Temperature, not variations in snowfall, is causing the dramatic shrinkage of Peru's Quelccaya Ice Cap, a symbol of global climate change, a U.S. study found. Researchers at Dartmouth College used field mapping combined with the dating methods and ice cores to examine how the ice cap -- the largest ice mass in the tropics -- has expanded and retreated over the past millennium, the university reported Tuesday. An analysis suggests temperature has been the driving force behind the glacial expansion and retreat of the ice cap 18,000 feet above sea level in the Peruvian Andes. "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 said. "This result agrees with ... earlier suggestions that these tropical glaciers are shrinking very rapidly today because of a warming climate." The advances and retreats of other glaciers in tropical South America are similar to those of the Peruvian ice cap, indicating a regionally consistent pattern of past climate conditions, the researchers said.