BOX 2.1

•   What are the implications of the recent dramatic shifts in the Arctic from predominantly multiyear ice to first-year ice, and how will the associated complexities of this regime shift affect sea ice variability and predictability?

•   In a rapidly changing Arctic regime, how will forcings and couplings between the various components of the ocean, atmosphere, cryosphere, and seafloor and land systems modify or influence the processes governing the characteristics of the sea ice cover?

•   What are the impacts of extreme events and feedback mechanisms on Arctic sea ice evolution and our ability to predict it?

•   How will the changing Arctic sea ice characteristics and dynamics affect stakeholders on a variety of timescales, including prediction requirements?

Adding to the complexity of the natural system is a range of human interactions. Humans not only influence the Arctic (e.g., impacts of oil spills, ship discharges, and land and sea greenhouse gas emissions), they are also influenced by it (e.g., decisions to pursue commercial shipping routes and offshore developments in response to a changing ice cover, long-term strategies for Arctic security, and development of future Arctic monitoring systems). The Arctic sea ice cover, therefore, cannot be viewed in isolation, as it is constantly responding to a host of regional and global forces, and these are in turn directly influencing the ice cover’s seasonal and decadal presence or absence. Treating the Arctic as an integrated whole and a vital component of the global system is necessary to significantly advance our understanding of the sea ice cover as part of a complex system.

Key Challenge: Impacts of the Regime Shift of Arctic Sea Ice

Understanding how the recent regime shift in the Arctic sea ice cover, resulting in a significant reduction in the amount of multiyear ice compared with first-year ice, affects the processes governing the atmosphere-sea ice-ocean system and the models and observations used to study and predict Arctic sea ice dynamics.

The recent decline in the extent of Arctic summer sea ice has resulted in a dramatic shift in its composition (Figure 2.2). First-year ice is becoming more prevalent within the Arctic Basin, reducing the size of the multiyear ice pack (e.g., Maslanik et al., 2011). Furthermore, the multiyear ice that does remain is younger and thinner (Haas et al., 2008; Comiso, 2012). This rapid change to a new state is likely to have important implications for sea ice variability (Goosse et al., 2009; Hutchings and Rigor, 2012) and, ultimately, predictability (Holland et al., 2011). For instance, recent research suggests that first-year ice is not only more

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