SAN FRANCISCO--"As wide as all the world, great, high, and unbelievably white in the sun, was the square top of Kilimanjaro." Those evocative words by Ernest Hemingway describe a scene that will vanish within 20 years, according to new field research. More than 80% of the ice on Africa's highest peak has melted since the early 20th century, joining other glaciers that are ebbing from the world's tropical mountains at an accelerating rate.
Ice in the tropics sits at the knife edge of climate change. Slight temperature increases push the snowline to ever-higher altitudes, saturating fields of ice with water. Glaciers, which normally drain slowly from an ice cap and maintain a steady size, begin to melt and retreat. "Tropical glaciers are a bellwether of human influence on the Earth system," says Will Steffen, director of the International Geosphere-Biosphere Program in Stockholm, Sweden. Indeed, the past decade's warm years have sounded that bell with unexpected force.
Aerial mapping of Kilimanjaro's summit in February 2000 revealed a 33% loss of ice since the last map in 1989 and an 82% decline since 1912, says geologist Lonnie Thompson of Ohio State University's Byrd Polar Research Center in Columbus. Last week, Thompson's colleagues measured the ice levels at survey poles that they had inserted last year; more than a meter of ice had melted in 12 months, out of a total thickness of 20 to 50 meters. "It won't take many more years like that to completely melt the ice fields," Thompson said here on 18 February at a meeting of the American Association for the Advancement of Science, which publishes ScienceNOW.
Moreover, Thompson has documented runaway melting at Quelccaya, a massive ice cap in the Andes of Peru. Surveys reveal that Quelccaya's main drainage glacier has retreated 155 meters per year since 1998. That's 32 times faster than the rate between 1963 and 1978. As the ice disappears, Thompson says, Peru will lose sources of irrigation and hydroelectric power. It and other countries may need to burn more fossil fuels to compensate, exacerbating the warming trend.
Steffen praises the research as the kind of dramatic evidence that policy-makers can use to help change the way people interact with the environment. "This is exceptionally important work," he says, especially because Thompson's team has tracked these and other ice fields for 25 years. Thompson notes another sobering consequence: Without corings from tropical ice packs in the future, researchers will lose a valuable way to reconstruct temperature and precipitation patterns in the tropics for the last several thousand years.
Ohio State University news release, with photos