The Regional Impacts of Climate Change

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8.3.1.2. Impacts, Vulnerabilities, and Adaptation

The projected northward shift of the southern boundary of permafrost areas will alter ecosystem structure and functioning, with subsequent impacts on associated infrastructure and wildlife through terrain slumping, increased sediment loadings in rivers and lakes, and dramatically altered hydrology.

Approximately half of the wetland areas of North America are located in Alaska, the NorthWest Territories, and the Yukon (Table 8-1). Most of these wetlands rest on continuous or discontinuous permafrost, the distribution of which would be altered by climate warming.

The northward shift of the southern boundary of discontinuous and continuous permafrost areas is projected to be about 500 km by the middle of the 21^st century (Anisimov and Nelson, 1996; IPCC 1996, WG II, Chapter 7; Prowse, 1997). This shift would have profound effects within the altered areas (as summarized by Prowse, 1997). The melting of widespread ground ice will result in downslope soil movement, bank failure, and massive terrain slumping, leading to increases in sediment loads to rivers and lakes. This process will in turn affect spawning areas, oxygen levels, and stream/wetland sediment budgets. A deeper active layer will reduce overland flow as infiltration and active layer storage capacity increase. Peatlands are projected to disappear from south of 60�N in the Mackenzie Basin (Cohen, 1997a); patchy arctic wetlands currently supported by surface flow would not persist. Lakes and ponds, which have permafrost hydrological divides, are more likely to drain laterally or to groundwater systems.

Landscape alteration on this scale has serious implications for hydrology, wildlife, cultural values, and lifestyles. The effects will likely extend to infrastructure and transportation-including the integrity of foundations (pipelines, bridges, and buildings), water-control structures, ice-roads, and tailings. Altered flooding patterns and sediment loadings will impact internationally significant wetland habitat such as the Peace-Athabasca-Slave delta, the Mackenzie delta, and habitats associated with Hudson Bay and Queen Maud Gulf lowlands.

Many northern peatlands could become sources rather than sinks for atmospheric carbon.

A primary impact of future climate change in nonforest terrestrial ecosystems is the projected reduction of subarctic (tundra/taiga) ecosystems (IPCC 1996, WG II, Chapter 2). Neilson et al. (see Annex C) estimate that tundra and taiga ecosystems may be reduced by as much as one- to two-thirds of their present size. This reduction will have an impact on regional storage of carbon in the higher latitudes of North America and may result in a shift from a net sink to a net source of CO₂ for the tundra region (Anderson, 1991; Oechel et al., 1993). Climate warming also may cause reduction in total species biodiversity and total surface area covered by tundra vegetation, as well as decreased releases of methane from tundra plant communities as a result of alterations in the hydrological cycle, drier surface soils, and an increase in surface oxidation (IPCC 1996, WG II, Chapter 2).

Loss of migratory wildfowl and mammal breeding and forage habitats will occur within the southern Arctic ecozone, which is projected to nearly disappear from mainland areas.

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