Cause, conseguenze e strategie di mitigazione Proponiamo il primo di una serie di articoli in cui affronteremo l’attuale problema dei mutamenti climatici. Presentiamo il documento redatto, votato e pubblicato dall’Ipcc - Comitato intergovernativo sui cambiamenti climatici - che illustra la sintesi delle ricerche svolte su questo tema rilevante.

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Climate Change 2007: The Physical Science Basis.

The Intergovernmental Panel on Climate Change (IPCC) Technical Paper Climate Change and Water draws together and evaluates the information in IPCC Assessment and Special Reports concerning the impacts of climate change on hydrological processes and regimes, and on freshwater resources – their availability, quality, use and management. It takes into account current and projected regional key vulnerabilities, prospects for adaptation, and the relationships between climate change mitigation and water. Its objectives are:

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Climate change and water.

he prospect that increases inatmospheric concentrationsof greenhouse gases willhave measurable effects on theearth’s climate over the next fewdecades has attracted a vastresearch effort. Climatologistshave faced two main challenges.The first has been to distinguishthe signal of human-induced cli-mate change from the noise ofinterannual and decadal naturalvariability. The second has been topredict probable climate scenariosfor the future. Climate monitoringover the past century and long-term reconstructions of climateover the past millennium indicatethat the earth is indeed warmingup (Fig. 1)

http://uni-landau.de/umwelt/study/content/files/archiv/h.schulz/ws09/biodiversitaet_und_naturschutz/hughes 2000.pdf

Biological consequences of global warming: is the signal already

Increasing greenhouse gas concentrations are expected to have significant impacts on the world's climate on a timescale of decades to centuries. Evidence from long-term monitoring studies is now accumulating and suggests that the climate of the past few decades is anomalous compared with past climate variation, and that recent climatic and atmospheric trends are already affecting species physiology, distribution and phenology.

Biological consequences of global warming: is the signal already apparent?

Large changes in the wintertime atmospheric circulation have occurred over the past two decades over the ocean basins of the Northern Hemisphere, and these changes have had a profound effect on regional distributions of surface temperature and precipitation. The changes over the North Pacific have been well documented and have contributed to increases in temperatures across Alaska and much of western North America and to decreases in sea surface temperatures over the central North Pacific. The variations over the North Atlantic are related to changes in the North Atlantic Oscillation (NAO). Over the past 130 years, the NAO has exhibited considerable variability at quasi-biennial and quasi-decadal time scales, and the latter have become especially pronounced the second half of this century. Since 1980, the NAO has tended to remain in one extreme phase and has accounted for a substantial part of the observed wintertime surface warming over Europe and downstream over Eurasia and cooling in the northwest Atlantic. Anomalies in precipitation, including dry wintertime conditions over southern Europe and the Mediterranean and wetter-than-normal conditions over northern Europe and Scandinavia since 1980, are also linked to the behavior of the NAO. Changes in the monthly mean flow over the Atlantic are accompanied by a northward shift in the storm tracks and associated synoptic eddy activity, and these changes help to reinforce and maintain the anomalous mean circulation in the upper troposphere. It is important that studies of trends in local climate records, such as those from high elevation sites, recognize the presence of strong regional patterns of change associated with phenomena like the NAO.

Decadal Variations in Climate Associated with the North Atlantic Oscillation

Snow cover distribution strongly affects soil temperatures and, thus, plays a decisive role in determining permafrost distribution patterns. Redistribution of snow by avalanches and snow drift significantly affects the snow-melt pattern and soil temperatures in steep avalanche slopes of high mountain areas. At Fluela Pass, 2380 m a.s.l., eastern Swiss Alps, the presence and origin of permafrost that occurs at the base of an avalanche-affected slope below the regional lower limit of discontinuous permafrost was studied by field investigations and numerical simulations. Local permafrost distribution has been determined in former studies by applying geophysical methods and this was confirmed with two boreholes drilled at the slope base and in the avalanche starting zone. Temperature measurements confirm the presence of a 10 m thick permafrost body with temperatures close to the freezing point at the slope base. Numerical simulations of different snow-cover scenarios for 2002/03 demonstrate the particular effect on soil temperatures of high snow drift accompanying intense snow falls in early winter, controlling the duration of constant zero temperatures at the base of the snow pack at the beginning of the snow period. Copyright © 2004 John Wiley & Sons, Ltd.

Temperatures in two boreholes at Flüela Pass, Eastern Swiss Alps: the effect of snow redistribution on permafrost distribution patterns in high mountain areas

Climate scenarios for the time horizon of 2050 in the Swiss Alps as simulated by using high-resolution ensemble modeling indicate most likely changes in temperature /precipitation by + 2°C / + 10% in winter and + 3°C / - 20% in summer. 
Such a development would lead to the vanishing of about 75% of the existing glacier surface and deep warming of permafrost in mountain peaks. Corresponding impacts would mainly concern rather dramatic changes in landscape appearance, slope stability and the water cycle. The formation of lakes in the forefields of retreating or even collapsing glaciers together with the decreasing stability of rock walls leads to an increasing probability of major rock falls impacting onto water bodies and triggering dangerous flood waves. A special recommendation was therefore provided to systematically assess the safety of 
natural, artificial and newly forming lakes in the Alps.

Climate, glaciers and permafrost in the Swiss Alps 2050: scenarios, consequences and recommendations

Diverses caracteristiques de la neige, isotopes (δ 18 O, 3 H), conductivite electrique, poussieres, trace d'elements et pollen ont ete etudies dans une tranchee englobant environ deux ans et demi d'accumulation neigeuse afin de determiner une «clef» pour l'interpretation stratigraphique des carottages dans les regions de neves froids en haute-montagne sur le Colle Gnifetti (4 450 m s.m., Mont Rose). On observe que la forte influence du vent mene a des phenomenes de melange et de resedimentation des couches superficielles. Toutefois, sur la base de l'information tiree de la combinaison des differents parametres observes, il est possible de dater une grande part des couches de neige et parfois d'en determiner l'origine. En plus des horizons de glace, qui n'apparaissent que dans les couches estivales, des indices marquants sont les poussieres sahariennes, caracterisees par la pointe de teneur en poussiere et de conductivite

Accumulation characteristics on a cold high-alpine firn saddle from a snow-pit study on Colle Gnifetti. Monte Rosa, Swiss Alps

The advance and retreat of mountain glaciers during historical and Holocene time periods refl ect preindustrial changes in ice mass and corresponding energy fl uxes. Quantitative data analysis can be based on a simple approach comparing assumed steady state situations separated by time intervals of decades to a century. Detailed information spaning the past two millennia is available for the Great Aletsch Glacier, the largest glacier in the European Alps, including an extraordinary number of absolute age and geometry determinations from historical documents, radiocarbon dating of fossil trees and tree-ring analyses. Rates of mass change and associated energy fl uxes, during the 20th century as a whole, lie between the average and the extreme of historical values, but appear to have recently increased beyond these limits.

Wilfried Haeberli

Papers

Temperatures in two boreholes at Flüela Pass, Eastern Swiss Alps: the effect of snow redistribution on permafrost distribution patterns in high mountain areas

Climate, glaciers and permafrost in the Swiss Alps 2050: scenarios, consequences and recommendations

Accumulation characteristics on a cold high-alpine firn saddle from a snow-pit study on Colle Gnifetti. Monte Rosa, Swiss Alps

Alpine Glacier Mass Changes During the Past Two Millennia

Global Warming and Mountain Permafrost