The reversibility of sea ice loss in a state-of-the-art climate model

• Published in: Geophysical Research Letters
• Main Authors: Armour, K. C., Eisenman, I., Blanchard-Wrigglesworth, E., McCusker, K. E., Bitz, C. M.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: American Geophysical Union 2011
• Subjects: reversibility; sea ice; tipping point; Arctic; Arctic Ocean; Dorian; Sea ice
• Online Access: https://doi.org/10.1029/2011GL048739

Rapid Arctic sea ice retreat has fueled speculation about the possibility of threshold (or 'tipping point') behavior and irreversible loss of the sea ice cover. We test sea ice reversibility within a state-of-the-art atmosphere–ocean global climate model by increasing atmospheric carbon dioxide until the Arctic Ocean becomes ice-free throughout the year and subsequently decreasing it until the initial ice cover returns. Evidence for irreversibility in the form of hysteresis outside the envelope of natural variability is explored for the loss of summer and winter ice in both hemispheres. We find no evidence of irreversibility or multiple ice-cover states over the full range of simulated sea ice conditions between the modern climate and that with an annually ice-free Arctic Ocean. Summer sea ice area recovers as hemispheric temperature cools along a trajectory that is indistinguishable from the trajectory of summer sea ice loss, while the recovery of winter ice area appears to be slowed due to the long response times of the ocean near the modern winter ice edge. The results are discussed in the context of previous studies that assess the plausibility of sea ice tipping points by other methods. The findings serve as evidence against the existence of threshold behavior in the summer or winter ice cover in either hemisphere. © 2011 American Geophysical Union. Received 29 June 2011; accepted 15 July 2011; published 20 August 2011. We gratefully acknowledge support from National Science Foundation grants OCE-0256011 and ARC-0909313, the Davidow Discovery Fund, and a NOAA Climate and Global Change Postdoctoral Fellowship to IE administered by the University Corporation for Atmospheric Research. We thank Dorian Abbot, Gerard Roe, Brian Rose and Michael Winton for valuable discussions, and Eric Rignot, the editor. The Editor thanks an anonymous reviewer for his assistance in evaluating this paper. Published - Armour2011p15718Geophys_Res_Lett.pdf