Final Report: Source Attribution of Radiative Forcing in Chemical Transport Models
EPA Grant Number:
Source Attribution of Radiative Forcing in Chemical Transport Models
Henze, Daven K
University of Colorado at Boulder
EPA Project Officer:
June 1, 2012 through
May 31, 2014
(Extended to May 31, 2016)
Source Attribution of Radiative Forcing in Chemical Transport (2011)
Global Climate Change
Air Quality and Air Toxics
The project objective was to account for the radiative forcing impacts of aerosols and tropospheric ozone (O3) from changes to their precursor emissions owing to air quality and greenhouse gas policies. This was accomplished through the following research tasks:
1. Quantify the impacts of emissions from each sector, in each model grid cell, on the global and regional radiative forcing of tropospheric O3 and aerosols.
2. Assess the radiative forcing consequences of emissions scenarios designed to target combinations of aerosol and greenhouse gas reductions.
This project focused on advancing and merging our studies of the impacts of short-lived climate forcers on both health and climate, and evaluating the transient climate impacts of both short-lived climate forcers and co-emitted greenhouse gases. Our initial work (Henze, et al., 2012) included the direct aerosol radiative forcing. Last year, we included indirect and semi-direct effects, as well as contributions from the albedo feedback of black carbon deposited on snow and ice (Lacey and Henze, 2015). This is achieved through the application of scaling factors to account for indirect and semi-direct forcing. These scaling factors draw from multi-model comparisons such as ACCMIP and the 5th Assessment Report of the Intergovernmental Panel on Climate Change (IPCC). To account for the contribution of BC emissions to the radiative forcing of BC deposition on snow and ice, we first perform an additional adjoint model calculation to estimate the contribution of emissions of BC in each grid cell to BC deposited on snow and ice. These results then are used to spatially distribute the global mean estimated snow/ice albedo radiative forcing of 0.15 Wm-2. In addition, while our first study focused on the impact of global radiative forcing, now we have considered regional radiative forcing, and combined these with absolute regional temperature potentials (ARTPs) derived from climate model simulations by Shindell (2012) to estimate the changes in temperature across four latitudinal bands associated aerosol precursor emissions. In the final year of this project, we extended these methods to estimate the transient climate responses to both aerosols and greenhouse gases, and we combined these estimated climate forcings with calculations of health impacts from PM2.5. These results are described in a manuscript in Proc. Nat. Acad. Sci. (Lacey, et al., 2017).
These updates to our attribution method have been applied in a case study estimating the climate impacts of carbonaceous aerosol from cookstoves (Lacey and Henze, 2015). Cookstove use is globally one of the largest unregulated anthropogenic sources of primary carbonaceous aerosol. While reducing cookstove emissions through national-scale mitigation efforts has clear benefits for improving indoor and ambient air quality, and significant climate benefits from reduced greenhouse gas (GHG) emissions, climate impacts associated with reductions to co-emitted black (BC) and organic carbonaceous (OC) aerosol are not well characterized. Here, we attribute direct, indirect, semi-direct, and snow/ice albedo radiative forcing and associated zonal surface temperature changes to national-scale carbonaceous aerosol cookstove emissions using a new combination of adjoint sensitivity modeling and climate-model parameterizations. Bounds are placed on these estimates, drawing from current literature ranges for aerosol radiative forcing along with a range of solid fuel emissions characterizations. We estimate a range of 0.16 K warming to 0.28 K cooling with a central estimate of 0.06 K cooling from the global removal of cookstove aerosol emissions. At the national scale, countries' climate impacts range from net warming (e.g., Mexico and Brazil) to net cooling, although the range of estimated impacts for all countries span zero given uncertainties in radiative forcing estimates and fuel characterization. We identify similarities and differences in the sets of countries with the highest emissions and largest cookstove temperature impacts (China, India, Nigeria, Pakistan, Bangladesh, and Nepal), those with the largest temperature impact per carbon emitted (Kazakhstan, Estonia, and Mongolia), and those that would provide the most efficient cooling from a switch to fuel with a lower BC emission factor (Kazakhstan, Estonia, and Latvia). For the year 2050, the impacts from the phased removal of global solid fuel cookstove emissions is a global average surface temperature cooling of 77 mK (ranging from a 20 mK warming to 278 mK cooling) and an avoidance of 260,000 (137,00 - 268,000) annual premature deaths due to ambient PM2.5 exposure cumulatively avoiding 10.5 (5.55 - 10.80) million cumulative premature deaths from 2000 to 2050. Aerosols contribute 41% to the central estimate of net global cookstove climate impacts by 2050 and alone may be cooling or warming with large uncertainties based on fuel type and aerosols' climate impacts. However, the net climate impacts of cookstove emissions reductions are very likely cooling, when considering the benefits of curbed GHG emissions, an aspect that becomes increasingly prominent on longer time-horizons. National-scale contributions of cookstove emissions to global premature deaths due to ambient PM2.5 exposure are driven by primary organic carbonaceous aerosol. The results presented here provide valuable information for climate impact assessments across a wide range of cookstove initiatives.
Fig. 1 The top 20 countries ranked in terms of three variables: population using solid fuels for cooking (blue), total net contribution to the global surface temperature change from the emissions from cookstove solid fuel emissions (green), and the total net contribution to global premature deaths from exposure to ambient PM2.5 from cookstove solid fuel emissions (red). From Lacey, et al.(2017).
on this Report
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Henze DK, Shindell DT, Akhtar F, Spurr RJD, Pinder RW, Loughlin D, Kopacz M, Singh K, Shim C. Spatially refined aerosol direct radiative forcing efficiencies. Environmental Science & Technology 2012;46:9511-9518.
Lacey F, Henze D. Global climate impacts of country-level primary carbonaceous aerosol from solid-fuel cookstove emissions. Environmental Research Letters 2015;10(11):114003
Lacey FG, Henze DK, Lee CJ, van Donkelaar A, Martin RV. Transient climate and ambient health impacts due to national solid fuel cookstove emissions. Proceedings of the National Academy of Sciences 2017;114(6):1269-1274.
Shindell DT. Evaluation of the absolute regional temperature potential. Atmospheric Chemistry and Physics 2012;12(17):7955-7960.
adjoint sensitivity, environmental policy, air quality regulations, fine particulate matter, PM2.5, climate change, remote sensing
Progress and Final Reports:
2012 Progress Report
2013 Progress Report
2014 Progress Report