Glaciers exist on all continents except Australia and at virtually all latitudes from the tropics to the poles. Mountain glaciers, such as those that exist at higher elevations in the mid-latitudes and tropics, are particularly sensitive indicators of climate change. As climate changes, the balance between inputs and outputs may change, resulting in a change in thickness and the advance or retreat of the glacier. Temperature, precipitation, humidity, wind speed, and other factors such as slope and the reflectivity of the glacier surface all affect the balance between inputs and outputs. There is widespread evidence that glaciers are retreating in many mountain areas of the world.
Glacial retreat is also prevalent in the higher elevations of the tropics.
Although there is considerable variability at the regional and local scales and over shorter time periods, the overall global signal shows mass loss and retreat of glaciers during the last century. The shrinking of glaciers will likely have a significant socioeconomic impact in some mountain regions, though the exact local impacts remain uncertain and will vary. Regions that lose major parts of their glacier cover will experience alterations in hydrology. Also, because revegetation of terrain is slower at high altitudes, deglaciated areas will be subject to erosion and decreased stability, heightening the need to protect buildings, roads, communication links, and other structures. For areas dependent on tourism, uncertain snow cover during peak winter sports seasons, natural hazards such as rock and ice falls, or loss of scenic beauty are of particular concern.