Stretching across a vast volcanic plain in Peru, the Quelccaya Ice Cap is the tropics’ largest sheet of ice—for now. Climate shifts are taking their toll, according to scientists who note that the glacier has been not only losing ice over the last few decades but doing so over an accelerating rate. And following a study recently published in the journal Geology, many scientists are now more certain than ever that the ice loss is due to rising temperatures.
It may hardly sound like a surprise that a glacier’s retreat would be due to warming climate, but researchers monitoring the Quelccaya and other shrinking glaciers in the tropics have had their honest doubts. Some have hitherto suggested that decreased snowfall might be the culprit, for example.
The Geology study, however, identifies temperature as the first and foremost driving factor. Led by Justin Stroup, a Dartmouth College doctoral candidate in Earth sciences; and Meredith Kelly, a Dartmouth assistant professor of Earth sciences; the study’s research team compiled extensive data on the Qori Kalis, a valley glacier that is a major outlet for the Quelccaya Ice Cap, and constructed a timeline of this glacier’s waxing and waning across the past 500 years.
Next, they compared the glacier’s movements to records of ice accumulation on the Quelccaya plateau. Long cylinders of ice previously drilled and extracted by Lonnie Thompson, an Ohio State University geologist, were the source of these records.
If snowfall is the main factor behind the ice gain or loss, then the valley glacier should gain ice when more ice accumulates on the Quelccaya, and lose ice when the Quelccaya’s ice accumulation hits a dry spell. Stroup, Kelly, and their team found the opposite: The valley glacier lost ice during some periods of high accumulation and gained ice during some periods when the Quelccaya’s ice accumulation was low.
Temperature, not snowfall, is evidently the chief driver, according to the researchers. They have the backing of Thompson, who has long argued that the glacier could be thought of as a large thermometer.
Their conclusion is a troubling one as far as this glacier is concerned. Thompson’s analyses indicate that in the last 25 years, the glacier has lost a volume of ice that took 1,600 years to build up.
This glacier is no anomaly, by the way. Land ice is melting across the tropics and throughout the planet, and showing marked increases in the rate of ice loss during the last three decades. Quelccaya could be a microcosm of melting trends throughout the globe, according to the researchers, who plan to conduct further studies of more glaciers elsewhere on the globe.