Risk of glacial flooding is rising in the tropics

One hears about how the glaciers of Greenland and Antarctica are losing ice, and so threatening to raise sea levels — perhaps quite dramatically.

But mountain ranges across the globe are strewn with far smaller glaciers that are suffering perhaps an even bigger wallop from rising temperatures. And now new research suggests their retreat could, quite literally, be deadly in some cases to communities living below.

In a new study in the journal The Cryosphere, Simon Cook of Manchester Metropolitan University in the U.K. and British and Bolivian colleagues examine the mountain glaciers of the Bolivian Andes in particular, which are typically classified as “tropical glaciers.” The Andes feature such high elevations that even those in tropical or equatorial countries can have glaciers.

“There are three glaciated ranges that we looked at, and we actually classified glacier change across that spine of mountains that run through Bolivia,” said Cook, the study’s lead author. “And we found that sadly, the glaciers there have shrunk by more than 40 percent since the 1980s.”

He and his colleagues used satellite data to investigate the way glaciers had changed in the Bolivian Andes between 1986 and 2014. They found that about 88 square miles of glacier cover disappeared during the study period — around 43 percent of the total area that had existed in 1986.

Previous reports have suggested temperatures in the region have risen by about 0.15 degrees Celsius each year between 1950 and 1994 and may be warming at an even higher rate now.

Millions of citizens in Bolivia rely on these glaciers for fresh water as they melt in the spring. Smaller glaciers means less meltwater will be available to feed the water systems.

Also, as the glaciers shrink, they tend to leave behind large pools of meltwater, constrained by walls of soil, rock and other debris that built up as the ice eroded the landscape.

The largest of these lakes are believed to hold more than 16 billion gallons of water — that’s equivalent to about 25,000 Olympic swimming pools. Because these piles of debris are essentially the only thing holding the water back, these pools can pose a serious danger to nearby communities.

“Those lakes can burst and wash away villages or infrastructure downstream,” Cook said.

The paper highlights what may be an under-recognized, but growing, crisis for the world’s tropical glaciers. Cook noted the research suggests most of the Bolivian glaciers will probably be gone by the end of the century — and that’s a big problem for the human communities nearby.

“Not only have they got reduced meltwater, but they’re going to be directly in the path of some of these potential floods, if they occur,” he said.