Polar bears depend on sea ice to persist over a sufficient portion of the year for them to catch enough seals and gain enough weight to survive over periods when the ice is absent. A recent study, partially supported by DOE, examined the extent to which better outcomes for polar bears can be achieved through the mitigation of greenhouse gas emissions. A key issue is the possible existence of a "tipping point" for Arctic sea ice, or a threshold of global mean temperature beyond which the sea ice remaining at the end of the melt season undergoes an irreversible and unstoppable decline. To test this hypothesis, and to indirectly assess the potential value of greenhouse gas mitigation for polar bears, the investigators looked at the relationship between global mean temperature and sea ice metrics. Simulations were performed with the DOE supported National Center for Atmospheric Research Community Climate System Model version 3, which does a credible job in representing present-day sea ice and predicting the recent decline of Arctic sea ice. For several greenhouse gas scenarios, the model indicated that sea ice metrics varied smoothly and roughly linearly with changes in global mean temperature providing evidence against the existence of a tipping point. A further experiment showed that the loss of sea ice is neither irreversible nor unstoppable. The study suggests that greenhouse gas mitigation has strong potential benefits for the conservation of polar bear habitat.
Reference: Amstrup, S. C., E. T. DeWeaver, D. C. Douglas, B. G. Marcot, G. M. Durner, C. M. Bitz and D. A. Bailey. 2010. "Greenhouse Gas Mitigation Can Reduce Sea-Ice Loss and Increase Polar Bear Persistence," Nature (468), 955–58. doi:10.1038/nature09653.
Contact: Renu Joseph, SC-23.1, (301) 903-9237, Dorothy Koch, SC-23.1, (301) 903-0105
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