In a recent scientific paper, researchers report that high altitude glaciers in the tropical Andes mountain range have been retreating at increasing rate since the 1970s. The researchers blame the melting on rising temperatures as the South American region has warmed about 0.7°C over the past 50 years (1950-1994). This unprecedented retreat of glaciers could affect water supply to the Andean countries in the short term. The report was published by The Cryosphere, an Open Access journal of the European Geosciences Union (EGU).
Scientists from Europe, South America and the US worked on the paper, noting that glaciers worldwide are retreating at a rate unprecedented in over 300 years. Gaciers have been retreating at a moderate pace as Earth warmed after the peak of the Little Ice Age, which lasted from the 16th to the mid-19th century. However, in the last few decades, the melt rate has increased steeply in the tropical Andes. Andean glaciers have shrunk by an average of 30-50% since the 1970s, according to Antoine Rabatel, lead author of the study.
Glaciers are retreating in the tropical Andes, but it is especially pronounced for small glaciers at low altitudes, says the report. 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. This is twice the rate of the larger, high-altitude glaciers. Said Rabatel, “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.” Glacier mass balance is equal to the difference between ice accumulation and ablation (melting and sublimation) in a glacier. Scientists express the annual mass balance in metre water equivalent (m w.e.). A loss of 1.2 m w.e. corresponds to a reduction of about 1.35 metres in ice thickness.
The report notes that the amount of rainfall in the region changed little during the same period and thus cannot account for changes in the retreat of the glaciers. It concludes that climate change is to blame for the melting, noting that regional temperatures increased an average of 0.15°C per decade over the 1950-1994 period.
“Our study is important in the run-up to the next IPCC report, coming out in 2013,” said Rabatel. The Intergovernmental Panel on Climate Change (IPCC) pointed out that tropical glaciers are important indicators of recent climate change. They are particularly sensitive to temperature changes. The tropical Andes host 99% of all tropical glaciers in the world, mostly in Peru.
A news release from the institute asserts that "The research is also important to anticipate the future behaviour of Andean glaciers and the impact of their accelerated melting on the region. “The ongoing recession of Andean glaciers will become increasingly problematic for regions depending on water resources supplied by glacierised mountain catchments, particularly in Peru,” the scientists write. Without changes in precipitation, the region could face water shortages in the future."
The Santa River valley in Peru will be most affected, predicted the report, since hundreds of thousands of people depend on glacier water for agriculture, domestic consumption, and hydropower. Cities could face shortages. “Glaciers provide about 15% of the La Paz (Bolivia) water supply throughout the year, increasing to about 27% during the dry season,” said Bolivian researcher Alvaro Soruco.
The scientists synthesized data collected for decades, some dating to the 1940s. “The methods we used to monitor glacier changes in this region include field observations of glacier mass balance, and remote-sensing measurements based on aerial photographs and satellite images for glacier surface and volume changes,” explained Rabatel. Data was collected in Colombia, Ecuador, Peru and Bolivia for an area of almost a thousand square kilometres. This is equal to about 50% of the total area covered by glaciers in the tropical Andes in the early 2000s. “This study has been conducted with scientific motivations, but if the insight it provides can motivate political decisions to mitigate anthropogenic impact on climate and glacier retreat, it will be an important step forward,” Rabatel concluded.