Image: Lonnie G. Thompson

Ice cores extracted from deep within a Himalayan glacier leave little doubt that the earth's temperatures are on the rise. The detailed record revealed by the cores shows that both the past century and the past decade were the warmest over the past 1,000 years, according to a report in the September 15 issue of the journal Science.

An international team of scientists retrieved the samples from an ice field more than 20,000 feet high, on the flank of Mt. Xixabangma, located on the southern rim of the Tibetan Plateau. "This is the highest climate record ever retrieved," says Lonnie G. Thompson, an author on the paper, "and it clearly shows a serious warming."

Chemical analyses of the cores also revealed a number of drought events that took place between the 13th and 19th centuries--the results of monsoon failures. One such episode of failure of the South Asian monsoon had particularly catastrophic results: drought gripped the region from 1790 to 1796, claiming the lives of more than 600,000 people in one region of India alone. "And that was at a time when global populations were much less than they are today," Thompson notes. "If a similar event occurred today, the social and economic disruptions would be horrendous."

Although the report does not explain what might have sparked those changes in the monsoon cycle, Johnson is certain about why things have been heating up. "There is no question in my mind," he asserts, "that the warming is in part, if not totally, driven by human activity."