The average distance above sea level on the glacier is around 54-hundred-70 meters.

　　The Quelccaya ice cap is the largest tropical ice cap on Earth.

　　Paleoclimatologist Doctor Lonnie Thompson says they believe inside is an annual record of the earth's climatic changes covering the last 18-hundred years.

　　科学家在冰川中寻找历史线索

　　"The day will come when there will no longer be a Quelccaya Ice Cap and the history that is preserved here will no longer be available, so in many ways we are also salvaging a history of our past that will be lost as the earth continues to warm,."

　　Thompson and his team spent a week in June on the Quelccaya glacier, drilling ice and snow samples to measure the isotopes in the annual dust layers.

　　The isotopes provide a history of precipitation, allowing the glaciologists to analyse the ice layer-by-layer through the centuries to try to understand how ancient weather shifted.

　　Flecks of dust, falling seasonally, enable them to count down the years, much like the rings in a tree.

　　The chemistry of the snow can also help scientists trace the effects of human pollution, such as chemicals and metals in the atmosphere.

　　Researcher Doctor Emilie Beaudon is looking into this aspect of the research in the Andes.

　　"We don't know how well they (contaminants) are deposited in the ice cap yet, but our objective is to try to measure that, and since the ice cap is meant to melt and those contaminants are meant to be released on the environment we would like to quantify this contamination and see if it could have any impact on on human health."

　　Photographs taken over a 33-year period suggest the speed of their research is becoming more urgent, as parts of the glacier have been disappearing by as much as 50-percent over the past 3-decades.

　　A World Bank report drafted in 2009 suggests global climate change threatens the complete disappearance of the Andes' tropical glaciers within the next 20 years, putting precious water, energy and food sources at risk.

　　For CRI, I'm Wang Mengzhen