Studie: Himalayas gletschere smelter hurtigere end troet
Det kan få barske følger for 1/5 af menneskeheden, som er afhængig af vandet fra de store floder, der udspringer i det enorme bjergmassiv - på længere sigt er konsekvenserne uoverskuelige.
JOHANNESBURG, 20 July 2012 (IRIN): The Himalayan glaciers that feed major south Asian rivers like the Indus, the Brahmaputra and the Ganges are melting more rapidly, reveals a major new study which says that soaring (stigende) global temperatures are not the only reason.
The study, led by Yao Tandong, director of the Institute of Tibetan Research at the Chinese Academy of Sciences in Beijing, and eminent glaciologist and paleo-climatologist Lonnie Thompson of Ohio State University, is the most comprehensive examination so far of the region’s glaciers.
"The status of the glaciers had been a bone of contention," reported the weekly science journal, Nature, whose sister publication, the peer-reviewed journal, Nature Climate Change, published the study.
"Earlier this year, an analysis of seven years' worth of measurements, taken by the Gravity Recovery and Climate Experiment (GRACE) satellite mission, suggested that high-altitude Asian glaciers on the whole are losing ice only one-tenth as fast as previously estimated, and that glaciers on the Tibetan plateau are actually growing."
The GRACE mission is a joint partnership between the US National Aeronautics and Space Administration (NASA) and the Deutsche Forschungsanstalt für Luft und Raumfahrt (DLR) in Germany.
"Since a number of papers... have been published, based on a seven-year GRACE data set, it was important to look at the longer-term retreat story, as climate is generally considered a 30-year average of the weather," Thompson said.
Studied 30 years of data
The scientists studied 30 years of data from the field, and satellite and weather records to examine the retreat of 82 glaciers, the area reduction of 7.090 glaciers, and mass-balance change - the difference between the accumulation and loss of ice of 15 glaciers in the seven larger regions of the Himalayas, the Tibetan Plateau and the Pamir Mountains.
Glaciers in this region give birth to major rivers across Southeast Asia and the Far East, from the Ganges to the Mekong, the Yellow and the Yangtze, which provide water to 20 percent of the world's population.
"For the glaciers studied, approximately nine percent of the area of ice that was present in the early 1970s had disappeared by the early 2000s. Where we had decadal (årtilang) information, we could show that the rate of retreat had accelerated," Thompson said.
"Potential consequences of glacier changes would be unsustainable water supplies from major rivers, and geohazards (glacier-lake expansion, glacier-lake outbursts and flooding), which might threaten the livelihoods and wellbeing of those in the downstream regions," the study warned.
A sustained glacier retreat would increase the volume of water in rivers and also sediments, which could choke (opstemme) water supply, affecting agriculture.
When glaciers retreat, lakes commonly form behind the newly exposed debris (affald) - soil and rock called a moraine - which is carried along by the leading edge of the ice wall.
Rapid accumulation of water in these lakes could lead to a sudden breach of the moraine dam, causing a possibly catastrophic glacial lake outburst flood (GLOF).
In the recent past, Nepal alone has been affected by 21 GLOF events, and 200 potentially dangerous glacial lakes have been documented across the Himalayan region.