TY - JOUR T1 - Contribution of the Greenland Ice Sheet to sea level over the next millennium JF - Science Advances Y1 - 2019 A1 - Aschwanden, Andy A1 - Fahnestock, Mark A. A1 - Truffer, Martin A1 - Brinkerhoff, Douglas J. A1 - Hock, Regine A1 - Khroulev, Constantine A1 - Mottram, Ruth A1 - Khan, S. Abbas AB - 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. VL - 5 UR - http://advances.sciencemag.org/lookup/doi/10.1126/sciadv.aav9396 ER - TY - JOUR T1 - Design and results of the ice sheet model initialisation experiments initMIP-Greenland: an ISMIP6 intercomparison JF - The Cryosphere Y1 - 2018 A1 - Goelzer, Heiko A1 - Nowicki, Sophie A1 - Edwards, Tamsin A1 - Beckley, Matthew A1 - Abe-Ouchi, Ayako A1 - Aschwanden, Andy A1 - Calov, Reinhard A1 - Gagliardini, Olivier A1 - Gillet-Chaulet, Fabien A1 - Golledge, Nicholas R. A1 - Gregory, Jonathan A1 - Greve, Ralf A1 - Humbert, Angelika A1 - Huybrechts, Philippe A1 - Kennedy, Joseph H. A1 - Larour, Eric A1 - Lipscomb, William H. A1 - Le clec'h, Sébastien A1 - Lee, Victoria A1 - Morlighem, Mathieu A1 - Pattyn, Frank A1 - Payne, Antony J. A1 - Rodehacke, Christian A1 - Rückamp, Martin A1 - Saito, Fuyuki A1 - Schlegel, Nicole A1 - Seroussi, Helene A1 - Shepherd, Andrew A1 - Sun, Sainan A1 - van de Wal, Roderik A1 - Ziemen, Florian A. AB - 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. VL - 12 UR - https://www.the-cryosphere.net/12/1433/2018/ ER - TY - JOUR T1 - Modeling Winter Precipitation Over the Juneau Icefield, Alaska, Using a Linear Model of Orographic Precipitation JF - Frontiers in Earth Science Y1 - 2018 A1 - Roth, Aurora A1 - Hock, Regine A1 - Schuler, Thomas V. A1 - Bieniek, Peter A. A1 - Pelto, Mauri A1 - Aschwanden, Andy KW - Alaska KW - downscaling KW - glacier mass balance KW - Juneau Icefield KW - Modeling KW - orographic precipitation KW - snow accumulation VL - 6 UR - http://journal.frontiersin.org/article/10.3389/feart.2018.00020/full ER - TY - JOUR T1 - Sediment transport drives tidewater glacier periodicity Y1 - 2017 A1 - Brinkerhoff, Douglas A1 - Truffer, Martin A1 - Aschwanden, Andy AB - 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. VL - 8 SN - 2041-1723 UR - https://doi.org/10.1038/s41467-017-00095-5 IS - 1 JO - Nature Communications ER - TY - JOUR T1 - Bayesian Inference of Subglacial Topography Using Mass Conservation JF - Frontiers in Earth Science Y1 - 2016 A1 - Brinkerhoff, Douglas J A1 - Aschwanden, Andy A1 - Truffer, Martin AB - 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. VL - 4 UR - http://journal.frontiersin.org/article/10.3389/feart.2016.00008 ER - TY - JOUR T1 - Complex Greenland outlet glacier flow captured JF - Nature Communications Y1 - 2016 A1 - Aschwanden, Andy A1 - Fahnestock, Mark A A1 - Truffer, Martin VL - 7 UR - http://www.nature.com/doifinder/10.1038/ncomms10524 ER - TY - JOUR T1 - Geodetic measurements reveal similarities between post-Last Glacial Maximum and present-day mass loss from the Greenland ice sheet JF - Science Advances Y1 - 2016 A1 - Khan, Shfaqat A A1 - Sasgen, Ingo A1 - Bevis, Michael A1 - van Dam, T. A1 - Bamber, Jonathan L A1 - Wahr, John A1 - Willis, Michael A1 - Kjaer, K. H. A1 - Wouters, Bert A1 - Helm, Veit A1 - Csatho, Beata A1 - Fleming, Kevin A1 - Bjork, A. A. A1 - Aschwanden, Andy A1 - Knudsen, Per A1 - Munneke, Peter Kuipers VL - 2 UR - http://advances.sciencemag.org/cgi/doi/10.1126/sciadv.1600931 ER - TY - JOUR T1 - Modeling the evolution of the Juneau Icefield between 1971 and 2100 using the Parallel Ice Sheet Model (PISM) JF - Journal of Glaciology Y1 - 2016 A1 - Ziemen, Florian A A1 - Hock, Regine A1 - Aschwanden, Andy A1 - Khroulev, Constantine A1 - Kienholz, Christian A1 - MELKONIAN, ANDREW A1 - ZHANG, JING VL - 62 ER - TY - JOUR T1 - Modelled glacier dynamics over the last quarter of a century at Jakobshavn Isbræ JF - The Cryosphere Y1 - 2016 A1 - Muresan, Ioana S. A1 - Khan, Shfaqat A. A1 - Aschwanden, Andy A1 - Khroulev, Constantine A1 - Van Dam, Tonie A1 - Bamber, Jonathan A1 - van den Broeke, Michiel R. A1 - Wouters, Bert A1 - Kuipers Munneke, Peter A1 - Kjær, Kurt H. VL - 10 UR - http://www.the-cryosphere.net/10/597/2016/ ER - TY - JOUR T1 - A synthesis of the basal thermal state of the Greenland Ice Sheet JF - Journal of Geophysical Research: Earth Surface Y1 - 2016 A1 - MacGregor, Joseph A. A1 - Fahnestock, Mark A. A1 - Catania, Ginny A. A1 - Aschwanden, Andy A1 - Clow, Gary D. A1 - Colgan, William T. A1 - Gogineni, S. Prasad A1 - Morlighem, Mathieu A1 - Nowicki, Sophie M. J. A1 - Paden, John D. A1 - Price, Stephen F. A1 - Seroussi, Helene UR - http://doi.wiley.com/10.1002/2015JF003803 ER - TY - JOUR T1 - Greenland ice sheet mass balance JF - Reports on Progress in Physics Y1 - 2015 A1 - Khan, Shfaqat A. A1 - Aschwanden, Andy A1 - Bjørk, Anders A A1 - Whar, John A1 - Kjeldsen, Kristian K. A1 - Kjær, Kurt H. AB - 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. PB - IOP Publishing VL - 78 UR - http://dx.doi.org/10.1088/0034-4885/78/4/046801 ER - TY - JOUR T1 - Role of model initialization for projections of 21st-century Greenland ice sheet mass loss JF - Journal of Glaciology Y1 - 2014 A1 - Aðalgeirsdóttir, Guðfinna A1 - Aschwanden, Andy A1 - Khroulev, Constantine A1 - Boberg, Frederik A1 - Mottram, Ruth A1 - Lucas-Picher, P. KW - ice and climate KW - ice-sheet modeling VL - 60 UR - http://www.igsoc.org/journal/60/222/t13j202.html ER -