Powered by clean natural gas? No fracking way[footnoteRef:1] [1: http://sallyhayati.wordpress.com/2014/04/12/powered-by-clean-natural-gas-no-fracking-way/ ]

Warning: the C doesnt really stand for Clean

Sally Hayati, The Environmental Priorities NetworkApril 10, 2014

ABSTRACTCNG bus tailpipe emissions are not significantly better than new or retrofitted diesel buses. But the effect on global warming of CNG buses is significantly worse than diesel buses. Battery electric bus (BEB) or hybrid diesel bus technologies have lower well-to-wheels emissions than CNG & are available now.Environmentalists should therefore advocate that bus fleets purchase battery electric buses, not CNG, to expand the fleet or replace old buses. Until full replacement with clean renewable energy options such as BEB can be achieved, older diesel buses should be retrofitted with the best modern emissions controls, or if necessary, new diesel or hybrid diesel buses purchased, rather than investing in new CNG buses and infrastructure (fueling stations and safety modifications). The large investment needed to convert to CNG will lock in fossil fueled transportation for decades to come. Electrification of the transportation sector is an essential step towards using clean, 100% wind, water, and sun energy.

Despite an increased awareness of the environmental harm caused by unconventional drilling for natural gas and growing battles against fracking nationwide, natural gas is still favored by many environmentalists and government agencies as a bridge fuel for power generation and transportation. In the South Bay the Harbor Community Benefit Foundation (HCBF) awarded a grant to the Boys & Girls Clubs of LA Harbor to buy two Compressed Natural Gas (CNG) school buses and scrap an older diesel bus. On February 27, 2014 HCBF hosted a Crush the Bus celebration at the scrap yard to advertise the permanent community health benefit to be derived from crushing an older diesel bus and buying two CNG buses. School children were brought to observe and learn from the event; invitations were distributed on progressive email lists; supporting politicians and agencies claimed environmental credit in YouTube videos.[footnoteRef:2] More than one Crush the Bus announcement and news report[footnoteRef:3] referred to clean natural gas (CNG) buses instead of compressed. This positive perception of natural gas is not limited to HCBF; by 2012 the Sierra Club had taken more than $26 million from natural gas interests to support its anti-coal work (this practice has since stopped).[footnoteRef:4] [2: https://www.youtube.com/watch?v=LSmomOeU6qU ] [3: http://losangeles.cbslocal.com/video/9894332-hawaiian-gardens-students-learn-about-recycling-at-crush-the-bus-event/ ] [4: http://science.time.com/2012/02/02/exclusive-how-the-sierra-club-took-millions-from-the-natural-gas-industry-and-why-they-stopped/ ]

Environmentalists should be more wary. Scientists tell us that The climatic effect of replacing other fossil fuels with natural gas varies widely by sector (e.g., electricity generation or transportation) and by the fuel being replaced (e.g., coal, gasoline, or diesel fuel), distinctions that have been largely lacking in the policy debate.[footnoteRef:5] Only careful analysis and measurements can accurately determine the climate impact of various energy options. Fortunately, several such studies have been performed and we need to take heed, because there is little benefit and substantial environmental harm in powering vehicles with CNG instead of diesel fuel. [footnoteRef:6] [5: http://www.pnas.org/content/109/17/6435.full.pdf, Alvarez, Greater focus needed on methane leakage ] [6: The replacement of gasoline with CNG is also not recommended, but replacing coal with natural gas to generate electricity apparently does reduce GHG emissions somewhat, at least over a 100-year time frame. That calculation used the 2012 IPCC value for methanes GWP, however, which has since been increased from 25 to 34. ]

We now consider three environmental claims made by HCBF,[footnoteRef:7] that switching from diesel to CNG buses [7: http://hcbf.org/blog/watch-diesel-school-bus-get-crushed/#more-1942 ]

[1] Reduces fossil fuel consumption, [2] reduces greenhouse gas emissions by a significant amount, and [3] reduces diesel particulate matter by 98% per mile.

As for the first claim, switching to CNG does not reduce fossil fuel consumption. Natural gas is, of course, a fossil fuel. And a California Energy Commission study estimated that heavy-duty CNG vehicles consume up to 8% more fossil fuel than diesel.[footnoteRef:8] CNG does use 99% less petroleum over its life cycle compared to gasoline.[footnoteRef:9] But diesel buses average more miles per gallon (MPG) than CNG buses because they operate under high pressure and convert a larger percentage of the fuel's available energy into usable work.[footnoteRef:10] [8: http://www.energy.ca.gov/2007publications/CEC-600-2007-004/CEC-600-2007-004-F.PDF Table 3-11] [9: http://www.afdc.energy.gov/vehicles/natural_gas_emissions.html ] [10: http://www.afdc.energy.gov/pdfs/47919.pdf The Business Case for CNG in Municipal Fleets, 2010]

Does switching from diesel to CNG vehicles reduce greenhouse gas emissions?

Switching from diesel to CNG vehicles almost certainly increases greenhouse gas (GHG) emissions. It is true that natural gas in general emits less of the greenhouse gas carbon dioxide (CO2) during combustion than other fossil fuels, because methane has a lower CO2 to energy content than other fossil fuels. But this isnt the whole story.

First, while it is true that replacing coal with natural gas in power plants results in significantly lower CO2 emissions from combustion, replacing diesel fuel with compressed natural gas in vehicles only modestly lowers CO2 emissions.[footnoteRef:11] UPS estimated that CNG truck CO2 emissions are 7% less than equivalent diesel trucks. This is because diesel is an energy dense fuel, and due to higher compression ratios and lean-burn combustion, diesel buses with emissions controls are 15-20% more efficient than CNG buses (up to 30% without emissions controls).[footnoteRef:12] [11: . http://climatetechwiki.org/technology/cng , ] [12: http://www.nrel.gov/vehiclesandfuels/fleettest/pdfs/31227.pdf ]

Second, any valid comparison of fuel options must consider not just tailpipe emissions of CO2, but also the well-to-wheels emissions of all GHGs. In particular, there is considerable leakage of unburned methane, a potent greenhouse gas, during the production, storage, transportation, and use of natural gas. [footnoteRef:13] Because methane has a significantly higher global warming potential (GWP-see text box) than CO2, even a relatively small methane leakage rate can eclipse CNGs limited tailpipe CO2 benefit over diesel. [13: There is a smaller amount of methane leakage during oil extraction also, which is accounted for in comparison between diesel and CNG fuel.]

BACKGROUND INFO: the Global Warming Potential (GWP) of greenhouse gases (GHG). Greenhouse gases are those gases in the atmosphere that can absorb and emit infrared radiation (heat). The 5 primary atmospheric greenhouse gases are water vapor, carbon dioxide, methane (CH4), nitrous oxide, and ozone. A gass global warming potential (GWP) is determined by the amount of heat it absorbs and emits for a given mass (radiative forcing) and its atmospheric lifetime (the percentage of a gas emission that persists in the atmosphere after a specified time). Global warming potential for each gas is defined relative to the same mass of CO2 and evaluated for a specific timescale. So carbon dioxide by definition has a GWP of 1 over all time periods. Compared to CO2, methane has a higher radiative forcing but a shorter lifetime, so it has a larger GWP on a 20-year scale than it does on a 100-year scale.

One 2012 study, using a GWP of 25 for methane, calculated that for CNG to immediately reduce climate impacts from heavy-duty vehicles, well-to-wheels leakage must be reduced below 1%.[footnoteRef:14] In other words, if methane leakage is more than 1%, net greenhouse gas emissions will increase if we switch from diesel to CNG. This is bad news, because even the low 2013 EPA estimate puts leakage at 1.5%. Sixteen scientists recently confirmed in a 2014 study based on a review of 20 years of technical literature on natural gas emissions (> 200 technical publications) that powering trucks and buses with natural gas instead of diesel fuel probably makes the globe warmer.[footnoteRef:15] [14: http://www.pnas.org/content/early/2012/04/02/1202407109.full.pdf+html ] [15: http://news.stanford.edu/news/2014/february/methane-leaky-gas-021314.html ]

Worse yet, there is evidence that the actual average methane leakage rate is significantly greater than 1.5%. Several recent studies suggest that the overall methane leakage rate from natural gas production is higher, by approximately 50%, than even the previous 2012 EPA cap of 3%, and that super emitters exist with 12% leakage rates.[footnoteRef:16] Yet in spite of this mounting evidence, in 2013 the EPA lowered its estimate from 3% to 1.5%. Another 2013 study stated, Regional methane emissions due to fossil fuel extraction and processing could be 4.9 2.6 times larger than in EDGAR, the most comprehensive global methane inventory. These results cast doubt on the US EPAs recent decision to downscale its estimate of national natural gas emissions by 2530% [in 2013].[footnoteRef:17] A different study indicates that the greatest source of uncertainty in explaining increasing atmospheric methane is the oil and gas industry, which has been underestimated in past studies.[footnoteRef:18] There is also evidence that unconventional drilling techniques (e.g., fracking) result in 30% to 100% more methane leakage than conventional natural gas extraction.[footnoteRef:19] If true, methane leakage rates will increase with the surge in fracking and other unconventional drilling techniques. [16: http://link.springer.com/article/10.1007%2Fs10584-011-0061-5#page-1, 2011, Howarth, GHG from Shale NG http://onlinelibrary.wiley.com/doi/10.1002/grl.50811/abstract 2013, Karion, Airborne measurements of methane http://www.pnas.org/content/early/2013/11/20/1314392110.abstract, 2013, Miller, Anthropogenic methane http://www.epa.gov/ttnchie1/conference/ei20/session6/gpetron.pdf, Petron, 2012, Estimation of Emissions CO] [17: http://www.pnas.org/content/110/50/20018.full , 2013, Miller, Anthropogenic emissions of methane in the US.] [18: http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0CDkQFjAB&url=http%3A%2F%2Fwww.researchgate.net%2Fpublication%2F236884936_Quantifying_sources_of_methane_using_light_alkanes_in_the_Los_Angeles_basin_California%2Ffile%2F5046351f6bb17d7e62.pdf&ei=xgI2U7bbNc3eyAGhy4GYCg&usg=AFQjCNEYSPvKHZjpFaDqTr7JFZDJ-Kp6pw&sig2=ExQe48SSSluOjjtOsXoiUg&bvm=bv.63808443,d.aWc ] [19: http://oilprice.com/Energy/Energy-General/New-Study-Finds-Higher-Methane-Emissions-from-Fracking.html ]

Such high methane leakage rates from natural gas exploitation, in the 3-10% range, have very serious implications. One 2011 study calculated that unless the leakage rate is kept below 2.5%, replacing coal with natural gas in power plants increases net GHG emissions and global warming for decades to come.[footnoteRef:20] Assuming leakage rates towards the upper half of the estimated range, a 2012 publication found that converting a fleet of heavy-duty diesel vehicles to CNG would increase radiative forcing for 280 years, leading to faster and higher levels of global warming than if the fleets had remained diesel.[footnoteRef:21] Such conversions are very frequent now. [20: http://thinkprogress.org/romm/2011/09/09/315845/natural-gas-switching-from-coal-to-gas-increases-warming-for-decades/ ] [21: http://www.pnas.org/content/early/2012/04/02/1202407109.full.pdf+html ]

As terrifying as these conclusions are, they are too conservative. Methane is now known to be a significantly more potent greenhouse gas than was earlier thought. Almost every study cited in this paper used the 2007 IPCC methane global warming potential (GWP) of 25 in their calculations, whereas the more accurate 2013 value is 34, 36% higher. If study calculations were repeated using the new GWP value, the result would be that the leakage rate should be appreciably less than 1% for CNG fuel to be no worse than diesel, and appreciably less than 2.5% for natural gas to be better than coal for electricity generation. Meanwhile methane continues to leak at a rate that is almost certainly significantly higher than that.

Methane Global Warming Potential (GWP)Lifetime(yrs)GWP Time Horizon

20 yrs100 yrs

2007 IPCC AR4 p21212 7225

2013 IPCC AR5 p71412.48634

Here there is one last nail in the CNG coffin: Most studies use the 100-year time scale to compare the global warming potential of methane compared to CO2. But because methane is less persistent in the atmosphere than CO2, its warming effects are most apparent on the 20-year time scale, when it has a GWP of 86! Shorter time scales are important because within a decade or two we could reach tipping points leading to abrupt and irreversible changes, such as the release of methane from thawing permafrost or the acceleration of polar ice cap melting.[footnoteRef:22] [22: http://newscenter.berkeley.edu/2013/12/03/report-warns-of-climate-change-tipping-points-within-our-lifetime/, Abrupt Impacts of Climate Change. ]

Is CNG the best option to achieve lower bus tailpipe emissions?

The reduction of tailpipe emissions was HCBFs primary goal. It is true that new CNG buses have 98% lower particulate matter emissions than older diesel buses. But other options provide similar or better reductions, without increasing greenhouse gas emissions beyond current levels, as CNG does. Battery Electric Buses have zero tailpipe emissions, superior to CNG buses

Battery electric buses (BEB) have zero tailpipe emissions and are superior to CNG buses, clean diesel, or hybrid diesel in terms of local pollution abatement. Electricity is a more efficient way to deliver energy than diesel combustion, but well-to-wheels GHG emissions of electric vehicles depends on the mix of energy sources used for power generation and manufacturing. One study of electric vehicle carbon emissions found that, compared to other nations, the US has a high-intermediate level of carbon emissions from manufacturing and power grid. At this level, electric vehicles have approximately the same GHG emissions as a diesel vehicle (or a gasoline hybrid).[footnoteRef:23] Therefore, on average and at this time in the US, a switch from diesel to battery electric vehicles will not have a measurable effect on GHG emissions. In California, where the carbon emissions from the power grid are somewhat lower than the national average, there may be a small reduction in GHG emissions. [23: http://shrinkthatfootprint.com/wp-content/uploads/2013/02/Shades-of-Green-Full-Report.pdf ]

As the US changes the energy mix powering our electric grid to include more wind, water, and sun (WWS) energy or a lower-carbon mix of fossil fuels, the GHG emissions of electric vehicles will go down accordingly. In countries with low carbon power today, such as Iceland and Paraguay, electric vehicles result in less than half the emissions of the best gasoline hybrids. [footnoteRef:24] [24: http://shrinkthatfootprint.com/wp-content/uploads/2013/02/Shades-of-Green-Full-Report.pdf ]

But we must not wait until we have a low carbon electric grid to begin transitioning to battery electric vehicles. The transportation sector will need to be electrified before we can transition 100% of our energy needs to WWS power.[footnoteRef:25] It is vitally important to deploy electric vehicle technology on a large scale as quickly as possible. As long as our transportation sector directly burns fossil fuel, we will not be able to reduce GHG emissions sufficiently or quickly enough to adequately limit global warming.[footnoteRef:26] [25: http://www.stanford.edu/group/efmh/jacobson/Articles/I/JDEnPolicyPt1.pdf . All end uses that feasibly can be electrified will use WWS power directly, and remaining end uses use WWS power indirectly in the form of electrolytic hydrogen, produced by WWS energy. Some transportation would include hydrogen fuel cell vehicles (HFCVs), and some high temperature industrial heating would include hydrogen combustion. Other useful transportation technologies include hybrid BEV-HFCVs, hybrid hydrogen fuel cell-battery systems (ships), and liquefied hydrogen combustion (aircraft), all produced using WWS energy. For further discussion & why biofuel is not a an environmentally sound alternative, see http://www.stanford.edu/group/efmh/jacobson/Articles/I/JDEnPolicyPt1.pdf] [26: http://www.stanford.edu/group/efmh/jacobson/Articles/I/JDEnPolicyPt1.pdf ]

Why did HCBF choose CNG over battery electric buses? This isnt clear, but their website points to a Natural Resources Defense Council (NRDC) website on diesel school buses that evaluated three alternatives: green diesel, battery electric, and CNG. This NRDC website was last updated in March 200113 years ago![footnoteRef:27] Their out-of-date advice was that battery electric buses were not yet viable but may be on the horizon. [27: As of April 10, 2014.]

In fact, since 1992 Chattanooga, TN has provided free battery-electric shuttle bus services using the original buses manufactured by Advanced Vehicle Systems.[footnoteRef:28] In 2010 the worlds first heavy duty, battery-electric, fast-charge bus started operation in Pomona, CA at Foothill Transit. The Proterra EcoRide BE35 uses lithium-titanate batteries and is able to fast-charge in less than 10 minutes.[footnoteRef:29] Proterra manufactures an Altoona-tested all-electric bus, approved at the federal testing ground for public transit vehicles.[footnoteRef:30] In 2013 the Chinese company BYD Motors, with an office in LA and manufacturing facility in Lancaster, won contracts to provide battery electric buses to the city of Long Beach and LA Metro.[footnoteRef:31] [28: http://www.afdc.energy.gov/pdfs/chatt_cs.pdf ] [29: http://www.proterra.com/index.php/mediacenter/companynews/proterra_launches_first_deployment_of_all-electric_zero-emission_buses/ ] [30: http://la.streetsblog.org/2013/06/12/opinion-metro-dont-make-the-same-mistake-long-beach-transit-did-on-electric-buses/ ] [31: http://www.huffingtonpost.com/2014/04/01/byd-china-electric-car_n_4964233.html , snafus recently led to contract cancellation and a new competition for the Long Beach contract.]

Then in 2013, the SST-e battery electric school bus arrived. Built by Trans Tech Bus[footnoteRef:32] the zero-emissions all-electric school bus is available with 80 or 100 miles of range and can be 50-percent charged in less than an hour. The Kings Canyon Unified School District (KCUSD) in Californias San Joaquin Valley started using the SST-e in 2014 to transport its students. The bus passed all KCUSD and California Highway Patrol inspections and certifications and is the first all-electric bus to be approved for student transportation in the US. The California Air Resources Board contributed $400,000 to the pilot program in the form of cost-offsetting vouchers,[footnoteRef:33] and theCalifornia Hybrid and Zero-Emission Truck and Bus Voucher Incentive Project (HVIP) also provided funds. For now, these buses are approximately twice as expensive as new (green) diesel buses. But HVIP funding is available for Californiaschool districts to offset about half of the incremental additional cost of eligible hybrid and battery-electric medium- and heavy-duty vehicles.[footnoteRef:34] [32: http://www.transtechbus.com ] [33: http://thinkprogress.org/climate/2014/03/04/3359551/electric-school-bus-2/ ] [34: http://www.californiahvip.org/about-the-project, CA HYBRID TRUCK & BUS VOUCHER INCENTIVE PROJECT ]

Older diesel buses retrofitted with modern emissions controls or new diesel buses give reductions similar to CNG buses

Environmentalists should strive in every case to replace fossil fuel with WWS energy or with electricity. If economic or other factors absolutely prevent this, we should advocate the least harmful alternative. In this case, that alternative is modern green or clean diesel. Hybrid diesel technology is another option. Older diesel buses retrofitted with modern exhaust emissions controls or modern diesel buses both achieve reductions in particulate matter (PM), hydrocarbon (HC), and nitrogen oxide (NOx) emissions that are essentially equivalent to CNG, as shown in Table 1.[footnoteRef:35] [35: http://www.catf.us/resources/publications/view/162, 2012, MJB&A, Clean Diesel vs CNG Buses: Climate Impacts, or see cached version at http://webcache.googleusercontent.com/search?q=cache:pe4EHyzhuoYJ:www.catf.us/resources/publications/files/20120227-Diesel_vs_CNG_FINAL_MJBA.pdf+&cd=1&hl=en&ct=clnk&gl=us&client=safari ]

NOxPMHC

Diesel bus 201294%98%89%

CNG bus 201280%99%100%

Table 1. Reductions in emissions compared to a 2000 model year diesel bus, according to EPAs MOVES emissions modelAs the US Department of Energy explains, Due to increasingly stringent emissions regulations, the gap has narrowed between tailpipe emissions benefits from natural gas vehicles (NGVs) and conventional vehicles [e.g., diesel] with modern emissions controls. As promoted by the EPA Clean School Bus program, smelly older diesel buses can be retrofitted with modern catalysts and particulate matter filters to meet emissions standards. In fact, as of January 1, 2014, Californias Air Resources Boards (CARB) On-Road Heavy-Duty Diesel Vehicles (In-Use) Regulation requires all older diesel buses and trucks on the road to be retrofitted to bring them up to modern standards.[footnoteRef:36],[footnoteRef:37] CARBs Lower-Emission School Bus Program provides grant funding for the cost of retrofitting older diesel school buses.[footnoteRef:38] [36: http://www.arb.ca.gov/msprog/onrdiesel/onrdiesel.htm] [37: http://transportpolicy.net/index.php?title=California:_Diesel_Risk_Reduction_Program ] [38: http://www.arb.ca.gov/msprog/schoolbus/schoolbus.htm ]

Why did HCBF purchase CNG buses instead of retrofitting their existing or purchasing clean diesel buses? The 2001 advice from NRDC was that green diesel technology hasn't been certified by any government agency and wont be available until at least 2006 because low-sulfur diesel fuel wasnt available. These objections are clearly out of date. All diesel fuel in California has been low-sulfur for eight years now and green diesel technology is commercially available and certified. Both California and the EPA have programs that evaluate and verify diesel emissions control strategies and products. Summary and Conclusion

Most fundamentally, natural gas is a fossil fuel, and like all fossil fuels it is dirty. Extracting, transporting, and using it causes ecological damage, including pollution and global warming from GHG emissions. According to the IPCC, given current carbon emissions, the high-end of the likely range for an increase in global temperature is 8 F by the end of the century.[footnoteRef:39] To prevent this catastrophe we must begin now to replace fossil fuels with renewable WWS energy for all purposes.[footnoteRef:40] Power plants must be transitioned to using WWS energy, distributed rooftop solar built and installed, and the transportation and heating sectors electrified or switched to hydrogen fuel, which can be produced using WWS energy. We cant afford to mess around with compressed natural gas. [39: http://whatweknow.aaas.org/wp-content/uploads/2014/03/AAAS-What-We-Know.pdf, AAAP 2014 report ] [40: http://www.stanford.edu/group/efmh/jacobson/Articles/I/JDEnPolicyPt1.pdf, Mark Z. Jacobson, https://www.academia.edu/5946852/The_technical_geographical_and_economic_feasibility_for_solar_energy_to_supply_the_energy_needs_of_the_US, Vasilis Fthenakis, 2008 ]

Any older diesel buses that cannot be replaced now with battery electric buses should be retrofitted with modern emissions controls to reduce emissions until such time as they can be replaced. Even purchasing new low-emissions diesel buses or hybrid diesel would be preferable to purchasing CNG buses and fueling stations. CNG vehicles are more harmful than diesel in terms of climate change, plus the needed investment in CNG infrastructure (fueling stations and safety mods) could lock in that fossil fuel solution for decades to come.[footnoteRef:41] As the industry group Natural Gas Vehicles for America points out, While air quality is still critical in California, its the [long term] cost savings of natural gas that drive many transit agencies to switch to natural gas. Agencies need long-term commitments to CNG to recoup infrastructure costs with lower fuel cost. Any infrastructure transition should be to battery electric buses, not CNG. We lose precious time if we must make two transitions, first to CNG, and later to battery electric. [41: Prices quotes for a 2013 bid to Denver, CO: long clean diesel bus $637,000, CNG bus $698,519, hybrid electric bus $846,000. Costs of making 2 diesel stations CNG-capable >$28 million. http://www.denverpost.com/news/ci_23996557/rtd-picsk-diesel-over-natural-gas#ixzz2ybsPZKGn; 2012 estimates 40 hybrid-diesel bus $545,000, an equivalent clean diesel bus cost $370,000, and a CNG bus cost $430,000. 39 BYD electric bus ad: $550,000. http://publicsolutionsgroup.com/Websites/publicsolutionsgroup/files/Content/1417809/Transit_Hybrid-Diesel_vs._CNG.pdf ]

History shows that market-driven transitions from one fuel to another take a very long time. Oil supplied only 5% of the worlds energy in 1915; by 2014 it still has not captured even 50% of the energy market from the earlier fuels wood and coal.[footnoteRef:42] Some have hoped as we pass peak oil that business would move expeditiously toward renewable energy for economic reasons. The frenzy to exploit unconventional oil and gas and well-funded global warming denial campaign alert us to the fact that if this ever happens, it wont be soon enough. Logic, reason, and public disapproval cant trump the profit motive within multinational corporations. Only a collective effort backed by the power of organized people, strong enough to compel government action and maintain other collective efforts such as worker and consumer clean energy co-ops, can get us where we need to be quickly enough to avert climate disaster. [42: http://www.nature.com/scientificamerican/journal/v310/n1/full/scientificamerican0114-52.htm ]

Scientific uncertainty over key parameters such as methane leakage & GWPThere is, of course, uncertainty over the exact level of methane leakage, partly because scientists dont have adequate site access. But there is also pressure by interest groups to use estimates that are lower than what general scientific consensus allows. One University of Texas study,[footnoteRef:43] supported in part by the natural gas industry, found that the level of methane leakage was 1.5%, lower than what other researchers found. But their sampling was not random nor large enough to be statistically valid; the drilling operators chose the sampling times and locations; and the study accounts only for leakage during production, not during transportation or use. Nine natural gas companies, out of thousands of US producers, volunteered for the study and only 0.1% of national gas wells were sampled.[footnoteRef:44] The gas producers were allowed to review and make comments on the report before publication. But still, this study shows that leakage is already at 1.5% at the well site, even for the best fracked wells with operators that know they are being watched. Meanwhile, direct measurements show that atmospheric methane is at an all-time high and increasing.[footnoteRef:45],[footnoteRef:46] The EPA currently uses a value of 1.5% leakage. Another parameter subject to political pressure is global warming potential. The IPCC uses scientific agreement to arrive at values for important parameters like GWP; such estimates therefore tend to be conservative. But many agencies feel additional pressure from interest groups to remain more conservative than the data require. Up until 2013 the EPA assumed methane GWP of 21, 19% less than the IPCC value of 25. The EPA finally accepted the higher value of 25 in 2013, just as the IPCC, based on new studies, increased methane GWP to 34, 36% higher. These parameters are important: the 1.5% leakage of a greenhouse gas with a global warming potential of 25 is easier to ignore than the 7% leakage of one with a GWP of 34. [43: http://thinkprogress.org/climate/2013/09/19/2646881/study-fracked-wells-methane-emissions-super-emitters/ ] [44: http://www.edf.org/climate/methane-studies/faq ] [45: http://motherboard.vice.com/blog/atmospheric-methane-has-hit-record-levels-and-its-not-totally-clear-why ] [46: http://www.edf.org/climate/methane-studies/faq ]

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