Edited by William C. Clark, Harvard University, Cambridge, MA, and approved April 17, 2007 (received for review January 23, 2007)
CO2 emissions from fossil-fuel burning and industrial processes have been accelerating at a global scale, with their growth rate increasing from 1.1% y−1 for 1990–1999 to >3% y−1 for 2000–2004. The emissions growth rate since 2000 was greater than for the most fossil-fuel intensive of the Intergovernmental Panel on Climate Change emissions scenarios developed in the late 1990s. Global emissions growth since 2000 was driven by a cessation or reversal of earlier declining trends in the energy intensity of gross domestic product (GDP) (energy/GDP) and the carbon intensity of energy (emissions/energy), coupled with continuing increases in population and per-capita GDP. Nearly constant or slightly increasing trends in the carbon intensity of energy have been recently observed in both developed and developing regions. No region is decarbonizing its energy supply. The growth rate in emissions is strongest in rapidly developing economies, particularly China. Together, the developing and least-developed economies (forming 80% of the world's population) accounted for 73% of global emissions growth in 2004 but only 41% of global emissions and only 23% of global cumulative emissions since the mid-18th century. The results have implications for global equity.
Author contributions: M.R.R., P.C., C.L.Q., J.G.C., and C.B.F. designed research; M.R.R., G.M., P.C., and J.G.C. performed research; M.R.R., G.M., P.C., and G.K. analyzed data; and M.R.R., G.M., G.K., and C.B.F. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
↵ ‡‡ CO2 data are available at www.cmdl.noaa.gov/gmd/ccgg/trends.
↵ §§ Yamaji, K., Matsuhashi, R., Nagata, Y., Kaya, Y., An Integrated System for CO2/Energy/GNP Analysis: Case Studies on Economic Measures for CO2 Reduction in Japan. Workshop on CO2 Reduction and Removal: Measures for the Next Century, March 19, 1991, International Institute for Applied Systems Analysis, Laxenburg, Austria.
This article contains supporting information online at www.pnas.org/cgi/content/full/0700609104/DCI.
↵ ¶¶ EIA, www.eia.doe.gov/emeu/international/energyconsumption.html; CDIAC, http://cdiac.esd.ornl.gov/trends/emis/tre_coun.htm; United Nations Statistics Division, http://unstats.un.org/unsd/snaama/selectionbasicFast.asp; and World Economic Outlook of the International Monetary Fund, www.imf.org/external/pubs/ft/weo/2006/02/data/download.aspx.
Freely available online through the PNAS open access option.
