Quantifying immediate radiative forcing by black carbon and organic matter with the Specific Forcing Pulse

Abstract

Abstract. Climatic effects of short-lived climate forcers (SLCFs) differ from those of long-lived greenhouse gases, because they occur rapidly after emission and because they depend upon the region of emission. The distinctive temporal and spatial nature of these impacts is not captured by measures that rely on global averages or long time integrations. Here, we propose a simple measure, the Specific Forcing Pulse (SFP), to quantify climate warming or cooling by these pollutants, where we define "immediate" as occurring primarily within the first year after emission. SFP is the amount of energy added to or removed from a receptor region in the Earth-atmosphere system by a chemical species, per mass of emission in a source region. We limit the application of SFP to species that remain in the atmosphere for less than one year. Metrics used in policy discussions, such as total forcing or global warming potential, are easily derived from SFP. However, SFP conveys purely physical information without incurring the policy implications of choosing a time horizon for the global warming potential.Using one model (Community Atmosphere Model, or CAM), we calculate values of SFP for black carbon (BC) and organic matter (OM) emitted from 23 source-region combinations. Global SFP for both atmosphere and cryosphere impacts is divided among receptor latitudes. SFP is usually greater for open-burning emissions than for energy-related (fossil-fuel and biofuel) emissions because of the timing of emission. Global SFP for BC varies by about 45% for energy-related emissions from different regions. This variation would be larger except for compensating effects. When emitted aerosol has larger cryosphere forcing, it often has lower atmosphere forcing because of less deep convection and a shorter atmospheric lifetime.Correspondence to: T. C. Bond (yark@illinois.edu) A single model result is insufficient to capture uncertainty. We develop a best estimate and uncertainties for SFP by combining forcing results from 12 additional models. We outline a framework for combining a large number of simple models with a smaller number of enhanced models that have greater complexity. Adjustments for black carbon internal mixing and for regional variability are discussed. Emitting regions with more deep convection have greater model diversity. Our best estimate of global-mean SFP is +1.03 ± 0.52 GJ g −1 for direct atmosphere forcing of black carbon, +1.15 ± 0.53 GJ g −1 for black carbon including direct and cryosphere forcing, and −0.064 (−0.02, −0.13) GJ g −1 for organic matter. These values depend on the region and timing of emission. The lowest OM:BC mass ratio required to produce a neutral effect on top-ofatmosphere direct forcing is 15:1 for any region. Any lower ratio results in positive direct forcing. However, important processes, particularly cloud changes that tend toward cooling, have not been included here.Global-average SFP for energy-related emissions can be converted to a 100-year GWP of about 740 ± 370 for BC without snow forcing, and ...

Global and regional temperature-change potentials for near-term climate forcers

“…Hence, provided that the time horizon chosen is much longer than the lifetime of the aerosol (α H ), the AGWP is also simply equal to the equilibrium response to a unit step change in emissions and is independent of the time horizon. A similar argument was made by Bond et al (2011) where they introduced the specific forcing pulse (SFP) (units J kg −1 ). For short-lived species (α H ) the global SFP is simply a scaling of the AGWP.…”

“…The impact of BC deposition on snow albedo is also very uncertain. Bond et al (2011) estimate that it adds about 20 % to the RF for BC emissions from NA, EU and SA, and about 10 % for EA emissions. This might be expected to preferentially increase the temperature responses in the Arctic latitudes.…”

Black carbon concentration and deposition estimations in Finland by the regional aerosol–climate model REMO-HAM

“…atmosphere (a couple of days to less than 2 weeks), it has been considered as a candidate species for immediate reduction of climate forcing, as part of short-term climate control strategies (Levy et al, 2008;Bond et al, 2011;UNEP and WMO, 2011). Therefore, proper BC modelling is needed and stands out as being of great interest among atmospheric scientists.…”

Evaluation of the absolute regional temperature potential

“…The forcing per unit emission term is a single timeseries for emissions from any location for well-mixed greenhouse gases (WMGHGs), but for short-lived compounds this will depend on the location and timing of emissions (Berntsen et al, 2005;Bond et al, 2011;Naik et al, 2007). Recent studies have provided estimates of this term for short-lived species, including (Bond et al, 2011) and (Henze et al, 2012). The second term in the sum is a matrix hereafter called the RTP coefficients and abbreviated RTPcoeff a ,a where a and a indicate the forcing and response areas, respectively.…”