15.3 Assumptions about future trends

15.3.1 Key regional impacts with importance to the global system

We expect climate change in the polar regions to have many direct regional impacts; however, those regional direct impacts may have global implications through the following processes and feedbacks.

• Reflectivity of snow, ice and vegetation: snow, ice and vegetation play vital roles in the global climate system, through albedo and insulation effects. Since the TAR, increasing evidence has emerged indicating a more rapid disappearance of snow and sea-ice cover in some areas (e.g., Siberia, Alaska, the Greenland Sea), and consequent changes of albedo may be leading to further climate change (e.g., Holland and Bitz, 2003).
• Retreat of glaciers and ice sheets, freshwater runoff, sea level and ocean circulation: the retreat of glaciers in the Arctic and more rapid melting of the edges of the Greenland ice sheet (Section 15.2.1), together with observed increases in river runoff (Peterson et al., 2002), the major contributor, will alter the freshwater budget of the Arctic Ocean. Further changes are expected and could influence ocean circulation with global impacts (Lemke et al., 2007).
• Arctic terrestrial carbon flux: although models project that Arctic terrestrial ecosystems and the active layer will be a small sink for carbon in the next century, processes are complex and uncertainty is high. It is possible that increased emissions of carbon from thawing permafrost will lead to positive climate forcing (Sitch et al., 2007). Whether such emissions reach the atmosphere as methane or as carbon dioxide is important, because, on a per molecule basis, methane has more than 20 times the warming influence (Anisimov et al., 2005b).
• Migrating species: species that seasonally migrate from lower latitudes to polar regions rely on the existence of specific polar habitats, and if those habitats are compromised the effects will be felt in communities and food webs far beyond the polar regions. These habitats are likely to be compromised by direct or consequential climate change impacts such as drying of ponds and wetlands, and also by multiple stresses (e.g., land-use changes, hunting regulations).
• Methane hydrates: significant amounts of methane hydrates are contained in sediments, especially on Arctic continental shelves. As these areas warm, this methane may be released, adding to the greenhouse gas concentration in the atmosphere (Sloan, 2003; Maslin, 2004).
• Southern Ocean carbon flux: climate models indicate that stratification of the Southern Ocean will change. This could change the community structure of primary producers and alter rates of draw-down of atmospheric CO₂ and its transport to the deep ocean.