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Climate feedbacks - the connectivity of the positive ice/snow albedo feedback, terrestrial snow and vegetation feedbacks and the negative cloud/radiation feedback Climate feedbacks - the connectivity of the positive ice/snow albedo feedback, terrestrial snow and vegetation feedbacks and the negative cloud/radiation feedback
Feedback refers to the modification of a process by changes resulting from the process itself. Positive feedbacks accelerate the process, while negative feedbacks slow it down. Part of the uncertainty around future climates relates to important feedbacks between different parts of the climate system: air temperatures, ice and snow albedo (reflection of the sun’s rays), and clouds. An important positive feedback is the ice and snow albedo feedback...
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
3
World ocean thermohaline circulation (alternative version) World ocean thermohaline circulation (alternative version)
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
3
Historical trends in carbon dioxide concentrations and temperature, on a geological and recent time scale Historical trends in carbon dioxide concentrations and temperature, on a geological and recent time scale
The most recent geological history, in the last hundred thousand years, has been characterised by cycles of glaciations, or ice ages. The historic temperatures, through these times, have been low, and continental ice sheets have covered large parts of the world. Through ancient air, trapped in tiny bubbles in the Antarctic ice, we have been able to see what the temperature cycle was at that time, and also the concentration of carbon dioxide (CO2)...
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
4
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.
18 Apr 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
4
Estimated contributions to sea-level rise (1993-2003) Estimated contributions to sea-level rise (1993-2003)
The two main reasons for sea-level rise are thermal expansion of ocean waters as they warm, and increase in the ocean mass, principally from land-based sources of ice (glaciers and ice caps, and the ice sheets of Greenland and Antarctica). Global warming from increasing greenhouse gas concentrations is a significant driver of both contributions to sea-level rise. From 1955 to 1995, ocean thermal expansion is estimated to have contributed about 0....
01 Oct 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
4
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
3
Change in the age of ice on the Arctic Ocean, comparing September ice ages in 1988, 1990, 2001 and 2005 Change in the age of ice on the Arctic Ocean, comparing September ice ages in 1988, 1990, 2001 and 2005
The age of sea ice in the Arctic is changing, and not only the extent and concentrations. Studies show that in recent years there is a higher proportion of younger ice to older ice than was observed in the late 1980s. This analysis is based on results from a simulation using drifting buoy data and satellite-derived ice-concentration data. The darker the colour, the older the ice.
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
5
Trends in Arctic temperature, 1880-2006 Trends in Arctic temperature, 1880-2006
A history of Arctic land temperature anomalies from 1880 through 2006 is shown in this figure. The zero line represents the average temperature for 1961–1990. In the late 1800s the Arctic was relatively cold, although there is some uncertainty around these early temperature estimates. The Arctic warmed by about 0.7ºC over the 20th century. There was a warm period in the 1920s to 1940s and cold periods in the early 1900s and in the 1960s. Over th...
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
4
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
2
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
4
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
5
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
4
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
4
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
3
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
3
Arctic temperature anomaly patterns Arctic temperature anomaly patterns
Natural climate variability is organized into spatial patterns of high and low pressure regions, represented by the Arctic Oscillation (also called the Northern Annular Mode) and North Pacific patterns in the Northern Hemisphere, and the Southern Annular Mode in the Southern Hemisphere. The patterns of surface temperature anomalies when the Arctic Oscillation and Northern Pacific patterns are in their positive extreme are shown in this fi...
01 Jun 2007 - by Hugo Ahlenius, UNEP/GRID-Arendal
3
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
5
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
3
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
3
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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