Icecap

An Icecap is a thick layer of ice covering the peak of a mountain or other area of land, it may further be described as perennial or permanent because it remains in place throughout the year or years. The National Geographic defines an Icecap as ' a glacier .. . less than 50,000 square kilometres (19,000 square miles)' where an Ice sheet is defined as 'glacial ice covering more than 50,000 square kilometres (19,000 square miles)'.

The definition or an ice cap as permanent or perennial is however used less and less because icecaps previously thought of as permanent have been decreasing in size and number due to the impacts of climate change. The National Geographic reports 'Mount Kilimanjaro, Tanzania, the tallest mountain in Africa, used to have enormous ice caps on its summit. Today, the Furtwangler glacier is the mountain's only remaining ice cap, at 60,000 square kilometres (23,166 square miles). The Furtwangler glacier is melting at a very rapid pace, however, and Africa may lose its only remaining ice cap.'

The Vatnajökull ice cap is approximately. 7700 km2 (covering ca 8% of Iceland) and is considered by some Europe’s largest ice cap by volume, although it has lost more than 15% of its volume during the last century, as reported by the associated National park.

The Severny Island ice cap on Severny Island, in Russia covers 40% of Severny Island (which is the 30th largest island in the world) at total area of approximately 20,500 km2(7,900 sq mi) which when considered part of Europe, would make it the largest glacier by area. Scientific America reported in 2019 that the nearby Vavilov Ice ca lost about 9.5 billion tons of ice in the preceeding six years.

The largest single mass of ice on Earth is the Antarctic ice sheet which covers an area of almost 14 million square kilometres (14 square miles) and contains 30 million km3 of ice. The academic journal nature reported that this ice sheet lost 2,720 ± 1,390 billion tonnes of ice between 1992 and 2017, which corresponds to an increase in the mean sea level of 7.6 ± 3.9 millimetres (errors on one standard deviation)

The largest glacier in the world, is Antarctica's Lambert Glacier, one of the world’s fastest-moving ice streams. Ice streams are parts of an ice sheet that move faster than the sheet as a whole. The current (2022) rate of melt of the Lambert Glacier is though to be 5 metres a year, though this may increase not only from continued emissions but also changing microclimates due to seas being darker than glaciers and thus absorbing rather than reflecting heat.

NB Global Warming of 1.5 ºC, Glossary, published by the Intergovernmental Panel on Climate Change (IPCC) in 2018, defines glacier as: ‘A perennial mass of ice, and possibly firn and snow, originating on the land surface by the recrystallisation of snow and showing evidence of past or present flow. A glacier typically gains mass by accumulation of snow, and loses mass by melting and ice discharge into the sea or a lake if the glacier terminates in a body of water. Land ice masses of continental size (>50,000 km2) are referred to as ice sheets.’

It defines an ice sheet as: 'A mass of land ice of continental size that is sufficiently thick to cover most of the underlying bed, so that its shape is mainly determined by its dynamics (the flow of the ice as it deforms internally and/or slides at its base). An ice sheet flows outward from a high central ice plateau with a small average surface slope. The margins usually slope more steeply, and most ice is discharged through fast flowing ice streams or outlet glaciers, in some cases into the sea or into ice shelves floating on the sea. There are only two ice sheets in the modern world, one on Greenland and one on Antarctica. During glacial periods there were others.’

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[edit] External links

• https://www.nature.com/articles/s41586-018-0179-y
• https://www.nationalgeographic.com/environment/article/big-thaw