A temperature warming of >2.5 oC (coolantarctica.com) observed in the Antarctic Peninsula over the last 40 years has been the largest surface warming on the planet. In response, nearly 90 per cent of the glaciers in this region are in retreat with a succession of ice shelf disintegrations. The increase in surface run off, as a consequence of melting, has damaged the structural integrity of the ice shelves, leaving these vulnerable to collapse. The disintegration of these ice shelves has a cascading effect on the ice sheet dynamics.
Recently parts of the Larsen ‘C’ Ice shelf (Fig 1)in the Antarctic Peninsula where part of the ice shelf twice the size of Luxembourg broke off on June 17, 2017, and is now adrift in the Weddell Sea. The Larsen C ice shelf is now >12 per cent smaller in area than before the calving—an event that has changed the landscape of the Antarctic peninsula and left the Larsen C ice shelf at its lowest extent ever recorded. This event was preceded by the loss of parts of Wilkins Ice shelf in 2008 and Larsen ‘B’ Ice Shelve in 2002.
The ice sheets in the west Antarctic too are getting eroded (Rignot, 2008) due to ocean warming and same is the fate of several glaciers in this area. The Pine Island Glacier (Fig 2) which was recorded as a fast receding glacier in the western Antarctic was noted to have grounded on a bed rock in 1970s. The warm ocean waters undercut the base of the glacier causing its thinning and recession at a rapid speed. This resulted in breaking off of a large frontal part of the glacier on September 23, 2017 which became afloat in the Amundsen Sea embayment as a new iceberg having an area of about 185 sq km.
Though eastern Antarctica does not show alarming ice mass loss as compared to the Antarctic Peninsula and western Antarctica, but on a regional scale in Antarctica, average change in mass for the period 1992-2011 have been estimated to be -71+ 53 Gt per year (Shepherd et al., 2012). There has been an increase in the rate of ice loss at 21 +2 Gt per year, (Rignot et al., 2011). Between this period, the ice sheets of Greenland, East Antarctica, West Antarctica, and the Antarctic Peninsula changed in mass by –142 ± 49, +14 ± 43, –65 ± 26, and –20 ± 14 gigatonnes per year, respectively. Since 1992, the polar ice sheets have contributed, on average, 0.59 ± 0.20 millimeter per year to the rate of global sea-level rise (Rignot, 2008). While agreeing for the ice mass loss in Peninsulas and Western Antarctica, a NASA study by Zwally (2017) and others are in disagreement over ice loss in eastern Antarctica where they say ice gain exceeds the losses.
The picture of Antarctic ice shelves remains critical. New research projects report that doubling of surface melting of Antarctic ice shelves by 2050 and that by 2100 melting may surpass intensities associated with ice shelf collapse, if greenhouse gas emissions from fossil fuel consumption continue at the present rate (Trusel et al., 2015.).
The scene in the Arctic is more alarming with Arctic sea ice extent, both perennial and multiyear sea ice, showing decrease in every successive decade since 1979. Temperatures in the Arctic are increasing twice as fast as the global average, and the most rapid warming is recorded during the winter months. The Arctic sea ice grows and thickens during winter and therefore warmer winter air temperatures may further impede ice growth and expansion, accelerating the effects of global warming. Sea ice-depleted oceanic areas are absorbing solar radiation, thereby warming the lower atmosphere and enhancing in atmospheric water vapour content during summer and early autumn, which leads to Arctic temperature amplification—a vicious cycle, that further decreases sea ice cover. That the Arctic Ocean is changing profoundly and shifting to a new regime, where younger and thinner ice packs are replacing older, thicker sea ice is visible through successive space images. These changes, with decreasing sea ice cover since 1979 will have regional and global consequences. As per a report of the NSID, the Arctic lost 37,000 sq km of ice, each day, in just the first ten days of June last year (2016) (Fig 3). The elastic response of the crustal deformation in terms of uplift rate, as measured in Greenland also confirms Arctic ice loss (Khan, et al., 2010).
Himalaya, the third Pole, is the largest accumulation of snow and ice after the other two Polar Regions. The 2400 km long mountain chain passes through three different climate zones from Afghanistan to Myanmar via India-Nepal and Bhutan (Fig 4). The northwestern parts are influenced by westerly disturbances, central and eastern parts are fed by the Indian Summer Monsoons (ISM) while a transition or a Cusp in between these two zones (Himachal Pradesh glaciers, Fig 5) receive precipitation from both westerlies and ISM. The glaciers accordingly, as also taking other parameters like bed rock topography, orientation, etc. presents a variation in so far as their dynamics is concerned from one region to another. The glaciers in the extreme north in Karakoram exhibit some advance while most of the others are reported to be thinning (Kulkarni and Pratibha, 2017), though the terminal snouts of some big glaciers are reported to have stabilized in the last decade (Ajai, 2017). The picture for smaller glaciers is however different, as most of these are receding.
As per Kulkarni and Pratibha (2017) Himalayan glaciers, on an average, have been retreating at a rate of 15.5+11.8 m per year with a loss of an area of 13.6+.7.9 per cent since the last four decades. However, the result of the long term monitoring of glaciers in three main basins of Himalaya i.e. Ganga, Indus and Brahmaputra in the two periods of 1989-90 to 2001-04 and 2001-02 to 2010-11 by Space Applications Centre (SAC) of ISRO has presented a different picture. During the former period, 76 per cent of the glaciers have shown retreat, 7 per cent have advanced and 17 per cent have shown no change. In the case of the latter (2001-02 to 2010-11) period of observation only 12.3 per cent of glaciers have shown retreat, 86.6 per cent have shown stable glacial fronts and only 0.9 per cent have shown advancement (Ajai, 2017). On a long term basis, the glaciers are losing area and thinning out except in the Karakoram Mountains.
Ajai, 2017. Inventory and monitoring of Snow and Glaciers of the Himalaya using Space data. (In) Goel, P.S., Ravindra, R., and Chattopadhyay, S (Eds.), Science and Geopolitics of the White World, Arctic- Antarctic-Himalaya. Springer Polar Geography, Springer International Publishing, 95-113.
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https://www.coolantarctica.com/Antarctica fact file/science/global_warming.