Polar ice caps
The mass results of polar ice caps in Antarctica and Greenland has been negative for the past decade, although some parts of Antarctica are thickening as a result of increased snowfall. Mass loss occurs in coastal areas due to the rapid flow of some glaciers to the ocean.
In July 2015, an international team of 17 climatologists from the United States, France, Germany and China, led by James Hansen, published a study that concluded that climate change has a highly dangerous character even limited to 2 °C. This study is still in the form of a discussion paper, an article submitted to the experts for discussion in Atmospheric, Chemistry and Physics, an open access journal of the European Geoscience Union. This team emphasizes that the economic and social cost of the loss of functionality of coastal cities is incalculable in practice.
However, the last IPCC Group 1 report, published in September 2013, does not mention this, setting sea level rise at a maximum of 0.8 meters by the end of the century. But this figure does not take into account a possible destabilization of the caps, the experts having considered that this subject was not mature enough. The scientific study is based on observations of the climate of 130,000 years ago, during the interglacial that preceded our own, called Eeman, a period of about 15,000 years, with average temperatures of about 2 °C more than those before the industrial revolution.
Certainly the cause of this warming was in an orbital configuration whose effects were amplified by the climatic feedbacks of the planet, and not in a greenhouse effect reinforced by emissions from fossil energy like today, but the end of this interglacial, whereas the initial cause of warming – the celestial mechanics warming the northern hemisphere more during the boreal summer – no longer worked, seems paradoxical: it is at this moment that the sea level rises from about 6 meters above current level according to Australian coral analysis; the only possible explanation is a massive and rapid loss of ice from the two polar ice caps, probably due to a sudden change in ocean circulation.
Researchers have therefore explored scenarios of ice sheet collapse: when they assume the accelerated melting of Greenland, the North Atlantic and Europe are colder than today around 2100. If the two ice caps are destabilized simultaneously, a land of extreme contrasts appears, with high and medium latitude
There is a warming and partial thawing of Arctic permafrost. Between one-third and one-half of Alaska’s permafrost is only one degree below the thawing temperature. In Siberia, permafrost thaw lakes are forming, causing significant releases of methane. The release of methane is in the order of 14 to 35 million tons per year on all Arctic lakes. The carbon-14 analysis of this methane proves that it has been frozen for thousands of years.
Retreat of mountain glaciers
(A map of the change in the thickness of mountain glaciers since 1970. Decrease in orange and red, thickening in blue. )
With a few exceptions, most of the mountain glaciers surveyed are in retreat. The decline of continental glaciers has been observed almost universally since the 1970s to 1980s, with a marked increase since the 1990s.
Many works document this decline and seek to explain it. Such a decline seems entirely consistent with warmer weather, however this assumption is uncertain, with some glaciers beginning to retreat in the mid-19th century after the end of the Little Ice Age. The advance or retreat of glaciers is recurrent and linked to many factors, among which precipitation or the El Niño phenomenon play an important role. For example, the current retreat of the Chamonix Sea of Ice uncovers human remains from the Middle Ages, proof that the glacier has already shrunk more than today in a historically close period.
The decline of mountain glaciers, particularly in western North America, Asia, the Alps, Indonesia, Africa (including Kilimanjaro), and tropical and subtropical regions of South America, has been used as a qualitative proof of the rise in global temperatures since the end of the 19th century by the IPCC in its 2001 report.
(Change in snow accumulation at the top of Kilimanjaro: first photo taken on February 17, 1993, second on February 21, 2000. Kilimanjaro lost 82% of its glacier during the twentieth century and it may have disappeared in 2020 according to an article published in the journal Science in 2002.)
The causes of the retreat of the Kilimanjaro glacier in Africa are debated and are a good example of the complexity of global warming and the circumspection necessary in data analysis. For some climatologists, this decline is due to a decrease in snowfall since the 19th century. For others, global warming is involved, as tropical glaciers are shrinking globally and Kilimanjaro ice has withstood a long drought 4,000 years ago.
As regards the Himalayan glaciers, it is necessary to underline the limited number of data. A 2006 study found that an increase in seasonal runoff from the Himalayan glaciers resulted in an increase in agricultural production in northern India during the 20th century. In 2007, reliable data only existed for 50 Indian glaciers, out of more than 9,500. According to a 2009 report by the Indian Ministry of the Environment, the Himalayan glaciers that are the sources of the largest rivers in Asia – Ganges, Indus, Brahmaputra, Yangtze, Mekong, Salween and Yellow River – are receding. However, this report remains cautious in these conclusions:
“It is premature to say that Himalayan glaciers are backing up abnormally due to global warming. A glacier is influenced by a variety of physical factors and a complex interconnection of climatic factors. “
In 2016, two glaciers in the Aru region of Tibet collapsed sharply, the only known documented case being the collapse of the Kolka Glacier in the Caucasus in 2002.
In the Andes, the Chacaltaya glacier, which was home to the highest ski resort, disappeared altogether in 2009. In general, tropical Andean glaciers have decreased by 30 to 50% in 30 years. Because of this decrease, the water supply of La Paz, capital of Bolivia could become problematic.