Glacial Retreat In The Andes

Glacial melt

Glaciers have always been a lure to the adventurous side of the human psyche, the fact they are disappearing is one of the most persuasive arguments for climate change. Nobody can deny that there must be a reason for spectacular changes in ice volume over relatively short periods of time. Skeptics might point to alternative theories behind glacial melt, a decrease in precipitation, a change in humidity or wind. However, on a global scale the main line of thinking is that air temperature is the primary factor that controls the recent glacial melt. The IPCC (2001) show how for a mid-latitude glacier, a 1 degree centigrade rise in temperature would have the same impact as cloudiness or precipitation decreasing by 30% and 25% respectively. Despite this being the case for mid-latitude glaciers Sicart et al. (2003 in Coudrain et al., 2005) suggest that for tropical glaciers the reason for retreat is more complex, stating that the most important factors could actually be those that determine the local albedo. For all glaciers a shift in the equilibrium line upwards means that more ablation will be taking place in relation to accumulation and the glacier will be retreating.

Tropic Glaciers in the Andes – small glaciers

Andean tropical glaciers are unlike the alpine glaciers; ablation takes place consistently throughout the year. The melting is at its highest when the strongest radiation coincides with the highest amount of precipitation (Coudrain et al., 2005). Glacial retreat in this area has been particularly significant for small glaciers. The Chacaltaya glacier in Bolivia has now disappeared, a glacier that had been dated back to 18,000 years BP. The link below shows a map of the retreat over time:

http://news.bbc.co.uk/1/hi/8046540.stm

Glacial retreat in the Andes has not been uniform over the last century; instead it is driven by changes in temperature on a decadal time scale, which are driven by the ENSO mechanism (Coudrain et al., 2005). The warm periods see a negative mass balance (ablation > accumulation) of glaciers whereas during the colder periods there is a positive glacier mass balance. Whilst decadal temperature has driven variations in the rates of retreat the overall pattern has been an increasing average air temperature. Carrasco et al. (2005) report a warming of 1.3-2.1 degrees centigrade in minimum near surface temperature in central Chile between 1961 and 2001.

Examples

Jordan  et al. (2005) – Using aerial photography to quantify the evolution of glacial surface area of the Cotopaxi Volcano ice cap, found a stagnation between 1956 to 1976 and then a strong retreat from 1976 to 1997 where the glaciers lost around 30% of their mass.

Rivera et al. (2005) – found that ice capped volcanoes in the Chilean Lake District had retreated significantly during recent decades. Between 1987 and 2003 the glaciers decreased in area by 0.45km² per year. Thought to be driven mainly by climatic factors.

Mark et al. (2005) – estimated glacial melt contribution to stream flow in the Cordillera Blanca (Peru). Finding that 66% was from glacial melt, which doesn’t bode well for when there are no more glaciers in the area.

My View

Glacial melt water stores a significant amount of freshwater (69.6% of the worlds freshwater). Unfortunately the recent pattern of glacial retreat is likely to lead to water shortages people, bound to impact on health but also on the economies of many countries that rely on the energy that melt water supplies throughout the year.