Rising Temperatures Blamed For Peruvian Glacier Retreat

Glaciers are known to be the most sensitive indicators of the accelerating change in climate.  A new study has found that tropical glaciers show signs of shrinkage and retreat as a result of rising temperatures.

The study, conducted by researchers at  Dartmouth College, Hanover,  revealed that Peru's Quelccaya ice cap, the world's largest tropical ice sheet,  has been melting at an accelerating pace in  recent decades and this had made it a symbol for global climate change.

It was assumed till date that the ice caps were melting over the decades due to the dramatic change in climate and not because of other factors like reduced snowfall.  The new study confirms that temperature is the driving factor for the fluctuating size of the Quelccaya Ice Cap that sits 18,000 feet above the sea level in the Peruvian Andes.

In the study led by Meredith Kelly, Darmouth Glacial Geomorphologist, the researchers examined the rate at which the Quelccaya Ice Cap expanded and retreated over the past millennium by combining field mapping with the beryllium-10 surface exposure dating technique and the ice cores.

Using this technique they dated the thinning and shrinking over the past 500 years of the glacier called Qori Kalis, a major outlet glacier from the Quelccaya Ice Cap.  The ice cores used for the analysis were collected by an Ohio State University paleoclimatologist , Lonnie Thompson. This is the first time that researchers are comparing the record of the past glacial events with the annual dating of the ice core record taken from the same ice mass.

In the last millennium a Little Ice Age took place, a small cooling event, but the scientists were clueless as to what event triggered the temperatures to drop.

The researchers say the glacier sediments (beryllium-10 ages of moraines) hold clues regarding the past events of Qori Kalis.

The study shows that Qori Kalis, which is being monitored by Thompson since the 1960s, progressed toward the Holocene before 520 years ago and ever since then it has retreated with very little re-advances.

Holocen, is the present geological epoch that began some 11,500 years ago when the glaciers around the world began to retreat. By comparing the moraine data with the ice core data it is evident that temperature has been a major driving force of glacial expansion and retreat.  And other factors like snowfall were just secondary causes for the glacier's retreat.

"This is an important result since there has been debate about the causes of recent tropical glacial recession - for example, whether it is due to temperature, precipitation, humidity, solar irradiance or other factors," says Kelly, a co-author of the study. "This result agrees with Professor Thompson's earlier suggestions that these tropical glaciers are shrinking very rapidly today because of a warming climate."

The researchers also claim that the melting of other tropical South American glaciers is similar to  Qori Kalis.  They conclude that the rising temperature is a major controlling factor for the tropical glaciers. But some scientists disagree claiming precipitation has a major role in glaciers retreating.

"I actually believe that finding is probably accurate, but I don't see that they make a compelling case for that with this study,"  Douglas R. Hardy of the University of Massachusetts, Amherst, who worked extensively on Quelccaya, said to New York Times.

The study was published in the journal Geology.