Here are some selected abstract from the IGSOC 2017 conference, that are relevant to the potential collapse of the WAIS:
https://www.igsoc.org/symposia/2017/boulder/proceedings/proceedings.html76A2543
The potential for positive feedback between deglaciation of the West Antarctic Ice Sheet, decompression-melt-induced subglacial volcanism and resultant sea-level rise
John Behrendt, Wesley LeMasurier
Corresponding author: John Behrendt
Corresponding author e-mail: john.behrendt@colorado.edu
Melting of the West Antarctic Ice Sheet (WAIS) would raise global sea level ~3 m. WAIS flows through the volcanically active West Antarctic rift system (WARS); heat flow is high beneath WAIS. Satellite altimetry shows rapid retreat of ice shelves bordering WAIS resulting from climate change. GRACE satellite data indicate accelerating mass loss from WAIS, reducing basal pressure. Aeromagnetic surveys over WAIS revealed >1000 high-amplitude magnetic anomalies, indicative of the late Cenozoic–recent age subglacial volcanic rocks at its base. Increased volcanic activity resulting from decompression mantle melting beneath a thinning WAIS may serve as a positive feedback mechanism that could further destabilize WAIS. In both Iceland and on midocean ridges, dated volcanism suggests decompression mantle melting associated with reductions in either ice or water loads drives significant volcanism. Acceleration of volcanic activity as the WAIS thins could enhance the rate of ice loss and accelerate global sea level rise.
76A2568
Ice sheets and sea level: to rise, or not to rise, that is no longer the question
Sophie Nowicki
Corresponding author: Sophie Nowicki
Corresponding author e-mail: sophie.nowicki@nasa.gov
On 18 April 2017, the New York Times published an article entitled ‘When Rising Seas Transform Risk into Certainty’, illustrating that rising sea level is now in the public eye. When thinking about sea level, the question is no longer whether levels are rising, but how to increase confidence in projections of ice-sheet evolution and reduce the uncertainty in projection of sea level. These questions lie at the heart of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6), the first time that an effort dedicated to ice sheets is part of the climate model endeavor (CMIP) that forms the foundation of the IPCC reports. This presentation will introduce ISMIP6, review progress made in both the ice sheet and climate modeling communities in order to improve our understanding of how ice sheets contribute to the climate system, before exploring the challenges ahead and how anyone with an interest in the polar regions can contribute to this new venture.
76A2573
Coupled ice shelf–ocean modelling and complex grounding line retreat for Pine Island Glacier
Jan de Rydt, Hilmar Gudmundsson
Corresponding author: Jan De Rydt
Corresponding author e-mail: janryd69@bas.ac.uk
Recent observations and modelling work have shown a complex mechanical coupling between Antarctica’s floating ice shelves and the adjacent grounded ice sheet. A prime example is Pine Island Glacier, West Antarctica, which has a strong negative mass balance caused by a recent increase in ocean-induced melting of its ice shelf. The mass loss coincided with the retreat of its grounding line from a seabed ridge on which it was at least partly grounded until the 1970s. At present, it is unclear what caused the onset of this retreat, and how feedback mechanisms between the ocean and ice-shelf geometry have influenced the ice dynamics. To address these questions, we present results from an offline coupling between a state-of-the-art shallow-ice flow model with grounding-line resolving capabilities, and a three-dimensional ocean general-circulation model with a static implementation of the ice shelf. We simulate the retreat from an idealized seabed ridge in response to changes in the ocean forcing, and show that the retreat becomes irreversible after 20 years of warm ocean conditions. A comparison with experiments with a simple depth-dependent meltrate parameterization demonstrates that such parameterizations are unable to capture the details of the retreat process, and they overestimate mass loss by more than 40% over a 50-year timescale. In a second set of experiments, we used the coupled model to simulate the evolution of all Amundsen Sea glaciers under a range of warm and cold ocean scenarios.
76A2592
West Antarctic surface elevation change from CryoSat-2 radar altimetry and multi-mission lidar mapping
Tyler Sutterley, Isabella Velicogna, Eric Rignot, Jeremie Mouginot, Thorsten Markus, Tom Neumann
Corresponding author: Tyler Sutterley
Corresponding author e-mail: tyler.c.sutterley@nasa.gov
We present estimates of surface elevation change at the Bellinghausen Sea, Amundsen Sea and Getz regions of the West Antarctic Ice Sheet (WAIS) from CryoSat-2 radar altimetry measurements and a combination of satellite and airborne laser altimetry measurements. These regions are currently some of the most responsible for sea-level rise from the Antarctic continent. Our radar altimetry method combines Level-2 elevation measurements from the low-resolution mode (LRM) and the interferometric synthetic aperture mode (SARin) of the synthetic aperture interferometric radar altimeter (SIRAL) ranging instrument. Our laser altimetry method combines measurements from the Airborne Topographic Mapper (ATM), the Land, Vegetation and Ice Sensor (LVIS) and the Ice Cloud and land Elevation Satellite (ICESat-1). The laser altimetry method allows us to extend the records of each instrument, increases the overall spatial coverage compared to a single instrument, and produces high-quality, coherent maps of surface-elevation change. We compare elevation-change measurements for major outlet glaciers in West Antarctica to assess the regional stability. We find CryoSat-2 and laser altimetry estimates produce comparable rates of elevation change in regions with lower surface slopes. The agreement is lower in regions with mountainous terrain and small outlet glaciers.
76A2595
Land ice in version 2.0 of the Community Earth System Model
William Lipscomb, Jeremy Fyke, Gunter Leguy, Jan Lenaerts, William Sacks, Leo van Kampenhout, Miren Vizcaino
Corresponding author: William Lipscomb
Corresponding author e-mail: lipscomb@ucar.edu
The summer 2017 release of the Community Earth System Model version 2 (CESM2) includes major advances, compared to CESM1, in the treatment of ice sheets and their interactions with the climate. The dynamic ice sheet model is version 2.1 of the Community Ice Sheet Model (CISM2.1), which has a higher-order velocity solver (suitable for simulating fast flow in ice streams and ice shelves) and improved treatments of basal and calving physics. In long spin-ups for the initMIP-Greenland project, the modeled Greenland ice extent, volume and surface velocity agree well with observations. In coupled runs, the Community Land Model (CLM) computes the ice-sheet surface mass balance (SMB) in multiple elevation classes, and the coupler downscales the SMB to the fine-scale CISM grid. Recent CLM snow physics improvements give a more realistic SMB for both Greenland and Antarctica. CESM2 supports two-way coupling of ice sheets, with ice-sheet evolution feeding back conservatively on land-surface types and elevation. A developmental version of CISM, which includes a grounding-line parameterization and an ocean plume model, has been verified for marine ice-sheet benchmark experiments and has the potential to be used for dynamic Antarctic simulations in future versions of CESM.
76A2598
Characterizing uncertainty in projected changes of Antarctic surface temperature, precipitation and sea ice extent
David Schneider
Corresponding author: David Schneider
Corresponding author e-mail: dschneid@ucar.edu
Some of the largest uncertainties in projected anthropogenic climate change impacts occur in or are linked to Antarctica and the Southern Ocean. Projected changes in Antarctic surface mass balance, sea-ce extent and surface temperature differ widely among current-generation climate models, and this uncertainty likely has roots in the mean states (climatologies) of the models. In this presentation, we will highlight projected changes in surface air temperature and precipitation over the Antarctic Ice Sheet and relate the magnitude of these changes to the initial climatology of the model. To characterize the roles of natural variability and model (structural) uncertainty in the spread of these projections, we will use output from the Community Earth System Model Large Ensemble as well as the CMIP5 archive.
76A2599
Observations of recent climate change in East Antarctica outpace future model simulations
Brooke Medley, Joseph McConnell, Thomas Neumann, Carleen H. Reijmer, Sepp Kipfstuhl, Michael Sigl
Corresponding author: Brooke Medley
Corresponding author e-mail: brooke.c.medley@nasa.gov
The West Antarctic Ice Sheet (WAIS) is experiencing rapid warming and substantial ice-mass loss, designating it as one of the regions most vulnerable to change in Antarctica, especially in comparison to the more massive East Antarctic Ice Sheet (EAIS), which is thought to be undergoing little or no mass change. Thus, researchers consider the high, dry EAIS stable with little warming and no significant change in snowfall since 1957. Here, we present new observations of snow accumulation and air temperature near Kohnen station in Queen Maud Land that suggest that this region can experience climate change at a pace similar to or potentially more rapid than observations from WAIS. Over the past 75 years, snow accumulation has increased 5.2 ± 3.7% per decade, a rate that is 1.5 times more rapid than any 75-year interval in the previous nearly 2000 years (1–1850 CE). The recent 20-year mean annual accumulation is 16.5 mm w.e. larger than the preindustrial mean of 66.2 mm w.e. Similarly, annual air temperature has been increasing by 1.1 ± 0.7 °C per decade since 1998, with significant seasonal increases in autumn and spring. By comparing our observed changes with output from the Community Earth System Model, we find that the observed rates of accumulation and temperature change outpace the model simulations by several decades even under the high-emission RCP8.5 scenario.
76A2619
Effects of climate variability on marine ice-sheet stability
Matthew Hoffman, Jeremy Fyke, Stephen Price
Corresponding author: Matthew Hoffman
Corresponding author e-mail: mhoffman@lanl.gov
Theory, modeling, and observations indicate that marine ice sheets on a retrograde bed are only conditionally stable. Previous modeling studies have shown that rapid, unstable retreat can occur when steady ice-shelf basal melting causes the grounding line to retreat past restraining bedrock bumps. Here we explore the initiation and evolution of unstable retreat when the ice-shelf basal melt forcing includes temporal variability mimicking realistic climate variability. We use the three-dimensional, higher-order Model for Prediction Across Scales-Land Ice (MPASLI) model in an idealized model configuration similar to Pine Island Glacier. We find that climate variability has a complex relationship to marine ice-sheet stability and can delay or accelerate unstable retreat.