For decades now scientists have observed rapid melting in the Quelccaya Ice Cap in Peru. The glacier ebbs and flows each year, as do all glaciers, but each year it also shrinks a little bit more than the previous year. A 2006 study concluded with the ice cap had lost 20% of its area since 1978 and that the rate of this decrease was increasing.
Until now, we didn't know for sure what was causing the ice cap to shrink and retreat. But a study published this week in the journal Geology reveals the truth: warming temperatures, not reduced snowfall or any other cause, are to blame.
The Quelccaya Ice Cap is a tropical glacier, located 18,000 feet above sea level.
"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," study co-author Meredith Kelly of Dartmouth College said in a press release. Kelly is a glacial geomorphologist who studies the processes that shape landforms. Her team conducted the study on ice cores previously obtained by Ohio State University paleoclimatologist Lonnie Thompson who has been visiting the Peruvian glacier since the early 1960s. "This result agrees with Professor Thompson's earlier suggestions that these tropical glaciers are shrinking very rapidly today because of a warming climate," Kelly said. Thompson was not involved in the current paper.
The ice cores collected by Thompson were tested by Kelly and her team, who were looking for radioactive isotopes called beryllium-10 in the glacial sediment within the ice. Beryllium-10 is used to date the amount of time rock has been at the Earth's surface and is frequently used to determine the dates of glacial advances and retreats (glaciers pick up and drop sediment, called moraines, as they grow and retreat). Their research showed that the Qori Kallis outlet glacier, part of the bigger ice cap, extended to its maximum position about 520 years ago. It then retreated and has since had only minor re-advances. The researchers compared the sediment with the ice core record and determined that temperature changes drove the glacial expansions and retreats.
Dr. Thompson told the New York Times that he believes temperature is the cause of the shrinking glaciers. Last year he documented that the Qori Kalis glacier has lost 1,600 years of growth in the past 25 years. The Times also interviewed other scientists who have studied glaciers. One praised it, while another believed the findings but said he didn't "see that they make a compelling case."
Related on MNN: