Reductions in Arctic sea-ice cover have well-documented effects on polar bear populations and on marine mammals such as ring seals and bowhead whales, which are concentrated near the sea-ice edge. Shifting sea-ice geography and seasonality affects migration, feeding, and breeding patterns for these species. This also impacts circum-Arctic native populations, as the changing ice season affects travel conditions and traditional hunting practices. Changes in the seasonality and extent of open water have unclear implications for marine invertebrates and algal populations. Arctic Ocean ecology is expected to become more akin to that of the adjacent subpolar seas in future decades, although changes will likely be confined to the summer and fall; winter ice cover is still extensive over the Arctic.
Opening of the Arctic for shipping, tourism, and natural resource development is anticipated as summer passage becomes more safe and reliable. This creates commercial possibilities, but it also creates environmental and development challenges for the Arctic region.
Sea, lake, and river ice offer a flat, solid surface that is exploited for ice roads, seasonally connecting remote communities to the "transportation grid." Reduced ice cover has major effects on communities that rely on winter ice roads, as air transportation is the only other way to access these sites for shipping and provision of goods and services. This is an expensive alternative and it leads to isolation. Reductions in river ice cover at lower latitudes also affect the timing and frequency of ice-j am floods, with effects on riparian ecology and flood frequencies. More open water can also lead to increased production of frazil ice, which affects structures and civil engineering works (e.g. frazil buildup over water intakes).
Permafrost degradation has a number of well-documented ecological and societal consequences, in particular effects on infrastructure from ground subsidence and slope failure. Roads, pipelines, and buildings at high latitudes have always faced this challenge, due to the temperature effects of development (i.e. changing land cover), but climate warming is adding to the challenge. The combination of reduced sea ice and sea level rise is giving increased ocean storm swell in some regions of the Arctic, such as the Mackenzie delta, driving high rates of coastal erosion where ground ice is exposed to warm ocean waters.
Active layer deepening and thawing of permafrost are also accompanied by changes in surface hydrology, nutrient cycling, and vegetation cover. Loss of ice alters the water table, and because topography is subtle in many low-jying tundra and peatland areas, surface drainage patterns are evolving rapidly. Soil microbial activity (decomposition) is also accelerated in thawed and warmed ground. Partially compensating for this is an increase in photosynthetic activity and deepening of peat formation in thawed ground, which can lead to stored carbon: an atmospheric sink. Overall, net carbon release to the atmosphere from permafrost thaw is a potentially large positive feedback to future climate change, but there is large uncertainty in this.
Arctic and alpine ecology and hydrology are evolving as a consequence of reduced glacier and permafrost cover. It takes a long time—decades to centuries—for vegetation to move in after the retreat of glaciers, but alpine ecosystems are gradually shifting uphill. A more immediate impact of glacier retreat is the depletion of late-summer streamflow in alpine catchments. Reductions in seasonal snowpack and glacier cover are causing reduced summer streamflow in most alpine environments. This affects downstream communities and in-stream ecology, through both lower flows and increased water temperatures. Water resource management needs to adapt to expected increases in winter and early spring flows, an earlier freshet, and reduced flows from midsummer to fall in mountain-fed streams.
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