frontiers for future research in the field, including challenges and opportunities.

The workshop planning committee (Appendix D) proposed three working themes to the participants in advance of the workshop. They were selected to help guide and focus the workshop discussions and to provide context to the participants as they considered frontiers in climate change and polar ecosystems. The three organizing themes were:

Polar regions are warming faster than any other part of the Earth system (Holland and Bitz, 2003; Bekryaev et al., 2010). The effects are manifested as atmospheric warming, decreasing extent and duration of sea ice cover, glacier retreat, permafrost thawing, increasing river discharge, loss of snow cover, and shifting ecosystem structure and function. Some of this polar amplification is caused by the well-studied albedo effect, but other drivers and feedbacks are less well understood. For example, how is the loss of coastal glacial ice mass in Antarctica linked to ozone depletion, changes in the Southern Annular Mode, sea ice feedbacks, or is it responding to an integration of all these? How can the scientific community address uncertainty in assessing the individual roles of snow and ice cover, atmospheric and oceanic circulation, and cloud cover and water vapor in recent observations of warming near-surface air temperatures? What are the contributions of these potential drivers to both Arctic and Antarctic temperature amplifications, and how will they change over the next few decades?

The identification and prediction of thresholds and tipping points (see Box 1.1) in natural systems likely presents one of the greatest challenges facing those scientists investigating climatic and environmental change since the intrinsic properties can be nonlinear and abrupt. In the polar regions, there is considerable risk of passing thresholds and tipping points caused by the rapid response of the cryosphere system (including the atmosphere, ocean, and biosphere) to increased anthropogenic forcing. This issue is a potential frontier that warrants investigation to identify current and future early warning signals that will allow the world to prepare for future conditions and allow societies the opportunity to adapt.