Using black carbon metrics in climate policy

Disclaimer: This publication was developed under Cooperative Agreement No. X3 83232801 awarded by the U.S. Environmental Protection Agency to the American Association for the Advancement of Science. It has not been formally reviewed by the EPA. The views expressed in this document are solely those of the author and do not necessarily reflect those of the Agency. The EPA does not endorse any products or commercial services mentioned in this publication.

Figures & data

Table 1. BC warming potentials.

	Original number from source paper	Fossil soot plus snow albedo	Direct BC effect	Direct BC plus snow albedo
Bond and Sun (2005)	680	NA	680	NA
Jacobson (2005)	330–700	420b	NA	NA
Hansen et al. (2007)	500	568a	885a	1272a
Jacobson (2007)	840–1280	765b	NA	1340b
	1500–2240
Reddy and Boucher (2007)	480/761	NA	480	761
Rypdal et al. (2009)	640–1320c	NA	640–1130c	700–1320c
Bold numbers are the originals from source papers, italic numbers include calculations by this author. (a) Values for Hansen metrics extrapolated directly from underlying numbers provided in paper. Original value of 500 included estimate of aerosol indirect cloud effects. (b) Values for Jacobson metric are adjusted for lifetime differences: the 2005 paper assumed a lifetime of 30–95 years, and the 2007 testimony assumes a 30–50 year CO2 lifetime, whereas the Bern carbon cycle response function approximation from the IPCC AR4 effectively matches a CO2 lifetime of 58 years. Therefore, a factor of 0.6 can be applied to bring a GWP using a 30-year lifetime estimate into agreement with the Bern cycle approximation. (c) Rypdal et al. estimates are regional, not global.

Figure 1. (a) Word 3 Future US BC emissions from on-road sources under business as usual and also with a policy assuming that all diesel retrofits available for less than $50K/lifetime Mg of BC abated are implemented in 2010. (b) The tall, blue curve shows the radiative forcing change from the BC reductions in Figure 1a. The long, green curve shows the radiative forcing change from a reduction of CO₂ in each year of the program that would result from trading the BC reductions for CO₂ reductions at a GWP of 1000. This highlights the difference in the temporal nature of radiative forcing changes resulting from BC and CO₂ emission reductions.

Figure 2. US CO₂ equivalent emissions of BC by sector. Sensitivity ranges include the highest BC (including snow albedo effect) and lowest BC (no indirect effect) from Table 1. Net BC + OC includes negative CO₂ equivalents ranging from 0 (over ice and snow) to −250 (including indirect effects).