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The Cryosphere An interactive open-access journal of the European Geosciences Union
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Volume 12, issue 1
The Cryosphere, 12, 39-47, 2018
https://doi.org/10.5194/tc-12-39-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.
The Cryosphere, 12, 39-47, 2018
https://doi.org/10.5194/tc-12-39-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 08 Jan 2018

Research article | 08 Jan 2018

Influence of temperature fluctuations on equilibrium
ice sheet volume

Troels Bøgeholm Mikkelsen, Aslak Grinsted, and Peter Ditlevsen Troels Bøgeholm Mikkelsen et al.
  • Centre for Ice and Climate, Niels Bohr Institute, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark

Abstract. Forecasting the future sea level relies on accurate modeling of the response of the Greenland and Antarctic ice sheets to changing temperatures. The surface mass balance (SMB) of the Greenland Ice Sheet (GrIS) has a nonlinear response to warming. Cold and warm anomalies of equal size do not cancel out and it is therefore important to consider the effect of interannual fluctuations in temperature. We find that the steady-state volume of an ice sheet is biased toward larger size if interannual temperature fluctuations are not taken into account in numerical modeling of the ice sheet. We illustrate this in a simple ice sheet model and find that the equilibrium ice volume is approximately 1m SLE (meters sea level equivalent) smaller when the simple model is forced with fluctuating temperatures as opposed to a stable climate. It is therefore important to consider the effect of interannual temperature fluctuations when designing long experiments such as paleo-spin-ups. We show how the magnitude of the potential bias can be quantified statistically. For recent simulations of the Greenland Ice Sheet, we estimate the bias to be 30Gt yr−1 (24–59Gt yr−1, 95% credibility) for a warming of 3°C above preindustrial values, or 13% (10–25, 95% credibility) of the present-day rate of ice loss. Models of the Greenland Ice Sheet show a collapse threshold beyond which the ice sheet becomes unsustainable. The proximity of the threshold will be underestimated if temperature fluctuations are not taken into account. We estimate the bias to be 0.12°C (0.10–0.18°C, 95% credibility) for a recent estimate of the threshold. In light of our findings it is important to gauge the extent to which this increased variability will influence the mass balance of the ice sheets.

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The atmospheric temperature increase poses a real risk of ice sheets collapsing. We show that this risk might have been underestimated since variations in temperature will move the ice sheets to the tipping point of destabilization. We show this by using a simple computer model of a large ice sheet and investigate what happens if the temperature varies from year to year. The total volume of the ice sheet decreases because a cold year followed by an equally warm year do not cancel out.
The atmospheric temperature increase poses a real risk of ice sheets collapsing. We show that...
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