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Attribution of climate forcing to economic sectors
Edited by A R Ravishankara, NOAA Earth System Research Laboratory, Chemical Sciences Division, Boulder, CO 80305, and approved December 22, 2009 (received for review June 11, 2009)

Abstract
A much-cited bar chart provided by the Intergovernmental Panel on Climate Change displays the climate impact, as expressed by radiative forcing in watts per meter squared, of individual chemical species. The organization of the chart reflects the history of atmospheric chemistry, in which investigators typically focused on a single species of interest. However, changes in pollutant emissions and concentrations are a symptom, not a cause, of the primary driver of anthropogenic climate change: human activity. In this paper, we suggest organizing the bar chart according to drivers of change—that is, by economic sector. Climate impacts of tropospheric ozone, fine aerosols, aerosol-cloud interactions, methane, and long-lived greenhouse gases are considered. We quantify the future evolution of the total radiative forcing due to perpetual constant year 2000 emissions by sector, most relevant for the development of climate policy now, and focus on two specific time points, near-term at 2020 and long-term at 2100. Because sector profiles differ greatly, this approach fosters the development of smart climate policy and is useful to identify effective opportunities for rapid mitigation of anthropogenic radiative forcing.
Footnotes
- 1To whom correspondence should be addressed. E-mail: nunger{at}giss.nasa.gov.
Author contributions: N.U. designed research; and N.U. performed research; and N.U., T.C.B., J.S.W., D.M.K., S.M., D.T.S., and S.B. analyzed data; and N.U. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information on-line at www.pnas.org/cgi/content/full/0906548107/DCSupplemental.