National Geographic : 2006 Feb
Skiers take to the slopes of Sestriere, Italy, site of many skiing events in the 2006 Winter Olympics. Some 600 ski resorts now dot the Alps, which stretch more than 650 miles across eight nations (map). Scientists predict that as the permanent snow line rises along with temperatures, half those resorts could close by 2050. Less ice and snow cover means less runoff to feed Europe's major rivers. And as permafrost melts, some steep slopes-and the structures built on them-become destabilized.