Changes

The main hydraulic-fracturing-related air emissions are methane emissions from the wells during fracturing and emissions from hydraulic fracturing equipment, such as compressor stations. According to the study conducted by professor Robert W. Howarth et al. of Cornell University, "3.6% to 7.9% of the methane from shale-gas production escapes to the atmosphere in venting and leaks over the lifetime of a well." According to the study, this is at least 30% and perhaps even 100% more than from conventional gas production. The study explains these higher emissions with hydraulic fracturing and drill out following the fracturing.<ref name="howarth">{{cite journal | url= http://www.springerlink.com/content/e384226wr4160653/fulltext.pdf | title=Methane and the greenhouse-gas footprint of natural gas from shale formations|last1=Howarth |first1=Robert W. |last2=Santoro |first2=Renee |last3=Ingraffea |first3=Anthony | journal = Climatic Change | publisher = Springer Publishing| pages= 679–690 |volume=106 |issue=4 | doi = 10.1007/s10584-011-0061-5 |date=13 March 2011| accessdate = 2012-05-07 | format = PDF}}</ref> Methane gradually breaks down in the atmosphere, forming carbon [[dioxide]]. It means its greenhouse-gas footprint is worse than coal or oil for timescales of less than fifty years.<ref name="howarth"/><ref name="howarth2">{{cite journal |title=Should Fracking Stop? Extracting gas from shale increases the availability of this resource, but the health and environmental risks may be too high. ''Point: Yes, it's too high risk'' |last=Howarth |first=Robert W. |last2=Ingraffea |first2=Anthony |pages=271–275 |issue=477 |date=15 September 2011 |journal= Nature | doi=10.1038/477271a}}</ref> However, several studies have argued that the paper was flawed and/or come to completely different conclusions, including assessments by experts at the US Department of Energy,<ref name=Skone>{{cite web |last=Skone |first=Timothy J. |title=Life Cycle Greenhouse Gas Analysis of Natural Gas Extraction & Delivery in the United States |publisher=National Energy Technology Laboratory |date=12 May 2011 |url=http://cce.cornell.edu/EnergyClimateChange/NaturalGasDev/Documents/PDFs/SKONE_NG_LC_GHG_Profile_Cornell_12MAY11_Final.pdf | format = PDF |accessdate=4 February 2012}}</ref> by Carnegie Mellon University<ref name=Jiang>{{cite journal |first1=Mohan |last1=Jiang |first2=W Michael |last2=Griffin |first3= Chris |last3= Hendrickson | first4=Paulina |last4=Jaramillo | first5= Jeanne |last5= VanBriesen | first6= Aranya | last6 = Venkatesh |year=2011 |title=Life cycle greenhouse gas emissions of Marcellus shale gas | url = http://iopscience.iop.org/1748-9326/6/3/034014/pdf/1748-9326_6_3_034014.pdf | format = PDF |journal=[[Environmental Research Letters]] | publisher = IOP Publishing |volume=6 |issue=3 |doi=10.1088/1748-9326/6/3/034014 |accessdate=4 February 2012}}</ref> and the University of Maryland,<ref name=Hultman>{{cite journal |first1=Nathan |last1=Hultman |first2= Dylan |last2= Rebois |first3= Michael |last3= Scholten |first4=Christopher |last4=Ramig |year=2011 |title=The greenhouse impact of unconventional gas for electricity generation | url = http://iopscience.iop.org/1748-9326/6/4/044008/pdf/1748-9326_6_4_044008.pdf | format = PDF |journal=Environmental Research Letters | publisher = [[IOP Publishing]] |volume=6 |issue=4 |doi=10.1088/1748-9326/6/4/044008 |accessdate=4 February 2012}}</ref> as well as by the Natural Resources Defense Council, which concluded that the Howarth ''et al''. paper's use of a 20-year time horizon for global warming potential of methane is "too short a period to be appropriate for policy analysis."<ref name=Lashof>{{cite web |last=Lashof |first=Dan |title=Natural Gas Needs Tighter Production Practices to Reduce Global Warming Pollution |publisher=Natural Resources Defense Council |date=12 April 2011 |url=http://switchboard.nrdc.org/blogs/dlashof/natural_gas_needs_tighter_prod.html |accessdate=4 February 2012}}</ref> In January 2012, Howarth's colleagues at [[Cornell University]] responded with their assessment, arguing that the Howarth paper was "seriously flawed" because it "significantly overestimate[s] the fugitive emissions associated with unconventional gas extraction, undervalue[s] the contribution of 'green technologies' to reducing those emissions to a level approaching that of conventional gas, base[s] their comparison between gas and coal on heat rather than electricity generation (almost the sole use of coal), and assume[s] a time interval over which to compute the relative climate impact of gas compared to coal that does not capture the contrast between the long residence time of {{CO2}} and the short residence time of methane in the atmosphere."<ref name=Cathles>{{cite journal |last1=Cathles |first1=Lawrence M. |last2=Brown |first2=Larry |last3=Taam |first3=Milton |last4=Hunter |first4=Andrew |year=2011 |journal=Climatic Change |doi=10.1007/s10584-011-0333-0 |accessdate=4 February 2012}}</ref> The authors of that response conclude that "shale gas has a GHG footprint that is half and perhaps a third that of coal," based upon "more reasonable leakage rates and bases of comparison." Howarth et al. responded to this criticism: "We stand by our approach and findings. The latest EPA estimate for methane emissions from shale gas falls within the range of our estimates but not those of Cathles et al, which are substantially lower."<ref name=Howarth3>{{cite journal |last1=Howarth |first1=Robert W. |last2=Santoro |first2=Renee |last3=Ingraffea |first3=Anthony |title=Venting and leaking of methane from shale gas development: Response to Cathles et al. |url=http://www.springerlink.com/content/c338g7j559580172/fulltext.pdf | format = PDF |journal=[[Climatic Change]] | publisher = [[Springer Publishing|Springer]] |volume= |issue= |doi= 10.1007/s10584-012-0401-0 |date = 1 February 2012 |accessdate=4 February 2012}}</ref><ref>{{cite news |url=http://www.ipsnews.net/news.asp?idnews=106531 |title=Shale Gas a Bridge to More Global Warming |author=Stephen Leahy |date=24 January 2012 |agency=[[Inter Press Service|IPS]] |accessdate=4 February 2012}}</ref>