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Friday, September 11, 2009

T. Toniazzo et al., J. Climate 2004: Climatic impact of a Greenland deglaciation and its possible irreversibility

Hat tip to reader Steve Church in Canada!

Journal of Climate, Vol. 17, pp. 21-33, 2004

Climatic impact of a Greenland deglaciation and its possible irreversibility

T. Toniazzo (Hadley Centre for Climate Prediction and Research, Met Office, Bracknell, Berkshire, U.K.), J. M. Gregory (Hadley Centre for Climate Prediction and Research, Met Office, Bracknell, Berkshire, and Centre for Global Atmospheric Modelling, Department of Meteorology, University of Reading, Reading, U.K.), P. Huybrechts (Alfred-Wegener-Institut fur Polar- und Meeresforschung, Bremerhaven, Germany, and Department Geografie, Vrije Universiteit Brussel, Brussels, Belgium)

(Manuscript received 30 December 2002, in final form 19 June 2003.)


Warmer climate conditions persisting for a period of many centuries could lead to the disappearance of the Greenland ice sheet, with a related 7-m rise in sea level. The question is addressed of whether the ice sheet could be regenerated if preindustrial climate conditions were reestablished after its melting. The HadCM3 coupled atmosphere–ocean GCM is used to simulate the global and regional climate with preindustrial atmospheric greenhouse gas composition and with the Greenland ice sheet removed. Two separate cases are considered. In one, the surface topography of Greenland is given by that of the bedrock currently buried under the ice sheet. In the other, a readjustment to isostatic equilibrium of the unloaded orography is taken into account, giving higher elevations. In both cases, there is greater summer melting than in the current climate, leading to partially snow-free summers with much higher temperatures. On the long-term average, there is no accumulation of snow. The implication of this result is that the removal of the Greenland ice sheet due to a prolonged climatic warming would be irreversible.

1. Introduction

As greenhouse-gas-forced global warming progresses in the course of the present century, it is expected that the surface mass balance of the Greenland ice sheet will become negative [Ohmura et al. 1996; Thompson and Pollard 1997; Gregory and Lowe 2000; see also Church et al. 2001 in the IPCC Third Assessment Report (TAR)].

At present, the Greenland ice sheet maintains near-zero mass balance through surface melting and discharge of icebergs into the sea, in roughly equal shares (TAR, Table 11.5). Its high altitude (3200 m at the summit) and its cold surface ensure very cold local climatic conditions in central Greenland, and a permanent cold high pressure center that forces cyclone systems (and hence precipitation) to skirt along its sides with little penetration into the interior (see, e.g., Murphy et al., 2002). Seasonal melting is even more confined to the margins of the ice sheet. Modeling studies (summarized by TAR, Table 11.7) all agree that under global warming Greenland will become warmer and wetter, but there is consensus that the increasing precipitation will not be sufficient to balance the increasing melting.

Palaeoclimatic studies confirm a large sensitivity of the Greenland regional climate to warm global conditions (Dahl-Jensen et al., 1993; Cuffey & Clow, 1997; Cuffey & Marshall ,2000). In an anthropogenic warming scenario, even after CO2 concentrations are stabilized, progressive melting of the ice sheet will continue. A climate more than about 38 °C warmer over Greenland persisting for a period of a thousand years or longer could result in a complete destruction of the ice sheet (Huybrechts & De Wolde, 1999; Greve, 2000; TAR).

A direct consequence of this would be a global-average sea level rise of about 7 m.

Here we investigate the extreme scenario in which the ice sheet has disappeared completely. The main question we ask is whether an ice sheet would tend to reform on Greenland if the climate were returned to the present-day climate. To this end, we perturb a simulated present-day climate by removing the Greenland ice sheet.

Link to large pdf file of the complete paper:

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