Once the stuff of legends, the East African equatorial glaciers that gave birth to the Nile River are melting at an unprecedented rate and will disappear in a generation, conclude scientists who surveyed the ice cover for the first time in a decade. The alleged culprit is no big surprise: climate warming. The loss of the glaciers portends dramatically higher rates of malaria and worrisome effects on local economies, the researchers warn.
Africa's Rwenzori Mountains--long revered as the "Mountains of the Moon"--straddle the border between the republics of Congo and Uganda. More than 100 years ago, the first surveyors of glaciers estimated their span at about 6.5 square kilometers. To determine current ice cover in the Rwenzoris, a team led by hydrologist Richard Taylor of University College London conducted field mapping and assessed the latest satellite images of the glaciers. The team found that some glaciers are receding by tens of meters annually, and the total area covered by ice shrunk by one-half between 1987 and 2003. With less than one square kilometer of ice remaining, the glaciers will likely vanish within 20 years, the researchers report today in Geophysical Research Letters.
Climatologists generally blame the shrinkage of glaciers on a pair of factors: rising air temperatures and falling rates of precipitation. In this case, data from weather stations in Uganda show that while the air has warmed by about 0.5 degrees Celsius per decade in the Rwenzori Mountain highlands since the 1960s, precipitation hasn't changed significantly. This argues strongly that higher temperatures alone are causing the glaciers' retreat, Taylor says.
The effects on the local human population--numbering about a million on the Ungandan side of in the Rwenzori Mountains--could be severe. Tourism based on the glaciers will certainly suffer, while impacts on the area's rare plants and wildlife remain unclear, says Taylor. Also, the surging incidence of malaria, which jumped from 157,000 cases in 1998 to 457,000 cases in 2004 in one district alone, is at least partly fueled by warmer temperatures that have allowed mosquitoes to colonize previously inhospitable highland areas, he adds.
"Documenting tropical glacier retreat is important because it provides an independent check on temperature increase in the tropics," says Raymond Pierrehumbert, a University of Chicago climatologist. While the current research suggests a predominant role for warming air temperatures, he says, detailed climate modeling is needed to strengthen the case.