Long-term evolution and critical thresholds of the Antarctic Ice Sheet

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Abstract

Due to very weak snowfall on the Antarctic Ice Sheet and the slow ice motion in its interior, it is expected that it might take at least several thousand years to regrow if its mass was substantially reduced by dynamic ice discharge triggered by global warming. Consequently, any significant ice loss from Antarctica that occurs within the next century will be irreversible on a multi-centennial to millennial time scale. Because of the ice sheet’s enormous potential to raise global sea levels by almost 60 metres, this poses a serious threat to coastal populations and ecosystems.

In this study, a first step towards an assessment of the question of reversibility and stability behaviour of Antarctic Ice Sheet retreat is taken. Several long-term numerical simulations (~10⁵ years) with the Parallel Ice Sheet Model (PISM) are conducted to investigate the ice sheet’s behaviour under a set of idealised global mean temperature forcing scenarios of different levels and durations.

The results underpin the fragility of the Antarctic Ice Sheet and prove its sensitivity to future anthropogenic emissions. On the time scales considered, even small perturbations of regional atmospheric and oceanic temperatures cause long-term irreversible mass loss in the model. This implies the existence of tipping thresholds, which trigger, once transgressed, the operation of strong positive feedback mechanisms such as the Marine Ice Sheet Instability feedback or the surface mass balance—elevation feedback. The results also suggest multiple stable equilibrium states under any given forcing.