Glaciers Are Melting at Their Fastest Rate for 5,000 Years
Steve Conner
The scientists, led by Lonnie Thompson of Ohio State University, present three lines of evidence pointing to a dramatic melting of glaciers in both the Andes and the Himalayas: a change in the chemical isotopes of the ice cores, the widespread retreat of glaciers and the uncovering of frozen plants that had been buried for thousands of years.
"These three lines of evidence argue that the present warming and associated glacier retreat are unprecedented in some areas for at least 5,200 years," the scientists wrote in the Proceedings of the National Academy of Science. "The ongoing global-scale, rapid retreat of mountain glaciers is not only contributing to global sea-level rise but also threatening freshwater supplies in many of the world's most populous regions."
Professor Thompson said the research was based on nearly 50 scientific expeditions to seven mountain glaciers over the past three decades, including the Huascaran and Quelccaya ice caps in Peru, the Sajama ice cap in Bolivia and the Dunde and Puruogangri ice caps in China. He said: "We have a record going back 2,000 years and when you plot it out, you can see the medieval warm period [from 1000 to 1300] and the little ice age [from 1600 to 1850]. And in that same record, you can clearly see the 20th century and the thing that stands out is how unusually warm the last 50 years have been. There hasn't been anything like it, not even in the medieval warm period.
"The fact that the isotope values in the last 50 years have been so unusual means that things are dramatically changing."
The most dramatic evidence comes from 28 sites where the retreating ice has exposed plants that have been frozen and preserved for between 5,000 and 6,000 years by the glacier's base.
"This means that the climate at the ice cap hasn't been warmer than it is today in the last 5,000 years or more," Professor Thompson said. "If it had been, then the plants would have decayed."