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The Quelccaya Ice Cap is the largest glaciated area in the tropics. Located in the Cordillera Oriental section of the Andes mountains of Peru, the ice cap is at an average altitude of and spans an area of . As with the majority of the Earth's glaciers, the Quelccaya Ice cap has retreated significantly since it was first studied. Since 1978 the icecap has lost approximately 20% of its area,〔 *〕 and the rate of retreat is increasing. Comparing pictures taken in 1963 and 1978, an annual retreat rate of was estimated. In the first few years of the 21st century, the annual retreat was measured to be as much as , more than 40 times as fast. The major outlet glacier from the Quelccaya Ice Cap, the Qori Kalis Glacier, has also retreated significantly since 1963. ==Ice core study== Lonnie Thompson and his research team have drilled ice cores from Quelccaya that date back almost 2,000 years and have used them to study changes in atmospheric conditions over this period. In these samples, the oxygen isotope ratio, oxygen-18 to oxygen-16, has risen abruptly in the last 50 years, an indicator of regional warming. As the ice cap is retreating, it is exposing almost perfectly preserved, unfossilized plant specimens that have been dated to 5,200 years before present, indicating that it has been more than 50 centuries since the ice cap was smaller than it is today. Ice cores taken from Upper Fremont Glacier in the U.S. state of Wyoming show an oxygen isotope profile similar to that of the Quelccaya ice cores at the end of the Little Ice Age, a period of cooler global temperatures between the years 1550 and 1850. The sudden alterations in the oxygen isotope ratio found in ice core samples from these two glaciers, which are at great distance from each other, provide evidence of a sudden global climate change in the mid-latitude regions of the planet at this time.〔 〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Quelccaya Ice Cap」の詳細全文を読む スポンサード リンク
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