Processes and landforms connected with ice/debris-transport systems in cold mountain areas provide signals of environmental change, constitute archives of past conditions and have an impact on human living conditions. It is useful to evaluate the significance of the phenomena involved in relation to ongoing trends of atmospheric temperature rise.

The clearest signals of atmospheric warming can be obtained from glacier geometry and permafrost temperature. In addition to the pronounced memory function of perennial ice, latent heat exchange at glacier surfaces as well as heat conduction in permafrost essentially filter out high frequency disturbances. The combination of these effects leads to excellent signal-to-noise ratios at the decadal to secular time scale. The loss of glacier mass is a most effective, direct energy sink, whereas cumulative glacier length reduction is a delayed, heavily smoothed, but also heavily enhanced, reflection of secular mass loss. Twentieth-century mass loss of low-latitude mountain glaciers roughly corresponds to assumed anthropogenic greenhouse forcing and, despite great regional variability, may show the first overall signs of acceleration since about 1980. Degradation (warming and thawing) of mountain permafrost, as a less direct energy sink, can be pronounced locally but is generally much less well documented and reflects considerably smaller energy fluxes than glacier shrinkage.

A number of archives contain information on past (pre-industrial) conditions not influenced by human activity. Ice cores from cold high-altitude firn areas reflect atmospheric composition over time scales of years to millennia. Then too, repeatedly measured temperature profiles from reasonably deep boreholes drilled into cold firn or negative-temperature bedrock can be interpreted with respect to thermal histories over time intervals of decades to centuries. Glaciers contain rockfall deposits over time intervals of years to centuries, but events reaching the accumulation area become visible by flow emergence only after decades to centuries. Debris cones, rock glaciers and moraines reflect frost-shattering activity and debris production during the entire Holocene time period (millennia); debris-flow deposits have accumulated (or have been accumulating) during about the same time interval. Important archeological finds (Oetztal Ice Man, Lötschental Bows) in disappearing ice patches on high mountain permafrost indicate that the extent of glacierisation and permafrost existence in the European Alps may now have reached the "warm" limit of Holocene variability. Organic matter in this new type of archive could shed most important information on periods of minimum Holocene ice extent in mountain areas and should be investigated further.

The most spectacular impacts are due to low-frequency high-magnitude events such as major rockfalls, outbursts of glacial/periglacial lakes, debris flows and river floods with high sediment load. The reduction in the stability of steep slopes with the disappearance of glaciers and changes in permafrost not only affects loose sediments such as moraines, scree slopes, etc., but also fissured rock walls. With increasing exposure and the production of debris, the sediment balance of meltwater streams must be assumed to change. However, the disappearance of perennial ice also influences the river regime (seasonality of discharge, storage capacity of the catchment) and the snow characteristics (temperature, metamorphosis, stability with respect to the release of avalanches and meltwater in spring/early summer). Not the least impact may be the sometimes dramatic change in landscape appearance, especially in view to the slow colonization of freshly exposed debris by vegetation.

What about soils? Assuming a simple vertical shift of climate and vegetation zones due to global warming, soil processes will not follow in the same way. This fact is due to the diverse environmental mosaic, characterized by sharp geomorphologic and geologic boundaries. Soils are strongly related to geology, relief and complex sedimentary cover-beds. These factors will hardly change in a warmer atmosphere. Therefore it will be difficult for soils to ‘move’ corresponding to possible shifts of vegetation belts. In addition, soil types need at least centuries or even millennia to change. In case of fast climate change, some soils may never reach their climax. At the landscape level, the most probable changes concerning soils might occur in the physical processes. In case that temperatures will increase, for example, the soil area stabilized by permafrost may decrease and soil erosion rise.

1 - Debris flow at Piz Lagrev, Eastern Swiss Alps, endangering an important high mountain road in the Upper Engadin.
 

2 - Mass movement processes on steep slopes are well recognized by media people as demonstrating the endangered alpine environment to the public in global change discussions.

29 August 2011
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