The snows — and ice — of Kilimanjaro could melt away within two decades or less, according to the latest survey of ice field remaining on the storied Tanzanian peak.

Researchers who conducted the survey conclude that a major cause of the ice loss is very likely to be the rise in global temperatures. Although changes in cloudiness and precipitation may also play a role, they appear less important, particularly in recent decades.

In fact, measurements by scientists from Ohio State University (OSU) indicate that the loss of ice volume from thinning between 2000 and 2007 is now roughly equal to that from shrinking, or retreating. Their findings were recently published in the journal Proceedings of the National Academy of Sciences.

Paleoclimatologist Lonnie Thompson, a professor of earth sciences at OSU, and his colleagues amassed a trail of data showing the rapid loss of ice atop Africa’s highest mountain:

• Eighty-five per cent of the ice that covered Mount Kilimanjaro in 1912 was lost by 2007, and 26 per cent of the ice left in 2000 is now gone;
• A radioactive signal marking the 1951-52 “Ivy” atomic tests that was detected in 2000 — 1.6 metres below the surface of the Kilimanjaro — ice is now lost, with an estimated 2.5 metres missing from the top of the current ice fields;
• Elongated bubbles trapped in the frozen ice at the top of one of the cores indicates that surface ice has melted and refrozen. There is no evidence of sustained melting anywhere in the rest of the core that dates back 11,700 years;
• Even 4,200 years ago, a drought in that part of Africa that lasted about 300 years and left a thick (about one-inch) dust layer, was not accompanied by any evidence of melting. These observations confirm that the current climate conditions over Mount Kilimanjaro are unique over the last 11 millennia.

“This is the first time researchers have calculated the volume of ice lost from the mountain’s ice fields,” said Thompson, a research scientist with Ohio State’s Byrd Polar Research Center. “If you look at the percentage of volume lost since 2000 versus the percentage of area lost as the ice fields shrink, the numbers are very close.”

While the loss of mountain glaciers is most apparent from the retreat of their margins, Thompson said the thinning of the ice fields from the surface is equally troubling.

The summits of both the Northern and Southern Ice Fields atop Kilimanjaro have thinned by 1.9 metres and 5.1 metres, respectively. The smaller Furtwangler Glacier, which was melting and water-saturated in 2000 when it was drilled, has thinned as much as 50 per cent between 2000 and 2009.

“The fact that so many glaciers throughout the tropics and subtropics are showing similar responses suggests an underlying common cause,” Thompson said. “The increase of Earth’s near surface temperatures, coupled with even greater increases in the mid- to upper-tropical troposphere, as documented in recent decades, would at least partially explain the observed widespread similarity in glacier behaviour.”

Thompson said the changes occurring on Mount Kilimanjaro mirror those on Mount Kenya and the Rwenzori Mountains in Africa, as well as in tropical glaciers high in the South American Andes and in the Himalayas.

“The fact that so many glaciers throughout the tropics and subtropics are showing similar responses suggests an underlying common cause,” he said. “The increase of Earth’s near-surface temperatures, coupled with even greater increases in the mid- to upper-tropical troposphere, as documented in recent decades, would at least partially explain the observed widespread similarity in glacier behaviour.”