1.3.1.2 Summary of cryosphere

There is abundant and significant evidence that most of the cryospheric components in polar regions and in mountains are undergoing generalised shrinkage in response to warming, and that their effects in the environment and in human activities are already detectable. This agrees with the results presented in Chapter 9 of WGI (Hegerl et al., 2007), which concludes that the observed reductions in Arctic sea ice extent, decreasing trend in global snow cover, and widespread retreat and melting of glaciers are inconsistent with simulated internal variability, and consistent with the simulated response to anthropogenic gases. The observed effects of cryosphere reduction include modification of river regimes due to enhanced glacial melt, snowmelt advance and enhanced winter base flow; formation of thermokarst terrain and disappearance of surface lakes in thawing permafrost; decrease in potential travel days of vehicles over frozen roads in the Arctic; enhanced potential for glacier hazards and slope instability due to mechanical weakening driven by ice and permafrost melting; regional ocean freshening; sea-level rise due to glacier and ice sheet shrinkage; biotic colonisation and faunal changes in deglaciated terrain; changes in freshwater and marine ecosystems affected by lake-ice and sea-ice reduction; changes in livelihoods; reduced tourism activities related to skiing, ice climbing and scenic activities in cryospheric areas affected by degradation; and increased ease of ship transportation in the Arctic.

1.3.2 Hydrology and water resources

This section focuses on the relationship of runoff, lake levels, groundwater, floods and droughts, and water quality, with observed climate variability, climate trends, and land-use and land-cover changes reported since the TAR. The time period under consideration is primarily 1975 to 2005, with many studies extending to earlier decades. Observed changes in precipitation and aspects of surface hydrology are described in more detail by Trenberth et al. (2007), Section 3.3.