Perspectives from Ecuador and Bolivia
By Jai Chowdhry Beeman and Jean Carlos Ruiz Hernández
In the summer of 2007, a small glacier disappeared north of La Paz, Bolivia.
At 17,000 feet above sea level, the small mountain Chacaltaya is a mere foothill of its giant, glaciated brothers Huayna Potosi and Illimani. Accessible by taxi on a dirt road from the city of El Alto, its small glacier had been used as a marked ski run long ago.
The Chacaltaya glacier became a local symbol of changing climate: a mountain stripped of its ice by temperatures rising at unprecedented rates as we emit greenhouse gases into the atmosphere. And similar changes are happening across the Andes.
Here, we tell two stories, from the perspective of scientists training to understand glaciers and how they change in response to climate. The first, from Ecuador, is a look into why, and more importantly, how we study glaciers and their responses to modern climate change. The second, from Bolivia, takes a journey from the Altiplano, up a glacial valley, and into the past.
Jean Carlos Ruiz Hernández, Ecuador
Glaciers are like animals: they move, change, grunt and are always angry, notes Bear Grylls in his popular TV series Man vs. Wild. This colorful description captures why we feel so attracted to these colossi, and why some of us spend our lives exploring and studying them.
People tend to have questions for glaciologists. Some of the most common: how long will we have glaciers? What will be the socioeconomic impact of changes in freshwater availability for populations that depend, in part, on the water stored in glaciers?
The responses to these questions are not so simple. For a glacier to survive, it needs to receive at least the same mass in precipitation that it loses by melt. When melt dominates, the glacier begins to recede. As a result of anthropogenic global warming, the interior tropical Andes are experiencing an increase in temperature and higher precipitation variability. Glaciers in this part of the world are retreating as a result.
Tropical glaciers are highly sensitive to temperature changes, even on the hourly scale. In the tropical Andes, small streams can form as the sun warms the front of a glacier in the morning, only to disappear at night. Over longer periods of time, they testify to oceano-atmospheric phenomena, like the El Niño Southern Oscillation, itself well referenced in popular culture. In El Niño years in Ecuador, snow amounts are reduced and temperature increases, an ideal combination for glacier mass loss. La Niña years, on the other hand, tend to induce small losses or even slight increases in mass.
The Antisana massif, a colossus rising to 19,000 feet above sea level, is home to the most observed glacier in Ecuador. Located 25 miles outside of the capital, Quito, its ice cap covers around seven square miles, just a bit less than the land area of Cambridge, Massachusetts (for our Boston-area ReVista readers). In the Antisana massif, a complex network of water catchments has been installed, which supplies some of the water to the 2.5 million inhabitants of Quito.
Quito counts on glacial sources for five to ten percent of the city’s water supply and will suffer less from glacier retreat than a city like La Paz, for example, where glaciers provide up to 30 percent of the dry season water source.
These conclusions are obtained through long campaigns of observation and measurement. We make regular trips to the Antisana massif and other mountains to place instruments: meteorological stations, weirs to measure streamflow, stakes and pits to measure glacier mass. We add information from satellites that allow us to estimate precipitation, snow cover and topography. In Ecuador, public and private institutions together with international cooperation allow us to continue this work.
Antisana is a laboratory for glaciologists, ecologists, biologists and hydrologists. Here, numerous Ecuadoran and international students have trained at the undergraduate and postgraduate levels. And from Antisana, we will be able to answer the urgent questions about how mountain water systems will respond to the climate change that we are exposed to. It’s in our hands to generate and study the data to provide the answers.
Jai Chowdhry Beeman, United States
The changes on Antisana in Ecuador and the disappearance of the Chacaltaya glacier in Bolivia are part of a much longer story. Earth’s changing orbit and climate, through glaciers, have left their traces in the mountains.
I was introduced to this record of changes during the year that I worked as an intern at the Instituto de Hidraulica e Hidrologia/Institut de Recherche pour le Développement in La Paz. For a couple days every two weeks or so, I would travel with other technicians and students, both from Bolivia and abroad, to the glaciers in the Charquini and Huayna Potosi massifs to download meteorological data and measure glacier mass. Usually, I was drawn to parts of the mountains further afield for the weekends as well to explore.
Leaving El Alto, on the edge of the Altiplano, we would head towards the Cordillera Real. The foothills of the cordillera are cut by wide, u-shaped valleys, where streams connect the high mountains to the altiplano.
These u-shaped valleys during the last glaciation were filled with ice. During the glaciation, responding to lower solar radiation amounts, ice sheets had formed over much of North America and northern Europe. Smaller caps covered high mountain regions as well: huge glaciers carved out the valleys that now surround the Alps, the Himalayas and the Andes. Rises known as terminal moraines, formed by debris forced downslope by flowing ice, cross the outlets of these valleys and mark the past extent of these glaciers.
The road out of El Alto crosses a terminal moraine to enter the Milluni Valley on its way to the Huayna Potosi and Charquini massifs. Using cosmogenic isotopes, whose concentrations vary slowly over time, Smith et al. (2005, Science) date these moraines to between 34,000 and 23,000 years old. During this period, huge glaciers would have loomed over the plateau where El Alto now reigns.
After 23,000 years ago, the glaciers began to retreat. And this age is probably not a coincidence. Earth’s orbit constantly undergoes change. Around 24,000 years ago, the Earth began to receive more sunlight. As temperatures rose, the massive glaciers that had spread out of the Andes would likely have begun to lose ice. Their fronts would have melted more rapidly than they could be replenished by ice flowing down from the mountains.
The changes in the amount of solar radiation associated with glaciations and deglaciations, though, are small, and the climate system does not respond quickly to these changes. Rather, feedbacks in the climate system: greenhouse gases, which re-emit radiation in the form of heat, and ice loss at the polar caps, which increases the amount of radiation the Earth system can retain, for example, can accelerate warming over thousands of years. Then, mechanisms in the ocean and the atmosphere, like the ENSO variations that determine each year’s variations on Antisana, transport this heat across the globe.
These mechanisms are likely responsible for variations as the glaciers retreated to higher altitudes. Jomelli et al (2014, Nature) indicate that another advance likely occurred here around 14,500 years ago, during the period known as the Antarctic Cold Reversal. The glacier advance during this period in the Andes coincided, remarkably, with lower temperatures recorded in archives across the Southern Hemisphere and a pause in the deglacial CO2 increase.
Moving up into the mountains, a much more recent sequence of terminal moraines, dated by Rabatel et al. (2008, Quaternary Research) to the 17th to 19th centuries, crosses the increasingly narrow, steep valleys. These moraines testify to a more recent period of glacial advance, known as the Little Ice Age.
At the end of the road winding up Milluni valley, we arrive at a parking lot. Here, there is a refuge for mountaineers and a seismic station. Continuing along a path, we arrive at the tongue of Zongo glacier.
This current position of Zongo glacier, which has retreated significantly even over the last few decades, is indicative of a new period of climate, called the Anthropocene: the epoch of pronounced human influence. The story is well known: the Industrial Revolution introduced greenhouse gas emissions into the climate system, provoking rising temperatures and a corresponding change in weather patterns. Chacaltaya’s south-facing glacier that may have once been a tributary of the ice field flowing to the Altiplano, would vanish. Its neighbor Charquini Sur, one of the glaciers I would visit every two weeks, loses mass from almost all of its surface most years.
These modern changes are reflective of changes in climate that are rapid and complex. But we have a reference with which to understand how they will proceed. In paleoclimate archives across the globe, we have a record, albeit an imperfect one, of a true-scale experiment in climate change. These archives range from moraines; ice cores like that recently drilled on Illimani, Bolivia’s highest peak, by the IceMemory project; tree rings; lake and ocean sediments; speleothems; and many others, each recording different components of Earth’s climate. The climate changes that occurred during the past, like those that caused glaciers to retreat above La Paz, might be indicative of what we should expect for the future.
The continued development of a network of paleoclimate records in the Andes will be imperative for this century, as we attempt to understand how climate will change and how we might adapt. These records allow us to constrain the behavior of climate mechanisms in the past. In turn, we can attempt to understand how these mechanisms will operate under changing climate in the future.
Jai Chowdhry Beeman is a Ph.D. candidate at the Université Grenoble Alpes, where his most recent work is on the last deglaciation as recorded in Antarctic ice cores. He worked as a publications intern for ReVista during his time as an undergraduate at Harvard. His time at ReVista took him to Bolivia and the glaciers of the high Andes.
Jean C. Ruiz Hernández is an Assistant Professor of Physics at the Transportation Management career of the Chimborazo Polytechnic School in Riobamba-Ecuador. His research work focuses on the impacts of climate variability on partial glaciarized catchments and water management. He will begin a Ph.D. at the Université Pierre et Marie Curie this spring.