Following is a summary of expert opinion of potential impacts from climate change by the end of the century.
The source is the Fourth Assessment Report, published in 2007 by the UN's Nobel-winning scientists, the Intergovernmental Panel on Climate Change (IPCC).
The magnitude of impacts will mainly depend on the level of warming, which the panel predicted would be in a range of 1.8-4.0 C (3.2-7.2 F) by 2100, a figure that two recent studies have said could be under-estimated by up to 2.4 C (4.3 F).
ASIA: Between 120 million to 1.2 billion Asians will experience increased water stress by 2020, and 185 to 981 million by 2050. Cereal yields in South Asia could drop in some areas by up to 30 percent by 2050.
Even modest sea-level rises will cause flooding and economic disruption in densely-populated mega-deltas, such as the Yangtze, Red River and Ganges-Brahmaputra.
Cholera and malaria could increase, thanks to flooding and a wider habitat range for mosquitoes.
In the Himalayas, glaciers less than four kilometers (2.5 miles) long will disappear entirely if average global temperatures rise by 3 C (5.4 F). This will initially cause increased flooding and mudslides followed by an eventual decrease in flow in rivers that are glacier-fed.
Per-capita water availability in India will drop from around 1,900 cubic metres (66,500 cubic feet) currently to 1,000 cu. metres (35,000 cu. ft.) by 2025.
AFRICA: Likely to be the worst-hit continent. Hundreds of millions are "very likely" -- a 90 percent certainty -- to face severe shortfalls in food and drinkable water by 2080, probably sooner.
Climate change will shorten growing seasons and render swathes of land unusable for agriculture, with yields declining by as much as 50 percent in some countries. A rise of 60 to 90 million hectares (150 to 220 million acres) of arid and semi-arid land is projected by 2080.
Food security will be "severely compromised", with an additional 80 to 200 million people at risk of hunger by 2080. By that date, sub-Sahara Africa may account for 40 to 50 percent of the world's undernourished, compared with about 25 percent today.
Half a billion Africans will face acute scarcities of drinkable water if average global temperatures rise only 2 C (3.6 F) compared to 1990 levels. Cholera, meningitis and dengue fever will increase in extent and impact.
Big deltas such as the Nile and the Niger face flooding and economic disruption caused by rising sea levels.
EUROPE: Mediterranean countries can brace for a higher risk of severe droughts, reduced harvests and deadly heatwaves.
High-latitude European nations will face flooding and severe weather, but this could be balanced by longer growing seasons and expanded areas for agriculture and forestry.
In Alpine regions, rising temperatures could badly damage the ski industry and wipe out up to 60 percent of plant and animal species.
The percentage of river basin areas that are "severely water stressed" is predicted to jump from 19 percent today between 34 and 36 percent in the 2070s.
Wintertime floods are likely to increase in Europe's maritime regions, while snowmelt-related floods and flash floods will hit central Europe.
Hydropower potential is expected to decline by 20-50 percent in the Mediterranean region but increase by 15-30 percent in Northern and Eastern Europe.
Biodiversity will be badly affected: "A large percentage of the European flora is likely to become vulnerable, endangered, or committed to extinction by the end of this century," the report says.
AMERICAS: Global warming will power up tropical storms and heatwaves in North America and threaten species extinction and hunger in the South.
Common to each American hemisphere will be a greater burden from water stress and health risks from heat, storms, infectious disease and urban smog.
In Alaska and Canada, thawing of permafrost and loss of sea ice are set to accelerate, posing a threat to mammals such as seals and polar bears, encouraging invasive species and "severely" challenging the lifestyle of the native Inuit.
Fast-growing cities on the coast will be increasingly vulnerable to storms, which will be amplified by sea-level rise.
In the first decades of the 21st century, climate change will boost forest production and rain-fed agriculture. But this will be partly balanced by a greater range of insect pests and diseases.
In Latin America, tropical glaciers are "very likely" to disappear by the early 2020s, reducing water availability and hydropower generation in several countries.
Frequency and intensity of hurricanes in the Caribbean basin is likely to increase.
By the 2020s, between seven and 77 million people in Latin America are likely to suffer from inadequate water supplies, a figure that could rise to 60-150 million by 2100.
A rise of 2 C (3.6 F) and decreases in soil water would turn eastern Amazonia and the tropical forests of central and southern Mexico into savannah.
OCEANIA
Invasive species and habitat loss, species extinction and the resultant hit to tourism are risks that are "virtually certain" to increase in Australia, New Zealand and Pacific island nations.
The most vulnerable ecosystems are the Great Barrier Reef, southwestern Australia, the Kakadu wetlands, rainforests and alpine areas.
Water problems that already plague southern and eastern Australia are "very likely" to increase by 2030. River flow from Australia's Murray-Darling Basin could fall by 10-25 percent by 2050.
By 2050, agriculture and forestry products are likely to be reduced over "much" of southern and southeastern Australia and parts of eastern New Zealand. But in the south and west of New Zealand crop yields are likely to increase.
In Pacific island states, sea-level rise and increase in seawater temperature will accelerate beach erosion and degrade natural defences such as mangroves and coral reefs, in turn hitting tourism.
Port facilities at Suva, Fiji, and Apia, Samoa, could be swamped by a 0.5 metre (19.5-inch) rise in sea level combined with waves associated in a one-in-a-half-century cyclone. Farming production will fall by between two and 18 percent by 2030.
POLAR REGIONS
Arctic:
By 2100, the extent of Arctic sea ice could shrink by 22-33 percent, depending on the emissions scenario. Arctic glaciers, ice caps and the Greenland ice sheet will suffer "important reductions" in thickness and range, but this magnitude is difficult to predict.
Northern hemisphere permafrost is projected to decrease in extent by 20-35 percent by 2050. Seasonal thawing is likely to increase by 15-25 percent by this date. The runoff from this thaw will disrupt local ecosystems.
Climate change will have a major impact on the Arctic's four million people.
Antarctica:
Land ice loss from the Antarctic peninsula, which has had one of the highest observed increases in temperature anywhere in the world, will continue.
Projections for summer sea ice range from a slight increase to a near complete loss of summer sea ice.
Uncertainty surrounds the future of the Antarctic ice sheet, where most of the world's freshwater is locked up. There is evidence of deglaciation on the Western Antarctic ice sheet, but some experts suggest this could be a lingering result of the last Ice Age, some 12,000 years ago, rather than recent man-made global warming.
(Note: since the 2007 IPCC report, further evidence has emerged that has fuelled alarm for polar regions, notably the loss of several iceshelves in Antarctica and an abrupt shrinkage of summer ice in the Arctic).
Taken from.. http://www.spacedaily.com/2006/091129012558.dfuosq75.html
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