Glacier shrinkage in the Andes and consequences for water resources - Editorial

The state of mountain glaciers is a good climatic indicator of the global warming of the planet - one of most spectacular, and persuasive, manifestations of climate change. Numerous studies worldwide show a widespread, and well documented, retreat of mountain glaciers in non-polar regions of the world during the 20th century (IPCC, 2001). In fact, many glaciers have been shrinking for even longer, since the temperature minima of the Little Ice Age (17th-19th centuries), but a clear acceleration of the glacier retreat has been observed during recent decades. Glacier retreat is an undeniable fact and poses several questions: what is the reason for it and what are the observed and projected impacts? The likely reason is climate change and the primary impacts refer to glacier-based water resources and systems dependent on them. The glacier changes reflect mainly accumulated changes in temperature and precipitation. The relationship between glacier and temperature may depend on a number of factors, such as the geometry of the glacier and its surroundings, glacier area and depth, and those controlling the heat fluxes (summertime cloudiness, albedo, humidity, wind). On the global scale, air temperature is considered to be the most important factor controlling glacier retreat. For a typical mid-latitude glacier, a 1 degree C temperature rise would have the same effect as much greater decreases in cloudiness (by 30%) or precipitation (by 25%) (IPCC, 2001). In several areas, the climatic anomalies have been strongly influenced by the El Nino-Southern Oscillation (ENSO) events. The warm (El Nino) phase of ENSO, influencing the phase of precipitation at the altitudes of the glacier accumulation zone, has become more intense, more frequent, and more long-lasting in recent decades (IPCC, 2001).