Unprecedented glacier melting in the Andes blamed on climate change
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| Edubucher/Wikimedia Commons |
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. These conclusions are published
January 22 in The Cryosphere, an
Open Access journal of the European Geosciences Union (EGU). 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, according to Antoine Rabatel, researcher at
the Laboratory for Glaciology and Environmental Geophysics in Grenoble, France,
and lead author of the study.
Glaciers
are retreating everywhere in the tropical Andes, but the melting is more
pronounced for small glaciers at low altitudes, the authors 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 [see note]) 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," says Rabatel.
The
researchers further report that 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.
"Our
study is important in the run-up to the next IPCC report, coming out in
2013," says Rabatel. The Intergovernmental Panel on Climate Change (IPCC)
has pointed out that tropical glaciers are key indicators of recent climate
change as they are particularly sensitive to temperature changes. The tropical
Andes host 99% of all tropical glaciers in the world, most of them in Peru.
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, 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.
In
their comprehensive review of Andean glaciers, the scientists synthesised data
collected over several decades, some dating as far back as 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," explains Rabatel.
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.
The
research was conducted to provide the scientific community with a comprehensive
overview of the status of glaciers in the tropical Andes and determine the rate
of retreat and identify potential causes for the melting. But the authors hope
the results can have a wider impact.
"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 concludes.
Note
Glacier
mass balance is 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.
Source: European
Geosciences Union
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