|Unprecedented glacier melting in the Andes blamed on climate change|
Glaciers in the tropical Andes have been retreating at increasing rate since the 1970s, scientists write in the most comprehensive review to date of Andean glacier observations. The researchers blame the melting on rising temperatures as the region has warmed about 0.7°C over the past 50 years (1950–1994). This unprecedented retreat could affect water supply to Andean populations in the near future, according to a paper in The Cryosphere.
The international team of scientists – uniting researchers from Europe, South America and the US – shows in the new paper that, since the 1970s, glaciers in tropical Andes have been melting at a rate unprecedented in the past 300 years. Globally, glaciers have been retreating at a moderate pace as the planet warmed after the peak of the Little Ice Age, a cold period lasting from the 16th to the mid-19th century. Over the past few decades, however, the rate of melting has increased steeply in the tropical Andes. Glaciers in the mountain range have shrunk by an average of 30–50% since the 1970s.
Glaciers are retreating everywhere in the tropical Andes, but the melting is more pronounced for small glaciers at low altitudes. Glaciers at altitudes below 5,400 metres have lost about 1.35 metres in ice thickness (an average of 1.2 metres of water equivalent) per year since the late 1970s, twice the rate of the larger, high-altitude glaciers. Because the maximum thickness of these small, low-altitude glaciers rarely exceeds 40 metres, with such an annual loss they will probably completely disappear within the coming decades. The amount of rainfall in the region did not change much over the past few decades and, therefore, cannot account for changes in glacier retreat. Instead, climate change is to blame for the melting: regional temperatures increased an average of 0.15°C per decade over the 1950–1994 period.
Without changes in precipitation, the region could face water shortages in the future. The Santa River valley in Peru will be most affected, as its hundreds of thousands of inhabitants heavily rely on glacier water for agriculture, domestic consumption, and hydropower. Large cities, such as La Paz in Bolivia, could also face shortages. »Glaciers provide about 15% of the La Paz water supply throughout the year, increasing to about 27% during the dry season«, says Alvaro Soruco, a Bolivian researcher who took part in the study. The study takes into account data collected for glaciers in Colombia, Ecuador, Peru and Bolivia, covering a total of almost a thousand square kilometres. This corresponds to about 50% of the total area covered by glaciers in the tropical Andes in the early 2000s.