Considering thermal‐viscous collapse of the Greenland ice sheet

Abstract

We explore potential changes in Greenland ice sheet form and flow associated with increasing ice temperatures and relaxing effective ice viscosities. We define “thermal‐viscous collapse” as a transition from the polythermal ice sheet temperature distribution characteristic of the Holocene to temperate ice at the pressure melting point and associated lower viscosities. The conceptual model of thermal‐viscous collapse we present is dependent on: (1) sufficient energy available in future meltwater runoff, (2) routing of meltwater to the bed of the ice sheet interior, and (3) efficient energy transfer from meltwater to the ice. Although we do not attempt to constrain the probability of thermal‐viscous collapse, it appears thermodynamically plausible to warm the deepest 15% of the ice sheet, where the majority of deformational shear occurs, to the pressure melting point within four centuries. First‐order numerical modeling of an end‐member scenario, in which prescribed ice temperatures are warmed at an imposed rate of 0.05 K/a, infers a decrease in ice sheet volume of 5 ± 2% within five centuries of initiating collapse. This is equivalent to a cumulative sea‐level rise contribution of 33 ± 18 cm. The vast majority of the sea‐level rise contribution associated with thermal‐viscous collapse, however, would likely be realized over subsequent millennia.

The ‘Alice in Wonderland’ mechanics of the rejection of (climate) science: simulating coherence by conspiracism

“…One contrarian argument is that Greenland is not capable of this type of catastrophic collapse (Ollier 2007), based on the premises that Greenland's glaciers are not melting from the surface down, and that they are not sliding down an inclined plane lubricated by meltwater. Both of those premises are false (Colgan et al 2015;Phillips et al 2013), with ice loss from Greenland in recent years being greater than at any time since at least 1840 (Box and Colgan 2013). At the same time, contrarians also argue that Greenland used to be green in the times of the Vikings (Bolt 2007), implying that significant amounts of the ice sheet was melted (while incidentally failing to acknowledge the metres of sea level rise that would have accompanied such a degree of melt).…”

Recent Progress in Greenland Ice Sheet Modelling

“…Finally, the long-term future evolution of the ice sheet thermal state has been schematically simulated with a thermodynamic model [46] to study the possibility of a thermalviscous collapse, which implies that the ice sheet disintegration is accelerated by warming of the ice. Results indicate that the lower part of the ice column where most of the deformation occurs could be warmed to the pressure-melting point within a few centuries [46].…”

Open-source modular solutions for flexural isostasy: gFlex v1.0

“…As a first example to utilize both the ability of gFlex to generate solutions with variable effective elastic thickness and its incorporation into GRASS GIS, gFlex is used along with a simple and efficient GIS-enabled glacier and ice cap model modified from the work of Colgan et al (2015) to model a hypothetical expansion of the Iceland Ice Cap. While the importance of flexural isostasy in ice dynamics modeling has long been well-known (cf.…”

“…The ice cap model used here (cf. Colgan et al, 2015) employs a shallow-ice approximation with basal sliding as a linear function of driving stress, which is intentionally much simpler than the modeling approach (Hubbard, 2006) that Hubbard et al (2006) used to model the Last Glacial Maximum (LGM) Iceland Ice Cap. This is because the goal here is to show schematically the importance of including lateral variations in elastic thickness on the reconstructed thickness of an ice cap for a given paleoclimate, with less emphasis on actually reproducing any particular extent of the Iceland Ice Cap.…”