The Andes, including portions of Argentina, Bolivia, Chile, Colombia, Ecuador, Peru, and Venezuela, have a population of about 85 million (nearly half of the total regional population), with about 20 million more people dependent on Andean water resources in the large cities along the Pacific coast of South America. As a thin geographical line along the Pacific coast, the Andes represent one of the most fragile cryosphere regions, with most glaciers shrinking at rapid and often highly visible rates.
Bolivia used to boast the world’s highest ski resort, Chacaltaya, which began operating a lift in 1939; it closed its doors for good in 2011. Of greater significance to development, the region’s peoples, the largest Andean cities and much of its agriculture rely at least in part on glacial or snow runoff for drinking water, hydroelectricity, and agriculture, especially in the summer months. Climate predictions here are extremely complex, due to the sharp vertical rise of the Andes from sea level and the dependence of many climate factors on changes in El Niño patterns (Kohler and Maselli 2009).
Glaciers have retreated in all Andean countries over the last three decades due to atmospheric warming, with a mean decadal increase in temperature of 0.34°C reported for the past 25 years at high elevations, similar to that of polar regions (Herzog et al, 2011). A recent extensive survey of climate change impact patterns across the Andes (Rabatel et al. 2013) concluded that current glacier retreat over the last three decades is unprecedented since at least the Little Ice Age (mid-17th-early 18th century). Although a few glaciers have shown sporadic gains, the trend has been quite negative over the past 50 years, with slightly more glacial loss in the Andes than other cryosphere regions. This loss nearly quadrupled in scale beginning in the late 1970s through 2010 compared to 1964-1975. The loss is most pronounced on small glaciers at low altitudes: these could disappear in the coming years or decades (Figure 3).
Figure 3: Land Glacier Ice Loss. (Source: IPCC AR4 (2007) based on Dyurgenov and Meyer (2004). ) Figure (a) shows the cumulative mass lost over time; Figure (b) shows the relative contribution of loss in each region to sea-level rise.
Temperatures have increased at a high rate of 0.10 °C per decade in the Andes over the last 70 years. Variability in the surface temperature of the Pacific Ocean (which is related to El Niño) also seems to be a large factor governing changes in glaciers, with precipitation apparently playing a lesser role. The higher frequency of El Niño events and changes in its timing and other patterns since the late 1970s, together with a warming troposphere over the tropical Andes, may explain much of the recent dramatic shrinkage of glaciers in this part of the world.
The Andes contribute a significant portion of river basin water supply, with up to 35 percent annually from glaciers or snowfall in some of the more arid regions of Peru and Chile (Vergara et. al. 2007). The small glaciers of the northern Andes play a lesser role in water resources, though they greatly impact delicate and unique high mountain ecosystems such as the paramo, puna, and Andean cloud forests. In all regions, however, glaciers can be the most important source of runoff during dry seasons, affecting water availability for irrigation and other uses. Concerns for both drinking water and hydroelectric power already have arisen in La Paz, Lima, and Quito (Buytaert et al. 2011). The effects may also be felt on Andean valley agriculture (Stern 2006), including from changes in the contribution of melt water supporting regional economies in Argentina and Chile.
Andean hydropower supplies 81 percent of the electricity for Peru, 73 percent for Colombia, 72 percent for Ecuador, and 50 percent for Bolivia. Decreases in water levels in Andean rivers, probably due to reductions in snowfall in the Andes, have already led to a 40-percent reduction in hydroelectricity generation in some regions of Argentina. Scientists fear that some regions of Peru and Ecuador have already surpassed “peak water”, when increased glacier runoff from greater melting begins to decline. Hundreds of thousands of people living downstream may face a future of lower flows in the warmest months — and seasonal water scarcity as a result (CONDESAN 2012). In addition, the frequency of events such as flooding, landslides, and wildfires increased by almost 40 percent in the region between 2001‐2010 compared to the previous decade, dominated by disasters caused by excess water (EM‐DAT (WHO) 2011).
Patagonia adjoins the southern Andes, with a population of two million in Argentina and Chile. The southern and northern Patagonian ice fields comprise the largest mass of ice in the southern hemisphere outside of Antarctica, but some of its glaciers are melting up to 100 times faster than at any time in the past 350 years, and at rates faster than any other large glacier region in the world. The annual rate of sea-level rise from loss of glacial mass in Patagonia doubled from 2000‐2005 (compared to the previous 25 years), with reductions of up to 50 percent in the Argentinean Tierra del Fuego (López Arenas, and Ramírez Cadena 2010; Gardner et al. 2013). The quantity of ice lost from Patagonia is more than the entire content of Lake Erie in North America. Ice fields rapidly lost volume throughout the 2000s, thinning at even the highest elevations (Glasser et al. 2011). This rapid melting, based on satellite observations, suggests the ice field’s contribution to global sea-level rise has increased by half since the end of the 20th century, jumping from 0.04 millimeters per year to about 0.07 mm and accounting for 2 percent of annual sea-level rise since 1998 (Willis, Melkonian, Pritchard, and Rivera 2012).
 República de Argentina Annual Report to UNFCCC (2007).