Three-Quarters of Climate Change Is Man-Made

http://www.scientificamerican.com/article.cfm?id=three-quarters-of-climate

By Quirin Schiermeier and Nature magazine | December 5, 2011

Natural climate variability is extremely unlikely to have contributed more than about one-quarter of the temperature rise observed in the past 60 years, reports a pair of Swiss climate modelers in a paper published online December 4. Most of the observed warming—at least 74 percent—is almost certainly due to human activity, they write in Nature Geoscience.

Since 1950, the average global surface air temperature has increased by more than 0.5 degree Celsius. To separate human and natural causes of warming, the researchers analyzed changes in the balance of heat energy entering and leaving Earth—a new "attribution" method for understanding the physical causes of climate change.

Their findings, which are strikingly similar to results produced by other attribution methods, provide an alternative line of evidence that greenhouse gases, and in particular carbon dioxide, are by far the main culprit of recent global warming. The massive increase of atmospheric CO2 concentrations since pre-industrial times would, in fact, have caused substantially more surface warming were it not for the cooling effects of atmospheric aerosols such as black carbon, they report.

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