Long-term natural variability and 20th century climate change
- aAtmospheric Sciences Group, Department of Mathematical Sciences, University of Wisconsin, Milwaukee, WI 53201
- bScripps Institution of Oceanography, University of California at San Diego, La Jolla, CA 92093
Communicated by Robert May, University of Oxford, Oxford, United Kingdom, July 31, 2009 (received for review February 20, 2009)
Global mean temperature at the Earth's surface responds both to externally imposed forcings, such as those arising from anthropogenic greenhouse gases, as well as to natural modes of variability internal to the climate system. Variability associated with these latter processes, generally referred to as natural long-term climate variability, arises primarily from changes in oceanic circulation. Here we present a technique that objectively identifies the component of inter-decadal global mean surface temperature attributable to natural long-term climate variability. Removal of that hidden variability from the actual observed global mean surface temperature record delineates the externally forced climate signal, which is monotonic, accelerating warming during the 20th century.
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