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FIGURE 1.1 Arctic sea ice extent has recently undergone extraordinary decline: March 2012 (left) and September 2012 (right). The two periods that define the annual sea ice extent cycle are March, at the end of winter, when the ice is at its maximum extent, and September, at the end of summer, when the ice reaches its annual minimum extent. The purple line indicates the median maximum and minimum ice extents in the given month for the period 1979-2000. Compared with the 1979-2000 average, the September 2012 minimum was 49 percent smaller. SOURCE: Updated from Fetterer et al. (2002), Sea Ice Index, National Snow and Ice Data Center.

the marine food chain has increased (e.g., Arrigo and van Dijken, 2011) and sea ice-dependent marine mammals continue to lose habitat (e.g., Thomas and Laidre, 2011). Increases in the greenness of tundra vegetation and permafrost temperatures are linked to warmer land temperatures in coastal regions, often adjacent to the areas of greatest sea ice retreat (e.g., Bhatt et al., 2010).

Given the expectation for a continued increase in the global temperature throughout the 21st century (e.g., Meehl et al., 2007), the declining trends in Arctic sea ice extent and multiyear ice composition are expected to continue. Associated changes will likely result in greater marine access to the Arctic (e.g., for commercial shipping and offshore natural resource development) and increased coastal erosion, as well as a range of local, regional, and hemispheric changes in the climate and ecological systems.

The current and projected conditions and activity levels in the Arctic call for an



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