Distinguishing Aerosol Impacts on Climate over the Past Century

Koch, D.; Menon, Surabi; Genio, Anthony D. Del; Ruedy, R.; Igor, Alienov,; Schmidt, Gavin A.

doi:10.1175/2008jcli2573.1

Cited by 141 publications

(145 citation statements)

References 49 publications

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“…We estimate the AIE by taking the difference in net cloud radiative forcing between time periods (Figure 2) for the simulations with ACI and the simulations without. The past AIE is −2.0 Wm −2 , higher than previous GISS model estimates (Menon et al, 2008a;Koch et al, 2009) and estimates based on constraints from the temperature record using a parameterized AIE treatment in a similar version of the GISS model (Hansen et al, 2005). However, changes in CDNC in the Koch et al (2009) simulations are about half of that obtained in this study since the Koch et al study used a different set of emissions that had a lower sulfate burden change.…”

Section: Aerosol Direct Radiative Forcing and Aiecontrasting

confidence: 59%

“…As expected CC increased from PI to PD due to ACI. Without including aerosol-induced changes to clouds, CC decreases between PD and PI, due to climate-related changes that tend to decrease CC with increased GHG warming, as also found by Koch et al (2009). Figure 1 shows the spatial distribution of the aerosol-induced changes in cloud properties between PD-PI and 2050-PD.…”

Section: Resultsmentioning

confidence: 82%

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Impacts of aerosol-cloud interactions on past and future changes in tropospheric composition

et al. 2009

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Abstract. The development of effective emissions control policies that are beneficial to both climate and air quality requires a detailed understanding of all the feedbacks in the atmospheric composition and climate system. We perform sensitivity studies with a global atmospheric composition-climate model to assess the impact of aerosols on tropospheric chemistry through their modification on clouds, aerosol-cloud interactions (ACI). The model includes coupling between both tropospheric gas-phase and aerosol chemistry and aerosols and liquid-phase clouds. We investigate past impacts from preindustrial (PI) to present day (PD) and future impacts from PD to 2050 (for the moderate IPCC A1B scenario) that embrace a wide spectrum of precursor emission changes and consequential ACI. The aerosol indirect effect (AIE) is estimated to be −2.0 Wm −2 for PD-PI and −0.6 Wm −2 for 2050-PD, at the high end of current estimates. Inclusion of ACI substantially impacts changes in global mean methane lifetime across both time periods, enhancing the past and future increases by 10% and 30%, respectively. In regions where pollution emissions increase, inclusion of ACI leads to 20% enhancements in in-cloud sulfate production and ∼10% enhancements in sulfate wet deposition that is displaced away from the immediate source regions. The enhanced in-cloud sulfate formation leads to larger increases in surface sulfate across polluted regions (∼10-30%). Nitric acid wet deposition is dampened by 15-20% across the industrialized regions due to ACI allowing additional re-release of reactive nitrogen that contributes to 1-2 ppbv increases in surface ozone in outflow regions. Our model findings indicate that ACI must be considered in studCorrespondence to: N. Unger (nunger@giss.nasa.gov) ies of methane trends and projections of future changes to particulate matter air quality.

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Section: Aerosol Direct Radiative Forcing and Aiecontrasting

confidence: 59%

Section: Resultsmentioning

confidence: 82%

Impacts of aerosol-cloud interactions on past and future changes in tropospheric composition

et al. 2009

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“…2 in Warren and Wiscombe (1995). The resulting decrease in snow albedo averaged over the Arctic is 0.4 % in winter and 0.8 % in spring 2008 (0.6 % for spring [2007][2008][2009]), lower than previous estimates of 1.1-4.7 % Koch et al, 2009a). By convolving this result with the GEOS-5 incoming solar radiation at the surface we deduce a surface radiative forcing over the Arctic ( …”

Section: Bc Deposition In the Arctic And Implications For Radiative Fmentioning

confidence: 68%

“…The vertical distribution of aerosols has important implications for radiative forcing (Koch et al, 2009a). Two coordinated aircraft campaigns with carbonaceous aerosol measurements were conducted in April 2008 out of Fairbanks, Alaska: the NASA Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) and the NOAA Aerosol, Radiation and Cloud Processes affecting Arctic Climate (ARCPAC) .…”

Section: Introductionmentioning

confidence: 99%

Sources of carbonaceous aerosols and deposited black carbon in the Arctic in winter-spring: implications for radiative forcing

et al. 2011

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Abstract. We use a global chemical transport model (GEOSChem CTM) to interpret observations of black carbon (BC) and organic aerosol (OA) from the NASA ARCTAS aircraft campaign over the North American Arctic in April 2008, as well as longer-term records in surface air and in snow (2007)(2008)(2009). BC emission inventories for North America, Europe, and Asia in the model are tested by comparison with surface air observations over these source regions. Russian open fires were the dominant source of OA in the Arctic troposphere during ARCTAS but we find that BC was of prevailingly anthropogenic (fossil fuel and biofuel) origin, particularly in surface air. This source attribution is confirmed by correlation of BC and OA with acetonitrile and sulfate in the model and in the observations. Asian emissions are the main anthropogenic source of BC in the free troposphere but European, Russian and North American sources are also important in surface air. Russian anthropogenic emissions appear to dominate the source of BC in Arctic surface air in winter. Model simulations for 2007-2009 (to account for interannual variability of fires) show much higher BC snow content in the Eurasian than the North American Arctic, consistent with the limited observations. We find that anthropogenic sourcesCorrespondence to: Q. Wang (wang2@fas.harvard.edu) contribute 90 % of BC deposited to Arctic snow in JanuaryMarch and 60 % in April-May 2007-2009. The mean decrease in Arctic snow albedo from BC deposition is estimated to be 0.6 % in spring, resulting in a regional surface radiative forcing consistent with previous estimates.

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“…Koch et al (2009) summarized cryosphere forcing estimates, which range from +0.01 to +0.16 W m −2 and vary widely with the method of parameterization and the reference value of emission. However, some of these estimates use different emission rates and some are less physically based.…”

Section: Total Cryosphere Forcingmentioning

confidence: 99%

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

et al. 2011

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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 ...

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Distinguishing Aerosol Impacts on Climate over the Past Century

Cited by 141 publications

References 49 publications

Impacts of aerosol-cloud interactions on past and future changes in tropospheric composition

Impacts of aerosol-cloud interactions on past and future changes in tropospheric composition

Sources of carbonaceous aerosols and deposited black carbon in the Arctic in winter-spring: implications for radiative forcing

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

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