The multi-millennial Antarctic commitment to future sea-level rise

Abstract

Atmospheric warming is projected to increase global mean surface temperatures by 0.3 to 4.8 degrees Celsius above pre-industrial values by the end of this century. If anthropogenic emissions continue unchecked, the warming increase may reach 8-10 degrees Celsius by 2300 (ref. 2). The contribution that large ice sheets will make to sea-level rise under such warming scenarios is difficult to quantify because the equilibrium-response timescale of ice sheets is longer than those of the atmosphere or ocean. Here we use a coupled ice-sheet/ice-shelf model to show that if atmospheric warming exceeds 1.5 to 2 degrees Celsius above present, collapse of the major Antarctic ice shelves triggers a centennial- to millennial-scale response of the Antarctic ice sheet in which enhanced viscous flow produces a long-term commitment (an unstoppable contribution) to sea-level rise. Our simulations represent the response of the present-day Antarctic ice-sheet system to the oceanic and climatic changes of four representative concentration pathways (RCPs) from the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. We find that substantial Antarctic ice loss can be prevented only by limiting greenhouse gas emissions to RCP 2.6 levels. Higher-emissions scenarios lead to ice loss from Antarctic that will raise sea level by 0.6-3 metres by the year 2300. Our results imply that greenhouse gas emissions in the next few decades will strongly influence the long-term contribution of the Antarctic ice sheet to global sea level.

Sea-level response to melting of Antarctic ice shelves on multi-centennial timescales with the fast Elementary Thermomechanical Ice Sheet model (f.ETISh v1.0)

“…Given the differences in approach with continental-scale ice sheet models, such as AISM-VUB (Huybrechts, 1990(Huybrechts, , 2002, ANICE (de Boer et al, 2013), GRISLI (Ritz et al, 2015), ISSM (Larour et al, 2012), PISM (Bueler and Brown, 2009), PISM-PIK Winkelmann et al, 2011;Golledge et al, 2015), PSU-ISM (Pollard and DeConto, 2012a), RIMBAY (Thoma et al, 2014) or SICOPO-LIS (Sato and Greve, 2012), verification of the f.ETISh model requires a detailed comparison with existing benchmarks. These are generally based on results of the models cited above.…”

“…Ocean forcing is based on constant forcing values of sub-shelf melting M, ranging from 0 to 50 m a −1 underneath the freely floating ice shelves surrounding the Antarctic ice sheet and between 0 and 6.25 m a −1 for the Ronne-Filchner and Ross ice shelves (factor 8 less compared to the freely floating ice shelves). Melting is only applied to fully floating grid cells, without taking into account the fractional area of grounded grid points that are actually afloat, as done in a few studies (Feldmann et al, 2014;Golledge et al, 2015). All forcings are applied as a sudden change in temperature/melt rate starting from the initialized model.…”

“…Since then several marine ice sheet models of the Antarctic ice sheet have been developed, with varying ways of treating the grounding line, i.e. by increasing locally spatial resolution at the grounding line (Favier et al, 2014;Cornford et al, 2015), by making use of local interpolation strategies at the grounding line (Feldmann et al, 2014;Feldmann and Levermann, 2015;Golledge et al, 2015;Winkelmann et al, 2015) or by parametrizing grounding-line flux based on boundary layer theory (Pollard and DeConto, 2009;Pollard et al, 2015;DeConto and Pollard, 2016).…”

To what extent are land resource managers preparing for high-end climate change in Scotland?

“…The reality of the worst is that the world is currently headed for an average increase in temperature of 4°C and beyond (Gasser et al 2015;Stafford Smith et al 2011). The current high-end trajectory would lead to severe climate change impacts, as reported for sea-level rise (Golledge et al 2015), flood risk (Alfieri et al 2015) and water scarcity (Schewe et al 2014) among others. Impacts and adaptation to high-end climate change (HECC) are currently a key focus of European Union (EU) project funding, with three complementary projects that focus on regional and local impacts and adaptation across a range of land, water and coastal ecosystems (High-end climate research EU website 2016).…”

A Numerical Model Investigation of the Role of the Glacier Bed in Regulating Grounding Line Retreat of Thwaites Glacier, West Antarctica

“…This is the case because direct observation in the Antarctic is challenging and because time and spatial scales of observation are often mismatched with the fundamental scales of the underlying processes. Nevertheless, model projections of future change are 8 of critical importance and are routinely produced (Goelzer et al, 2013;Golledge et al, 2015;Nowicki et al, 2013). Here I focus on the subglacial environment of Thwaites Glacier in the AS sector of the West Antartica, and in particular the influence of (estimated) bed morphology on model projections.…”