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FACTBOX - The science spurring talks on a U.N. climate pact

(Reuters) - World leaders meet in New York on September 22 to try to revive stalled talks on a new climate treaty that were partly spurred by scientists’ bleak findings in 2007 about likely heatwaves, floods, desertification and rising sea levels.

Following are highlights of that report, by the U.N.’s Intergovernmental Panel on Climate Change (IPCC), and some more recent findings. IPCC chairman Rajendra Pachauri says evidence for global warming has strengthened in the past two years.


“Warming of the climate system is unequivocal,” the IPCC said. Two studies published in the past year found evidence of warming in Antarctica, the only continent previously outside the global trend.


The IPCC said it was “very likely” -- a 90 percent probability -- that most of the temperature rise in the past half century was because of human emissions of greenhouse gases, mostly from burning fossil fuels.


Temperatures are likely to rise by between 1.1 and 6.4 Celsius (2.0 and 11.5 Fahrenheit) and sea levels by between 18 cms and 59 cms (7-23 inches) this century -- by more if a thaw of Antarctica and Greenland accelerates, the IPCC said.

Africa, the Arctic, small islands and Asian mega-deltas are likely to be especially affected by climate change.

U.N. Secretary-General Ban Ki-moon said this month that sea levels may rise by 0.5 to 2 metres this century. He said that summer ice on the Arctic Ocean -- which shrank to a record low in 2007 -- could virtually disappear by 2030.


-- Risks to unique and threatened systems, such as polar or high mountain ecosystems, coral reefs and small islands.

-- Risks of extreme weather events, such as floods, droughts and heatwaves.

-- Distribution of impacts -- the poor and the elderly are likely to be hit hardest, and countries near the equator, mostly the poor in Africa and Asia, generally face greater risks such as of desertification or floods.

-- Overall impacts -- there is evidence since 2001 that any benefits of warming would be at lower temperatures than previously forecast and that damages from larger temperature rises would be bigger.

-- Risks of “large-scale singularities,” such as rising sea levels over centuries; contributions to sea level rise from Antarctica and Greenland could be larger than projected by ice sheet models.


Governments have a wide range of tools -- higher taxes on emissions, regulations, tradeable permits and research. An effective carbon price could help cuts, the IPCC said.

It said emissions of greenhouse gases would have to peak by 2015 to limit global temperature rises to 2.0 to 2.4 Celsius over pre-industrial times, the strictest goal assessed. In July 2009, the Group of Eight and major economies agreed at a summit in Italy to seek to limit warming to 2 Celsius.

The IPCC said costs of fighting warming will range from less than 0.12 percent of global gross domestic product (GDP) per year for the most stringent scenarios until 2030 to less than 0.06 percent for a less tough goal. In the most costly case, that means a loss of GDP by 2030 of less than 3 percent.