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Global temperatures could rise substantially more because of increases in carbon dioxide in the atmosphere than previously thought, according to a new study by US and Chinese scientists whose findings appeared just two days after the UN climate summit failed to finalise strategies to reduce or curb global emissions of greenhouse gases.
Current computer simulations of future climate suggest that global temperature may rise by 1.5-4 degrees Celsius in response to a doubling of carbon dioxide. The new study shows that carbon dioxide doubling could raise temperatures by 7-9 degrees Celsius.
The researchers used a long-term model for assessing climate change, confirming a similar British study released recently that said calculations for man-made global warming may be underestimated by between 30-50%. The British study released on December 6 also researched the Pliocene Era, between 3-5 million years ago.
Their findings published online by Nature Geoscience focused on a period 3-5 million years ago -- the most recent episode of sustained global warming with a geography similar to today’s, a Yale University statement said. This was in order to look at the earth’s long-term sensitivity to climate fluctuations, including in changes to continental ice sheets and vegetation cover on land.
More common estimates for climate change are based on relatively rapid feedback to increases in carbon dioxide, such as changes to sea ice and atmospheric water vapour. The US and Chinese researchers studied the chemical composition of material drilled from several sites in the Pacific and the Atlantic, focusing on compounds produced by a family of algae sensitive to atmospheric carbon dioxide levels.
Using sediment drilled from the ocean floor, the scientists’ reconstruction of carbon dioxide concentrations found that “a relatively small rise in CO2 levels was associated with substantial global warming 4.5 million years ago”.
The researchers, using geochemical tools as peepholes into the earth’s history, found that a relatively small rise in atmospheric carbon dioxide was associated with substantial global warming about 4.5 million years ago. The new findings suggest that atmospheric carbon dioxide levels during peak temperatures were between 365 parts per million (ppm) and 415 ppm -- which is comparable to the present-day concentration of about 386 ppm.
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Infochange News & Features, January 2010
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