ABSTRACT
During the last two decades, evidence of global warming has accumulated, with a + 0.76°C temperature increase on average between 1850-1899 and 2001-2005 for the Earth (0.57°C to 0.95°C; IPCC, 2007). There is now very high confi dence that this warming results from the parallel increase in carbon dioxide from a preindustrial value of 280 ppm to 379 ppm in 2005, at a rate that is one hundred times faster than that which dominated over the last 20,000 years (IPCC, 2007). A recent global projection of surface temperature changes in mountainous areas concluded that these areas will likely warm during the twentyfi rst century at a rate two or three times higher than that recorded during the twentieth century (Nogues-Bravo et al., 2007). Switzerland has already experienced warming of + 1.35°C during the twentieth century, an increase that is twice the observed temperature increase averaged over the entire northern hemisphere (Rebetez and Reinhard, 2008). During the same period, annual mean precipitation has not changed signifi cantly. However, extreme weather events have become signifi cantly more frequent, with long periods of either continued precipitation or drought becoming more common, while snow cover has declined at elevations < 1,300 m (Rebetez, 2002). Thus, climatic change in Switzerland is emblematic of climate change occurring in mountain regions worldwide.
