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Cryosphere - winter seasons, Northern and Southern Hemispheres Cryosphere - winter seasons, Northern and Southern Hemispheres
Seasonal variation in the extent of ice and snow cover is greatest in the Northern Hemisphere. Imagine the Earth with white caps on the top and bottom. The top cap increases by a factor of six from summer to winter, while the bottom cap only doubles from summer to winter. This difference is due to snow cover: in the Northern Hemisphere snow cover on land varies from less than 2 million km2 in the summer to 40 to 50 million km2 in the winter3. The...
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Population, area and economy affected by a 1 m sea level rise (global and regional estimates, based on today's situation) Population, area and economy affected by a 1 m sea level rise (global and regional estimates, based on today's situation)
Even for today’s socio-economic conditions, both regionally and globally, large numbers of people and significant economic activity are exposed to sea-level rise. The densely populated megadeltas are especially vulnerable to sea-level rise. More than 1 million people living in the Ganges- Brahmaputra, Mekong and Nile deltas will be directly affected simply if current rates of sea-level rise continue to 2050 and there is no adaptation. More than 5...
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Trends in Arctic sea ice extent in March (maximum) and September (minimum) in the time period of 1979–2008 Trends in Arctic sea ice extent in March (maximum) and September (minimum) in the time period of 1979–2008
For the Northern Hemisphere (primarily the Arctic), observations using remote sensing technologies have been used to measure the extent and the to assess the development. Despite considerable year-to-year variability, significant negative trends are apparent in both maximum and minimum ice extents, with a rate of decrease of -2.9% per decade for March and -10.5% per decade for September (linear least squares reqression). The differences in extent...
18 Apr 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Permafrost extent in the Northern Hemisphere Permafrost extent in the Northern Hemisphere
Permafrost zones occupy up to 24 per cent of the exposed land area of the Northern Hemisphere. Permafrost is also common within the vast continental shelves of the Arctic Ocean. This subsea permafrost formed during the last glacial period when global sea levels were more than 100 m lower than at present and the shelves were exposed to very harsh climate conditions. Subsea permafrost is slowly thawing at many locations. Permafrost of various tempe...
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Time series of freeze-up and break-up dates from selected Northern Hemisphere lakes and rivers, 1846–1995 Time series of freeze-up and break-up dates from selected Northern Hemisphere lakes and rivers, 1846–1995
Limited by the availability of detailed observations, most historical evaluations of changes in freshwater ice have focused on relatively simple characteristics, such as the timing of autumn freeze up and spring break up, and maximum ice-cover thickness. Based on 27 long-term (about 150-year) records from around the Northern Hemisphere, Magnuson and others (Figure 8.1) discovered that freeze up has been delayed by approximately six days per hundr...
01 May 2010 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Example of enhanced water levels produced from river ice, Liard River, Canada Example of enhanced water levels produced from river ice, Liard River, Canada
The lower curve shows the correspondence between river flow and water levels under open-water conditions. The much greater maximum water levels possible under ice-jam conditions are illustrated by the upper curve. The transition in break-up severity from dynamic to thermal break-up effects (see text) is depicted by the gradually shaded area between the two curves. Dots are observed annual maximum water levels during the spring break up. The 1990...
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Greenland, showing rates of surface-elevation change between the late 1990s and 2003 Greenland, showing rates of surface-elevation change between the late 1990s and 2003
Mass-balance estimates for Greenland show thickening at high elevations since the early 1990s at rates that increased to about 4 cm per year after 2000, consistent with expectations of increasing snowfall in a warming climate. However, this mass gain is far exceeded by losses associated with large increases in thinning of the ice sheet near the coast. Total loss from the ice sheet more than doubled, from a few tens of billions of tonnes per year ...
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Antarctica, topographic map Antarctica, topographic map
Antarctic is the fifth largest continent of the world at 14 million square kilometres and is covered by a permanent continental ice sheet. The ice is distributed in two major ice sheets, the East Antarctic and the West Antarctic, and in addition there are shelf ice, extending over the sea water. Antarctic inland ice ranges in thickness up to 5000 m, with an average thickness of about 2400 m, making Antarctica by far the highest of the continents....
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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The Cryosphere, world map The Cryosphere, world map
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 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Sea ice concentration change over the 21st century as projected by climate models Sea ice concentration change over the 21st century as projected by climate models
The data are taken from climate model experiments of 12 (out of 24) different models that were conducted for the IPCC Assessment Report 4 using the SRES A1B greenhouse gas emission scenario. Plots on the right show changes in late summer and those on the left show changes in late winter. Notes: 1) sea ice extent is the area in which a defined minimum of sea ice can be found. sea ice concentration is the proportion of the ocean area actually cover...
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Arctic temperatures in the 20th century, modeled and observed Arctic temperatures in the 20th century, modeled and observed
Observed Arctic winter land temperatures and IPCC model recreations for the 20th century. Note that although these model runs are able to capture the range of Arctic warm and cold periods, the timing of the peaks varies, suggesting that the early 20th century warming was due to random causes, while the increases at the end of the century shown by all the models supports CO2 as an external forcing of the Arctic climate system.
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Projected increase (days) of the navigation season through the Northern Sea Route as an average of 5 ACIA model projections Projected increase (days) of the navigation season through the Northern Sea Route as an average of 5 ACIA model projections
The Northern Sea Route (NSR) is a seasonally ice-covered marine shipping lane along the Russian coasts, from Novaya Zemlya in the west to the Bering Strait in the east. The NSR is administered by the Russian Ministry of Transport and has been open to marine traffic of all nations since 1991. For trans-Arctic voyages, the NSR represents a saving in distance of up to 40 per cent from Northern Europe to northeastern Asia and northwestern North Ameri...
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Variations in snow depth and ice cover, alpine lake at Hardangervidda plateau, Norway Variations in snow depth and ice cover, alpine lake at Hardangervidda plateau, Norway
Climate warming means that lowland lakes typically are experiencing longer ice-free periods, promoting greater biological productivity. However, despite this warming trend, biological productivity may be reduced, at least temporarily, in alpine areas with increased winter precipitation. During years with high winter precipitation in alpine areas of western Norway, in spite of higher temperatures, fish growth and recruitment were lower than in low...
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Arctic sea ice minimum extent in September 1982 and 2008 Arctic sea ice minimum extent in September 1982 and 2008
The red line indicates the median minimum extent of the ice cover for the period 1979–2000. This figure compares the Arctic sea ice extent in September for the years 1982 (the record maximum since 1979) and 2008. The ice extent was 7.5 million km2 in 1982 and only 5.6 million km2 in 2005 and down to 4.3 million km2 in 2007. As has been observed in other recent years, the retreat of the ice cover was particularly pronounced along the Eurasian coas...
18 Apr 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Ice avalanches of the Nevados Huascarán in Peru Ice avalanches of the Nevados Huascarán in Peru
Many disasters have been recorded from the glaciers in the Cordillera Blanca. The 1962 and 1970 events originating from Glaciar 511 on the Nevados Huascarán, the highest peak of which is at 6768 m above sea level in the Peruvian Andes, were particularly severe. On 10 January 1962, an ice avalanche took place with an estimated starting volume of 10 million m3; the avalanche travelled down 16 km and destroyed the city of Ranrahirca, where 4000 peop...
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Increases in annual temperatures for a recent five-year period, relative to 1951-1980 Increases in annual temperatures for a recent five-year period, relative to 1951-1980
Warming is widespread, generally greater over land than over oceans, and the largest gains in temperatures for the planet are over the North American Arctic, north central Siberia, and on the Antarctic Peninsula. These recent increases in temperature are confirmed by changes in other features: loss of sea ice, shift of tundra to shrub vegetation, and migration of marine and terrestrial ecosystems to higher latitudes.
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Trends in Arctic sea-ice extent in March (maximum) and September (minimum) in the time period of 1979–2006 Trends in Arctic sea-ice extent in March (maximum) and September (minimum) in the time period of 1979–2006
For the Northern Hemisphere (primarily the Arctic), observations using remote sensing technologies have been used to measure the extent and the to assess the development. Despite considerable year-to-year variability, significant negative trends are apparent in both maximum and minimum ice extents, with a rate of decrease of 2.5 per cent per decade for March and 8.9 per cent per decade for September (linear least squares reqression). The differen...
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Mountain permafrost patterns and temperature gradients Mountain permafrost patterns and temperature gradients
Steep terrain and strong variability in surface temperatures are typical of mountain permafrost. The cross section in the foreground shows the complex distribution of subsurface temperatures characteristic of mountains, with the isotherms (lines linking points of equal temperature) nearly vertical in the ridge of the mountain. In the background, the colours on the mountain surface illustrate the strong variability in ground temperatures caused by...
01 Jun 2007 - by Stephan Gruber, University of Zürich. Hugo Ahlenius, UNEP/GRID-Arednal
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Arctic delta pond ecosystems, seasonal flooding and adaptation Arctic delta pond ecosystems, seasonal flooding and adaptation
The physical development and ecosystem health of river deltas in cold regions are strongly controlled by ice processes and thus are highly susceptible to the effects of climate change. As an example, the photograph shows a typical lake/pond and river network in the Peace-Athabasca Delta (Canada), one of the largest freshwater deltas in the world. The water budget and sediment-nutrient supply for the multitude of lakes and ponds that dot the ripar...
01 Nov 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Trends in snow-covered area for the Northern Hemisphere 1922-2005 Trends in snow-covered area for the Northern Hemisphere 1922-2005
Observations of snow-covered area for the Northern Hemisphere show a significant development in the later 20th century, with a reduction of the area covered by snow in the spring (March-April) from some 38 million km2 in the 1930-ies to todays 35 million km2. Snow represents an important resource for water, ecosystems and human activities, as well as for reflecting incoming sun light. The linear trend shows a decrease in snow-covered area of 2.7 ...
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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