A report led by Oregon State University’s Andreas Schmittner and published by the journal explains that CO2-linked warming measurements have tended to go back only 150 years, the BBC writes.
But the new study threw the thermometer back 21,000 years to the most recent ice age, and discovered that the earth was warmer then than earlier estimates had indicated. Thus, the planet has not warmed to the extent previously assumed.
"This implies that the effect of CO2 on climate is less than previously thought," Schmittner explained.
Assuming an eventual doubling of CO2 above pre-industrial levels, the report models a rise in Earth's surface temperatures of between 1.7C and 2.6C. That reins in a 2007 report by the Intergovernmental Panel on Climate Change, which projected a rise of between 2.0C to 4.5C given the same doubling.
Not that we’re off the hook.
“The researchers said people should still expect to see ‘drastic changes’ in climate worldwide, but that the risk was a little less imminent,” the BBC reports.
According to the New York Times, the results had surfaced earlier but made it into Science after peer review.
In a related Science article, Gabriele Hegerl from the University of Edinburgh was cautious about the findings. She recommended applying other models, according to the BBC.
And Climatologist Andrey Ganopolski, from Germany’s Potsdam Institute for Climate Impact Research, told the BBC that he would not make strong conclusions based on the new report, precisely because it incorporates temperatures from a colder period, when the relationship between CO2 and surface temperature was different than it is today.
"The results of this paper are the result of the analysis of [a] cold climate during the glacial maximum (the most recent ice age)," he said. "There is evidence the relationship between CO2 and surface temperatures is likely to be different [during] very cold periods than warmer."
Science has published a jargony abstract that will make sense to those of you who talk the talk.
Photos: Top, NASA/Kathryn Hansen via Flickr; Bottom, NASA Goddard Space Flight Center via Flickr