The melting snows of Kilimanjaro near the African equator have become a symbol of global warming but is there really a link between the two? Two geophysicists, Philip Mote and Georg Kaser don’t think so. In an article in the journal American Scientific the two scientists have identified other causes.
Global warming is the obvious reason for the world’s melting glaciers which have been in retreat since the end of the mini ice-age over 150 years ago. However equatorial glaciers have a dynamic of their own. At the summit of the tropical African mountains the temperatures are below zero.
Snow accumulates over many seasons and transforms into ice. To understand their life cycle one has to understand the energy and mass balances. Since 2000 measures have shown that there has been less snowfall in the region. If the balance is negative and the glacier will loose mass.
Kilimanjaro - shrinking snows (photo: Nasa)
However Kilimanjaro is special. The mountain has an ice cap and a number of glaciers. The ice cap, up to 40 meters thick, sits at 5700 meters on the summit of the highest volcanic peak, Kibo. The glaciers descend the sides of Kibo to 5200 meters. At these altitudes temperatures are rarely above -3C, air temperature is therefore not the prime suspect for the melting of Kili’s glaciers.
Ice is also lost by a process of sublimation. Energy from sunlight striking the glacier causes ice to transform directly into water vapour which then dissipates in the atmosphere. Increase the amount of sunlight, say to due less cloud cover or a change in the sun’s output due to natural cycles and you increase the amount of ice lost.
The researchers belief this is the principal cause of the loss of ice in the high equatorial glaciers and not an increase in mean temperature identified by Lonnie Thompson and his colleagues in a paper from the Ohio University in 2000.
The research says that it is a process that has been happening for more than a century with most of the ice lost before 1953. They blame the configuration of the glacier as well as a change in weather patterns over the Indian Ocean which mean less cloud cover and snowfall.
