The social cost of atmospheric release

The social cost of atmospheric release Drew T. Shindell 0 ) Nicholas School of the Environment, Duke University , PO Box 90328, Durham, NC 27708 , USA I present a multi-impact economic valuation framework called the Social Cost of Atmospheric Release (SCAR) that extends the Social Cost of Carbon (SCC) used previously for carbon dioxide (CO2) to a broader range of pollutants and impacts. Values consistently incorporate health impacts of air quality along with climate damages. The latter include damages associated with aerosol-induced hydrologic cycle changes that lead to net climate benefits when reducing cooling aerosols. Evaluating a 1 % reduction in current global emissions, benefits with a high discount rate are greatest for reductions of co-emitted products of incomplete combustion (PIC), followed by sulfur dioxide (SO2), nitrogen oxides (NOx) and then CO2, ammonia and methane. With a low discount rate, benefits are greatest for PIC, with CO2 and SO2 next, followed by NOx and methane. These results suggest that efforts to mitigate atmosphere-related environmental damages should target a broad set of emissions including CO2, methane and aerosol/ozone precursors. Illustrative calculations indicate environmental damages are $330-970 billion yr1 for current US electricity generation (~14-34 per kWh for coal, ~4-18 for gas) and $3.80 (1.80/+2.10) per gallon of gasoline ($4.80 (3.10/+3.50) per gallon for diesel). These results suggest that total atmosphere-related environmental damages plus generation costs are much greater for coal-fired power than other types of electricity generation, and that damages associated with gasoline vehicles substantially exceed those for electric vehicles. - To examine these issues, I explore here the economic damages associated with a marginal change in the atmospheric release of individual pollutants owing to their effects on climate and air quality. Prior studies have provided compelling demonstrations of the importance of linkages between climate change and air quality valuation (e.g. (Caplan and Silva 2005; Nemet et al. 2010; Tollefsen et al. 2009)) and of the incorporation of economics into emission metrics (e.g. (Johansson 2012; Tanaka et al. 2013)), but typically have not fully represented the climate impact of short-lived emissions, especially aerosols and methane (e.g. (International Monetary Fund 2013; Muller et al. 2011; NRC 2010)). As opposed to previous estimates of damages associated with particular activities (e.g. electricity generation (European Commission 1995)), the general values presented here allow valuation of the impact of any sector or any policy scenario whose emissions are known. While many uncertainties remain in this type of analysis, and hence caution is advised in using these values in policy decisions, this evaluation of a wide variety of pollutants nevertheless allows exploration of how society values human welfare at different timescales and in response to different environmental threats. This work builds upon the Social Cost of Carbon (SCC), a widely used methodology for valuation of the estimated damages associated with an incremental increase in carbon dioxide (CO2) emissions in a given year. The US Government describes it as being Bintended to include (but not limited to) changes in net agricultural productivity, human health, property damages from increased flood risk, and the value of ecosystem services due to climate change.^ (US Government 2013; hereafter USG 2013; see also Electronic Supplementary Material (ESM)). Thus social costs for emissions of other pollutants should at minimum include their impacts on these same quantities (health, agriculture, etc.). This applies even when their effects take place via different processes than for CO2. For example, pollutants such as black carbon (BC), organic carbon (OC), sulfur dioxide (SO2) or methane (CH4), affect human health both by altering climate as CO2 does (hereafter climate-health impacts) but also by more directly degrading air quality (hereafter composition-health impacts). Hence this work assesses impacts of atmospheric pollutants regardless of the route by which they occur. It thus also builds upon prior valuation of air quality-related health impacts of emissions (e.g. (Muller et al. 2011)). Ideally, the social costs of emissions to the atmosphere should include all affected components of human welfare. Here I evaluate a broad Social Cost of Atmospheric Release (SCAR) for emissions of the pollutants that are the major drivers of global mean climate change (Myhre et al. 2013) and of the global health burden from poor air quality (particulate matter and ozone; (Lim et al. 2012)) (Table 1). Unlike the SCC, which has nearly always been evaluated for well-mixed greenhouse gases only, the SCAR metric spans a wide range of pollutants, and thus facilitates discussion of the relative importance of those emissions with primarily a near-term influence (years to decades; aerosols, ozone precursors, methane and HFC-134a), including their compositionhealth impacts, and those with effects that are large over long-terms (centuries; long-lived greenhouse gases such as CO2 and N2O). 2 Methods 2.1 Basic climate damages The first component of the SCAR is climate damages that are proportional to global mean surface temperature change (equivalent to the traditional SCC). Global mean temperature changes are driven by the global mean radiative forcing (RF) caused by each emitted Table 1 Pollutants examined here and their major impacts Enhanced regional hydrologic cycle impact See ESM section 1.1 for discussion of additional pollutants that could be examined a The global mean surface temperature impact is also a proxy for the many additional climate impacts that occur alongside global mean temperature change, including changes in sea-level, rainfall, heatwaves, etc b The uncertainty encompasses this agent causing warming c Valuation of the health impacts of mercury emissions has been performed for the US (see ESM section 5), and is discussed in the calculations of US sectoral impacts only compound. RF for most emissions is based on the IPCC AR5 (Myhre et al. 2013). RF attributable to individual aerosol precursors including indirect cloud effects was not provided in AR5, and hence to incorporate this important component for SO2, BC and OC I use a combination of modeling and literature analysis (Shindell et al. 2012a; Shindell et al. 2009; United Nations Environment Programme and World Meteorological Organization 2011; hereafter UNEP 2011; see ESM). The relative uncertainties in RF presented in the AR5 (Myhre et al. 2013) are used for all emissions. These uncertainties, and all others used here, are assumed to be 595 % confidence intervals (CI). Forcing by non-CO2 emissions includes a component driven by the response of the carboncycle to temperature changes induced by those emissions (as in the calculations for CO2 itself) based on a reduced carbon upt (...truncated)