The Cryosphere Discuss., 6, 2621-2651, 2012
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This discussion paper has been under review for the journal The Cryosphere (TC). Please refer to the corresponding final paper in TC.
A recent bifurcation in Arctic sea-ice cover
V. N. Livina1 and T. M. Lenton2
1School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK
2College of Life and Environmental Sciences, University of Exeter, Exeter EX4 4PS, UK

Abstract. There is ongoing debate over whether Arctic sea-ice has already passed a "tipping point", or whether it will do so in future, with several recent studies arguing that the loss of summer sea ice does not involve a bifurcation because it is highly reversible in models. Recently developed methods can detect and sometimes forewarn of bifurcations in time-series data, hence we applied them to satellite data for Arctic sea-ice cover. Here we show that a new low ice cover state has appeared from 2007 onwards, which is distinct from the normal state of seasonal sea ice variation, suggesting a bifurcation has occurred from one attractor to two. There was no robust early warning signal of critical slowing down prior to this bifurcation, consistent with it representing the appearance of a new ice cover state rather than the loss of stability of the existing state. The new low ice cover state has been sampled predominantly in summer-autumn and seasonal forcing combined with internal climate variability are likely responsible for triggering recent transitions between the two ice cover states. However, all early warning indicators show destabilization of the summer-autumn sea-ice since 2007. This suggests the new low ice cover state may be a transient feature and further abrupt changes in summer-autumn Arctic sea-ice cover could lie ahead; either reversion to the normal state or a yet larger ice loss.

Citation: Livina, V. N. and Lenton, T. M.: A recent bifurcation in Arctic sea-ice cover, The Cryosphere Discuss., 6, 2621-2651, doi:10.5194/tcd-6-2621-2012, 2012.
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