While the retreat of glaciers and mountaintop ice in the mid-latitudes — where much of the world's human population lives — is definitely linked to global climate change, the same cannot be said of Kilimanjaro, the researchers wrote in the July-August edition of American Scientist magazine.
Kilimanjaro's icy top, which provided the title for an iconic short story by Ernest Hemingway, has been waning for more than a century, according to Philip Mote of the University of Washington in the United States and Georg Kaser of the University of Innsbruck in Austria.
Most of the retreat occurred before 1953, nearly two decades before any conclusive evidence of atmospheric warming was available, they wrote.
"It is certainly possible that the icecap has come and gone many times over hundreds of thousands of years," Mote, a climatologist, said in a statement.
"But for temperate glaciers, there is ample evidence that they are shrinking, in part because of warming from greenhouse gases."
Unlike mid-latitude glaciers, which are warmed and melted by surrounding air in the summer, the disappearance of Kilimanjaro's ice is driven by solar radiation, since the air around it is rarely above freezing, they wrote.
Kilimanjaro, an extinct volcano near Tanzania's border with Kenya, is the highest peak in Africa at 19,563 feet (5,963 meters) and attracts hordes of tourists and climbers for its spectacular views.
The researchers attributed the ice decline to complex interacting factors, including the vertical shape of the ice's edge, which allows it to shrink but not expand.
Decreased snowfall, which reduces ice buildup and determines how much energy the ice absorbs, also plays a role.
Much of Kilimanjaro's ice is vanishing by sublimation — where ice at very low temperatures converts straight to water vapor without going through a watery phase — rather than by melting, the scientists said.