Increased catchment weathering or internal processing in lakes and rivers.
North America, Europe (88 stations)
Bodaly et al., 1993; Sommaruga-Wograth et al., 1997; Rogora et al., 2003; Vesely et al., 2003; Worrall et al., 2003; Karst-Riddoch et al., 2005
average of 12 days during the last 150 years (Lemke et al., 2007) results in a corresponding reduction in skating activities in the Northern Hemisphere. In Europe there is some evidence for a reduction in ice-jam floods due to reduced freshwater freezing during the last century (Svensson et al., 2006). Enhanced melt conditions could also result in significant ice jamming due to increased break-up events, which can, in turn, result in severe flooding (Prowse and Beltaos, 2002), although there is a lack of scientific evidence that this is already happening.
Changes in lake thermal structure and quality/quantity of under-ice habitation in lakes have been reported, as well as changes in suspended particles and chemical composition (see Section 1.3.2). Earlier ice-out dates can have relevant effects on lake and river ecology, while changes in river-ice dynamics may also have ecological effects (see Section 1.3.4).
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.
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