SFU earth scientist Nicholas Roberts sampling sediments at La Paz, Bolivia, for measurement of Earth’s ancient magnetic field.

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New evidence that tropical ice caps existed in the Andes will help researchers understand near-future climate change

March 03, 2017
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By Justin Wong

Scientists have long suspected that ice caps formed repeatedly in the tropical Andes during the late Pliocene Epoch, but only evidence of a single glaciation was known until now.

A study by SFU earth scientists Nicholas Roberts and John Clague as well as René Barendregt from the University of Lethbridge reveals the first geological evidence of recurrent ice caps in the tropical Andes over 2.7 million years ago—including during Earth’s last long, globally warm period.

Peaks of the Central Andes north of La Paz, Bolivia, where the Chacaltaya glacier disappeared in 2009 as a result of increased melting. Sediments exposed in slopes in the foreground record multiple late Pliocene ice caps

Average global temperatures were typically 2-3 degrees Celsius warmer than today during the middle part of the late Pliocene Epoch, known as the mid-Piacenzian warm period, long before evidence suggests large ice caps first appeared in North America. Confirmation of tropical glaciers from this time period plays a pivotal role in how scientists understand changes in Earth’s past climate and will assist in forecasting near-future climate change.

Rapidly retreating glaciers on the Illimani massif, viewed from downtown La Paz, Bolivia.

“Given its timing and low-latitude location, this new discovery is particularly relevant to understanding global environmental change under conditions of increased atmospheric CO2 concentrations and warming temperatures similar to those projected for the end of this century.”

In their study, published in Nature Scientific Reports, the authors analyzed the record of the Earth’s past magnetic field stored in deeply buried glacial sediments at La Paz, Bolivia. The magnetic record showed that the glaciers reached the city's present location at least seven times between 3.4 and 2.7 million years ago.

Formation of the tropical ice caps when global climates were considerably warmer than today suggests that this part of the Andes had a greater elevation than today and possibly received more moisture. Such records add important new data that can be used in modelling the growth and disappearance of global ice sheets and climate change in general.

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