Coastal Impacts, Adaptation, and Vulnerabilities - Climate ...

Vulnerability and Impacts on Natural Resources 65on the snow den for warmth. About two-thirds of the world’s polar bears are projectedto be gone by the middle of this century. In 75 years, projections suggest that the wildpolar bear population will be gone entirely from Alaska (Janetos et al., 2008).ConclusionsThreshold shifts in ecosystems can have severe negative consequences for ecosystemservices, economic sustainability, and human health and well-being (Harley et al., 2006;Lubchenco & Petes, 2010; MEA, 2005). Recent papers have further advanced the dialogueon key research directions for elucidating threshold mechanisms and identifyingearly-warning signals of impending abrupt transitions (Groffman et al., 2006; Schefferet al., 2009); however, even though single-species responses to particular stressors oftenare fairly well known, mechanistic understanding of cumulative effects of multi-stressorinteractions, especially at the community level, remains elusive. A recent review of topresearch priorities for conservation and management cites the need to expand scientificunderstanding of multi-stressor interactions and thresholds (Fleishman et al., 2011).This includes methods to identify the triggers of threshold responses and to anticipatethe likely trajectory of post-threshold states under a range of future scenarios of climateand land-use change (Briske et al., 2006). Such information will be key to managers’ abilityto manage for change when threshold shifts occur (West et al., 2009).As the natural resources of coastal systems respond to changing climatic conditions,human modification and management of these systems is a major factor in the characterof the response. In many cases the capacity of coastal systems to reposition or reshapethemselves in response to climate drivers is constrained by the physical modificationsmade to accommodate and sustain human uses. This adds an additional level of complexityto forecasts of ecosystem responses. It also highlights the need for system-levelthinking as we work to adapt to the evolving conditions.