By Sid Perkins, Science News
The famed snows of Kilimanjaro may soon appear only in old tourist photos and a short story by Ernest Hemingway if current rates of melting persist, a new study suggests.
The warming climate of recent decades has caused high-altitude glaciers worldwide, and especially those in tropical areas, to shrink substantially (SN: 10/4/03, p. 215). Recent field studies conducted atop Tanzania’s Mount Kilimanjaro show that ice loss is proceeding apace on the African peak: More than a quarter of the ice cover present in the year 2000 had disappeared by late 2007, says Lonnie Thompson, a glaciologist at Ohio State University’s Byrd Polar Research Center in Columbus. He and his colleagues report their findings online November 2 in Proceedings of the National Academy of Sciences.
Data from aerial surveys supplement the team’s field studies, which show that Kilimanjaro’s melting has dramatically accelerated in recent decades, says Thompson. From 1912 to 1953, ice coverage declined by 1.1 percent per year. Between 1953 and 1989, the annual rate of ice loss jumped to 1.4 percent. From 1989 to the most recent survey in 2007, the ice-covered area dropped, on average, a whopping 2.4 percent per year, the researchers report.
Not only are the ice masses of Kilimanjaro receding farther up the peak, they’re thinning considerably — a trend detectable only by improved ground observations made in recent years. The thickest part of the peak’s 50-meter-thick Northern Ice Field thinned by 1.9 meters between 2000 and 2007, Thompson says. During the same period, Kilimanjaro’s Southern Ice Field — which was approximately 21 meters thick in 2000 — lost about 5.1 meters of ice thickness by 2007.
As Kilimanjaro’s glaciers thin, retreat and break into smaller pieces, the dark rocks surrounding the remaining ice will absorb more sunlight and heat up, accelerating the melting trend, says Thompson. “These ice bodies are remnants of a former climate,” he notes. At current rates of melting, permanent ice fields will disappear from Kilimanjaro by 2022, the researchers estimate.
In recent years, much scientific debate has centered on whether Kilimanjaro’s ice loss stems from melting due to global warming or from increased sublimation — the direct evaporation of ice — due to a climate shift that starved the peak of precipitation. Thompson’s field data, including the pattern and shape of bubbles in samples drilled from the ice masses, suggest that Kilimanjaro’s ice only began melting in recent decades.
The answer may not make much difference to people who live around the long-dormant volcano, because they don’t depend on meltwater from Kilimanjaro's peak to irrigate farmland or supply drinking water, says Tad Pfeffer, a glaciologist at University of Colorado’s Institute of Arctic and Alpine Research in Boulder. But, he adds, lessons learned from field studies there could help scientists better predict when glaciers elsewhere in the tropics — many of which people depend on for water — will eventually disappear. “Tropical glaciers are shrinking at fast and accelerating rates everywhere they occur,” he notes.