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Science  17 Jul 2009:
Vol. 325, Issue 5938, pp. 247
DOI: 10.1126/science.325_247c

Governmental representatives from almost every country will meet at the United Nations Climate Change Conference in Copenhagen, in December 2009, in order to attempt to agree on an effective international response to climate change. One of the thorniest and most important questions on the table is how best to determine CO2 emission reduction targets for the various participating countries. This task is rendered more difficult by the asymmetry between developed nations, whose emissions have caused most of the increase in atmospheric CO2 thus far; and less-developed nations, whose emissions have been low in the past but are expected to grow at a faster than average rate in the future. Chakravarty et al. propose that national reduction targets, for the near term, be based not on per capita emissions, but on the net excess emissions from the individual high emitters that are found in every country. This approach has the advantages of treating equally all those with the same emissions, regardless of nationality, and of not specifying how any nation meet its responsibilities for reducing CO2 emissions.

Proc. Natl. Acad. Sci. U.S.A. 106, 10.1073/pnas.0905232106 (2009).

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