Edited by William C. Clark, Harvard University, Cambridge, MA, and approved January 29, 2010 (received for review June 23, 2009)
CO2 emissions from the burning of fossil fuels are the primary cause of global warming. Much attention has been focused on the CO2 directly emitted by each country, but relatively little attention has been paid to the amount of emissions associated with the consumption of goods and services in each country. Consumption-based accounting of CO2 emissions differs from traditional, production-based inventories because of imports and exports of goods and services that, either directly or indirectly, involve CO2 emissions. Here, using the latest available data, we present a global consumption-based CO2 emissions inventory and calculations of associated consumption-based energy and carbon intensities. We find that, in 2004, 23% of global CO2 emissions, or 6.2 gigatonnes CO2, were traded internationally, primarily as exports from China and other emerging markets to consumers in developed countries. In some wealthy countries, including Switzerland, Sweden, Austria, the United Kingdom, and France, >30% of consumption-based emissions were imported, with net imports to many Europeans of >4 tons CO2 per person in 2004. Net import of emissions to the United States in the same year was somewhat less: 10.8% of total consumption-based emissions and 2.4 tons CO2 per person. In contrast, 22.5% of the emissions produced in China in 2004 were exported, on net, to consumers elsewhere. Consumption-based accounting of CO2 emissions demonstrates the potential for international carbon leakage. Sharing responsibility for emissions among producers and consumers could facilitate international agreement on global climate policy that is now hindered by concerns over the regional and historical inequity of emissions.
Author contributions: S.J.D. and K.C. designed research; S.J.D. performed research; S.J.D. and K.C. analyzed data; and S.J.D. and K.C. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/cgi/content/full/0906974107/DCSupplemental.
*Note that carbon embodied in exports of petroleum products does not include the carbon physically contained in the products, but only the emissions required to produce and transport them. The carbon contained in these fossil fuels would appear in the inventory of production emissions of the country where the CO2 is released to the atmosphere. That CO2 emission would be assigned to the inventory of consumption emissions of the country where the goods or services produced by those emissions was consumed.
