Valuing the Ozone-Related Health Benefits of Methane Emission Controls

Environ Resource Econ DOI 10.1007/s10640-015-9937-6 Valuing the Ozone-Related Health Benefits of Methane Emission Controls Marcus C. Sarofim1 · Stephanie T. Waldhoff2 · Susan C. Anenberg3 Accepted: 11 June 2015 © The Author(s) 2015. This article is published with open access at Springerlink.com Abstract Methane is a greenhouse gas that oxidizes to form ground-level ozone, itself a greenhouse gas and a health-harmful air pollutant. Reducing methane emissions will both slow anthropogenic climate change and reduce ozone-related mortality. We estimate the benefits of reducing methane emissions anywhere in the world for ozone-related premature mortality globally and for eight geographic regions. Our methods are consistent with those used by the US Government to estimate the social cost of carbon (SCC). We find that the global short- and long-term premature mortality benefits due to reduced ozone production from methane mitigation are (2011) $790 and $1775 per tonne methane, respectively. These correspond to approximately 70 and 150 % of the valuation of methane’s global climate impacts using the SCC after extrapolating from carbon dioxide to methane using global warming potential estimates. Results for monetized benefits are sensitive to a number of factors, particularly the choice of elasticity to income growth used when calculating the value of a statistical life. The benefits increase for emission years further in the future. Regionally, most of the global mortality benefits accrue in Asia, but 10 % accrue in the United States. This methodology can be used to assess the benefits of methane emission reductions anywhere in the world, including those achieved by national and multinational policies. Marcus C. Sarofim, Stephanie T. Waldhoff and Susan C. Anenberg have contributed equally to this work. B Marcus C. Sarofim Stephanie T. Waldhoff Susan C. Anenberg 1 U.S. Environmental Protection Agency (USEPA, 6207A), 1200 Pennsylvania Ave NW, Washington, DC 20460, USA 2 Joint Global Change Research Institute, Pacific Northwest National Laboratory, College Park, MD, USA 3 Environmental Health Analytics, LLC, Washington, DC, USA 123 M. C. Sarofim et al. Keywords Methane · Ozone · Mortality · Air pollution · SCC 1 Introduction Methane (CH4 ) is a relatively short-lived and potent greenhouse gas. It also reacts in the atmosphere to form ground-level ozone (O3 ) that is itself is a greenhouse gas as well as a pollutant that is associated with adverse health effects such as impaired respiratory health and premature mortality (US Environmental Protection Agency 2012) and damaged vegetation. Methane is emitted by natural sources, such as wetlands, and anthropogenic sources, such as agriculture, coal mines, municipal solid waste, oil and gas systems, and wastewater. Anthropogenic activities contribute approximately 50–65 % of total global methane emissions (IPCC 2013). While methane has long been considered to be an important greenhouse gas to target for climate change mitigation and is included in the basket of climate pollutants under the United Nations Framework Convention on Climate Change (UNFCCC), it has only recently been appreciated as a potential method to control surface ozone concentrations (West et al. 2006). Two voluntary international efforts, the Climate and Clean Air Coalition to Reduce ShortLived Climate Pollutants1 (CCAC) and the Global Methane Initiative,2 aim to reduce methane emissions from anthropogenic sources. Many national efforts that achieve methane emission reductions as a primary target or as a co-benefit are also underway, including regulations like the Oil and Natural Gas Air Pollution Standards and voluntary programs like the Natural Gas STAR Program, the AgSTAR Program, and the Landfill Methane Outreach Program in the US Given the many methane mitigation activities ongoing at international and national scales, valuing both the climate and health benefits of national and international actions to control methane emissions3 can inform policy decision-making. Although the 12-year methane lifetime is shorter than that of many greenhouse gases (e.g., N2 O has a lifetime of 110 years, chloro- and perfluoro-carbons lifetimes of thousands of years, and while CO2 doesn’t have a single lifetime, it is added to the carbon cycle for millennia), it lives longer in the atmosphere than the other major ozone precursors (nitrogen oxides, nonmethane volatile organic compounds, and carbon monoxide), with atmospheric lifetimes on the order of weeks or months depending on the gas (IPCC 2007). Ozone is formed as product of the methane oxidation process, and as a result, ozone production via methane occurs on the same decadal time scale as methane’s lifetime, long enough to be globally well-mixed in the atmosphere [e.g., (West et al. 2006)]. Therefore, the ozone response to methane emission reductions is mostly insensitive to the location in which the emissions were reduced (ibid). The relative uniformity of the ozone response to methane emissions allows for the quantification of ozone benefits for a particular location per tonne of methane emission reduced anywhere in the world. Similarly, the climate benefits of marginal reductions in methane, known as the Social Cost of Methane (SC–CH4 ) have been estimated in the literature [e.g. (Marten et al. 2014; Marten and Newbold 2012; Waldhoff et al. 2014)]. The US Government has also calculated benefits of methane reduction using the Social Cost of Carbon4 (SCC) and 1 www.unep.org/ccac. 2 https://www.globalmethane.org/. 3 Throughout this paper we refer to the benefits of methane mitigation, though our estimates are equally valid to estimate the damages of increases in CH4 emissions. For simplicity, we restrict our language to focus on the benefits of mitigation. 4 The SCC, as used by the US Government, is valued in units of $/t–CO . 2 123 Valuing the Ozone-Related Health Benefits of Methane Emission. . . the Global Warming Potential (GWP) of methane. Using a GWP of 25 (IPCC 2007) yields climate change benefits of (2011)$1,150/t–CH4 in 2020. The global ozone mortality benefits of methane mitigation estimated in this paper are of similar magnitude to the monetized climate benefits of methane mitigation. As we refer to it in this paper, the “social cost” of methane refers only to the climate impacts, though the term could be used to refer to all the impacts of methane including the health and agricultural impacts resulting from methane oxidation. A cost-benefit analysis can then be done by comparing these marginal benefits— SC–CH4 and ozone-related mortality—to the marginal cost of an emission control strategy. Previously, studies have used global chemical transport modeling to estimate the premature mortality impact of ozone reductions resulting from large reductions in methane emissions or concentration. These studies estimated that reductions of 20 % in anthropogenic methane emissions (West et al. 2006) or in (...truncated)