He presented his findings during the annual meeting of the American Association for the Advancement of Science in San Francisco. They're an indicator of massive changes taking place and a response to the changes in climate in the tropics. The retreat and loss of these massive ice bodies make up part of the evidence Thompson presented that has convinced him global warming has begun to make its mark on the planet. The higher the oxygen-18 enrichment, the warmer the atmospheric temperatures were when the ice formed from fallen snow. From these, he can extrapolate a history of regional temperatures.
Map showing drill sites spread across the tibetan Plateau.
A preliminary look at the isotopes in a core retrieved late last year from Puruogangri, an ice cap in the center of the Tibetan plateau north of Dasuopu, showed a similar enrichment and corresponding warming. While Thompson's team focused on the records preserved in the ice, his colleagues from the People's Republic of China, have analyzed 30 years of records from 178 weather stations spread across the Plateau. Those records show that between 1969 and 1990, the rate of warming has increased at higher elevation sites. That is consistent with the oxygen isotope measurements from the Tibetan ice cores, Thompson said. The retreat of the Kilimanjaro and Quelccaya ice caps are the most dramatic evidence, however.