Climate Benefits of U.S. EPA Programs and Policies That Reduced

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Policy Analysis

Climate benefits of U.S. EPA programs and policies that reduced methane emissions 1993-2013 April M Melvin, Marcus Sarofim, and Allison R. Crimmins Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b00367 • Publication Date (Web): 26 May 2016 Downloaded from http://pubs.acs.org on May 31, 2016

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Environmental Science & Technology

Climate benefits of U.S. EPA programs and policies that reduced methane emissions 1993-2013

April M. Melvin, [email protected], [email protected] AAAS S&T Policy Fellow hosted by the Climate Change Division, U.S. Environmental Protection Agency, 1200 Pennsylvania Ave. NW, Washington, DC 20460, USA

Marcus C. Sarofim*, [email protected] Climate Change Division, U.S. Environmental Protection Agency U.S. Environmental Protection Agency, 1200 Pennsylvania Ave. NW, Washington, DC 20460, USA *corresponding author

Allison R. Crimmins, [email protected] Climate Change Division, U.S. Environmental Protection Agency U.S. Environmental Protection Agency, 1200 Pennsylvania Ave. NW, Washington, DC 20460, USA

ACS Paragon Plus Environment


Table of Contents and Abstract Graphic Methane Global concentration

1993

Atm. conc.

Reductions

1993

2013

Temperature rise 1993

2013

∆T

Domestic reductions

2013


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1

Abstract

2

The United States (U.S.) Environmental Protection Agency (EPA) has established voluntary

3

programs to reduce methane (CH4) emissions, and regulations that either directly reduce CH4 or

4

provide co-benefits of reducing CH4 emissions while controlling for other air pollutants. These

5

programs and regulations address four sectors that are among the largest domestic CH4 emissions

6

sources: municipal solid waste landfills, oil and natural gas, coal mining, and agricultural manure

7

management. Over the 1993-2013 time period, 127.9 Tg of CH4 emissions reductions were

8

attributed to these programs, equal to about 18% of the counterfactual (or potential) emissions

9

over that time, with almost 70% of the abatement due to landfill sector regulations. Reductions

10

attributed to the voluntary programs increased nearly continuously during the study period. We

11

quantified how these reductions influenced atmospheric CH4 concentration and global

12

temperature, finding a decrease in concentration of 28 ppb and an avoided temperature rise of

13

0.006 °C by 2013. Further, we monetized the climate and ozone-health impacts of the CH4

14

reductions, yielding an estimated benefit of $255 billion. These results indicate that EPA

15

programs and policies have made a strong contribution to CH4 abatement, with climate and air

16

quality benefits.

17 18

Introduction

19

Atmospheric methane (CH4) concentrations have increased by about 150% since the industrial

20

revolution,1 due largely to human activities2 associated with fossil fuel extraction and

21

distribution, agricultural practices, waste management, and biomass burning.3 Methane is a

22

greenhouse gas (GHG) that contributes directly to climate warming due to its radiative

23

properties, as well as indirectly due to the photochemical production of other GHGs, including



24

stratospheric water vapor and tropospheric ozone (O3).4 Tropospheric O3 in turn, is a pollutant

25

linked to reduced air quality, human mortality and hospitalizations,5-9 and damage to agricultural

26

crops and other terrestrial plants.10-12 After carbon dioxide (CO2), CH4 is the largest driver of the

27

anthropogenic increase in radiative forcing (RF) and therefore contributes substantially to

28

climate warming.4

29 30

Methane has an atmospheric perturbation lifetime of about 12 years.4 Therefore, decreasing CH4

31

emissions could reduce the atmospheric CH4 concentration over relatively short time scales and

32

provide near-term climate benefits,3, 13, 14 while also lessening impacts of tropospheric O3

33

pollution on human health and terrestrial ecosystems.11 The United States (U.S.) Environmental

34

Protection Agency (EPA) has developed numerous programs and policies to reduce CH4

35

emissions. These include the establishment of voluntary emissions reductions programs,

36

regulations that directly limit vehicle CH4 emissions, and regulations that require control of other

37

pollutants, which provide the co-benefit of also capturing CH4. Collectively, these regulatory and

38

voluntary activities have focused on many of the largest CH4 emissions sources in the U.S.

39

including oil and natural gas systems, municipal solid waste landfills, coal mining, and animal

40

manure management, and have increased the fraction of CH4 emissions being controlled through

41

capture and/or combustion, instead of being emitted directly to the atmosphere. The EPA has

42

recently proposed additional regulations that would directly limit CH4 emissions in landfill and

43

oil and gas sectors. The analysis presented here is retrospective and does not quantitatively

44

address proposed rules or any future reductions from existing programs.

45


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Domestic efforts to reduce emissions from dominant sources date back to the early 1990s, when

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researchers at the EPA noted that capturing and utilizing CH4 could provide a cost-effective

48

strategy to reduce CH4 emissions while also providing a new fuel source, since CH4 is the

49

primary component of natural gas.13, 14 In 1993, the Clinton Administration put forth a Climate

50

Change Action Plan15 that directed the EPA to expand a newly formed Natural Gas STAR

51

partnership program (www.epa.gov/gasstar) that fosters public/private partnerships and promotes

52

the use of cost-effective technologies and practices to capture and use CH4 within the natural gas

53

sector.15 The Plan further called for the development of CH4 outreach and assistance programs to

54

facilitate the capture and use of CH4 produced at landfills and coal mines, and from animal

55

manure, leading to the creation of three additional voluntary CH4 emissions reductions programs

56

in 1994. The Landfill Methane Outreach Program (LMOP, www.epa.gov/lmop) and Coalbed

57

Methane Outreach Program (CMOP, www.epa.gov/cmop) were developed to address CH4

58

emissions from small municipal solid waste landfills and coal mining operations, respectively.

59

The AgSTAR program (www.epa.gov/agstar) was developed in collaboration with the U.S.

60

Department of Agriculture and was tasked with reducing CH4 emissions produced during liquid

61

manure management by encouraging biogas recovery and use. In each of these programs, strong

62

emphasis was placed on the development of voluntary partnerships between the federal, state,

63

and local governments, as well as with businesses and industry. These voluntary programs

64

subsequently provided the foundation for the creation of the Global Methane Initiative

65

(www.globalmethane.org), an international voluntary CH4 emissions abatement program

66

established in 2004. Programs also maintain a close relationship with the Climate and Clean Air

67

Coalition (www.ccacoalition.org), launched in 2012.

68



69

Federal regulations have provided both direct and indirect approaches to addressing CH4

70

emissions. Limits on CH4 emissions from light-duty16, 17 and medium- and heavy-duty vehicles18

71

were established to prevent increases in CH4 emissions from these sources. These are the only

72

existing U.S. regulations that directly regulate CH4 for climate purposes. Indirect CH4 emissions

73

reductions have resulted from the required control of other pollutants that pose a risk to human

74

health. Methane is co-emitted with volatile organic compounds and hazardous air pollutants from

75

some sources, including landfills and oil and natural gas production. Because the methane is co-

76

emitted, the capture and combustion targeting these other pollutants has the co-benefit of also

77

capturing CH4. This gas can then be either flared or used as an energy source. Regulations

78

providing this co-benefit include the 1996 “Landfill Rule”19 (and associated amendments20-22),

79

requiring the reduction of non-methane organic compounds from gas produced in large

80

municipal solid waste landfills, and the National Emissions Standards for Hazardous Air

81

Pollutants (NESHAP) Rule established in 1999 for oil and natural gas activities23 and expanded

82

in 200724 and 2012.25 In 2012, New Source Performance Standards (NSPS) were also finalized

83

for crude oil and natural gas production.25 In the coal mining and manure management sectors,

84

no federal regulations are currently in place (or proposed) that limit CH4 emissions.

85 86

The EPA continues to build on existing voluntary programs and regulations to further reduce

87

domestic CH4 emissions and address climate change. In March 2014, The White House released

88

the “Strategy to Reduce Methane Emissions”26 as part of President Obama’s Climate Action

89

Plan. This policy statement called for continued support and expansion of all domestic voluntary

90

CH4 programs and development of new regulatory actions. In July 2015, the EPA announced the

91

Natural Gas STAR Methane Challenge, a new voluntary initiative designed to increase voluntary


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CH4 abatement from oil and gas. New regulations have also been proposed that would increase

93

restrictions on landfill gas emissions at existing landfills,27 limit emissions from new and

94

modified landfills,28 and would require control of CH4 emissions from certain new and modified

95

sources in the oil and gas sector.29

96 97

As the U.S. continues to take steps to reduce domestic CH4 emissions to mitigate climate

98

warming, it is important to evaluate the effectiveness of EPA’s existing voluntary programs and

99

regulations that have influenced U.S. CH4 emissions. The EPA quantifies and reports CH4

100

emissions reductions from each of the voluntary programs on an annual basis. In many cases,

101

these data, along with CH4 emissions reductions values resulting from regulations and other

102

incentives or programs, are used in the development of the Inventory of U.S. Greenhouse Gas

103

Emissions and Sinks (hereafter GHG Inventory), released annually30 and submitted to the United

104

Nations Framework Convention on Climate Change (UNFCCC). These CH4 emissions

105

reductions data are also submitted to the UNFCCC as part of the U.S. Climate Action Report as

106

documentation of national actions and progress made in combating climate change. While the

107

emissions reductions values documented in these reports provide valuable information about

108

emissions trends, the climate benefits (i.e. the reduced warming resulting from fewer CH4

109

emissions) and additional qualitative impacts of the voluntary reductions programs have never

110

been evaluated. Further, no studies have quantified the contribution of U.S. CH4 emissions

111

reductions resulting from these programs and policies to the observed decrease in the rate of CH4

112

accumulation in the atmosphere in the 1990s, or the near constant atmospheric CH4

113

concentration observed from 1999 to 2006.3, 31

114



115

Using annual U.S. CH4 emissions reductions data reported by the EPA, we quantified how

116

reductions attributed to existing federal programs and policies influenced CH4 emissions trends

117

in the municipal solid waste landfill, oil and natural gas, coal mining, and manure management

118

sectors from 1993 through 2013. We compared these reductions to EPA estimates of national

119

CH4 emissions within the study sectors and discuss the relative impact of the programs and

120

policies. Further, we assessed how these U.S. CH4 emissions reductions influenced the global

121

atmospheric CH4 concentration and consequent changes in temperature over this time period.

122

Finally, we summarized the qualitative aspects of the voluntary programs within their respective

123

sectors, as well as the monetary benefits of reductions from all sources, estimated using the

124

Social Cost of Methane and O3-health damage estimates.

125 126

Methods

127

Methane emissions reductions data sources

128

Annual U.S. CH4 emissions reductions values used in this analysis have been previously

129

published in EPA reports. For the voluntary programs, only emissions reductions associated with

130

voluntary activities may be attributed to programs and therefore, the voluntary program data does

131

not include reductions resulting from regulations. It is possible that the CH4 emissions reductions

132

credited to these voluntary programs may have occurred without the programs, especially when

133

it is cost-effective to capture and use the gas. The programs therefore evaluate their successes

134

using many metrics that determine emissions reductions and qualitative benefits of the programs.

135

Each program has developed sector-specific methodologies to estimate these reductions which

136

incorporate reported and modeled CH4 emissions reductions, as well as information on project


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assistance, level of partner involvement, and for some sectors, Intergovernmental Panel on

138

Climate Change methodologies.

139 140

All CH4 emissions reductions data used in this analysis for the domestic voluntary programs

141

(AgSTAR, CMOP, LMOP, and Natural Gas STAR) were values previously published in EPA

142

reports. Emissions reductions for 2000-2013 were contained in the Climate Protection

143

Partnerships 2013 Annual Report32 and the 1993-1999 data were included in the 2010 Climate

144

Protection Partnerships Report.33 In some cases, direct CH4 emissions reductions values were not

145

presented independently for each program and these program-specific values were obtained

146

directly from EPA staff. Data from the 2010 Report were reported as a single annual value that

147

combined reductions from all programs voluntary programs. In the 2013 Annual Report,

148

emissions from AgSTAR and LMOP, were presented as the sum of direct CH4 emissions

149

reductions and avoided CO2 emissions, and in this quantitative analysis only the direct reductions

150

are included, because avoided CO2 emissions represent an indirect benefit of the programs.

151

Throughout this analysis, results for the AgSTAR program include only years 2000-2013

152

because data were unavailable prior to this time period. Qualitative voluntary program

153

information was acquired from EPA’s annual Climate Protection Partnerships Reports, program

154

websites, and communication with EPA staff. The CH4 emissions reductions calculated by the

155

individual voluntary programs used in this analysis are not explicitly reported in the GHG

156

Inventory for some sectors. In some cases, the GHG Inventory reports values for CH4 capture

157

and use without attributing the capture and use to specific programs. Methodological details for

158

GHG Inventory estimates are provided in the report.

159



160

Estimates of domestic CH4 emissions reductions resulting primarily from federal regulations

161

were obtained from the GHG Inventory.30 The GHG Inventory is the U.S. official annual GHG

162

inventory report to the UNFCCC. This report provides the most comprehensive estimates

163

available across domestic emission source sectors, provides a long-term record, and is

164

continuously updated to reflect the best information and methods available. We included CH4

165

emissions reductions resulting from regulations for municipal solid waste landfills and oil and

166

natural gas systems only, since these are the only large source sectors with existing regulations

167

that impact CH4 emissions. For landfills, the GHG Inventory reported gas-to-energy and flared

168

“Recovered” CH4 emissions that included reductions credited to both voluntary programs and

169

regulatory reductions stemming from the Landfill Rule. To avoid double counting emissions

170

credited to the voluntary LMOP, we subtracted the LMOP values obtained from the Climate

171

Protection Partnerships reports from the GHG Inventory values and used this difference for the

172

total emissions reductions attributed to the Landfill Rule. For oil and gas, the GHG Inventory

173

provided reductions attributed specifically to certain regulations (i.e. 1999 NESHAP) and

174

therefore we used those values. The 2012 amendments to NESHAP and the 2012 NSPS are

175

expected to have influenced 2013 CH4 emissions reductions values, however these reductions are

176

not explicitly quantified in the GHG Inventory (some reductions, e.g. for hydraulically fractured

177

gas well completions and workovers) are implicitly included in technology-specific calculations

178

and therefore the CH4 emissions reductions attributed to them could not be isolated for this

179

analysis. In this way, our analysis does not fully account for all reductions attributable to EPA

180

programs. We also obtained annual domestic CH4 emissions data by sector from the 2015 GHG

181

Inventory,30 to determine the impact of the programs and policies on sectoral emissions

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throughout the study period.


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183 184

In recent years, substantial amounts of new information on CH4 emissions have become

185

available through a number of channels, including EPA’s Greenhouse Gas Reporting Program

186

(GHGRP) and studies conducted by various organizations, government and academic

187

researchers, and industry.34-36 The GHGRP and some of the new studies provide information that

188

can be used to update or assess emission factors or activity data in the GHG Inventory. Other

189

recent studies evaluated source-based, bottom-up approaches to quantifying CH4 emissions (as is

190

used in EPA’s GHG Inventory), as well as atmospheric, top-down methods, and found that the

191

former approach tends to yield lower emissions estimates.37, 38 Others have also noted

192

discrepancies between the GHG Inventory and emissions estimates at local or regional scales

193

stemming from various factors including differences in equipment counts,39 whether emissions

194

from “super-emitters” are characterized,34 and the emissions factors used in calculating total

195

emissions from some sources.37 EPA reviewed new data and has made several updates to its CH4

196

estimates in the GHG Inventory. See for example, the public review draft of the Inventory of

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U.S. Greenhouse Gas Emissions and Sinks: 1990-2014.40 As data and methods are updated to

198

reflect improvements, historical values are revised as needed to ensure consistent methods are

199

applied to all inventory years. Therefore, the most recent GHG Inventory report emissions

200

estimates may differ from those presented here.

201 202

The emissions reductions presented in this analysis would be less sensitive to differences in

203

emissions values stemming from the abovementioned factors or from updates to the GHG

204

Inventory than the total sectoral emissions estimates. Therefore, the relative impact of CH4

205

emissions reductions on the sectoral and national CH4 emissions discussed in this analysis would



206

likely be smaller when using the emissions estimates developed by some of these other sources,

207

or when using the values in the public review draft of the GHG Inventory. The implications of

208

any future updates to the GHG inventory for this analysis would depend on the precise nature of

209

the updates, but would be expected to be more relevant for estimating baseline emissions than

210

reductions in CH4 emissions, which are the focus of this paper.

211 212

Atmospheric CH4 concentration, radiative forcing, and temperature

213

To estimate the impact of the CH4 emissions reductions on climate, we compared observed

214

atmospheric CH4 concentrations to a counterfactual world with no U.S. reductions (voluntary or

215

regulatory) in CH4 emissions from 1993 to 2013. Observed global CH4 concentration data used

216

here were obtained from the Advanced Global Atmospheric Gases Experiment.41-43 Similar

217

global CH4 values were available from the National Oceanic and Atmospheric Administration’s

218

Marine Boundary Layer44 and Annual Greenhouse Gas Index45 datasets. Mean monthly CH4

219

concentrations were averaged to estimate annual global mean concentration. Counterfactual

220

concentrations for each year were calculated by adding total CH4 emissions reductions values to

221

the observed CH4 concentrations. The cumulative change in atmospheric CH4 concentration, or

222

atmospheric burden (in Tg), attributed to domestic CH4 reductions was calculated by adding each

223

year’s emissions reduction value to the change in atmospheric burden from the previous year

224

using a decay rate of 12.4 years.4

225 226

Observed and counterfactual RF were estimated through the application of a simplified

227

expression provided in Myhre et al.4 (Supporting Information (SI), equation 1) and an adjustment


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factor of 1.65 was applied to account for tropospheric O3 and stratospheric water vapor produced

229

through the degradation of CH4 in the atmosphere. Change in global mean air temperature

230

attributed to reduced CH4 emissions was then derived from the calculated RF based on a

231

simplified equation presented in Shine et al.46 (SI, equation 2) using a best estimate of climate

232

sensitivity of 347 and bounds of 1.5 and 4.5.48

233 234

Results and Discussion

235

Methane emissions reductions and sectoral impacts

236

Annual CH4 abatement increased throughout most of the study period for both regulations and

237

voluntary programs, with some slowing in recent years (Figure 1). Cumulatively over this period,

238

70% of annual emissions reductions were the result of regulations and 30% were credited to

239

voluntary programs, with small inter-annual variation. Regulations were responsible for a total

240

reduction of 89.3 Tg CH4, while voluntary programs contributed an additional 38.6 Tg, for an

241

18% reduction in total domestic CH4 emissions between 1993 and 2013. Together, this

242

cumulative CH4 reduction is equivalent to approximately 5 times the CH4 emissions reported

243

from all U.S. sources in 2013.

244



245 246

Figure 1. Annual CH4 emissions reductions for the study period 1993-2013. Voluntary

247

reductions include reductions credited to EPA’s voluntary programs in the municipal solid waste

248

landfills, oil and natural gas, coal mining, and manure management sectors. Regulatory

249

reductions indicate CH4 reductions attributed primarily to federal regulation in the landfill sector.

250 251

Municipal solid waste landfills

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The 1996 Landfill Rule addressing emissions in the municipal solid waste sector is the single

253

largest source of CH4 abatement considered in this analysis and accounts for 98% of annual

254

regulatory reductions during the period 1999-2013 (when the NESHAP rule was also in effect)

255

and for 69% of CH4 emissions reductions from all voluntary programs and regulations during the

256

1993-2013 time period. A large increase in estimated CH4 abatement in 2010 can be seen in

257

Figure 2A. This increase is driven at least in part by use of a new municipal solid waste landfill

258

database created following EPA issuance of the 2009 Greenhouse Gas Reporting Rule.49 This

259

database is considered to contain the best verified data among available sources,30 indicating that


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regulatory CH4 reductions values published in the GHG Inventory prior to the incorporation of

261

this database in 2010 may have been an underestimate of reductions from this sector. There has

262

also been a trend toward consolidation of municipal solid waste landfill services, resulting in

263

fewer, larger landfill sites. As landfills become larger, they are more likely to reach the threshold

264

for regulatory compliance. This could result in greater collection and control of emissions and

265

influence the observed increase in CH4 abatement in recent years.

266

267



268

Figure 2. Total annual domestic CH4 emissions (obtained from the U.S. EPA Greenhouse Gas

269

Inventory) and CH4 emissions reductions within the municipal solid waste landfill (A), oil and

270

natural gas (B), coal mining (C), and manure management (D) sectors. For landfills and oil and

271

natural gas, data includes reductions resulting from existing regulations and voluntary programs.

272

For coal mines and manure management, only voluntary programs currently result in CH4

273

emissions abatement. Note the difference in scale between A/B, C and D.

274 275

Voluntary activities attributed to LMOP contributed an additional emissions reduction of 8.5 Tg

276

CH4 during the study period, with increasing annual reductions over time (Figure 3). Since

277

LMOP began in 1994, the program has assisted more than 600 domestic landfill gas energy

278

projects. In 2013, the program reported combined participation from 1,070 partners and

279

endorsers (nonprofit organizations that encourage members to capture and use landfill gas). This

280

includes a broad range of partnerships with communities, landfill owners, utility companies,

281

power marketers, state governments, project developers, tribes, and nonprofit organizations.

282


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283 284

Figure 3. Annual reductions in CH4 emissions attributed to EPA’s voluntary CH4 programs in oil

285

and natural gas (Natural Gas STAR), municipal solid waste landfills (LMOP), coal mining

286

(CMOP), and manure management (AgSTAR) from 1993 to 2013.

287 288

When considering both regulations and voluntary programs together, landfills were responsible

289

for about 75% of the total estimated national CH4 emissions abatement that occurred from 1993

290

to 2013. Data from the GHG Inventory indicates that national CH4 emissions from the landfill

291

sector have decreased by 40% over this time. Under a counterfactual scenario with no regulatory

292

or voluntary CH4 reductions, emissions from this sector would have increased instead of

293

decreased (Figure 2A). The largest difference between observed and counterfactual occurred in

294

2013, when programs and regulations resulted in a 66% (9.0 Tg CH4) reduction from what CH4

295

emissions would have been otherwise that year. We made the assumption for this analysis that all

296

CH4 emissions reductions provided in the GHG Inventory were the result of either federal

297

regulation or LMOP. Reductions categorized as regulatory prior to the implementation of the



298

Landfill Rule in 1996 shown in Figure 2A are likely the result of landfill gas energy projects that

299

began prior to the establishment of LMOP and the Landfill Rule, as a result of federal tax credits

300

and demonstrated efficiency, dependability, and cost savings resulting from adoption of CH4

301

capture and use technologies.50

302 303

Oil and natural gas

304

The oil and natural gas sector has seen reductions from both regulatory and voluntary actions.

305

The NESHAP Rule in the oil and natural gas sector, which requires controls on hazardous air

306

pollutants, accounted for 2% of the regulatory CH4 reductions occurring since rule finalization in

307

1999, and 1% of reductions from all CH4 abatement activities included in this analysis for the

308

entire study period. Although the NESHAP rule made a relatively small contribution to

309

emissions reductions, a nearly continuous increase in annual CH4 emissions reductions resulting

310

from this regulation was reported. Conversely, the voluntary Natural Gas STAR program had a

311

relatively large impact on U.S. CH4 abatement, accounting for 18% of total CH4 emissions

312

reductions between 1993 and 2013. Natural Gas STAR was also the primary source of reductions

313

among the voluntary programs (Figure 3), totaling 23.3 Tg CH4 for the study period. The Natural

314

Gas STAR program has grown to address CH4 emissions from all sectors of the natural gas

315

supply chain, and from oil production. The success of the domestic Natural Gas STAR program

316

led to a 2006 expansion to include international partners (though this analysis includes only

317

domestic reductions). In 2013, the program reported more than 130 partnerships in the U.S. and

318

abroad and the cumulative implementation of over 150 cost-effective technologies and best

319

management practices that reduce CH4 emissions as a result Natural Gas STAR program

320

activities.


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321 322

According to the EPA GHG Inventory, national CH4 emissions from oil and natural gas showed

323

a 14% decline between 1993 and 2013, with some small variability among years (Figure 2B).

324

This overall decline has been attributed to the voluntary programs, regulations, and replacement

325

and installation of new equipment.30 The counterfactual indicates that without existing programs

326

and policies, U.S. CH4 emissions from this sector would have increased slightly over the study

327

period. In recent years, the Natural Gas STAR program has shown a decrease in reported

328

voluntary CH4 abatement (Figure 3). This is likely driven by new federal and state-level

329

regulations in some oil and gas producing states that have resulted in fewer operations being able

330

to report reductions as voluntary. This decrease does not necessarily reflect a decline in CH4

331

abatement in the oil and gas sector, but a shift in abatement for some categories from voluntary

332

to regulatory activities. The regulation-driven CH4 emissions reductions quantified in this

333

analysis reflect only reductions attributed to the NESHAP regulations established in 1999, as

334

these regulations are explicitly quantified for the GHG Inventory. Reductions driven by state-

335

level policies and other regulatory activities, including the 2012 NSPS, have not been quantified

336

explicitly. In this way, this analysis may underestimate the reductions resulting from EPA

337

programs in this sector. For example, reductions of CH4 from meeting 2012 NSPS emissions

338

reduction requirements for hydraulically fractured gas well completions are taken into account in

339

the technology-specific calculations for this emission source in the GHG Inventory, and no

340

specific reduction values were available for use in this analysis.

341 342

Coal mining



343

Voluntary activities in the coal mining sector were responsible for 5% (6.6 Tg) of the total CH4

344

abatement between 1993 and 2013. Reductions tended to increase across the study period, with

345

some variation among years (Figure 3). Initially, CMOP focused on CH4 reduction from

346

degasification systems in active underground mines, where only about 25% of systems captured

347

and used CH4 in the mid-1990s. By 2010, over 80% of the CH4 captured in desgasification

348

systems was utilized as a fuel source.33 The success of capture in degasification systems led to

349

expansion into ventilation systems and projects in abandoned underground mines, as well as

350

some surface mines. In 2002, CMOP began implementation of the first domestic commercial-

351

scale demonstration of ventilation air oxidation technology in collaboration with the U.S.

352

Department of Energy and a publicly owned energy company. This technology has now been

353

incorporated into some new CMOP-related projects. In 2013, CH4 capture and use systems were

354

used in 17 active coal mines and 18 abandoned mines.32

355 356

National CH4 emissions from the coal mining sector reported in the GHG Inventory showed a

357

slight decrease during most study years, with the exception of increased emissions occurring in

358

2008-2010 (Figure 2C), the cause of which remains unclear. In a counterfactual situation without

359

CMOP, annual CH4 emissions would have been 6-14% higher between 1993 and 2013, with

360

greater reductions observed in more recent years.

361 362

Manure management

363

The AgSTAR program was responsible for 0.19 Tg of CH4 emissions reduction between 1993

364

and 2013 and accounted for 0.1% of reductions credited to voluntary programs. This estimate is


Page 20 of 36

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365

likely conservative because it does not include reductions during the 1994-1999 time period.

366

Although this was a small reduction compared to those reported for other programs, a relatively

367

large increase in CH4 abatement was observed within the program, increasing from 0.001 Tg

368

CH4 in 2000 to 0.03 Tg in 2013. Numerous activities contributed to these reductions, including

369

the development of demonstration farms to showcase biogas recovery systems, creation of

370

national standards for biogas technologies, and outreach with renewable energy industry leaders,

371

state and local governments, universities, and non-governmental organizations. AgSTAR has

372

also assisted states in the development of programs and policies that support greater adoption of

373

cost-effective biogas technologies. In addition to avoiding CH4 emissions and providing a

374

cleaner fuel source, AgSTAR notes the benefits of digester systems for reducing local air and

375

water pollution, generating byproducts such as manure fibers that can act as an additional

376

revenue source, and providing opportunities for rural economic development. Between 1994 and

377

2013, the AgSTAR program reported adoption of biogas recovery systems at 239 livestock farms

378

in the U.S.32

379 380

National CH4 emissions from the animal manure management sector reported in the GHG

381

Inventory increased by 56% between 1993 and 2013 (Figure 2D). This pattern was attributed to

382

an increase in the use of liquid manure management, especially on swine and dairy cow farms.30

383

The AgSTAR program addresses livestock manure handled as liquid and slurry, which makes up

384

the largest fraction of CH4 emissions from the manure management sector. In a counterfactual

385

situation without AgSTAR, annual emissions from this sector would have been 1.3% higher in

386

2013.

387



388

Impacts of U.S. programs and policies on global CH4 concentrations and temperature

389

In a counterfactual world without existing U.S. federal regulations and voluntary programs to

390

reduce CH4 emissions, global atmospheric CH4 concentrations would have been approximately

391

28 ppb higher than observed in 2013 (Figure 4). Regulations were responsible for approximately

392

20 ppb and the voluntary programs for 8 ppb. The difference between observed and

393

counterfactual CH4 concentrations grew throughout the study period due to the annual increase

394

in CH4 emissions reductions and the associated effect on atmospheric burden. The change in

395

global atmospheric CH4 concentration credited to U.S. actions resulted in a decrease in RF and

396

reduction in global mean temperature increase throughout the study period. In 2013, the

397

decreased RF reached 0.01 W m-2 and translated to a reduction in mean temperature of

398

approximately 0.006oC, assuming a climate sensitivity of 3 (Figure 5). The bounds for sensitivity

399

(1.5 and 4.5) indicated a global temperature reduction of 0.004oC and 0.007oC, respectively in

400

2013. Regulations were responsible for approximately 0.004oC of this change, and voluntary

401

programs for 0.002oC. For context, the global surface temperature increase over the 1993-2013

402

period, based on global land and ocean anomalies, was about 0.3 oC.51 This suggests that the U.S.

403

CH4 programs addressed in this paper have reduced global warming by about 2% over the past

404

two decades, which is a substantial contribution for mitigation activities addressing a subset of

405

emissions from a single nation. With further domestic or international action, a larger near-term

406

climate benefit could be achieved. These programs may also have indirect benefits in the form of

407

avoided CO2 emissions if CH4 burned for electricity generation displaces the use of other fossil

408

fuels, but this effect was not quantified in this analysis. The results presented here do not include

409

the effect on CO2 concentrations resulting from immediate production of CO2 due to combustion

410

of CH4, rather than delayed production resulting from oxidation of CH4 in the atmosphere. While


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411

the appropriate methodology for valuing a delay in release of a gas is an ongoing area of

412

research, a sensitivity analysis using the assumption that all CH4 reductions accounted for in this

413

analysis are immediately converted to atmospheric CO2 found a temperature impact in 2013 of

414

about 4% of the CH4 reductions (SI).

415

416 417

Figure 4. Observed global mean CH4 concentration and estimated counterfactual CH4

418

concentration in the absence of regulations and voluntary CH4 emissions reductions programs

419

included in this study.

420



Page 24 of 36

421 422

Figure 5. Estimated reduction in the global temperature increase attributed to U.S. CH4 emissions

423

reductions resulting from regulations and voluntary programs for the study period 1993-2013.

424

Values were calculated using a best estimate climate sensitivity of 3 (solid line), and bounds of

425

1.5 and 4.5 (dashed lines).

426 427

Figure 4 suggests a fairly constant atmospheric CH4 concentration between 1999 and 2006,

428

where the lines are relatively flat. This observation has been documented in other studies and

429

linked to both natural and anthropogenic causes, including changes in wetland emissions and

430

agricultural practices, the collapse of the Russian economy post 1992, and reductions in the

431

growth of CH4 emissions, including from the U.S. and Europe.31, 52, 53 Methane emissions

432

abatement in the U.S. increased throughout this period (Figure 1), suggesting that the programs

433

and policies included in our analysis, particularly landfill regulation, may have had a previously

434

underappreciated contribution to stabilizing the global CH4 concentration during this time .

435


Page 25 of 36


436

Estimated Monetized Benefits of Methane Reductions

437

In addition to physical metrics that demonstrate the impact of historical CH4 reductions on

438

climate, there have been recent advances in monetizing the benefits of CH4 abatement. Marten et

439

al.54, 55 calculated a Social Cost of Methane, which estimated that the net present value of CH4

440

emissions reductions in 2020 resulting from mitigation of climate damages is $1200/Mg (2011$)

441

at a discount rate of 3%. In addition to the climate damages of CH4, a number of studies have

442

analyzed impacts on health5, 56 and agriculture11 due to the creation of O3 by CH4 oxidation in the

443

atmosphere. Sarofim et al.9 found the net present value of methane reductions in 2020 resulting

444

from mitigation of O3-health damages to be $790/Mg (2011$) at a discount rate of 3%, using

445

assumptions that were designed to complement the Social Cost of Methane approach.54

446

Combining the two methods, the value of one Mg of CH4 reduced in 2020 would be $1990 at a

447

discount rate of 3%, with a range of $1200 to $2431 for discount rates of 5 and 2.5%,

448

respectively. Assuming a constant value of CH4 reductions, and not accounting for uncertainties

449

beyond the discount rate, the monetized health and climate benefits of 128 Tg of CH4 reductions

450

credited to U.S. voluntary programs and policies over the period 1993-2013 would be $255

451

billion at a discount rate of 3%, with a range of $154 to $311 billion depending on discount rate.

452

For comparison, 128 Tg of CH4 would be worth approximately $15 billion if it were captured

453

and sold (based on the mean price of natural gas in 2015 of $2.63 per million Btu,57 and

454

assuming natural gas is 100% CH4). More comprehensive cost-benefit analyses that incorporate

455

costs incurred to install and operate CH4 capture and use technologies would further refine

456

estimates of the monetary benefits of reducing CH4 emissions.

457 458



459

Conclusions

460

This quantification of the benefits of U.S. EPA regulations and voluntary CH4 programs

461

demonstrates substantial avoided increases in global CH4 concentration, RF, and temperature. In

462

sum, these programs accounted for a reduction of 127.9 Tg of CH4 over a 20-year period, leading

463

to a reduction of 28 ppb atmospheric CH4 concentration and an avoided 0.006 °C temperature

464

rise in 2013. The monetized climate and health benefits of CH4 and associated O3 reductions are

465

estimated to be $255 billion. Historically, the 1996 Landfill Rule accounted for 70% of the total

466

reductions, with the voluntary programs accounting for about 30%. Recently finalized rules,

467

including the 2012 NSPS for oil and gas, have also influenced emissions which are not

468

quantified here. Accounting for non-federal programs, and for international reductions resulting

469

from U.S. actions, would also increase estimated CH4 emissions reductions. There will also be

470

future benefits resulting from historical reductions and the continuation of existing programs.

471

Recently proposed rules within the landfill and oil and gas sectors would also have CH4

472

reduction benefits. In addition to these quantifiable CH4 benefits, the voluntary programs have

473

further facilitated the adoption of more cost-effective technologies and practices. Collectively,

474

these findings illustrate the benefits of a wide range of approaches taken historically to address

475

the risks of climate change and provide important insights moving forward, as programs and

476

policies to address U.S. CH4 emissions remain a priority for the Federal Government.

477 478

Supporting Information (SI)

479

Supporting information available: the Supporting Information describes the equations and

480

procedures used for calculating concentration, radiative forcing, and temperature changes for a


Page 26 of 36

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481

pulse of methane emissions, or for the acceleration of CO2 production resulting from flaring

482

methane. This material is available free of charge via the Internet at http://pubs.acs.org.

483 484

Acknowledgements

485

The authors would like to thank Melissa Weitz and additional EPA staff who provided

486

information used in this analysis and reviewed drafts of this manuscript. Thanks also to three

487

anonymous reviewers for providing constructive feedback to improve this manuscript. The

488

Landfill Methane Outreach Program generously provided the photographs use in the TOC

489

graphic. The views expressed in this paper are those of the authors and do not reflect those of the

490

U.S. Environmental Protection Agency.

491 492

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Climate Benefits of U.S. EPA Programs and Policies That Reduced

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