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CLIMATOLOGY

Thaw in the Andes

Aerial photos and satellite images show accelerated shrinking of South American glaciers

In Porto Alegre, RS

Nevado Illimani, seen from the Bolivian capital of La Paz: glaciers occupy 35% less area than they did in 1963

GETTYIMAGES / JOHN COLETTINevado Illimani, seen from the Bolivian capital of La Paz: glaciers occupy 35% less area than they did in 1963GETTYIMAGES / JOHN COLETTI

In 2009, the Chacaltaya Glacier utterly disappeared from the Bolivian landscape. It had been shrinking for some time because the amount of snow accumulating there each year was insufficient to maintain it. But no one expected it to vanish completely in such a short time, six years earlier than researchers had reckoned. Located about 30 kilometers north of the Bolivian capital of La Paz, Chacaltaya was a small glacier, but it was internationally known as the site of the world’s highest ski run, 5,300 meters above sea level, and for being the place where Brazilian physicist César Lattes did some of the experiments that led to the 1940 discovery of the pi meson, or pion, a subatomic particle. The early demise of Chacaltaya left Bolivians without a place to ski and made news around the world for a much more important reason: what happened there is also happening to many glaciers in the Andes and other regions of the planet. Specialists believe that the retreat of the Andean glaciers may signal the fate of much of the world’s tropical ice if the atmospheric temperature continues to rise at the rate seen in recent decades: melting into water.

Today the Bolivian glaciers cover about half the area they occupied in the mid-20th century. And, generally speaking, they are shrinking at an accelerated pace—especially the small glaciers of less than one square kilometer (km2) like Chacaltaya, according to recent studies by researchers at Brazil’s Federal University of Rio Grande do Sul (UFRGS) in partnership with Bolivian colleagues. “What we are seeing in the small Andean glaciers is an early indication of what could happen with the larger glaciers in this region and elsewhere,” explains glaciologist Jefferson Cardia Simões, director of the Climatic and Polar Research Center at UFRGS and coordinator of the Brazilian group.

In collaboration with a team headed by glaciologist Edson Ramírez of the Universidad Mayor de San Andrés, in La Paz, the Brazilian researchers are working on an extensive inventory of the Bolivian glaciers. Using aerial photographs and satellite images, they were able to do an updated assessment of the transformation undergone by about 600 glaciers scattered around two stretches of the Andes—the Cordillera Real and the Cordillera Apolobamba—in Bolivia, a country that holds 20% of the Andean tropical ice (approximately 99% of the world’s tropical ice is found in the Andes).

“We estimated about a 50% reduction in the surface area of the Bolivian glaciers during this period, which is a very rapid loss,” says geographer Rafael da Rocha Ribeiro, a member of Simões’ team and one of the authors of the inventory. “These glaciers are good indicators of climate change because they respond to changes very quickly,” he notes. The reason for this level of sensitivity is that in tropical mountainous regions, ice is found at a temperature of around zero degrees Celsius, the freezing point. Specialists call it “hot” or “temperate” ice, in contrast to the “cold” ice of the polar regions, which is at tens of degrees below zero.

In recent years, Ribeiro, along with Ramírez’ group, used high-precision GPS devices to mark the boundaries of some of the glaciers in the Cordillera Real, where Chacaltaya was located. A comparison of the current boundaries of 476 glaciers with those recorded in previous decades led them to estimate that the glaciers had lost 43% of their surface area in 40 years. In the 1970s they covered an area of 325 km2, and today they occupy only 185.5 km2, according to a paper presented last year at the General Assembly of the European Geosciences Union.

While analyzing a specific region of the Cordillera Real—Nevado Illimani, which is visible from La Paz—Ribeiro noted that the contraction of the glaciers had accelerated recently. The glaciers on Illimani had lost 12% of their area between 1963 and 1983, and they shrank twice that amount over the next three decades, as described in an article published in Annals of Glaciology.

Ana Maria Sanches, another geographer on Simões’ team, observed even more intense reduction in a group of glaciers located 250 kilometers north of Illimani, in the Cordillera Apolobamba on the border between Bolivia and Peru. In the 1975 to 2011 period, the Nevado Cololo ice mass lost 42% of its area—today only 24.7 km2 remain today—and  only 48 of the 122 original glaciers still exist.

The retreat of the glaciers is not generally homogeneous. The small glaciers are more abundant, but they are also the ones disappearing most rapidly. Ribeiro found that the large glaciers on Illimani lost an average of 15% of their area during the period analyzed, while the average rate of retreat among the small ones was nearly five times greater.

The melting of the glaciers is not limited to Bolivia. In Peru, which is home to most (70%) of the Andean tropical ice, the glaciers have already lost nearly one-fourth of their area in the last few decades. In a recent compilation about the current condition of the Andean glaciers, French glaciologist Antoine Rabatel, joined by other glacier specialists, asserts that between the 1970s and the present time, the glaciers in the tropical Andes have shrunk at a pace unprecedented in the past 300 years, from the time they began to recede following the end of the small ice age in the late 19th century. During the small ice age, the atmospheric temperature dropped about 0.6 degree.

In addition to being small, the Andean glaciers are becoming confined to the higher mountain elevations. “On Nevado Cololo, for example, there used to be glaciers below 4,500 meters,” Sanches points out. “Today they can only be found above 4,950 meters.”

The causes of the retreat of the Andean glaciers are still uncertain. There are clear signs that the regional climate has changed: the average temperature in the Andes rose 0.8 degree over the course of the past century and, from the late 1970s to the present day, there has been an increase in the frequency and intensity of the El Niño phenomenon—warming of the surface of the Pacific Ocean, which blocks moisture coming from the Amazon region and reduces precipitation in the form of snow.

Quelccaya ice cap in Peru: glacier melt created a lake that ruptured in 2006, flooding a nearby valley

GETTYIMAGES / PETER ESSICKQuelccaya ice cap in Peru: glacier melt created a lake that ruptured in 2006, flooding a nearby valleyGETTYIMAGES / PETER ESSICK

Specialists suspect that these regional changes are linked to planet-wide climate changes that appear to be ongoing and that the Intergovernmental Panel on Climate Change (IPCC) has already associated with human activities.

“The regional changes and the melting of the tropical glaciers [which are generally retreating worldwide, although some may have increased in size] coincide with the rise in global temperature,” explains Simões, who is also coordinator of Brazil’s National Institute of Science and Technology of the Cryosphere. But no one can categorically say that the reason is global warming, because glacier melting and other climatic phenomena are complex processes that involve many factors.

Despite that uncertainty, specialists believe that the effects of the shrinking of these glaciers will soon become clear, and will have local and even regional consequences. Most of these glaciers are small, less than two square kilometers. But they provide much of the water used to produce electricity, to sustain agriculture and to supply Andean cities—especially in autumn and winter, the driest period of the year.

A study conducted by Ramírez in 2008 showed that over the past 50 years, there has been a 44% to 55% reduction in the size of the glaciers feeding the rivers that supply some of the water used in the cities of La Paz and El Alto, which are home to a combined 1.5 million people. Although there has been no evidence to date of a diminished water supply, a number of researchers expect it will happen. “It is important to prepare the local communities for a future scenario in which the availability of water will change,” Ribeiro comments.

Simões fears that the accelerated melting will result in greater frequency of a type of natural disaster to which regions having glaciers, vulcanism and earthquakes—such as the Andes—are susceptible: the rupturing of lakes formed by glacier melt. In an article published in the journal Annals of Glaciology in 2011, American paleoclimatologist Lonnie Thompson relates what he and his team witnessed in Peru. From the time they began doing research on the Quelccaya ice cap in the 1970s, they monitored the increasing volume of a stream that ran near the camp, and the formation of a large lake at the head of the glacier. The lake, which was formed from glacier melt, ruptured in 2006 after an avalanche, flooding the valley just below it and eliminating the pasturelands where the inhabitants of a nearby village raised llamas.

Beyond the local impact, there may also be an as-yet-unknown regional effect. The glaciers on the eastern side of the Andes are the source of streams that increase in volume as they head eastward, feeding into major rivers in the Amazon Basin such as the Madeira and the Solimões. The Andes are the source of some of the sediments that fertilize these rivers and are then carried to the Atlantic. No one knows what might happen to these rivers and their ecosystems if the Andean glaciers and the sediments they bring were to diminish greatly in the coming decades. “We need to change the idea people have in Brazil that this ice won’t affect our country,” Simões says. “The entire western Amazon region is very close to this ice mass.”

Scientific articles
RIBEIRO, R.R. et al. 46 years of environmental records from the Nevado Illimani glacier group, Bolivia, using digital photogrammetry. Annals of Glaciology. v. 54 (63). Feb. 26, 2013.
RAMIREZ, E. et al. Glacier Inventory of the Cordillera Real – Bolivia using high resolution satellite images ALOS and CBERS-2B. Geophysical Research Abstracts. v. 14. EGU2012-11692. 2012.
THOMPSON, L.G. et al. Tropical glaciers, recorders and indicators of climate change, are disappearing globally. Annals of Glaciology. v. 52 (59). 2011.

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