Model shows polar ice caps can recover from warmer climate-induced melting

[OKIsItJustMe]

http://www.washington.edu/news/articles/model-shows-pol...

Aug. 17, 2011

Model shows polar ice caps can recover from warmer climate-induced melting

By Vince Stricherz
News and Information

A growing body of recent research indicates that, in Earth’s warming climate, there is no “tipping point,” or threshold warm temperature, beyond which polar sea ice cannot recover if temperatures come back down. New University of Washington research indicates that even if Earth warmed enough to melt all polar sea ice, the ice could recover if the planet cooled again.

In recent years scientists have closely monitored the shrinking area of the Arctic covered by sea ice in warmer summer months, a development that has created new shipping lanes but also raised concerns about humans living in the region and the survival of species such as polar bears.

In the new research, scientists used one of two computer-generated global climate models that accurately reflect the rate of sea-ice loss under current climate conditions, a model so sensitive to warming that it projects the complete loss of September Arctic sea ice by the middle of this century.

However, the model takes several more centuries of warming to completely lose winter sea ice, and doing so required carbon dioxide levels to be gradually raised to a level nearly nine times greater than today. When the model’s carbon dioxide levels then were gradually reduced, temperatures slowly came down and the sea ice eventually returned.

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http://www.agu.org/journals/pip/gl/2011GL048739-pip.pdf

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

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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.

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