There are likely to be significant and widespread consequences of glacial retreat and of the disappearance of glaciers. Many people across the world are dependent upon glaciers for water, energy, and safety. Additionally, many organisms, ecosystems, and ecosystem processes are reliant upon glaciers. Dr. Phil Porter of the University of Hertfordshire sums it up well when he says "There is a short-term danger of too much water coming out… and a greater long-term danger of there not being enough" (McKie, 2005).
Glaciers store about 75% of the world's freshwater. Some mountain cities and the surrounding regions are dependent upon glacier runoff for their freshwater supply (USGS, 2005), such as in South America. The Andes Mountains in South America are home to 70% of the world.s tropical glaciers, which provide water for drinking, agriculture, and hydropower for 30 million people (ESN, 2008). Quito, Ecuador, for example, draws 50% of its water supply from the Antizana and Cotopaxi glacier basins. La Paz, Bolivia draws 30% of its water supply from the same basins (Vergara et al., 2007). However, these glaciers are rapidly dwindling.
In some areas of Asia and the Andes increased glacial runoff has translated into more water in the areas' rivers. However, once the glaciers diminish, their hydrologic inputs will disappear as well. Many of the towns in the Andes region have already felt the impacts of water shortages for drinking water and agriculture. In El Alto, Bolivia, Vergara et al. (2007) mention "…water supply is now just about enough to meet demand during dry season." Despite projects to help with water supply, demand for water will outstrip supply in the La Paz-El Alto area by 2009. Quito, Ecuador is scheduled to run into serious water shortages by 2015 (Tehran Times, 2007). Additionally, crops have had to be relocated to higher areas that receive more water from the glacier, but that have poorer soil, limiting their yield. Domesticated animals such as alpaca are also suffering from lack of food, resulting in decreasing wool production. Where once the townspeople could rely on their own production, now they must buy fertilizer and other supplies (World Bank, 2008).
A report from the National Meteorology and Hydrology Service of Peru has found that Andean glaciers have lost 20% of their volume since 1970 (World Bank, 2008). Some, like the Chacaltaya glacier in Bolivia, have already lost up to 99% of their volume (World Bank, 2008). Scientists have predicted that the Andes will be glacier-free by mid-century (Tehran Times, 2007). In a 2007 interview, Walter Vergara, who was the lead author of the 2007 World Bank report and who also is the Bank.s lead climatologist, stated "All these ecosystems are changing very quickly. In fact, every year they change at a faster pace, which has all of us very alarmed" (Tehran Times, 2007).
A number of countries are highly dependent upon its glaciers and glacial runoff for energy production. In the Andes region, hydropower supplies 81% of Peru's electricity, 73% of Colombia's, 72% of Ecuador's, and 50% of Bolivia's (World Bank, 2008). In India, 50% of hydroelectric power is generated by runoff from Himalayan glaciers (Kargel, et al., 2002). Glacial runoff supplies hydropower for 50% of Switzerland's electricity as well (Paul et al., 2007). All of these countries face billions of dollars worth of investment in infrastructure to accommodate new types and sources of energy production, some of which release more greenhouse gases than hydroelectricity.
|Figure 4. "Contributions of GIC, Greenland, and Antarctic Ice Sheets to present-day rate of sea-level rise (s.l.r.), along with their respective volumes and areas." Image credit: Meier et al., Science, 2007.|
Humans will not be the only losers when it comes to depleted glacial runoff. "These changes are likely to have significant, widespread consequences for the fauna of alpine stream ecosystems," Brown et al. state in a 2007 report, "…it may be impossible to prevent the loss of species adapted to meltwater stream conditions as climate warms and snowpacks and glaciers shrink." Plants, animals, and other organisms that are strongly influenced by the hydrologic impacts of glacial ecosystems will suffer as river channel stability, water temperature, and suspended sediment load are drastically altered due to changes wrought by glacial wastage in meltwater contributions and valley geomorphology (Brown et al., 2007). Additionally, glacial runoff feeds a number of rivers and lakes, thereby serving significant purposes in the area ecosystems, as well as in general ecosystem processes. As glaciers disappear, the benefits of glacial systems and inputs of glacial runoff will likewise evaporate.
Because of rapid glacial melting and wasting, an increasing number of avalanches and floods have been occurring. Ice avalanches from steep or hanging glaciers, such as the 1996 avalanche from Gutz Glacier near Grindelwald, Switzerland, cause infrastructure damage and injury. Much more hazardous are glacial lake outburst floods (also called GLOFs or Jökulhlaups) which occur when glacial melt is dammed by unstable moraines at the terminus. The failure of this dam due to volcanic eruption, erosion, water pressure, avalanches or calving, or earthquakes, results in the release of the water in the glacial lake.
Glacial lake outburst floods have occurred across the world and at many scales. At the end of the last ice age, massive glacial outburst floods occurred, such as the Missoula Floods, which created the Columbia River Basin. The number of glacial lake outburst floods, however, has been increasing during the second half of the 20th century according to UNEP. A 2005 report in Nature indicated there has been a 10-fold increase in the number of glacial outburst floods over the past two decades alone. These floods are incredibly devastating, and result in economic losses as well as casualties. In 1985, water released from the Dig Tsho Lake in Nepal destroyed 14 bridges and caused $1.5 million in damage to a hydropower plant downstream. More recently, in 1994 an outburst at Luggye Tsho, 90km upstream from Punakha in Bhutan caused massive flooding and erosion on the Pho Chhu River, destroyed many buildings in the town, and resulted in 21 casualties (McKie, 2005). Accelerated glacial retreat due to climate change is already raising the likelihood and imminence of these types of catastrophes, especially in areas like the Alps, Andes, and Himalayas.
According to the IPCC's 2007 report, "The most important cryospheric contributions to sea level variations arise from changes in the ice on land (e.g., glaciers, ice caps, and ice sheets)." In a 2007 study, Meier et al. agree, stating "Ice loss to the sea currently accounts for virtually all of the sea-level rise that is not attributable to ocean warming." According to Meier et al. (2007), however, about 60% (see Figure 4) of the ice loss is from glaciers and ice caps rather than from the Greenland and Antarctic ice sheets.
Since 1961, total global sea level rise has been 3.1 ± 0.7 mm/year (Meier et al., 2007). Of that total, the IPCC (2007) points to glaciers as contributing about 0.50 ± 0.18 mm per year during the period between 1961 and 2003. During that period, the contributions to sea level rise of these glaciers accelerated — the rate increased to an average of 0.77 ± 0.22 mm per year from 1993 to 2003 (IPCC, 2007). As mentioned earlier, the largest glacial mass losses have been observed in Patagonia, Alaska, the northwest U.S., and southwest Canada. Therefore, the biggest contributions to sea level rise since the IPCC's Third Assessment Report in 2001 have come from Alaska, the Arctic, and Asia. (IPCC, 2007) (See Figure 5). According to Meier et al. (2007), this increase is "in part due to marked thinning and retreat of marine-terminating glaciers associated with a dynamic instability that is generally not considered in mass-balance and climate modeling." The study predicts that accelerating rates of glacial melt may lead to an additional 0.1 to 0.25 meter of additional sea level rise by 2100 above the IPCC projections (Meier et al., 2007). Luthcke et al. (2008) estimated that the glaciers draining into the Gulf of Alaska were responsible for 0.23mm/year of global sea level rise between 2003 and 2007.
|Figure 5. "Cumulative mean specific mass balances (a) and cumulative total mass balances (b) of glaciers and ice caps, calculated for large regions (Dyurgerov and Meier, 2005). Mean specific mass balance shows the strength of climate change in the respective region. Total mass balance is the contribution from each region to sea level rise." Image credit: IPCC (2007) based on Dyurgerov and Meier (2005).|