What are tropical glaciers and why do they matter?

The term “tropical glaciers” may sound like an oxymoron, but to one-sixth of the world’s population residing in places like South America, Africa and Indonesia, they represent a major water source that is rapidly melting away.

Like polar ice caps, tropical glaciers that are located high in the equatorial mountain ranges are disappearing due to global warming.

“These things are going, and they are going fast,” says Bryan Mark, a glaciologist at The Ohio State University. Most glaciers in the Andes Mountains of South America, he says, could melt in the next 30 years, threatening millions of people who depend on them for drinking water, electrical power generation and farming.

The Intergovernmental Panel on Climate Change, an international group of scientists who evaluate the risks of human-induced climate change, predicts that, based on current levels of greenhouse gas emissions, average global temperatures will likely rise three to six degrees Fahrenheit (two to four degrees Celsius) in the next several decades. Climate models predict this warming will be most pronounced at high altitudes where most tropical glaciers exist, says Mark, who studies glaciers in the Andes Mountains of South America.  Average temperatures in the Andes have already increased by about 1.8 degrees Fahrenheit (one degree Celsius) in the last 100 years, contributing to glacier melting.

The Andes mountain range contains the largest glaciated area in the tropics, the Qualccaya Ice Cap in Peru. This glacier has lost approximately 20 percent of its area since 1978 – and the rate of loss is increasing. The Qori Kalis Glacier, a protruding arm of Qualccaya, is melting 40 times faster than it was three decades ago, losing 672 feet (205 meters) of ice per year, according to Mark.

Mark is part of a team of international scientists and anthropologists studying the impact of melting glacier ice on landscape and water supply in the Cordillera Blanca range of the Andes in Peru. To determine changes in glacier volume, Mark analyzes laser scans of glacier topography taken by airplanes or satellites. He also measures the amount of water flowing from melting glaciers into streams and rivers in Peru.

Water shortages are not a problem yet, according to Mark. The residents of some glacier watersheds, areas of land through which the melted water passes, have even experienced an increase in water supply in recent years due to glacial runoff into streams and rivers. During the dry season, from June to October, glacial runoff can account for more than 30 percent of the total river flow in the populated Rio Santa watershed in the Peruvian highlands. But supplies may begin to run out as glaciers shrink in a warming world.

Runoff from melting glaciers has always fed the river during the dry season, but according to Mark, lost glacier volume is not being regenerated by precipitation during the wet season, like in the past. “We aren’t seeing diminished precipitation, but we are seeing a difference as to whether it’s staying frozen in the glacier or not,” he says. Warmer, more humid air means more rain and less snow, which leads to melting and less accumulation of glacier ice.

“There’s an annual input and return from those glaciers, like a bank account,” says Mark. “If you are withdrawing more than you are putting in, eventually your account is going to go dry.”

However, Mark doubts the Andean glaciers will disappear completely. “I suspect we aren’t going to see a totally ice-free Cordillera Blanca, not in my lifetime anyway,” he says. Because the sun’s rays hit the ice on the steep sections of the mountain range indirectly, they are less susceptible to melting. However, the preservation of this ice will not help villagers in danger of water shortage. Because these steep spots hold very thin ice, they are a less important water resource than the lower, valley glaciers that hold greater volumes of ice.

As these glaciers continue to dwindle in the next 30 years, finding enough water to sustain humans and wildlife in the Andes will be a “huge issue,” according to Douglas Hardy, a climate scientist at the University of Massachusetts Amherst.

Because the water flow varies so much from season to season in the tropics, researchers are looking into various options for water storage. Building river dams to make reservoirs of glacier melt may be the easiest way to store large amounts of water. But this approach could leave villages susceptible to flooding and their water supply susceptible to evaporation, according to Mark. Storage in underground aquifers is another possibility currently under investigation.

Groundwater stored in low-lying wetlands and grasslands, called pampas, may already contribute nearly half the water in the streams during the dry season, says Jeff McKenzie, a hydrogeologist at McGill University who works with Mark in the Cordillera Blanca to study the movement of groundwater. According to McKenzie, these underground aquifers will become increasingly important water resources as glaciers melt.

As for the impact on humans, “people are very aware of changes, because they are already taking place,” says Jeff Bury, a human geographer at the University of California, Santa Cruz, who studies human vulnerability and adaptation to climate change in the Cordillera Blanca. The perception among local indigenous people is that weather has become more erratic and extreme in recent years, with stronger rainstorms that can be damaging to crops. The indigenous people are very concerned about melting glaciers and water resources, according to Bury, because their livelihoods depend on it. Though awareness of climate change is widespread in the region, what to do about it is another question, one that may include future conflicts over natural resources.

“I don’t pretend to know what to do,” says Mark, who noted that there is great uncertainty over how fast and how much the tropical glaciers will melt. This depends largely on the future rate of man-made carbon emissions into the atmosphere.  Maintaining a sufficient water supply in the face of global climate change will be an increasingly formidable challenge, says Mark. In fact, he adds, managing water resources in a warming world is “possibly the defining problem of our century.”

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