan, Shfaqat A. %A Aschwanden, Andy %A Khroulev, Constantine %A Van Dam, Tonie %A Bamber, Jonathan %A van den Broeke, Michiel R. %A Wouters, Bert %A Kuipers Munneke, Peter %A Kjær, Kurt H. %B The Cryosphere %V 10 %P 597–611 %8 mar %G eng %U http://www.the-cryosphere.net/10/597/2016/ %R 10.5194/tc-10-597-2016 %0 Journal Article %J Journal of Geophysical Research: Earth Surface %D 2016 %T A synthesis of the basal thermal state of the Greenland Ice Sheet %A MacGregor, Joseph A. %A Fahnestock, Mark A. %A Catania, Ginny A. %A Aschwanden, Andy %A Clow, Gary D. %A Colgan, William T. %A Gogineni, S. Prasad %A Morlighem, Mathieu %A Nowicki, Sophie M. J. %A Paden, John D. %A Price, Stephen F. %A Seroussi, Helene %B Journal of Geophysical Research: Earth Surface %8 jul %G eng %U http://doi.wiley.com/10.1002/2015JF003803 %0 Journal Article %J Reports on Progress in Physics %D 2015 %T Greenland ice sheet mass balance %A Khan, Shfaqat A. %A Aschwanden, Andy %A Bjørk, Anders A %A Whar, John %A Kjeldsen, Kristian K. %A Kjær, Kurt H. %X Mass balance equation for glaciers; areal distribution and ice volumes; estimates of actual mass balance; loss by calving of icebergs; hydrological budget for Greenland; and temporal variations of Greenland mass balance are examined. %B Reports on Progress in Physics %I IOP Publishing %V 78 %P 26 %G eng %U http://dx.doi.org/10.1088/0034-4885/78/4/046801 %R 10.1088/0034-4885/78/4/046801 %0 Journal Article %J Journal of Glaciology %D 2014 %T Role of model initialization for projections of 21st-century Greenland ice sheet mass loss %A Aðalgeirsdóttir, Guðfinna %A Aschwanden, Andy %A Khroulev, Constantine %A Boberg, Frederik %A Mottram, Ruth %A Lucas-Picher, P. %K ice and climate %K ice-sheet modeling %B Journal of Glaciology %V 60 %P 782–794 %G eng %U http://www.igsoc.org/journal/60/222/t13j202.html %R 10.3189/2014JoG13J202