Glaciers and ice sheets: current status and trends
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- Frezzotti, M. & Orombelli, G. Rend. Fis. Acc. Lincei (2014) 25: 59. doi:10.1007/s12210-013-0255-z
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About 10 % of the land surface on Earth is covered by glacier ice, with an estimated total volume equivalent to about 66 m of potential sea-level rise. Almost the totality (99 %) of this volume is locked in the polar ice sheets, while less than 1 % forms all the other mountain glaciers and ice caps. In the last three decades, the general retreat of the mountain glaciers and the accelerated flow and ice loss from several outlet glaciers draining the Greenland and the Antarctic ice sheets came to general attention as a major evidence of climate warming and as a potential contribution to the sea-level rise, to local shortage of water resources and to other environmental risks. Here, we present a short review of the most recent data and assessments on the present status and on trends of glaciers and polar ice sheets. The Greenland ice sheet (12 % of total glacier ice volume) over the last three decades showed an increase of the extent of the surface melt area and an acceleration of many marine-terminating glaciers; as a consequence, the ice sheet is losing ice at an increasing rate that reached −263 ± 30 Gt/year in the 2005–2010 time interval, equivalent to a sea-level rise of 0.72 ± 0.08 mm/year. The much larger, higher and colder composite Antarctic ice sheet (87 % of total glacier ice volume), in the same 2005–2010 time interval, had an ice loss of −81 ± 37 Gt/year. Mountain glaciers and ice caps are retreating in all the major glacierized regions, with the exception of a few mountain areas where contrasting patterns have been observed. Although containing less than 1 % of the total glacier ice, mountain glaciers and ice caps suffered a total ice loss of −259 ± 28 Gt/year in the period 2003–2009, equivalent to a sea-level rise of 0.71 ± 0.08 mm/year. The overall contribution of glaciers and ice sheets is estimated equivalent to a sea-level rise of 1.50 ± 0.16 mm/year for the period 2003–2009, or about 60 % of the total sea-level rise in the same period. Various estimates of the total glacier contribution to the sea-level rise by the end of the twenty-first century have been recently proposed, ranging from a few decimeters to 2 m, with most plausible projections at about 0.5 m. Most probably Greenland, the Antarctic Peninsula and the West Antarctic ice sheet will continue to lose ice, while the sign of the East Antarctica contribution is uncertain. Mountain glaciers will most likely continue to lose ice, although at different rates in the various mountain regions. For the European Alps and the Southern Alps (New Zealand), a loss of more than 70 % of their present volume is expected by the end of the twenty-first century. The glaciers’ contraction in the mountain areas may cause slope failures, debris mobilization, outburst floods from glacial lakes, and water deficits, particularly in the summer season, in the arid zones in the coming decades. Together with other changes occurring in the cryosphere such as the Arctic sea-ice reduction, the snow cover decline and the permafrost degradation, the glacier retreat is considered part of a larger picture of environmental changes, directly or indirectly caused or increased by the human impact, leading to new environmental conditions, thus deserving to be indicated as the Anthropocene. Still more open to future responses is the consideration if the ongoing glacier reduction and the rise of the sea level will contribute to leave such a footprint in the geologic record as to require a new stratigraphic unit, a new time epoch in the billion years long history of the Earth.