How reversible is sea ice loss?

J K Ridley,J A Lowe,H T Hewitt

doi:10.5194/tc-6-193-2012

Abstract

Abstract. It is well accepted that increasing atmospheric CO2 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 CO2 is first ramped up to four times pre-industrial levels (4 × CO2), then ramped down to pre-industrial levels. We also examine the impact of stabilising climate at 4 × CO2 prior to ramping CO2 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.

Highlights

The decline of Arctic sea ice in response to increasing concentrations of atmospheric CO2 has been much studied in climate models (Gregory et al, 2002; Winton, 2006; Holland et al, 2006; Ridley et al, 2007; Wang and Overland, 2009)
In HadCM3, while the demise of the Arctic annual mean sea ice varies linearly with temperature over a wide range of values, the winter ice does show a more rapid decline as an apparent temperature threshold is reached. This only occurs after a large fraction of the winter ice has already been lost above a global warming of around 7 ◦C (Ridley et al, 2008)
Schroder and Connolley (2007) performed experiments for both the Southern and Northern Hemisphere sea ice using the HadCM3 climate model in which the ocean mixed layer was adjusted to represent that in ice free regions

Summary

Introduction

The decline of Arctic sea ice in response to increasing concentrations of atmospheric CO2 has been much studied in climate models (Gregory et al, 2002; Winton, 2006; Holland et al, 2006; Ridley et al, 2007; Wang and Overland, 2009). Schroder and Connolley (2007) performed experiments for both the Southern and Northern Hemisphere sea ice using the HadCM3 climate model in which the ocean mixed layer was adjusted to represent that in ice free regions.

Results

Conclusion