Climate change: Factfile on the scientific evidence23 ноября 2011, 15:56
Following is a snapshot of scientific evidence for global warming and its impacts ahead of the November 28-December 9 UN climate talks in Durban, South Africa.
Except where stated, the source is the Fourth Assessment Report published by the UN's Intergovernmental Panel on Climate Change (IPCC) in 2007.
-- Evidence of global warming is "unequivocal," with a more than 90-percent probability that humans are largely responsible. The main culprit is greenhouse gas from fossil fuels, which traps solar heat in the atmosphere, warming Earth's surface.
-- Levels of carbon dioxide (CO2) have risen by around a third since pre-industrial times and are now at their highest in 650,000 years. 2010 saw the largest single-year jump in CO2 emissions, from 8.6 to 9.1 billion tonnes, according to the US Department of Energy.
-- Since 1900, sea level has risen by 10-20 centimetres (four to eight inches). Global average surface temperature has risen by 0.8 degrees Celsius (1.44 degrees Fahrenheit). Average temperatures above land have risen far faster, by 0.91 C (1.64 F) since the mid-20th century, according to the Berkeley Earth Surface Temperature Project.
-- Climate change is already visible in sea-level rise, loss of alpine glaciers and snow cover, shrinking Arctic summer sea ice, thawing permafrost and poleward migration of many animals and plants towards cooler habitats.
-- By 2100, "best estimates" for the rise in global average surface temperatures run from 2.4-4.0 C (4.3-7.8 F) depending on fossil-fuel use. These figures also mask big variations, according to region and country.
-- In 2007, the IPCC projected sea levels will rise by at least 18 cms (7.2 inches) by 2100. Since then, many studies point to the risk of meltoff from the Greenland and West Antarctic ice sheets. Most experts now say a one-metre (39-inch) increase is plausible.
The Arctic ice. ©RIA Novosti
-- 20-30 percent of plant and animal species are threatened with extinction if average global temperatures increase by 1.5-2.5 C (2.7-4.5 F) compared to the average temperature during the two last decades of the 20th century.
Pink flamingoes. ©Reuters
-- In Africa, by 2020, up to 75 to 250 million people will be exposed to increased water stress. Yields from rain-fed agriculture in some African countries could be reduced by up to 50 percent. Desert-like areas could expand by five to eight percent by 2080.
A dried up river filled with sand winds its way across the desert near Gos Beida in eastern Chad. ©Reuters
-- In Asia, available fresh water will decrease by mid-century. Coastal mega-deltas will be at risk from flooding due to rising seas. Mortality due to diseases associated with floods and droughts will increase.
-- Extreme weather events such as heatwaves, droughts and rainstorms are likely to become more frequent and/or intensive, according to an IPCCC special report published on November 18.
-- To stabilise emissions at 445-535 parts per million (ppm) of CO2 equivalent would limit the overall rise in global warming since pre-industrial times to 2.0-2.8 C (3.6-5.0 F). Concentrations are currently about 390 ppm. A level of 450 ppm corresponds roughly to the target of 2.0 C (3.6 F) embraced by nations at the UN climate talks in Cancun in 2010.
-- Countries have to close a "gigatonne gap" of excess carbon emissions to meet the 2.0 C (3.6 F) target. A 2010 UNEP report set this at five to nine gigatonnes, a figure likely to be higher today. In October, researchers at the Institute for Atmospheric and Climate Science at ETH Zurich calculated emissions will have to fall by 8.5 percent by 2020 compared to 2010 and then continue to decline.