U.S. Oil/Gas Methane Emissions Science Tracker

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1	U.S. Oil/Gas Methane Emissions Science Tracker					Updated:June 2022
2	A new wave of science over the last 4 years reports that methane emissions from the U.S. oil and gas system are growing; that these emissions are twice the level reported by EPA; and that these emissions are significantly higher than reported in prior literature, from the wellhead to the stove top or the gas-fired power generator. These studies also report that U.S. production of oil and gas is a contributor to the unexpected global surge in atmospheric methane over the past decade. An authoritative assessment of the literature published in 2020 reports that methane emissions from the U.S. oil and gas operations are among the significant contributors to the recent surge in global methane levels (Jackson et al. 2020 and Saunois et al 2020) as does the IPCC WGI report published in August of 2021. Estimates of the size of this contribution, from across the literature, fall across a wide range, with some studies indicating that U.S. oil/gas production is one of the primary drivers, while others find that oil/gas production is only a very minor contributing factor. Seperately, analysts calculate that the exteme methane emissions from the U.S. gas sector effectively erase much of the GHG emissions reductions in the U.S. that were secured over the last 15 years in the switch from coal-fired power to gas-fired power. The tracker currently highlights over 30 studies published over the last 2 years months and several older studies that provide important context or findings. Of particular note, Zhang et al., Negron et al., Chen et al., Weller et al. provide extensive evidence that total emissions from the U.S. oil and gas system are significantly higher than estimated prior in the literature (e.g. as estimated by Alvarez et al. 2018 - which found emissions are about 60% higher than EPA estimates). Most recently, EDF conducted a study to update methodology of Alvarez et al. and apply it to 2019 methane emissions from the U.S. oil/gas system. The updated study finds that that methane emissions from the U.S. oil/gas system are twice the level reported by the EPA. The EPA has not updated the Federal estimate of methane emissions to account for the science going back to Alvarez et al. and futher. However, under Trump the EPA lowered it's estimates of methane emissions from the oil and gas sector. To date, the Biden Administration has maintained these estimates. For more information, contact: Hunter Cutting, hcutting@climatenexus.org
3	Authors	Key study	Surge Study	Emissions/Leaks Study	Title	Findings/Relevance	Date	Publication	Sample Media Coverage	More Coverage	Notes	Notes 2	Notes 3

4	U.S. House Science Committee Majority Staff, 2022				Seeing CH4 Clearly: Science-Based Approaches to Methane Monitoring in the Oil and Gas Sector	Report documents that "oil and gas companies have internal data showing that methane emission rates from the sector are likely significantly higher than official data reported to EPA would indicate."	6/8/2022	U.S. House of Representatives Committee on Science, Space, and Technology	Hill Heat
5	Deng et al. 2022				Comparing national greenhouse gas budgets reported in UNFCCC inventories against atmospheric inversions	Finds that methane emissions in the United States are increasing in striking contrast to the data the U.S. submits to the United Nations Framework Convention on Climate Change (UNFCCC) which reports a slight decrease in methane emissions. Attributes the difference to documented defficiencies in the methodology the U.S. employs to estimate emissions from the production and distribution of natural gas.	4/11/2022	Earth System Science Data
6	IPCC AR6 Working Group III, SPM, Skea et al. 2022				Climate Change 2022: Mitigation of Climate Change	Limiting warming to 1.5°C will require immediate and deep reductions in methane emissions and the most cost-effective reductions are in the fossil fuel sector. From Section C.1.2: “In pathways that limit warming to 1.5°C (>50%) with no or limited overshoot…global CH4 emissions are reduced by 34% [21–57%] in 2030 and 44% [31–63%] in 2040” [compared to modeled 2019 emissions]. “There are similar reductions of non-CO2 emissions by 2050 in both types of pathways: CH4 is reduced by 45% [25–70%]….Across most modelled pathways, this is the maximum technical potential for anthropogenic CH4 reductions in the underlying models (high confidence). From Section C.12.1. “Large contributions [towards limiting warming to 1.5°C] with costs less than USD20 tCO2-eq–1 come from solar and wind energy, energy efficiency improvements, reduced conversion of natural ecosystems, and CH4 emissions reductions (coal mining, oil and gas, waste).”	4/4/2022	IPCC
7	Chen et al. 2022				Quantifying Regional Methane Emissions in the New Mexico Permian Basin with a Comprehensive Aerial Survey	Estimates total O&G methane emissions in Permian Basin at 9.4% of gross gas production, which dwarfs the Environmental Protection Agency’s 1.4 percent estimate, based on a massive basin-wide aerial survey conducted throughout October 2018 to January 2020. New Mexico recently passed legislation banning routine flaring of excess natural gas. And Rystad energy reports that "The average flaring intensity across the 50 largest gas producers in the Permian was 1.6% in the third quarter of 2021, compared to 2.5% in the first half of 2021 and 3.2% in 2020." However, methane emissions are mostly driven by super major emitter events and flaring accounts for only 21% of the super major events (see Irakulis-Loitxate et al. 2021. See also Cusworth 2021). In addition, surveys conducted in 2021 report that methane emissions have rebounded to the levels witnessed prior to the pandemic slowdown (see Lyon et al. and follow studies in the notes columns). The survey was capable of measuring emissions from nearly every asset in an O&G producing region with an instrument capable of quantifying and attributing medium-to-large point-source emissions, allowing the researchers to identify emissions larger than any documented in ground-based surveys, and to obtain sample sizes orders of magnitude larger than prior approaches. The airborne survey repeatedly visited over 90% of the active wells in the survey region throughout October 2018 to January 2020, totaling approximately 98 000 well site visits. "The fact that a large sample size is required to characterize the heavy tail of the distribution emphasizes the importance of capturing low-probability, high-consequence events through basin-wide surveys when estimating regional O&G methane emissions."	3/23/2022	Environmental Science & Technology	Associated Press	Stanford Energy News	New York Times
8	IEA Methane Tracker Database, 2022				Methane Tracker Data Explorer	Finds that emissions from the U.S. oil and gas sector are 88% higher than the emisions reported by the U.S. EPA. See table "United States methane emissions from energy sources, comparison with UNFCCC and other estimates" on the country tab for the United States (accesse by the country pull down menu).	2/23/2022	IEA Methane Tracker Database
9	Rystad Energy, 2021				US gas flaring hit a record low in September, driven by improvements in the Bakken and Permian	Rystad reports that flaring across several major basins, including the Permian and the Bakken, dropped by 50% from the highs reached in 2018 and 2019. Rystad attributes the drop to the spread of "best practices that only major operators had previously adopted spread to smaller, independent players." However, methane emissions are mostly driven by super major emitter events and flaring accounts for only 21% of the super major events (see Irakulis-Loitxate et al. 2021). In addition, surveys conducted in 2021 report that methane emissions have rebounded to the levels witnessed prior to the pandemic slowdown (see Lyon et al. and follow studies in the notes columns).	12/15/2021
10	Lin et al. 2021				Declining methane emissions and steady, high leakage rates observed over multiple years in a western US oil/gas production basin	Finds a ~7% leakage in Uinta Basin natural gas infrastructure.	11/16/2021	Nature: Scientific Reports	University of Utah
11	Sargent et al. 2021				Majority of US urban natural gas emissions unaccounted for in inventories	For six U.S. cities the authors find the fugitive emissions city level distribution pipelines are two to three times the EPA estimate. "....we estimate NG losses from distribution and end use amount to 20 to 36% of all losses from the US NG supply chain, with a total loss rate of 3.3 to 4.7% of NG from well pad to urban consumer, notably larger than the current Environmental Protection Agency estimate of 1.4%"	10/25/2021	Proceedings of the National Academy of Sciences
12	Stavert et al. 2021				Regional trends and drivers of the global methane budget	An authoritative assessment of regional and sectoral methane emissions (building on Saunois et al. 2020) finds a major increase in U.S. methane emissions, driven by oil and gas operations. The authors report that "Some regions, including the United States, Central Asia, and Northern Africa, show an acceleration in emissions post 2010 (Figure 5). Both BU and TD methods link the USA post-2010 increase to the Fossil sector (Figure 6) with the GAINS and EDGAR BU estimates indicating a >100% increase in Oil&Gas emissions."	9/23/2021	Global Change Biology
13	Climate Trace				Climate Trace 2020 Global Inventory	Finds that the inventory reports on methane emissions from oil and gas operations submitted by countries party to the Paris Climate, including the U.S., only report about half of the emisisons observed by sattelite and other means. "In oil and gas production and refining, among the world’s top countries that submit regular inventories, emissions from oil and gas may collectively be around double (1 billion tons higher than) recent UNFCCC reports." The Climate Trace project rates the "inventory allignment" of the U.S. oil and gas emissions as "low." (See Trace report published by Clean Technica).	9/15/2021	Climate Trace: The Source	Clean Technica	Axios
14	IPCC AR6 Working Group I, Chapter 5, Canndell et al, 2021				Global Carbon and other Biogeochemical Cycles and Feedbacks	Confirms that fossil fuel production in the United States are a key contributor to the surge in global methane levels. Reports that: “Isotopic composition observations and inventory data suggest that concurrent emission changes from both fossil fuels and agriculture are playing roles in the resumed CH4 growth since 2007 (high confidence).” And: “The growth since 2007 is driven by increasing agricultural emissions from East Asia (1997–2017), West Asia (2005–2017), Brazil (1988–2017) and Northern Africa (2005–2017), and fossil fuel exploitations in temperate North America (2010–2017) (Lan et al., 2019; Crippa et al., 2020; Höglund-Isaksson et al., 2020; Jackson et al., 2020; Chandra et al., 2021).”	8/9/2021	IPCC
15	Irakulis-Loitxate et al. 2021				Satellite-based survey of extreme methane emissions in the Permian basin	"We use a new class of satellite measurements acquired during several days in 2019 and 2020 to perform the first regional-scale and high-resolution survey of methane sources in the Permian. We find an unexpectedly large number of extreme point sources (37 plumes with emission rates >500 kg hour−1), which account for a range between 31 and 53% of the estimated emissions in the sampled area. Our analysis reveals that new facilities are major emitters in the area, often due to inefficient flaring operations (20% of detections). These results put current practices into question and are relevant to guide emission reduction efforts."	6/30/2021	Science Advances
16	Dowd et al (forthcoming)				Quantifying the contribution of regional methane emissions to the global methane budget between 2009 and 2018 using the TOMCAT chemical transport model	Reports that “North America Fossil Fuel emissions are contributing to the increasing trend of SCA in northern high latitudes,” SCA being the seasonal cycle amplitude of atmospheric methane, i.e. the level of atmospheric methane (which cycles seasonally).	4/19/2021	EGU Presentation			Presentation reference
17	Cusworth et al 2021				Intermittency of Large Methane Emitters in the Permian Basin	Findings underscore the major role of intermitment super-emitters in driving methane emissions in the Permian. A relatively tiny number of Permian oil and gas sites are responsible for an extremely disproportionate amount of methane pollution, 123 of the 60,000 sites (0.205%) surveyed in the month-long study accounted for 29% of the region's methane pollution. Study conducted by Methane Source Finder, a joint project of NASA, the University of Arizona and Arizona State University.	6/2/2021	Environmental Science & Technology	E&E	NASA News	University of Arizona News
18	Lan et al. 2021				Improved Constraints on Global Methane Emissions and Sinks	Conducts a modeling project and concludes that "increased fossil fuel emissions are unlikely to be the dominant driver for the post 2006 global CH4 increase..." Allows that fossil fuel emissions could be a contributing factor but sees it as extremely limited. Acknowleges considerable uncertainty in the findings due to large gaps in data necessitating significant assumptions and other issues.	5/8/2021	Global Biogeochemical Cycles	NOAA News	ClimateWire
19	M.J. Bradley & Associates, 2021				Benchmarking Methane and Other GHG Emissions of Oil & Natural Gas Production in the United States	The analysis, commissioned by Clean Air Task Force and Ceres, finds that five of the ten biggest methane emitters are small producers, and overall, the 195 smallest producers were responsible for 22% of total emissions, despite only accounting for 9% of production. The largest emitter, Hilcorp Energy, reported almost 50% more methane emissions than Exxon Mobil despite pumping far less oil and gas, and had a leak rate nearly six times higher than the average of the top 30 producers.	6/1/2021	CATF/CERES	New York Times	Nexus Media News
20	Barkley et al. 2021				Analysis of Oil and Gas Ethane and Methane Emissions in the Southcentral and Eastern United States Using Four Seasons of Continuous Aircraft Ethane Measurements	Concludes that EPA methane inventories in the Southcentral and Eastern United States are underestimating methane emissions from O&G by 48%–76%. Measurements were collected from 2017 to 2019 as part of the Atmospheric Carbon and Transport (ACT) America aircraft campaign and encompass much of the central and eastern United States. "[Ethane] observations are compared with model-projected ethane values based on our current knowledge of ethane emissions, and those emissions are adjusted to best match the observed data. We find ethane emissions are grossly underestimated in the US. Because ethane is co-emitted with O&G methane sources, this underestimation of ethane reflects similar underestimations in O&G methane emissions."	5/5/2021	Journal of Geophysical Research: Atmospheres	The Hill
21	Lyon et al. 2021				Concurrent variation in oil and gas methane emissions and oil price during the COVID-19 pandemic	Finds that total methane emisssion in the Permian rebounded after the COVID pandemic slowdown.	5/3/2021	Atmospheric Chemistry and Physics	Financial Times		See further data on rebound, readings as of July 31, 2021, confirming emissions have returned to the levels prior to the pandemic slowdown.	See further analysis finding that "Although there was a large decrease in the volume of gas flared in late spring, due to the drop in production, there was no change in observed flare performance. We estimate at least 7% of Permian gas sent to flares is escaping directly into the atmosphere. This means companies are emitting 3.5 times more methane than what EPA assumes."	See this analysis of emisisons in late 2021
22	Kayrros, 2021				Appalachian Basin Outweighs the Permian as Top Methane Emitting Region in the U.S.	Finds that methane emissions from oil and gas operations in the Appalachian and Permian Basins in 2019 and 2020 were significantly higher than EPA estimates. Finds emissions decreased from 2019 to 2020 largely due to the impact of the Covid pandemic on energy demand. See Lyon et al. 2021 documenting rebound of emissions in the Permian post COVID slowdown	4/21/2021	Kayrros press release (PDF download)	Energy Wire	Natural Gas Intelligence
23	EDF 2021				2019 U.S. Oil & Gas Methane Emissions Estimate	This analysis updates the methodology of Alvarez et al by applying more recent studies (listed here) and analyzes methane emissions in 2019, finding that methane emissions from the oil and gas sectors (production through distribution) are in fact twice the EPA estimate, i.e. 16.2 million metric tons vs. the EPA estimate of 7.9 million metric tons.	4/1/2021	EDF	OCI Blog		See infographic produced on OCI blog
24	Maasakkers et al. 2021				2010–2015 North American methane emissions, sectoral contributions, and trends: a high-resolution inversion of GOSAT observations of atmospheric methane	Indicates that methane emissions from the production of oil and natural gas are up to 90% higher than annual EPA estimates. In the oil and gas production sectors "we find higher emissions than the GHGI by 35 % and 22 %, respectively. The most recent version of the EPA GHGI revises downward its estimate of emissions from oil production, and we find that these are lower than our estimate by a factor of 2.....We find an increasing trend in US anthropogenic emissions over 2010–2015 of 0.4 % a−1, lower than previous GOSAT-based estimates but opposite to the decrease reported by the EPA GHGI. Most of this increase appears driven by unconventional oil and gas production in the eastern US. "	3/22/2021	Atmospheric Chemistry and Physics	Weather Channel
25	IEA Methane Tracker Database				IEA Global Methane Tracker 2021	U.S. oil and gas sector methane emissions reported at 11.79 million metric tons, or 16.4% of the global total of just over 70 Mt for oil and gas operations worldwide in 2020. This figure for the U.S. oil and gas sector is nearly 50% higher than the EPA’s estimates for 2019. Ranked by total national methane emissions from oil and gas production, the U.S. stands at #2, slightly below Russia, but well ahead of the 3rd ranked nation (Iran). Ranked by intensity of methane emisisons (i.e. leakage), the U.S. stand well below Russia, but above other producers such as Saudi Arabia and Canada. While not publishing data from previous years, the IEA states emissions globally were around 10% down on 2019 due to lower oil and gas production as a result of the COVID pandemic. IEA reports that "A large portion of this drop occurred because of the fall in oil and gas production over the course of the year – especially in countries and regions where production has a high emissions intensity, notably Libya and Venezuela. Lower shale activity in the United States also played a role in bringing down these emissions." IEA also reports that reductions reductions in the large scale leaks obsrved by satetllites "were seen across a number of regions in 2020, but large levels of emissions were still seen across US shale plays, in Turkmenistan, and from pipelines in the Russian Federation. Conversely, relatively few large leaks were detected across major producers in the Middle East, including Iraq and Kuwait."	1/18/2021	IEA	S&P Global Platts
26	Williams et al., 2021				Methane Emissions from Abandoned Oil and Gas Wells in Canada and the United States	Finds that annual methane emissions from abandoned wells are underestimated by 20% in the U.S. Estimates the number of abandoned wells in the U.S. to be at least 4,000,000 wells.	1/5/2021	Environmental Science & Technology	Energy Wire
27	New Mexico Environment Department and U.S. Environmental Protection Agency				Significant emission increases from oil and gas operations confirm need for stronger rules and enforcement, greater industry compliance Leak rates in New Mexico’s Permian Basin increased 250% in 12 months	Flyers over found that the methane emissions leak rate has increased from 2 percent in 2019 to 5 percent in 2020 across the entire Permian Basin.	12/21/2020	New Mexico Environment Department and U.S. Environmental Protection Agency	Santa Fe New Mexican
28	EDF, 2020c				Methane and Air Toxics	Finds that methane emissions from the O&G sectors in New Mexico measured July 2017-Aug 2018 are 5 times (500%) the EPA estimate.	11/23/2020	EDF	Natural Gas Intelligence
29	Kayrros, 2020				Kayrros Surveillance Technology Reveals Dramatic and Unexpected Annual Increase in Large Methane Leaks	"When comparing the first eight months of 2019 to the same period in 2020, Kayrros Methane Watch has recorded a marked increase in the overall volume of methane emitted from large leaks around the world. Based on the number of methane hotspots detected in the oil and gas sector, visible methane emissions around the world have increased by approximately 32%. In Algeria, Russia and Turkmenistan, the increase is even higher, totaling over 40%." Kayrros "tracked a combined volume of visible large methane leaks of 10Mt, equivalent to over 800Mt of CO2 over a 20 year period, ...and the largest contributors were the US, Russia, Algeria, Turkmenistan, Iran and Iraq."	10/14/2020	Kayrros press release (PDF download)	Gizmodo	Washington Post
30	Deighton et al. 2020				Measurements show that marginal wells are a disproportionate source of methane relative to production	"We estimate that oil and gas wells in this lowest production category emit approximately 11% of total annual CH4 from oil and gas production in the EPA greenhouse gas inventory, although they produce about 0.2% of oil and 0.4% of gas in the US per year." "Implications: Low producing marginal wells are the most abundant type of oil and gas well in the United States, and a surprising number bof them are venting all or more of their reported produced gas to the atmosphere. This makes marginal wells a disproportionate greenhouse gas emissions source compared to their energy return, and a good target for environmental mitigation."	9/3/2020
31	Jackson et al. 2020				Increasing anthropogenic methane emissions arise equally from agricultural and fossil fuel sources	Summarizes Saunois et al 2020 and further investigates the sources of the surge. Summarizes "new estimates of the global methane budget based on the analysis of Saunois et al (2020)"...and compares "these estimates to mean values for the reference 'stabilization' period of 2000–2006 when atmospheric CH4 concentrations were relatively stable. We present data for sources and sinks and provide insights for the geographical regions and economic sectors where emissions have changed the most over recent decades."....."Increased emissions from both the agriculture and waste sector and the fossil fuel sector are likely the dominant cause of this global increase highlighting the need for stronger mitigation in both areas. Our analysis also highlights emission increases in agriculture, waste, and fossil fuel sectors from southern and southeastern Asia, including China, as well as increases in the fossil fuel sector in the United States." The assessment finds that anthropogenic sources are estimated to contribute almost all of the additional methane emitted globally to the atmosphere for 2017 compared to 2000–2006. Fossil fuel extraction and agriculture around the world are the two primary drivers of the surge, and North American fossil fuel emissions are among the significant contributors to the surge. Among the other key findings: Fossil fuel methane emissions from the United States account for 80 percent of the increase in North American methane emissions over the study period (2000-2006 v 2017). This increase is driven by gas and oil extraction and distribution. This research is a major advance in the growing body of study on the methane surge and its causes. Methane in the atmosphere reached a new record high in 2019. Estimates for 2018 and 2019 show increases in atmospheric methane of 8.5 and 10.7 ppb, respectively, two of the four highest annual increases since 2000. Methane concentrations are tracking with the warmest scenario of the Intergovernmental Panel on Climate Change. Climate policies overall, where present for methane mitigation, have yet to alter substantially the global emissions trajectory to date.	7/15/2020	Environmental Research Letters	New York Times	Scientific American
32	Saunois et al. 2020				The Global Methane Budget 2000-2017	An authoritative global assessment of the methane surge. Finds that the long-term rise in methane concentrations "is attributable in large part to increased anthropogenic emissions arising primarily from agriculture (e.g., livestock production, rice cultivation, biomass burning), fossil fuel production and use, waste disposal, and alterations to natural methane fluxes due to increased atmospheric CO2 concentrations and climate change." The authors also highlight that "Changes in the magnitude and temporal variation (annual to inter-annual) in methane sources and sinks over the past decades are characterized by large uncertainties."	7/15/2020	Earth System Science Data	Carbon Brief
33	Weller et al. 2020				A national estimate of methane leakage from pipeline mains in natural gas local distribution systems	"We estimate methane emissions from U.S. local distribution natural gas pipes using data collected from an advanced mobile leak detection platform. We estimate that there are 630,000 leaks in U.S. distribution mains, resulting in methane emissions of 0.69 Tg/year."...."Our national methane emissions estimate is approximately 5x greater than the current EPA GHGI estimate for pipeline mains in local distribution systems due to both a larger estimated number of leaks, and better characterization of the upper tail of the skewed distribution of emission rates."	6/10/2020	Environmental Science & Technology
34	EDF 2020b				EDF Analysis Finds Pennsylvania Oil and Gas Methane Emissions are Double Previous Estimate	EDF finds that Pennsylvania oil and gas methane emissions in 2017 to be double what Environmental Defense Fund documented for 2015. "Updated emission figures are double EDF’s analysis of 2015 data for three primary reasons: production levels in 2017 were notably higher than two years prior (an upward trend that has carried into 2020); use of additional state-specific data provides a more accurate picture of wells in the state and emission sources; and the 2018 Science study provides the best available scientific methods which demonstrate higher levels of emissions per well." The 2018 study referenced by EDF is Alvarez et al.	5/13/2020	EDF News
35	Zhang et al. 2020				Quantifying methane emissions from the largest oil-producing basin in the United States from space	Estimates 3.7% leakage/venting rate in Permian basin, more than twice the official EPA estimate for the region which accounts for roughly 15% of natural gas production. This estimate is also 60% higher than the 2.3% leakage rate estimated back in 2018 by Alvarez et al. NB: Alvarez did not assess the Permian basin directly but rather assumed methane emissions there are the same as the average of the other basins they did assess directly. Bloomberg quotes Howarth putting the study data in context: “The Permian Basin’s methane pollution accounts for about 10% of the total global increase in methane emissions from 2010 to 2020.”	4/25/2020	Science Advances	Inside Climate News	Bloomberg	Informal analysis pegged to this study and reported by Bloomberg indicates that the GHG emissions reductions in the U.S. over the last decade through coal-to-gas switching may have been largely if not entirely negated by methane leaks from production across the all basins.
36	Hmiel et al. 2020				Preindustrial 14CH4 indicates greater anthropogenic fossil CH4 emissions	Isotope research reports that methane emissions from global fossil fuel production over most of the 20th century and the first decade of the 21st century (not including the recent surge) are under-estimated by as much as 40%, while natural geologic sources (e.g. natural seeps) contribute correspondingly less. [this isotope analysis does not distinguish between coal-mine seeps vs. oil/gas production emissions]. Though disturbing, these findings include a silver lining. They indicate that better management of methane emissions from fossil-fuel production and distribution would have an even greater impact on global methane levels than understood prior.	4/22/2020	Nature	ANTSO News
37	EPA, 2020a				Inventory of U.S. Greenhouse Gas Emissions and Sinks, 2020	Per Reuters: "More than 3.2 million abandoned oil and gas wells together emitted 281 kilotons of methane in 2018, according to the data, which was included in the U.S. Environmental Protection Agency’s most recent report on April 14 to the United Nations Framework Convention on Climate Change. That’s the climate-damage equivalent of consuming about 16 million barrels of crude oil, according to an EPA calculation, or about as much as the United States, the world’s biggest oil consumer, uses in a typical day. The actual amount could be as much as three times higher, the EPA says, because of incomplete data. The agency believes most of the methane comes from the more than 2 million abandoned wells it estimates were never properly plugged. "	4/14/2020	EPA	Reuters
38	Ingraffea et al. 2020				Reported Methane Emissions from Active Oil and Gas Wells in Pennsylvania, 2014–2018	Finds that methane emissions in Pennsylvania are at least 15% higher than previously thought due to missing reports from accidental leaks from oil and gas wells. Researchers believe a similar under-counting is happening at the national level.	4/9/2020	Environmental Science and Technology	Environmental Health News	Daily Climate
39	PermianMap 2020				New Data: Permian Oil & Gas Producers Releasing Methane at Three Times National Rate	This data release from EDF PermianMap program of field and aircraft measurements estimates methane leakage in the Permian basin at 3.5%, consistent with Zhang et al. satellite study that estimates emissions at 3.7% - both more than twice the EPA estimate and 50-60% higher than the prior indepedendent estimate, Alvarez et al 2018 - which did not directly assess the Permian but rather estimated at the average of the other basins studied.	4/7/2020	EDF News	Energy Exchange
40	Dlugokencky, 2020				Trends in Atmospheric Methane	This data repository post of NOAA readings for global atmospheric methane in 2019 records that the recent surge in atmospheric methane has continued. Estimates that year-over-year increase for 2019 is 11.5 ppb Even allowing for the maximum estimated bias in this preliminary estimate (+/- 3 ppb) the final annual number for 2019 would stand as the 3rd biggest annual increase in methane over the last 20 years.	4/5/2020	NOAA/ESRL	Scientific American		For an overview of the science on the global surge in atmospheric methane see this brief by Climate Nexus hot linked here.
41	Kholod et al. 2020				Global methane emissions from coal mining to continue growing even with declining coal production	Methane emissions from active and abandoned coal mines is more than twice as high as prior estimates, higher than current estimate from oil/gas sector (which is also probably a severe underestimate).	3/24/2020	Journal of Cleaner Production	Carbon Brief		early on-line publication, print publication May 2020
42	Milkov et al. 2020				Using global isotopic data to constrain the role of shale gas production in recent increases in atmospheric methane	This isotope analysis responds to the argument that shale oil/gas developments "have been the greatest single cause of the recent global increase of atmospheric CH4" [apparently referencing Howarth 2019] and argues that the rise in "global atmospheric CH4 is not dominated by emissions from shale gas and shale oil developments." The authors acknowledge that "Fossil fuel production contributes to increasing atmospheric CH4."	3/20/20	Scientific Reports			The strength of the conclusions in the isotope analysis by Howarth, Milkov and others crucially depends upon the accuracy of isotope inventories for different/oil gas developments, which are not yet firmly established, as well as the accuracy of the other factors (sources and sinks) that also affect the balance of the global isotope ratio, factors that also are not yet firmly established. In other words, there is significant uncertainty underlying seemingly contradictory conclusions about the size of the contribution to the global surge made by U.S. oil/gas operations, though there is increasing convergence that U.S. oil/gas operations are, at the least, making a contribution.
43	Höglund-Isaksson et al. 2020				Technical potentials and costs for reducing global anthropogenic methane emissions in the 2050 timeframe –results from the GAINS model	Finds that "rapid growth in extraction of unconventional gas in North America" is one of the three primary drivers of the surge in atmospheric methane from 2007 to 2015 (end of study period).	2/27/2020	Environmental Research Communications
44	Negron et al. 2020				Airborne Assessment of Methane Emissions from Offshore Platforms in the U.S. Gulf of Mexico	Finds that, for the full U.S. Gulf of Mexico, oil and gas facilities emit approximately one-half a teragram of methane each year, comparable with large emitting oil and gas basins like the Four Corners region in the southwest U.S. The effective loss rate of produced gas is roughly 2.9% (note: this is just for basin production and does include all of the supply chain losses included in the scope of Alvarez et al). This leakage rate similar to large onshore basins primarily focused on oil, and twice as high as current inventory estimates. Note that Alvarez et al did not revise the estimate for off-shore production.	2/19/2020	Environmental Science and Technology	Phys.Org
45	Nisbet et al. 2020				Methane Mitigation: Methods to reduce emissions on the Path to the Paris Agreement	Comprehensive global analysis that identifies, assesses, and details the most practical near-term options for address rising atmospheric methane concentrations. Identifies reduction of leaks and venting by oil and gas operations as a major opportunity. Notes further that "Reducing emissions from ongoing anthropogenic activities such as fossil fuel production and intensive ruminant farming is essentially palliative: it helps but does not cure. More substantial reductions can be achieved by ending or substantially reducing the activities themselves, for example, by shifting entirely away from coal and gas as energy sources and by reducing ruminant emissions. But such actions require political debate and major social adjustments, which are outside the scope of this journal. The more limited mitigation options discussed here are less contentious and can be implemented within the framework of existing commitments to the UNFCCC Paris Agreement."	1/14/2020	Reviews of Geophysics	EOS Science News
46	He et al. 2020				Investigation of the global methane budget over 1980–2017 using GFDL-AM4.1	Employs an atmospheric chemistry model to attribute the global surge in methane to anthropogenic sources such as agriculture, energy, and waste sectors, and discounts the contribution of wetlands. "...analysis indicates that anthropogenic sources (such as agriculture, energy, and waste sectors) are more likely major contributors to the renewed growth in methane after 2006. A sharp increase in wetland emissions (a likely scenario) with a concomitant sharp decrease in anthropogenic emissions (a less likely scenario), would be required starting in 2006 to drive the methane growth by wetland tracer."	1/3/2020	Atmospheric Chemistry and Physics
47	Pandey et al. 2019				Satellite observations reveal extreme methane leakage from a natural gas well blowout	Reports the detection of large methane emissions from a gas well blowout in Ohio during February to March 2018, with a methane emission rate of 120 ± 32 metric tons per hour, twice that of the wideAliso Canyon event in California in 2015. Assuming the detected emission represents the average rate for he blowout period, the total methane emission from the well blowout is comparable to one-quarter of the entire state of Ohio’s reported annual oil and natural gas methane emission, or, alternatively, a substantial fraction of the annual anthropogenic methane emissions from several European countries. Study highlights the importance of super-emitters and the short-comings of a bottoms-up approach to estimating methane emissions, as accidents in the oil and gas sector can release large amounts of methane in short periods of time.	12/16/2019	Proceedings of the National Academy of Sciences
48	Saint-Vincent and Pekney, 2019				Beyond-the-Meter: Unaccounted Sources of Methane Emissions in the Natural Gas Distribution Sector	"...Diffuse CH4 plumes above cities that are not attributable to distribution pipelines or other NG infrastructure suggest many small beyond-the-meter leaks together contribute to large emissions. Here, we evaluate the distribution sector of the CH4 emissions inventory and make suggestions to improve the inventory by analyzing end-user emissions. Preliminary research into beyond-the-meter emissions suggests that while individually small, the appliances and buildings that make up the residential sector could contribute significantly to national scale emissions. Furnaces are the most leak-prone of appliances, contributing to 0.14% of total CH4 emissions from the NG sector in the United States. Combining measurements from whole house emissions and steady-state operation of appliances, we estimate that residential homes and appliances could release 9.1 Gg CH4 yearly in the United States, totaling over 2% of the CH4 released from the NG sector. While factors such as appliance age and usage, climate, and residential setting could influence the emissions profile of individual appliances, these preliminary estimates justify further exploration of beyond-the-meter emissions." Per correspondence with the authors "the EPA does not currently estimate and report beyond-the-meter emissions of methane directly or indirectly."	12/6/2019	Environmental Science & Technology
49	Duren et al. 2019				California's methane super-emitters	"We estimate net methane point-source emissions in California to be 0.618 teragrams per year (95 per cent confidence interval 0.523–0.725), equivalent to 34–46 per cent of the state’s methane inventory8 for 2016. Methane ‘super-emitter’ activity occurs in every sector surveyed, with 10 per cent of point sources contributing roughly 60 per cent of point-source emissions—consistent with a study of the US Four Corners region that had a different sectoral mix9. The largest methane emitters in California are a subset of landfills, which exhibit persistent anomalous activity. Methane point-source emissions in California are dominated by landfills (41 per cent), followed by dairies (26 per cent) and the oil and gas sector (26 per cent). Our data have enabled the identification of the 0.2 per cent of California’s infrastructure that is responsible for these emissions."	11/6/2019	Nature	California Methane Survey
50	Barkley et al. 2019				Forward Modeling and Optimization of Methane Emissions in the South Central United States Using Aircraft Transects Across Frontal Boundaries	Finds that methane emissions from the O&G sector (just production and gathering) in South Central USA are 1.8 times larger than EPA inventory estimates [This region accounts for nearly 40 percent of the man-made methane emissions in the U.S. (the study was able to distinguish between agricultural emissiona and O&G emissions by tracking ethane co-emissions). Region includes Arkansas, Texas, Louisiana and Oklahoma. When asked to comment, via correspondence, to compare the estimate in his study for the South Central region vs. the estimate by Alvarez for that same region, Barkley states: "1.8x is a national average in his study, and a south central average in my study, but going down to a basin level is going to have huge variability that would probably make it dangerous to compare to in that way." NB: this comparison is for production and gathering. It does not include leaks from processing and transmission.	10/29/2019	Geophysical Research Letters	Phys.Org	Science News
51	Howarth 2019				Ideas and perspectives: is shale gas a major driver of recent increase in global atmospheric methane?	This perspectives article analyzes istope data and the rapid rise in atmospheric methane over the past decade and argues that "that shale-gas production in North America over the past decade may have contributed more than half of all of the increased emissions from fossil fuels globally and approximately one-third of the total increased emissions from all sources globally over the past decade." This estimate stands at the high-end of the range of estimates, though it is consistent with at least one other estimate, Höglund-Isaksson et al. 2020.	8/14/2019	Biogeosciences	National Geographic		The strength of the conclusions in the isotope analysis by Howarth, Milkov and others crucially depends upon the accuracy of isotope inventories for different/oil gas developments, which are not yet firmly established, as well as the accuracy of the other factors (sources and sinks) that also affect the balance of the global isotope ratio, factors that also are not yet firmly established. In other words, there is significant uncertainty underlying seemingly contradictory conclusions about the size of the contribution to the global surge made by U.S. oil/gas operations, though there is increasing convergence that U.S. oil/gas operations are, at the least, making a contribution.
52	Jia and Shevliakova et al. 2019 (IPCC)				IPCC Special Report on Climate Change and Lands: Chapter 2 Land-Climate Interactions	The report highlights the role of agriculture in driving the global surge in atmospheric methane, but also assigns a role to U.S. oil and gas production. The Summary for Policy Makers notes that “ruminants and the expansion of rice cultivation are important contributors to the rising concentration” of atmospheric methane. Chapter 2 of the Report examines oil and gas production in the context of the growth of atmospheric methane and reports that: “Fugitive emissions likely contribute to the renewed growth after 2006” and points to increased fracking in America as a contributor: “the increased production of natural gas in the US from the mid 2000’s is of particular interest because it coincides with renewed atmospheric aCH4 growth” and notes that “The importance of fugitive emissions in the global atmospheric accumulation rate is growing.”	8/8/2019	IPCC
53	Plant et al. 2019				Large Fugitive Methane Emissions From Urban Centers Along the U.S. East Coast	Examines six old and leak‐prone major cities along the East Coast of the United States, representing nearly 12% of the U.S. population and 4 of the 10 most populous cities, focusing on older, leak‐prone urban centers. Finds methane emissions are more than twice EPA estimates. Estimates 0.75 Tg CH4/year is attributed to natural gas (equivalent to about 7.5% of direct leaks from production of natural gas nationally, well over triple the amount emitted by gas production in the Bakken shale formation in the U.S. Midwest.). These results highlight that current urban inventory estimates of natural gas emissions are substantially low, either due to underestimates of leakage, lack of inclusion of end‐use emissions, or some combination thereof. NB: 0.75 Tg CH4/year compares to the 0.44 Tg CH4/year assumed by Alvarez for local distribution leaks across the entire nation, an assumption taken directly from the EPA GHGI estimate.	7/15/2019	Geophysical Research Letters	Science
54	He et al. 2019				Atmospheric Methane Emissions Correlate With Natural Gas Consumption From Residential and Commercial Sectors in Los Angeles	Study on residential and commercial leaks methane emissions at the city level is Los Angeles finds a leakage rate of 1.4% and an annual emissions of 0.27 Tg CH4/year, compares to 0.44 Tg CH4/year assumed by Alvarez for local distribution leaks across the entire nation, an assumption taken directly from the EPA GHGI estimate.	7/15/2019	Geophysical Research Letters	Eureka Alert! AAAS
55	Maasakkers et al. 2019				Global distribution of methane emissions, emission trends, and OH concentrations and trends inferred from an inversion of GOSAT satellite data for 2010–2015	Reports that "2010–2015 increasing trend in atmospheric methane is mostly due to increasing emissions rather than decreasing OH concentrations. Most of the increase is in tropical wetlands, India, and China. Trends in North America and Europe are small." Reports that methane emissions from oil/gas operations in the U.S. are higher than reported to the UNFCCC (see Figure 6).	6/12/2019	Atmospheric Chemistry and Physics
56	Zhou et al. 2019				Estimation of methane emissions from the U.S. ammonia fertilizer industry using a mobile sensing approach	Discovered that methane emissions from ammonia fertilizer plants were 100 times higher than the fertilizer industry’s self-reported estimate. They also were three times higher than the Environmental Protection Agency (EPA) estimate for all industrial processes in the United States. On average, 0.34% of the gas used in the plants is emitted to the atmosphere. Total emissions were 28 gigagrams/year (0.028 Tg/year), equivalent to about 0.3% of the methane emissions from the production of natural gas.	5/28/2019	Elementa	Cornell Chronicle
57	Lan et al. 2019				Long‐Term Measurements Show Little Evidence for Large Increases in Total U.S. Methane Emissions Over the Past Decade	Finds that methane emission from U.S. oil and gas production have increase roughly 40% from 2006 to 2015 (end of study period).	4/13/2019	Geophysical Research Letters	Energy Exchange		See EDF analysis published in Energy Exchange which explains what Lan et al. mean by "large"
58	Zimmerle et al. 2019				Characterization of Methane Emissions from Gathering Compressor Stations: Final Report	The EPA recently used this study to revert to a "bottom-up" inventory method that reduced the EPA esimate of emisssions from natural gas gathering stations. Study provides a "bottom-up" count of emisssions from natural gas gathering stations. Back In 2016 EPA updated its inventory estimates for gathering stations using data from a study that used "top-down" monitoring of site-level emissions to estimate emissions (Marchese et al. 2015, listed here). But in April 2020 the EPA posted a new inventory that switched back to a bottom-up approach that counted-up individual components and estimated emissions by assuming a leak rate for each type of component, based on this study by Zimmerle et al. The bottom-up approach provides more granular detail about the sources of common/regular leaks but does not provide a good view of total emissions. As a result the EPA estimate decreased, going from 2.2 million metric tons of methane emissions from gathering stations in 2017 to 1.3 million under the method the EPA is now using.	3/30/2019	U.S. Department of Energy (DOE)	Bloomberg	Energy Exchange
59	Turner et al. 2019				Interpreting contemporary trends in atmospheric methane	Analyzes global surge in atmospheric methane, recommends responding by targetting emissions from natural gas production.	2/19/2019	Proceedings of the National Academy of Sciences
60	Nisbet et al. 2019				Very Strong Atmospheric Methane Growth in the 4 Years 2014–2017: Implications for the Paris Agreement	"Methane's increase since 2007 was not expected in future greenhouse gas scenarios compliant with the targets of the Paris Agreement, and if the increase continues at the same rates it may become very difficult to meet the Paris goals. There is now urgent need to reduce methane emissions, especially from the fossil fuel industry."	2/5/2019	Global Biogeochemical Cycles	Los Angeles Times
61	Miller et al. 2019				China’s coal mine methane regulations have not curbed growing emissions	Finds that emissions from China rose by 1.1 ± 0.4 Tg CH4 yr−1 from 2010 to 2015, culminating in total anthropogenic and natural emissions of 61.5 ± 2.7 Tg CH4 in 2015. The observed trend is consistent with pre-2010 trends and is largely attributable to coal mining.	1/29/2019	Nature Communications
62	Pandey et al 2019b				Influence of Atmospheric Transport on Estimates of Variability in the Global Methane Burden	Analyses the transport of methane across the atmoshere, find a faster increase in emissions in the Northern Hemisphere than in the Southern Hemisphere, particularly increases in the nothern mid-latitudes. Their analysis indicates that prior analyses of emissions by latitude under-estimate emissions from nothern mid-latitudes and overestimate emissions from other regions.	1/29/2019	Geophysical Research Letters
63	Thompson et al. 2018				Variability in Atmospheric Methane From Fossil Fuel and Microbial Sources Over the Last Three Decades	Reports that "This study uses atmospheric observations of methane and two related tracers, the isotopic ratio of carbon in methane and ethane, to constrain the sources and sinks of methane over the past three decades. The increase in methane between 2007 and 2014 is likely due to an increase in microbial sources, of 24–48 Tg/y (predominantly natural wetlands and agricultural), as well as fossil fuel sources, of 7–23 Tg/y. In contrast to other recent studies, a reduction in the atmospheric sink of methane was found not to be a significant factor in explaining the recent atmospheric increase." In this study, fossil fuel sources include coal, oil, and gas.The authors further: "Noteworthy is that the biomass burning emissions, though largely unchanged compared to the prior, decreased by 3.4 ± 1.7 Tg y−1 from 2006 to 2014, which is comparable to the result of Worden et al. (2017), who found a reduction in this source of 3.7 ± 1.4 Tg y−1 based on satellite retrievals of CH4, CO, and fire activity." This findings supports the conclusions of Worden et al which found that reduced wildfire emissions masked the increase in fossil fuel emissions, explaingin the istopic shift observed in parallel with increasing fossil fuel emissions. The authors conclude by noting: "Considering that the CH4 increase is likely to be partially due to an increase in the fossil fuel source, there may be a possibility to curb the growth by mitigating these emissions."	10/10/2018	Geophysical Research Letters
64	Alvarez et al. 2018				Assessment of methane emissions from the U.S. oil and gas supply chain	A capstone study. Estimates 2015 supply chain emissions are equivalent to 2.3% of gross U.S. gas production, about 60% higher than the EPA estimate at the time (EPA estimate have gone down even further in 2020). At 2.7% leakage rate, gas to power plants is worse than coal-fired power. Confirms the findings of a 2014 study by Brandt et al that suggested that leakage from natural gas systems was between 1.25 and 1.75 times larger than official inventories, implying a leakage rate of between 1.9% and 2.6%. Also confirms the findings of Miller et al 2013, a top-down study which finds methane emissions 50% above EPA estimates.	7/13/2018	Science	Financial Times
65	Sheng et al. 2018				2010–2016 methane trends over Canada, the United States, and Mexico observed by the GOSAT satellite: contributions from different source sectors	Finds that "US emission trends...account for about 20 % of the observed increase in global methane over the 2010–2016 period," and proportions that contribution roughly evenly between the U.S. national oil/gas system and Midwestern livestock ("possibly swine manure management").	3/20/2018	Atmospheric Chemistry and Physics
66	Dalsøren et al. 2018				Discrepancy between simulated and observed ethane and propane levels explained by underestimated fossil emissions.	Examination of ethane (not methane) levels provides further evidence of problems with official inventory estimates of methane sources. Authors report that "we show that observations of pre-industrial and present-day ethane and propane can be reproduced in simulations with a detailed atmospheric chemistry transport model, provided that natural geologic emissions are taken into account and anthropogenic fossil fuel emissions are assumed to be two to three times higher than is indicated in current inventories... The improved correspondence with observed ethane and propane in model simulations with greater emissions suggests that the level of fossil (geologic + fossil fuel) methane emissions in current inventories may need re-evaluation." See Dalsøren et al, 2018: Discrepancy between simulated and observed ethane and propane levels explained by underestimated fossil emissions.	2/26/2018	Nature Geoscience
67	Worden et al. 2017				Reduced biomass burning emissions reconcile conflicting estimates of the post-2006 atmospheric methane budget	Finds that fossil fuel source are responsible for half to two-thirds of the increase in atmospheric methane. Reports that a reduction of biomass burning (e.g. wildfires) is responsible for the decrease in the heavy isotope content of atmospheric methane, a shift that masked the increased contribution of fossil sources to atmospheric methane as those sources are weighted towards heavy isotopes.	12/20/2017	Nature Communications	NASA	Phys.org	NASA JPL News Release
68	Bruhwiler et al. 2017				U.S. CH4 emissions from oil and gas production: Have recent large increases been detected?	Find that overall methane emissions in the U.S. did not rise between 2000 and 2012 and deduces that flat trend is inconsistent with a large increase in methane emissions from the oil and gas sector.	3/18/2017	Journal of Geophysical Research Atmospheres
69	Saunois et al. 2016				The growing role of methane in anthropogenic climate change	"Unlike CO2, atmospheric methane concentrations are rising faster than at any time in the past two decades and, since 2014, are now approaching the most greenhouse-gas-intensive scenarios. The reasons for this renewed growth are still unclear, primarily because of uncertainties in the global methane budget. New analysis suggests that the recent rapid rise in global methane concentrations is predominantly biogenic-most likely from agriculture-with smaller contributions from fossil fuel use and possibly wetlands. Additional attention is urgently needed to quantify and reduce methane emissions. Methane mitigation offers rapid climate benefits and economic, health and agricultural co-benefits that are highly complementary to CO2 mitigation."	12/16/2016	Environmental Research Letters	New York Times
70	Helmig et al. 2016				Reversal of global atmospheric ethane and propane trends largely due to US oil and natural gas production.	Authors track and analyze rising ethane and propane levels (ethane, not methane) and show rising ethane level indicates that rising global methane levels are driven in large part by North American oil and natural gas development. Authors report: "Using data from a global surface network and atmospheric column observations we show that the steady decline in the ethane mole fraction that began in the 1970s halted between 2005 and 2010 in most of the Northern Hemisphere and has since reversed. We calculate a yearly increase in ethane emissions in the Northern Hemisphere of 0.42 (±0.19) Tg yr−1 between mid-2009 and mid-2014. The largest increases in ethane and the shorter-lived propane are seen over the central and eastern USA, with a spatial distribution that suggests North American oil and natural gas development as the primary source of increasing emissions. By including other co-emitted oil and natural gas non-methane hydrocarbons, we estimate a Northern Hemisphere total non-methane hydrocarbon yearly emission increase of 1.2 (±0.8) Tg yr−1.... Methane/ethane oil and natural gas emission ratios could suggest a significant increase in associated methane emissions..."	6/13/2016	Nature Geoscience	Science Daily
71	Hakola & Hellén 2016				The Return of Ethane	Authors analyze ethane trends (particularly as reported by Helmig et al) and conclude that oil and gas production in North America is responsible for 39% of the renewed increase in global methane levels. Authors report that "Combined with measurements of ethane that are representative of the free troposphere, and a large oil and gas field, the work by Helmig et al.2016 shows that ethane and propane concentrations in the Northern Hemisphere have taken an upward turn, largely as a by-product of the massive increase in oil and gas exploration in North America." Hakola & Heidi Hellén further report that "Time-series measurements of methane and ethane were significantly correlated during 2007–2014 (ref. 3), a period when global atmospheric methane concentrations began increasing again after stalling between 1999 and 2007. However, there was no correlation between ethane and methane concentrations in measurements earlier than 2007, or in measurements from the Southern Hemisphere, suggesting that oil and gas production have become more important sources of methane in the Northern Hemisphere since 2007. Based on the ethane-to-methane ratio of emissions and assuming that the increase in ethane emissions is entirely from oil and natural gas sources, these sources contributed at least 39% to the renewed methane increase." Hakola & Heidi Hellén further report that the Bakken shale formation alone "....is responsible for emissions on the order of 0.23 ± 0.07 terragrams of ethane per year, equivalent to 1–3% of all ethane emissions globally."	6/13/2016	Nature Geoscience
72	Marchese et al. 2015				Methane Emissions from United States Natural Gas Gathering and Processing	This top-down study was the basis for the EPA estimate of emissions from segment of the natural gas system devoted to gathering and compressing natural gas. In April of 2020, the EPA lowered it's estimate of methane emissions from this segment by reverting to a bottom up approach embodied by a new study, Zimmerle et al. 2020 (listed here). This study (Marchese et al. 2015) bya CSU-led study team attempted to measure a few large, episodic emission events with top-down methods. They estimate U.S. gathering station episodic emissions were 169 Gg CH4 but with a huge uncertainty of +426%/-96% due to the challenges of extrapolating emissions from these events. Note that most of the uncertainty is on the high side, not the low side.	8/18/2015	Environmental Science & Technology
73	Brandt et al. 2014				Methane Leaks from North American Natural Gas Systems	This assessment of the literature to date at the time (2014) reports that "Across years, scales, and methods, atmospheric studies systematically find larger CH4 emissions than predicted by inventories. [Emission factors] were also found to underestimate bottom-up measured emissions....the largest (e.g., national-scale) atmospheric studies (>1012 g CH4/year) suggest typical measured emissions ~1.5 times those in the GHGI."
74	Hamburg 2013				Methane: a Key to Dealing With Carbon Pollution?	EDF scientists re-ran the underlying math behind the widely referenced breakeven points in the 2012 Alvarez et al. paper. Under the coal to natural gas fuel-switching scenario, natural gas is indicated to be better for the climate than coal on the day the switch is made if less than 2.7% of natural gas produced is emitted before the point of use, versus the former 3.2%. Over long time horizons, the effects of any one-day leak begins to taper off as the leaked methane washes out of the atmosphere.	11/5/2013	Energy Exchange			NB: Alvarez et al. estimated leakage at 2.3% of production, while the 2.7% number is a percentage of consumption. Since some gas is emitted before being consumed, and more is used to drive pipeline compressors, etc., 2.3% of production is approximately 2.6% of consumption.
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