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Northern Hemisphere snow-cover extent anomalies 1966-2005 Northern Hemisphere snow-cover extent anomalies 1966-2005
Data from satellite monitoring from 1966 to 2005 show that mean monthly snow-cover extent in the Northern Hemisphere is decreasing at a rate of 1.3 per cent per decade. For the calendar year of 2006 average snow-cover extent was 24.9 million km2, which is 0.6 million km2 less than the 37-year average. In the Northern Hemisphere, spring and summer show the strongest decreases in snow-cover extent. Satellite observations of snow-cover extent show a...
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Projected temperatures in the 21th century Projected temperatures in the 21th century
Projected Arctic annual land temperature increases for the first half of the 21st century relative to the average temperature for 1980–99. The average of the IPCC models (the blue line) shows an increase of 3ºC by 2050. The averages of the runs from each of the 12 models show increases from 2–4ºC, the range of uncertainty in these model projections.
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Antarctica, showing rates of surface-elevation change derived from satellite radar-altimeter measurements Antarctica, showing rates of surface-elevation change derived from satellite radar-altimeter measurements
The figure shows rates at which the ice-sheet mass was estimated to be changing based on radar-altimeter data (black), mass-budget calculations (red), and satellite gravity measurements (blue). Rectangles depict the time periods of observations (horizontal) and the upper and lower estimates of mass balance (vertical). Measurements by satellite techniques based on gravity indicate mass loss at a rate of 138 ± 73 billion tonnes per year during 200...
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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The Cryosphere, components and world maps The Cryosphere, components and world maps
Snow and the various forms of ice - the cryosphere - play different roles within the climate system. The two continental ice sheets of Antarctica and Greenland actively influence the global climate over time scales of millennia to millions of years, but may also have more rapid effects on, for example, sea level. Snow and sea ice, with their large areas but relatively small volumes, are connected to key interactions and feedbacks at global scales...
01 Oct 2008 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Albedo of basic thick sea ice surface types Albedo of basic thick sea ice surface types
The albedo for different surface conditions on the sea ice range widely, from roughly 85 per cent of radiation reflected for snow-covered ice to 7 per cent for open water. These two surfaces cover the range from the largest to the smallest albedo on earth. Melting snow, bare ice and ponded ice lie within this range. There is a general decrease in the albedo of the ice cover during the melt season as the snow-covered ice is replaced by a mix of me...
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Melting ice on Mount Kilimanjaro, East Africa Melting ice on Mount Kilimanjaro, East Africa
Close to 50 per cent of the glaciers in Africa, on the Rwenzori Mountains, Mount Kenya and Kilimanjaro have disappeared, while larger glaciers – particularly on Kilimanjaro – have been fragmented. Changes in glacier area and volume are being used as indicators for global warming and climate change.
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Projected reduction in snow 2080-2100 Projected reduction in snow 2080-2100
Using one specific climate change model (ECHAM5) and the SRES A2 emission scenario (run 2) the projected loss of snow amounts to decreases of 60–80 per cent in monthly maximum snow water equivalent over most middle latitudes by the end of this century. The largest decreases are projected over Europe, while the model projects increases are in the Canadian Arctic and Siberia. Snow presents an important factor for ecosystems, water and human activit...
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Ice-albedo feedback process Ice-albedo feedback process
In spring, the ice is snow-covered and there is very little open water. Most sunlight is reflected, but some is absorbed. This absorbed sunlight leads to melting, which in turn reduces the ice albedo and increases the amount of open water. This causes the albedo to further decrease, increasing the rate of heating and further accelerating melting.
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Shrinking of Fedchenko Glacier in the Pamirs of Tajikistan Shrinking of Fedchenko Glacier in the Pamirs of Tajikistan
Significant loss of glaciers in Central Asia began around the 1930s, and become more dramatic in the second half of the 20th century and continue into the 21st century. Glacier area was reduced in the Tien Shan and in the Pamirs, including its largest Fedchenko Glacier. The debris-covered glacier tongue retreated by more than 1 km since 1933 and lowered by about 50 m since 1980.
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Trends in spring snow cover duration for the Northern Hemisphere, 1970-2004 Trends in spring snow cover duration for the Northern Hemisphere, 1970-2004
Examination of regional trends in spring snow-cover duration from 1969–2003 using NOAA snow-cover data shows the western United States to be among the regions with the strongest decreases. This supports results from studies based on measurements on the ground. Springtime snow cover shows a decline particularly in the Pacific Northwest region of the western United States, where snow water equivalent, a common snow cover measurement equivalent to t...
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Water towers of Asia - glaciers, water and population in the greater Himalayas-Hindu Kush-Tien Shan-Tibet region Water towers of Asia - glaciers, water and population in the greater Himalayas-Hindu Kush-Tien Shan-Tibet region
The Himalayas–Hindu Kush, Kunlun Shan, Pamir and Tien Shan mountain ranges function as water towers, providing water to people through much of Asia. The glacier-fed rivers originating from the Himalaya mountain ranges surrounding the Tibetan Plateau comprise the largest river run-off from any single location in the world. While the mountains are homes to some 170 million people, the rivers that drain these mountains influence the lives of about 4...
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Glacier front variations in the European Alps Glacier front variations in the European Alps
Large Alpine glaciers have retreated continuously since the mid- 19th century, whereas steep mid-sized glaciers reacted with readvances in the 1890s, 1920s and between the 1970s and 1980s due to the somewhat cooler and wetter periods. Small glaciers feature a high annual variability with a clear shrinking trend.
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Schematic diagram of glacier, permafrost and forest limits as a function of mean annual air temperature and average annual precipitation Schematic diagram of glacier, permafrost and forest limits as a function of mean annual air temperature and average annual precipitation
Glaciers and ice caps form around the world where snow deposited during the cold/humid season does not entirely melt during warm/dry times. This seasonal snow gradually becomes denser and transforms into perennial firn (rounded, well-bonded snow that is older than one year) and finally, after the air passages connecting the grains are closed off, into ice. The ice from such accumulation areas then flows under the influence of its own weight and t...
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Ice sheets, schematic illustration for Greenland and Antarctica Ice sheets, schematic illustration for Greenland and Antarctica
The ice cover in Greenland and Antarctica has two components – thick, grounded, inland ice that rests on a more or less solid bed, and thinner floating ice shelves and glacier tongues. An ice sheet is actually a giant glacier, and like most glaciers it is nourished by the continual accumulation of snow on its surface. As successive layers of snow build up, the layers beneath are gradually compressed into solid ice. Snow input is balanced by glaci...
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Annual snowfall pattern for a typical mountain environment, Columbine Pass, Colorado 1971-2000 Annual snowfall pattern for a typical mountain environment, Columbine Pass, Colorado 1971-2000
Mountain snow cover typically develops in the autumn and grows to a maximum depth in early spring. As day length and sun angles increase, so do air temperatures, causing snow cover to warm and begin to melt. Snow cover balances the availability of water in mountain environments. Where winter precipitation falls as rain, surface runoff occurs almost immediately. In contrast, snow stores water during the winter and then melts in the spring and ear...
01 Oct 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Mean snow-cover extent in the Northern Hemisphere 1966-2006 Mean snow-cover extent in the Northern Hemisphere 1966-2006
Snow occurs predominantly on the northern continents, on the sea ice of the Arctic Ocean and on Antarctica. On the Northern Hemisphere continents, snow covers a maximum mean area of 45.2 million km2, typically in January. The minimum snow-cover extent usually occurs in August and covers a mean area of 1.9 million km2, most of which is snow on the Greenland ice sheet and on mountain glaciers. As a result, snow cover is the surface characteristic r...
01 Oct 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Shrinking Lewis Glacier, Mount Kenya Shrinking Lewis Glacier, Mount Kenya
The tropical Lewis Glacier retreated by more than 800 m between 1893 and 2004 and lost almost 16 m water equivalent of its thickness between 1979 and 1996. Located on Mount Kenya, this is one of few locations in Africa with glaciers.
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Ratio of existing ski areas in the Alps with natural snow-reliability under current conditions and warmer conditions Ratio of existing ski areas in the Alps with natural snow-reliability under current conditions and warmer conditions
Winter tourism is a significant part of the economy of Alpine countries and the most important source of income in many regions. In Austria, winter tourism revenue makes up 4.5 per cent of GNP and half of the total income from tourism. Much of winter tourism is based around the ski industry, which is dependent on reliable snow conditions. Although snow fall is expected to increase at high elevations, it is winter temperatures that largely determi...
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Overview on glacier changes since the end of the Little Ice Age Overview on glacier changes since the end of the Little Ice Age
Glaciers and ice caps reached their Holocene (the past 10 000 years) maximum extent in most mountain ranges throughout the world towards the end of the Little Ice Age, between the 17th and mid-19th century. Over the past hundred years a trend of dramatic shrinking is apparent over the entire globe, especially at lower elevations and latitudes. Within this general trend, strong glacier retreat is observed in the 1930s and 1940s, followed by static...
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Population size of Peary caribou in the Canadian Arctic islands Population size of Peary caribou in the Canadian Arctic islands
In northwestern North America, recent warming has led to a dramatic increase in the number of days of above freezing temperatures during the migration period for the caribou (Rangifier tarandus). Thawing and subsequent re-freezing of snow results in ice layers in the snow pack which hinder travel of Rangifer and make it harder to cater for food. There have been catastrophic declines in the Peary caribou on the Arctic islands of North America and ...
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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