Tropical Glaciers: Super-Sensitive Climate Indicators

I was bummed that I wasn’t able to get this post up before we headed into the field last month. Here she is, and there’s more to come!

The Andes mountains split the remarkable country of Peru into a dry western side and a much wetter eastern side. At the top of many Andean cordilleras are sprawling  glaciers, which transform the tortured rock into towering, life-giving, worship-worthy pinnacles of ice and snow.  Indeed, the snow-covered mountains have been worshiped and revered by Quechua-speaking people for thousands of years and it’s almost impossible even for an atheist norteamericana like myself to not feel the spiritual pull of the ice.


Nevado Ausangate, one of the tallest and most sacred mountains in Peru.

The key thing about tropical glaciers is, they’re constantly close to the melting point. New snow accumulation and ice melt every day rather than accumulating throughout a long, cold winter. Small increases in temperature as a result of climate change therefore have led to the very rapid retreat and loss of volume in tropical Andean glaciers. You can see the retreat of the Puka glacier at my study site in a previous post. The high sensitivity of tropical glaciers to small changes in temperature and precipitation mean that they’ve provided some of our earliest and most significant evidence of large-scale effects of climate change.

As the ice melts away and isn’t replaced, the communities living below these tropical glaciers are at risk of losing their main source of water. Glacier water supports household activities and also the high-elevation wetlands that sustain rural livelihoods like alpaca farming through the dry season. Depending on the topography of the area, these communities are also at risk of experiencing deadly floods from the glacial meltwater. As the glaciers melt, large lakes usually form at the retreating end of the ice. These proglacial lakes are often weakly dammed by debris piles (moraines) and when those dams become overloaded, catastrophic outburst floods can devastate communities. To the north, in the Cordillera Blanca, something like 30,000 people have died from these types of floods over the last 100 years. In these ways, climate change and glacier loss directly impact the people living downslope.



Examples of lakes forming at the retreating edge of the Puka glacier (top photo) and the ice cliff.

The other side of this story is that glacier retreat is also causing environmental changes and creating brand new habitat. Where before there was ice, there are now piles of rock and sand and alpine lagunas which are being rapidly colonized by microbes, plants, animals. It’s a fascinating process to see on the ground and raises an infinite number of questions, like how long does it take for new ground and new lagoons to be colonized? How do the organisms disperse to these new locations? The arrival of plants with wind-dispersed seeds is less of a mystery than the aquatic copepods and macroinvertebrates (carried in the feathers and on the feet of ducks?) and amphibians (did my little frog friends really walk a kilometer with a 500 meter elevation gain through boulders and gravel under conditions that are incredibly dry and cold at night and dry, hot, and extremely high UV during the day??). What will happen to these new, extremely high-elevation ecosystems as the climate continues to warm and the glaciers continue to retreat? I really want to know…

Coming up: A report on our first two months of fieldwork and a little bit about the amazing vicuña.

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