February 26, 2014
Peru Ice Cap Shrinking Due To Warming Temps, Not Less Snowfall
Brett Smith for redOrbit.com - Your Universe Online
When we think about how climate change is shrinking glaciers around the world – we are probably imagining the massive sheets of ice around the Earth’s polar regions.
However, glaciers do exist in tropical latitudes, albeit at extremely high elevations, and a new study in the journal Geology has found that one of these tropical glaciers is shrinking as a result of warming temperatures – not lower snowfall levels as some scientists have asserted.
In the study, a team of American scientists used field mapping, a radioactive dating method and ice cores to determine how the Quelccaya Ice Cap, sitting 18,000 feet above sea level in Peru, has grown and retreated over the last thousand years. It is the first time a record of past glacial extents has been examined directly with an annually dated ice core from the same ice mass, the study researchers said.
The study team worked to determine the ages of glacier sediments that mark the last positions of Qori Kalis, an adjacent outflow glacier which has been monitored by Lonnie Thompson, an Ohio State University paleoclimatologist, since the early 1960s. The results show that Qori Kalis grew to its most advanced position 520 years ago and eventually retreated with only slight re-growths since that time. The study team’s analysis also suggested that temperature was the driving force of that glacial expansion and 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," said study author Meredith Kelly, a geologist at Dartmouth University. "This result agrees with… earlier suggestions that these tropical glaciers are shrinking very rapidly today because of a warming climate."
Over the last thousand years, a substantial cooling event referred to as the Little Ice Age took place, but experts don't really know what caused the cooling or its extent across the globe. Since the end of the Little Ice Age, glaciers around the world have been shrinking at significant rates – a phenomenon blamed on carbon emissions that began with the Industrial Revolution during the 19th century.
While most scientists agree that humans are the driving force behind climate change, many disagree on the specifics surrounding the rise in average global temperatures. For example, some scientists assert that tropical glaciers, like the Quelccaya Ice Cap, are shrinking due to lower precipitation levels and not rising temperatures.
Douglas R. Hardy, a University of Massachusetts, Amherst climatologist who worked extensively on Quelccaya, is one of those scientists who argued that temperatures play a secondary role in the shrinking of tropical glaciers.
“I actually believe that finding is probably accurate, but I don’t see that they make a compelling case for that with this study,” he told The New York Times.
Hardy and other critics have pointed out that the new study’s conclusion depended mostly on ice that accumulated over centuries, which was acquired by drilling into Quelccaya. That ice has been compressed over the centuries, meaning the data requires a certain amount of interpretation – the critics argued.