Glacier response to climate change

Glaciers are large-scale, highly sensitive climate instruments which, ideally, should be picked up and weighed once a year. Their fluctuations are among the clearest signals of climate change. A glacier is simply the surplus ice that collects above the permanent snowline where the losses to summer melting are less than the gains from winter accumulation. This creeping cap of annual layers, the névé, formed over many decades of winter snowfalls, is balanced lower down the mountain by losses to as many decades of summer melt. The higher the mountain rises above the permanent snowline, the more surplus snow accumulates, and the larger the glacier formed. A glacier always crosses the permanent snowline from the area of snow gain to the zone of ice loss. The altitude of this permanent snowline is the equilibrium line: it marks the altitude at which snow gain (accumulation) is exactly balanced by melt (ablation). If the temperature or snowfall changes even a little, the altitude of the equilibrium line shifts dramatically, with consequent change to the volume of the glacier. It is this mass balance that makes glaciers sensitive climate instruments that record year-by-year climate in the mountains