Mountains of the Moon: A final glimpse?

The Rwenzori Mountains, which stretch across equatorial East Africa, bordering Uganda and the Democratic Republic of Congo (DRC), were described by Ptolemy in AD 150 as 'Mountains of the Moon, whose snow feeds the lakes, sources of the Nile'. Though one doesn't immediately associate ice and snow with Africa, the glaciers found on this mountain range are indeed a key source for lakes which supply the (White) Nile (Taylor 2014). But in a warming world, how will this change?

The picturesque Rwenzori Mountains (Sources: left, right)

A study in 2006 by Richard Taylor et al revealed that if current trends of glacial recession continue, there will be no more ice in the Rwenzori Mountains within the next two decades. Our changing climate has caused an estimated reduction in glacier extent across the remaining three ice-covered summits (Mounts Speke, Stanley, and Baker) from 6.5km2 in 1906, to just 1km2 in 2003. In just under a century, the areal extent covered by glaciers has declined by ~84%. Taylor further estimates a decline in ice by ~0.2 square miles per decade (Carrington 2014). That's a pretty eye-opening prediction. 

Figure from Taylor et al (2006): a) Map of Uganda, Rwenzori Mts and meteorological stations, b) "Indicator glaciers", Elena and Speke, are shown with extent in glacial cover in 1955 compared to 1990, c) Visible declines in Elena Glacier's areal extent since 1906, d) LandSat7 ETM+ satellite image from 2003, showing Mount Speke's declining glacier extents since 1906.

A stark sight: retreat of Elena Glacier's terminus in just 2 years.
(Source: Richard Taylor)

When Taylor et al (2006) set out to measure the terminal positions of both Elena and Speke valley glaciers (see figure above), they found the recession trend between 1906-1990 appeared to be continuing at alarming rates. Elena's terminus has receded by ~400m since 1906, and 140m (+-17m) since 1990 alone (Taylor et al 2006). Speke's terminal retreat is somewhat more drastic, receding ~600m since 1906, and a vast 311m since 1993 (Taylor et al 2006)! Taylor et al (2006) attribute these differences in retreat due to dissimilar supplies of ice and snow from disparate elevation and morphology. These numerical values are informative, but as the saying goes, 'a picture is worth a thousand words', and I really feel the set of photographs taken by Taylor (above right) do exactly that. In just two years, there has been an enormous visible retreat of Elena Glacier's terminus.

What has caused this deglaciation? 

It is difficult to pinpoint the exact cause of glacial retreat in the Rwenzori Mountains, due to a lack of monitored meteorological observations in the area (Taylor et al 2006). However, Taylor et al (2006) find that air temperatures on land align with warming trends. Evidence does not support the idea that increased glacial recession is due to a reduction in precipitation (in this case, snowfall) (Taylor et al 2006). Conclusively, the team suggest that the observed decline in glacial extent in the Rwenzori Mountains is due to a rapidly warming environment, amplifying ice loss through evaporation, sublimation and melting. Albedo is also a significant player. As more of the glaciers are lost, more of the darkly-coloured rock is exposed, absorbing more solar radiation and thus enhancing warming trends; a positive feedback loop develops.

These mountains, amongst other frozen reservoirs in tropical East Africa, warrant increased efforts to monitor climatic variables and glacial volume and extent in the next crucial few decades. An explicit message is being sent by the visible loss of Africa's glaciers: the climate in this region is changing, and it is changing within the time-frame of our human lifetimes.

Why are these changes important for water?

Alpine glaciers situated near the equator are a vital freshwater reservoir, storing seasonal precipitation (due to the movement of the ITCZ). They act as a buffer, sustaining meltwater flows during dry seasons (Taylor et al 2009). Thus, the fact that a warming world threatens tropical glacier existence means that usage and amount of water available from the mountains will also change. Will alpine river discharge be drastically less during the dry season if deglaciation continues? Will flooding still occur at the base of the mountains during wet seasons? How will this impact the livelihoods of those who live within and around the mountains? Is it too late to reverse or slow these changes? These are all vitally important questions which I will be covering over the next couple of posts in a series of 'mini-blogs', focusing on the Rwenzori Mountains of East Africa.