TC The Cryosphere TC The Cryosphere 1994-0424 Copernicus Publications Göttingen, Germany 10.5194/tc-6-193-2012 How reversible is sea ice loss? Ridley J. K. 1 Lowe J. A. 1 Hewitt H. T. 1 Met Office, FitzRoy Road, Exeter, EX1 3PB, UK 13 02 2012 6 1 193 198 Copyright: © 2012 J. K. Ridley et al. 2012 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://tc.copernicus.org/articles/6/193/2012/tc-6-193-2012.html The full text article is available as a PDF file from https://tc.copernicus.org/articles/6/193/2012/tc-6-193-2012.pdf

It is well accepted that increasing atmospheric CO<sub>2</sub> results in global warming, leading to a decline in polar sea ice area. Here, the specific question of whether there is a tipping point in the sea ice cover is investigated. The global climate model HadCM3 is used to map the trajectory of sea ice area under idealised scenarios. The atmospheric CO<sub>2</sub> is first ramped up to four times pre-industrial levels (4 × CO<sub>2</sub>), then ramped down to pre-industrial levels. We also examine the impact of stabilising climate at 4 × CO<sub>2</sub> prior to ramping CO<sub>2</sub> down to pre-industrial levels. Against global mean temperature, Arctic sea ice area is reversible, while the Antarctic sea ice shows some asymmetric behaviour – its rate of change slower, with falling temperatures, than its rate of change with rising temperatures. However, we show that the asymmetric behaviour is driven by hemispherical differences in temperature change between transient and stabilisation periods. We find no irreversible behaviour in the sea ice cover.

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