The
retreat of glaciers since 1850, worldwide and rapid, affects the availability of fresh water for irrigation and domestic use, mountain recreation, animals and plants that depend on glacier-melt, and in the longer term, the level of the oceans. Studied by
glaciologists, the temporal coincidence of
glacier retreat with the measured increase of atmospheric
greenhouse gases is often cited as an evidentiary underpinning of
anthropogenic (human-caused)
global warming. Mid-latitude mountain ranges such as the
Himalayas,
Alps,
Rocky Mountains,
Cascade Range, and the southern
Andes, as well as isolated tropical summits such as
Mount Kilimanjaro in
Africa, are showing some of the largest proportionate glacial loss.
(IPCC)(Mölg)The Little Ice Age was a period from about 1550 to 1850 when the world experienced relatively cooler temperatures compared to the present. Subsequently, until about 1940, glaciers around the world retreated as the climate warmed. Glacial retreat slowed and even reversed, in many cases, between 1950 and 1980 as a slight global cooling occurred. However, since 1980 a significant global warming has led to glacier retreat becoming increasingly rapid and ubiquitous, so much so that some glaciers have disappeared altogether, and the existence of a great number of the remaining glaciers of the world is threatened. In locations such as the Andes of South America and Himalayas in Asia, the demise of glaciers in these regions will have potential impact on water supplies. The retreat of mountain glaciers, notably in western North America, Asia, the Alps, Indonesia and Africa, and tropical and subtropical regions of South America, has been used to provide qualitative evidence for the rise in global temperatures since the late 19th century.(IPCC2) (NSIDC) The recent substantial retreat and an acceleration of the rate of retreat since 1995 of a number of key outlet glaciers of the Greenland and West Antarctic ice sheets, may foreshadow a rise in sea level, having a potentially dramatic effect on coastal regions worldwide.
Crucial to the survival of a glacier is its mass balance, the difference between accumulation and ablation (melting and sublimation). (Mote and Kaser) Climate change may cause variations in both temperature and snowfall, causing changes in mass balance. A glacier with a sustained negative balance is out of equilibrium and will retreat. A glacier with sustained positive balance is also out of equilibrium, and will advance to reestablish equilibrium. Currently, there are a few advancing glaciers, although their modest growth rates suggest that they are not far from equilibrium.(Trabant)
Glacier retreat results in the loss of the low-elevation region of the glacier. Since higher elevations are cooler, the disappearance of the lowest portion of the glacier reduces overall ablation, thereby increasing mass balance and potentially reestablishing equilibrium. However, if the mass balance of a significant portion of the accumulation zone of the glacier is negative, it is in disequilibrium with the climate and will melt away without a colder climate and or an increase in frozen precipitation.
