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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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Trends in sea level, 1870-2006 Trends in sea level, 1870-2006
Coastal and island tide-gauge data show that sea level rose by just under 20 cm between 1870 and 2001, with an average rise of 1.7 mm per year during the 20th century and with an increase in the rate of rise over this period. This is consistent with the geological data and the few long records of sea level from coastal tide gauges. From 1993 to the end of 2006, near-global measurements of sea level (between 65°N and 65°S) made by high precision s...
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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Projected sea-level rise for the 21st century Projected sea-level rise for the 21st century
The projected range of global averaged sea-level rise from the IPCC 2001 Assessment Report for the period 1990 to 2100 is shown by the lines and shading. The updated AR4 IPCC projections made are shown by the bars plotted at 2095, the dark blue bar is the range of model projections (90% confidence limits) and the light blue bar has the upper range extended to allow for the potential but poorly quantified additional contribution from a dynamic res...
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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World ocean thermohaline circulation World ocean thermohaline circulation
The global conveyor belt thermohaline circulation is driven primarily by the formation and sinking of deep water (from around 1500m to the Antarctic bottom water overlying the bottom of the ocean) in the Norwegian Sea. When the strength of the haline forcing increases due to excess precipitation, runoff, or ice melt the conveyor belt will weaken or even shut down. The variability in the strength of the conveyor belt will lead to climate change in...
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Effects of sea-level rise on water resources of small islands and low-lying coastal areas Effects of sea-level rise on water resources of small islands and low-lying coastal areas
The water resources of small islands and low-lying coastal areas are very susceptible to sea-level rise. This figure illustrates the direct impacts on the water resources sector, as well as the plethora of higher-order impacts which affect not only that sector but most, if not all, other sectors including health, transport and agriculture.
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Monthly average sea ice extent globally and in both hemispheres Monthly average sea ice extent globally and in both hemispheres
In the Arctic, winter sea ice extends over an area of approximately 15 million km2 at its peak in March and up to 7 million km2 in September, at the end of the summer melt season. Corresponding numbers for the Southern Ocean around the Antarctic continent are approximately 3 million km2 in February during the Antarctic summer and 18 million km2 at the height of winter in September. In regions with seasonal sea ice, the ice cover achieves a thickn...
01 Oct 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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Projected winter temperature changes in the Arctic Projected winter temperature changes in the Arctic
The changes in cold-season mean temperatures over Arctic land regions are broken into three latitudinal bands for each region, as shown on the small map (which has an outer rim of 50° N). Error bars represent standard deviation from the mean. Where greater warming is projected at higher latitudes than at lower latitudes, temperature gradients will be reduced along large north-flowing rivers and this will likely reduce break-up severity. The rever...
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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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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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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Glaciers monitored through the World Glacier Monitoring Service Glaciers monitored through the World Glacier Monitoring Service
Worldwide collection of information about ongoing glacier changes was initiated in 1894 with the foundation of the International Glacier Commission at the 6th International Geological Congress in Zurich, Switzerland. Today, the World Glacier Monitoring Service continues to collect and publish standardized information on ongoing glacier changes. WGMS is a service of the Commission for the Cryospheric Sciences of the International Union of Geodesy ...
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Monthly average sea ice extent globally and in both hemispheres (radial) Monthly average sea ice extent globally and in both hemispheres (radial)
In the Arctic, winter sea ice extends over an area of approximately 15 million km2 at its peak in March and up to 7 million km2 in September, at the end of the summer melt season. Corresponding numbers for the Southern Ocean around the Antarctic continent are approximately 3 million km2 in February during the Antarctic summer and 18 million km2 at the height of winter in September. In regions with seasonal sea ice, the ice cover achieves a thickn...
01 Oct 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Regional changes in Arctic and Antarctic sea ice Regional changes in Arctic and Antarctic sea ice
There are major regional differences for the Arctic sea ice, with the strongest decline in ice extent observed for the Greenland Sea (10.6 per cent per decade). The smallest decreases of annual mean sea ice extent were found in the Arctic Ocean, the Canadian Archipelago and the Gulf of St. Lawrence. In the marginal Arctic seas off Siberia (the Kara, Laptev, East Siberian and Chukchi Seas) a slight negative, but not significant, trend in ice exten...
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
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Developing countries with environmental strategies Developing countries with environmental strategies
While many countries have shown indifference to environmental commitments made at Rio, the summit significantly helped legitimise environmental issues in political agendas worldwide: over 50 countries currently have national constitutions recognizing the rights of citizens to a healthy environment and many have national legislation to protect the environment.
29 Nov 2007 - by Philippe Rekacewicz, UNEP/GRID-Arendal
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Water Availability Trends Water Availability Trends
Water availability in developing countries (with and without arid climates) has declined by about 65 percent since the 1960s and continues to do so. Forecast indicate that water will become very scarce by 2020.
29 Nov 2007 - by Philippe Rekacewicz, UNEP/GRID-Arendal
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