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

• Published in: Geophysical research letters Vol. 38; no. 16
• Main Authors: Armour, K. C., Eisenman, I., Blanchard-Wrigglesworth, E., McCusker, K. E., Bitz, C. M.
• Format: Journal Article
• Language: English
• Published: Washington, DC Blackwell Publishing Ltd 20.08.2011; American Geophysical Union; John Wiley & Sons, Inc
• Subjects: Carbon dioxide; Climate change; Climate models; Cryosphere; Earth; Earth sciences; Earth, ocean, space; Exact sciences and technology; Global climate; Global climate models; Ice; Ice cover; Marine; Oceans; reversibility; Sea ice; State of the art; Summer; Thresholds; tipping point; Trajectories; Winter; Arctic Ocean; atmosphere; carbon dioxide; Summer; Climate models; global; climate; recovery; variability; Ice cover; trajectory; greenhouse gas; hysteresis; modern; Winter; Response time; sea ice; temperature; Reversibility; Polar region
• ISSN: 0094-8276; 1944-8007
• DOI: 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. Key Points Sea ice loss is reversible within a state‐of‐the‐art global climate model We find no evidence of threshold behavior in summer or winter sea ice cover Rapid sea ice retreat does not imply irreversibility