CO2 changes are found to have smaller impacts on temperature than first claimed

From the BBC:

Global temperatures could be less sensitive to changing atmospheric carbon dioxide (CO2) levels than previously thought, a study suggests.

The researchers said people should still expect to see "drastic changes" in climate worldwide, but that the risk was a little less imminent.

The results are published in Science.

Previous climate models have tended to used meteorological measurements from the past 150 years to estimate the climate's sensitivity to rising CO2.

From these models, scientists find it difficult to narrow their projections down to a single figure with any certainty, and instead project a range of temperatures that they expect, given a doubling of atmospheric CO2 from pre-industrial levels.

The new analysis, which incorporates palaeoclimate data into existing models, attempts to project future temperatures with a little more certainty.

Lead author Andreas Schmittner from Oregon State University, US, explained that by looking at surface temperatures during the most recent ice age - 21,000 years ago - when humans were having no impact on global temperatures, he, and his colleagues show that this period was not as cold as previous estimates suggest. . . .

The new models predict that given a doubling in CO2 levels from pre-industrial levels, the Earth's surface temperatures will rise by 1.7C to 2.6C (3.1F to 4.7F).

That is a much tighter range than the one produced by the Intergovernmental Panel on Climate Change's (IPCC) 2007 report, which suggested a rise of between 2.0C to 4.5C. . . .