climate change impacts of shale gas production

Climate Change Impacts of Shale GasProduction

JOHN BRODERICK* AND RUTH WOOD

ABSTRACT

The climate change impacts of shale gas are considered from a numberof perspectives. When normalised per unit of energy produced,greenhouse gas emissions from production and combustion appear tobe comparable to, or marginally higher than conventional sources ofnatural gas, with direct CO2 from combustion dominating. Substantialuncertainties in such estimates remain, and recent atmospheric stud-ies of methane emissions suggest that on-site measurements andemissions inventories from the US oil and gas industry may be sig-nificant underestimates. Shale gas is not a low-carbon energy source,and in the absence of an effective climate regime new gas reservescould have a substantial impact on cumulative CO2 emissions andhence the extent of climate change. The quantity of emissions that willlikely cause 2 1C of mean surface temperature rise is very low relative tocurrent emissions and trends, with a restricted time period withinwhich it is prudent to burn natural gas. The position of shale gas as atransition fuel and the relevance of comparison with coal as a fuelsource rely upon the assumptions that: (1) it completely displaces theuse of an alternative more-carbon-intensive fuel; (2) growth in energydemand does not outpace carbon intensity savings; and (3) it does notjeopardise the development of low- and zero-carbon energy systems. Itis not clear that these criteria are currently being met. Without a global

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Issues in Environmental Science and Technology, 39FrackingEdited by R.E. Hester and R.M. Harrisonr The Royal Society of Chemistry 2015Published by the Royal Society of Chemistry, www.rsc.org

*Corresponding author.

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carbon cap, the unconstrained use of shale gas is inconsistent with thecarbon budgets necessary to avoid dangerous climate change.

1 Introduction

Shale gas has been hailed as both a climate change hero and villain. Pro-ponents have argued that it has displaced higher-carbon fossil fuels in elec-tricity generation and transport in the USA, reducing national emissions,whilst there has also been widespread reporting in the popular press thatshale gas could have a greater climate change impact than burning coal. In-deed, the International Energy Agency (IEA) concluded in its World EnergyOutlook special report on the topic that substantial growth in unconventionalgas use in the global energy system would result in very significant levels ofclimate change, with a rise in temperature of the order of 3.5 1C.1

As with any energy technology, there are multiple perspectives to addresswhen considering the climate change impacts of shale gas. These are largelyrelated to the boundaries of the analysis. The following have been consideredwithin the scientific and policy literature, with most attention falling on life-cycle estimates and comparisons of Greenhouse Gas (GHG) emissions:

Life-cycle climate impacts, normalised per unit of gas, for comparisonwith other sources of gas, e.g. conventional production from the NorthSea or Liquified Natural Gas (LNG) imports from the Arabian Gulf;

Life-cycle climate impacts, normalised per unit of electricity, for com-parison with other generation sources, e.g. nuclear power or coal;

Cumulative impact of emissions from shale gas within the global energysystem; and

Indirect investment and policy impacts on the energy system of novelgas reserves.

This chapter provides an overview of research on these issues, identifyingthe key sources of emissions in shale gas production and situating thiswithin energy systems in order to understand the wider implications forclimate change.

2 Life-cycle Climate Impact of Shale Gas Production

2.1 Sources of Greenhouse Gas Emissions

Estimates of the life-cycle climate impact, colloquially termed the carbonfootprint, of shale gas have identified multiple sources of emissions from theexploration of a potential basin through to the delivery of natural gas to anend-user (see Table 1). Direct emissions arise from the combustion of fossilfuels for energy, intentional venting of methane for safety reasons, and un-intentional releases, termed fugitive emissions. Indirect emissions arise

105Climate Change Impacts of Shale Gas Production

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Table 1 Overview of emissions sources identified in the scientific literature8,10,14,21

Life cycle stage Activity Typical emissions sources

Extraction Well construction Combustion of fossil fuels for drilling machinery on site and transport tosite, including exploration and pilot wells. Cement, steel and drillingmud production for wells. Land clearance.

Well stimulation Combustion of fossil fuels for high pressure pumping of fracking fluidsand transport of water and proppant to site.

Well completion Episodic emissions from flaring or venting of gas during flowback beforecapture equipment installed at wellhead.

Workovers Energy and materials for cleaning of wells. Methane releases duringworkovers and liquid unloading.

Other point source emissions Wellhead and gathering equipment.Fugitive emissions Dispersed leaks from produced-water tanks, pneumatic valves not ac-

counted for as part of other assemblies.Water treatment Energy for treatment and disposal of produced water.Conclusion of production Energy for disposal of wastes and site remediation. Leakages from

abandoned wells.Processing Acid gas removal Energy consumed and GHGs released during amine recovery.

Dehydration Combustion and venting emissions from glycol regeneration.Fugitive emissions Dispersed leaks from pumps and pneumatic valves not accounted for as

part of other assemblies.Compressors Energy consumed and GHG leakages from production compressors.

Transport Pipeline construction Manufacture and installation of steel piping.Pipeline compressors Energy consumed and methane leakages from pipeline compressors.Pipeline fugitive emissions Methane leakages through joints.

End use Combustion CO2 and unburned methane from combustion.

106John

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from the manufacture and transport of drilling equipment, constructionmaterial, water, chemical additives and other physical necessities, and thetreatment of wastes, including wastewater.Many of the emissions sources are the same for shale gas as for gas

supplied from conventional wells, for instance, compression losses intransmission and distribution. Indeed, the largest component of the life-cycle climate impact, the quantity of CO2 released from combustion of thegas, varies only slightly due to the mixture of alkanes present, which is, inpractice, regulated in the UK by National Transmission System gas specifi-cations.2 Additional GHG emission sources from shale gas lie in the energyrequired for hydraulic fracturing; the manufacture of chemicals and trans-portation of both water and chemicals to the well site; and their subsequentdisposal and direct releases during well completion. Emissions from flow-back, the period following drilling when a mixture of gas, liquid and solids isremoved from the well to enable production, are the most substantial ofthese but may be mitigated to a large extent by reduced emissions com-pletions.3 Diffuse sources of emissions from sub-surface leakage, con-sidered to be most likely the result of well casing failure, from bothconventional and shale wells, have also been identified but not quantified.4

2.2 Quantitative Estimates of Life-cycle Climate Impacts

There are a number of estimates of the life-cycle climate impact of shale gasavailable in the literature in addition to those of other energy sources. Beforepresenting these figures it is worth considering some key issues in theirproduction. Comparison of life-cycle estimates for any product is problem-atic due to differences in system boundaries; metrics chosen to relate dif-ferent atmospheric effects of gases; assumed technology performance;allocation between multiple products; treatment of uncertainties; and dataquality.Choosing appropriate comparators and equivalent functional units is es-

sential, but is only a first step. In the case of fossil fuels, this is typicallyeither energy content (e.g. joules, J) or electrical energy subsequently gen-erated (e.g. kilowatt hours of electricity, kWh(e)). For shale gas, this canmake a substantial difference in comparisons with coal due to the muchgreater efficiency of the conversion technology. A coal-fired electricity planthas a thermal efficiency ranging from 36% (pulverised fuel) to 47% (newsupercritical plant), whilst a gas-fired power station ranges from 40 to 60%.5

Monte Carlo analysis,6 informed by a number of prior studies,712 suggeststhat the range in possible efficiency of gas power plants has a greater in-fluence on a well-to-wires life-cycle impact than the total uncertainty inquantities of upstream emissions.Whilst there have been efforts to harmonise life-cycle impacts for some

electricity generation technologies,13 there is as yet no systematic equivalentfor shale gas. As a result, the data are presented in Table 2 as relativestatements and ought to be considered with some caution. Furthermore, not


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all of the assessments are independent, the work by AEA (2012)14 andMacKay and Stone (2013)15 relies upon data presented in a number of theother studies.GHGs have different radiative properties, lifespans in the atmosphere and

interactions with other atmospheric components; a number of metrics areavailable for comparison of these differing impacts from emissions.16 GlobalWarming Potential (GWP) is the most commonly used metric for policyappraisal and life-cycle comparison. It integrates the warming effect of aninstantaneous release of gas, relative to carbon dioxide, over a chosen timeperiod, typically 100 years. The use of different time periods and differentestimates of GWP can significantly affect the quantitative and qualitativeconclusions of comparative emissions-accounting studies.Carbon dioxide and methane are the main GHGs arising from shale gas

production, with methane being the more potent of the two. It has an at-mospheric lifetime of 12.4 years and is subsequently oxidised to CO2 thougha series of reactions, with indirect effects on tropospheric ozone, strato-spheric water and sulfate aerosols.17 Most studies use the IntergovernmentalPanel on Climate Change (IPCC) Fourth Assessment Report, AR4 (2007),18

estimates of GWP, with a tonne of methane taken to have 25-times the im-pact of CO2 over a 100-year period. The most recent IPCC report, AR5(2013),19 has up-dated the advised values for methane to 28-times on a 100-year basis, if climate-carbon feedbacks are not accounted for, and 34-times ifthey are. Using these values would tend to increase the impact of upstreamemissions relative to combustion emissions and increase the importance ofmitigation of these sources.When ranking shale gas against coal or renewable sources of energy such

revision is unlikely to make a substantial difference. However, as can be seenfrom Table 2, presenting a 20-year comparison period can make a muchlarger difference and alter rankings between fossil fuel sources which have

Table 2 Estimates of comparative life-cycle climate impact of shale gas.

Study

Life-cycle climate impact of electricitygenerated from shale gas relative to:

MethaneGWP

Conventionalnatural gas Coal

Howarth et al. (2011)7 14 to 19% greater 18% lower tomore than 100%greater

33 and 105

Jiang et al. (2011)8 3% greater 20 to 50% lower 25Skone et al. (2011)9 3.4% greater 42 to 53% lower 25Stephenson et al. (2011)10 1.8 to 2.4% greater 30 to 50% lower 25Burnham et al. (2011)11 6% lower mean value

but statisticallyindistinguishable

52% lower

Hultman et al. (2011)12 11% greater 44% lower 25JISEA (2012)21 Very similar Less than half 25AEA (2012)14 1 to 8% greater 41 to 49% lower 25MacKay & Stone (2013)15 0.5 to 22% greater 49 to 53% lower 25

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substantially different profiles. Coal has a significantly greater carbonfootprint that is dominated by CO2 from combustion when compared withgas over a 100-year timescale. This ranking is reversed for higher levels ofmethane leakage if a 20-year comparison is made; it is this choice that ac-counts for Howarth et al.s (2011) report of higher impacts for gas, not theassumed rates of methane venting.7,10

The choice of comparison period is a value judgement, not borne from ascientific principle but related to the period over which one is concernedabout impacts.17 Given that equilibrium climate response depends uponcumulative emissions and is insensitive to the timing or peak rate of emis-sions, this shorter period does not seem appropriate to energy policyanalysis.20

Substantial uncertainties remain in the precise life-cycle impact of shalegas production,6 even in cases where detailed field work has been con-ducted.21 The majority of the quantitative shale gas studies identified inTable 2 take a bottom-up approach, i.e. identifying and summing pointsources from direct measurement or by reference to existing inventories,emissions factors and activity factors. However, a number of recent top-down studies, taking total atmospheric measurements and then attributingthese to sources by atmospheric modelling, have found substantial dis-crepancy with bottom-up inventory-based estimates.2224 In one case, a tightoil and gas field with processing facilities, the US Environmental ProtectionAgency inventory estimate of 1.7% leakage of methane, for the field as awhole, was found to be a substantial underestimate of the 2.3 to 7.7%leakage indicated by atmospheric monitoring.22 In a second case, leakage of6.2% to 11.7% was identified with a mean value 1.8 times the record forfield.23 National US emissions inventories have also been found to under-estimate total methane emissions by a factor of ca. 1.5 to ca. 1.7 times, withsubstantial regional discrepancies suggesting that emissions from fossil fuelextraction and processing could be 4.9 2.6-times larger than that recordedin inventories.24 Further work is required to identify the reasons for this andunderstand the contribution made by shale gas production. Such discrep-ancies suggest that greater attention should be paid to monitoring, theprocess of inventory production and background measurement prior todevelopment.25 Nevertheless, the broad conclusion that shale gas has a life-cycle climate impact that is within the range of other natural gas sourcesappears to be robust.

3 Shale Gas in the Global Energy System

To assess the impacts of shale gas production on climate change, it is ne-cessary to go beyond a simple assessment of the carbon intensity of the gas,to consider the potential role of shale gas in the global energy system.International agreements on climate change mitigation focus on theavoidance of dangerous climate change,26 defined and agreed as more than2 1C increase in global mean surface temperature above pre-industriallevels.27 This ambition is repeated in EU and UK climate policy.28 To


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mitigate climate change to this level, considerable reductions in CO2 andother greenhouse gases from the worlds energy system are necessary. Ifshale gas is to have a role in the worlds energy system, it must be consistentwith existing mandates for the avoidance of dangerous levels of climatechange. This section describes the direct and indirect roles of shale gas inthe worlds energy system and the associated changes in greenhouse gasemissions that might be expected.

3.1 The Significance of the Energy System in Contributing toClimate Change

Greenhouse gases, as defined by the Kyoto Protocol, include carbon dioxide(CO2), methane (CH4), nitrous oxide (N2O), sulfur hexafluoride (SF6) and agroup of chemicals called hydrofluorocarbons (HFCs). There are other gasesthat also trap heat, such as ozone and black carbon, however, it is the gasescontrolled under the Kyoto Protocol that cause the dominant anthropogenicinfluence on the atmosphere.17 Of these Kyoto gases, CO2 emissions dom-inate, being responsible for 76.7% of global emissions in 2004, the mainsource being fossil-fuel combustion, which was responsible for 56.6% ofglobal greenhouse gas emissions in the same year.29 CO2 emissions fromfossil-fuel combustion are also the fastest-growing source of GHGs globally,increasing by 50% between 1990 and 2012,29,30 with an average annual in-crease during the last decade of 3%.30 To successfully mitigate climatechange, addressing the dominant and growing amount of CO2 from fossilfuel combustion is essential. Thus the impact that shale gas exploitation hason the climate is dependent on the role it plays in the wider energy systemand how it contributes towards emissions reductions from fossil fuelcombustion.

3.2 Cumulative Emissions and Climate Change

The challenge of global mitigation positions shale gas in the context of thelimits placed on the amount of greenhouse gas emissions that can be re-leased this century while avoiding a 2 1C increase in global mean surfacetemperature. When shale gas and other fossil fuels are burnt they releaseCO2 into the atmosphere, with some of the CO2 being taken up by carbonsinks such as the oceans or vegetation, however, that which remains in theatmosphere (45% of CO2 emissions) remains there for over 100 years. ThusCO2 accumulates in the atmosphere and, as a greenhouse gas, traps heat.The amount of global warming that can be expected has been demonstratedto directly correlate with the accumulated amount of CO2 in the atmos-phere.17,31 Consequently there is a great deal of analysis to estimate theamount of cumulative emissions or an emissions budget that the at-mosphere can hold without going beyond a 2 1C increase in global meansurface temperature, or even higher.31,32 The limit of cumulative emissionsthat can be released into the atmosphere with a good probability of not


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causing global warming of 2 1C or more can be found in Table 1. The limittakes into account the ability of carbon sinks to absorb some of the CO2emitted into the atmosphere and sets aside a proportion of the budget fornon-CO2 greenhouse gases, providing the gross total CO2 from fossil fuelsand land-use change that can be released into the atmosphere with a goodchance of avoiding a 2 1C increase. The limit is based on what can be emittedbetween the years 2000 and 2050. This timeframe was chosen as it has themost significance to decision-makers today, however, this does not meanthat after 2050 fossil-fuel burning can resume. In fact, beyond 2050 thecumulative emissions budget is even lower, and analyses suggest net zero-CO2 emissions are necessary by around 2070 to avoid dangerous climatechange.33

3.3 Fossil Fuels in the Context of Emissions Budgets

In summary, to avoid dangerous climate change the most relevant metric isthe cumulative amount of greenhouse gases released during the next cen-tury, particularly in the next 35 years when decision-makers have the mostimmediate influence over emissions. Thus, not only the carbon intensity of afuel is important but the quantity of it which is used and, therefore, thecumulative amount of CO2 it contributes to the atmosphere.Table 3 demonstrates that, globally, 40% of the cumulative emissions

budget associated with avoiding more than 2 1C of warming has already beenused up. Global emissions from fossil-fuel burning, cement manufacturingand land-use change, released between 2000 and 2012, add up to 432 Gt CO2.The International Energy Agency estimate that non-energy-related CO2sources (e.g. from chemical processes, land-use change and deforestation)will release approximately 136 Gt CO2 in the period to 2050.

34 This leavesbetween 322 and 872 Gt CO2 that can be released into the atmosphere from2013 to 2050 from the energy sector. The average annual rate of fossil-fuel-related emissions between 2000 and 2011 is 29 Gt CO2 yr

1; continuingemissions at this rate would mean the remaining CO2 budget was used up by2023 (20% probability of exceeding 2 1C temperature increase) or 2042 (50%

Table 3 Comparison of the amount of CO2 from fossil fuel and land-use change thatcan be released into the atmosphere from 2000 to 2050 and emissions todate.

Global emissionsbudgetto avoid a 21C globaltemperature increase

890 Gt CO2(20% probabilityof exceeding 2 1C)

1000 Gt CO2(25% probability ofexceeding 2 1C)31

1440 Gt CO2(50% probabilityof exceeding 2 1C)

Amount emitted20002012.30

432 Gt CO2 432 Gt CO2 432 Gt CO2

Predicted non-energyCO2 emissions20122050.34

136 Gt CO2 136 Gt CO2 136 Gt CO2

Remaining CO2 budgetfor energy 20122050.

322 Gt CO2 432 Gt CO2 872 Gt CO2


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probability of exceeding 2 1C temperature increase), with zero budget re-maining thereafter. However, rather than stabilising, annual fossil-CO2emissions are increasing; between 2000 and 2012 the global annual emis-sions increased by 40%. The challenge, therefore, is significant, both to re-verse the upward trend in annual emissions and to reduce year-on-yearglobal emissions by 39%, depending on the year at which global emissionspeak and the reductions start (see Anderson and Bows (2011) for an exam-ination of alternative pathways and emission reduction rates).35 Theseconstraints are even more challenging if principles of equity between na-tions are incorporated. Given that it is developed/OECD nations that arechiefly responsible for the historical emissions of GHGs that have causedclimate change to date, and which will persist in the atmosphere for decadesto come, a climate regime that does not accord a greater emissions allo-cation to developing nations is unlikely to be internationally acceptable.When reasonable allowances for future emissions are allocated to de-veloping nations, the budget becomes more constrained for developed na-tions, with timescales for almost complete decarbonisation of their energysystems necessary well before 2050.35

Having quantified the remaining global carbon budget associated with 2 1C,we can now consider the availability of shale gas within this limit. Table 4shows the existing reserves and resources of fossil fuels in the world and theamount of CO2 that would be emitted if they were burnt without abatementmeasures. Burning conventional reserves of oil and gas alone would likely useup the entire CO2 budget, before burning any coal at all, or eating into theresources that are at present uneconomic to extract. Shale gas reserves repre-sent between 1.8 and 6.5 times the global budget and, if resources are includedas well, there is sufficient shale gas to occupy the budget 5.6 to 17.7-times over.

Table 4 Global energy reserves and resources and the associated CO2 emitted ifburnt unabated.

Reserves (EJ) Resources (EJ)Reserves(Gt CO2)

Resources(Gt CO2)

TotalPotentialCO2 (Gt)

Conventional oil 49007610 41706150 349574 297465 6651009Unconventionaloil

37505600 11 28014 800 254444 7651172 11021496

Conventional gas 50007100 72008900 271414 391519 684898Unconventionalgas

20 10067 100 40 200121 900 10913912 21827107 338310603

Coal 17 30021 000 291 000435 000 15102125 25 39544 022 30 29644 810

Source: Global Energy Assessment Table 7.1.51 Note that resource data are not cumulative anddo NOT include reserves, the GEA also includes additional occurrences which are not includedin the figures above; these include 440 000 EJ unconventional oil and 41 000 000 EJunconventional gas. Conversions from EJ to CO2 use IPCC emission factors for crude oil toestimate conventional oil CO2, shale oil figures to estimate unconventional oil; natural gasemission factors for both conventional gas and unconventional gas and the emission factors forcoking coal for coal. The upper and lower emission factors for each fuel have been applied to theupper and lower CO2 estimates, respectively.


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It is clear from the figures presented in Tables 1 and 2 that at a global levelthere is more fossil fuel energy available than can be used in a world that isserious about avoiding dangerous climate change. Numerous analyses havedemonstrated that a sizeable proportion of conventional fuel reserves mustremain in the ground if globally we are to avoid 2 1C or even 3 1C globalwarming; a fortiori, unconventional fuels should remain unburnt.36 So whyare unconventional fuels being currently exploited and plans being put inplace to facilitate their exploitation, given global agreements to avoid dan-gerous climate change? Putting aside the inertia of current global negoti-ations on mitigation, in part, while Table 4 presents global availability offuels, these resources are not endowed uniformly. Regional availability ofdifferent fossil fuels and demands differ, creating uneven market dynamics.There are regions of the world where access to conventional gas is morelimited, leading to reliance on coal; thus here, shale gas could, with thecaveats stated below, play a role. Shale gas has been described, therefore, asa transition fuel, enabling countries and regions currently highly reliant onthe more carbon-intensive coal generation to reduce the carbon intensity oftheir energy system as part of a low-carbon transition. The role of shale gasin a low-carbon transition is, therefore, dependent on where it is used andwhat it displaces this is determined at present, to a great extent, by energymarkets.

4 Shale Gas as a Transition Fuel

4.1 Conditions and Evidence to Date

The position of shale gas as a transition fuel relies on the assumptions that:(1) it completely displaces the use of an alternative more-carbon-intensivefuel choice; (2) growth in energy demand does not outpace carbon-intensitysavings; and (3) it acts as a bridge between current high-carbon-intensiveenergy systems based on coal and lower future systems where renewables,carbon capture and storage (CCS) and nuclear energy play a dominant role.First we consider part (1) and the evidence to date that this condition is

met by shale gas exploitation. Much of the potential benefit conveyed byshale gas derives from its potential to reduce the carbon intensity of elec-tricity production. The net effect of displacing coal with shale gas dependsvery much on the region of the world under consideration and the energyprices therein. In the case of the USA, with no national drivers to reduce coaluse, evidence suggests that during the rapid exploitation of shale gas andcorresponding price reduction, locally, within the USA, there was somedisplacement of coal use in electricity generation. In fact, between 2005 and2012 carbon emissions from energy use in the USA fell by 12%, in part due toa reduction in coal consumption of 25% during the same time frame.37

However, during the same time frame much of the displaced coal pro-duction was sold on global markets, exported and burnt elsewhere. The 32%drop in EU coal import prices between 2005 and 2011 and an increase of US


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coal exports to the EU of 187% have been attributed to the reduction in theUSAs demand for coal.38,39 While there were local emissions reductionsduring this time frame, due to the sale and combustion of US coal overseasa net reduction in CO2 cannot be guaranteed, net global reductions aredependent on what the USAs exported coal displaced. Similarly, othercountries such as China and India with significant amounts of coal-firedelectricity production may in future reduce CO2 through a switch to gas, withthe net effect dependent on what happens to the coal that is displaced fromtheir energy system; if shale gas is simply burnt as well as coal, as appears tobe the case at present, there is no net global carbon saving.As alluded to earlier, the impacts of shale-gas use on emissions differs

regionally, depending on the incumbent energy mix. In the UK and much ofEurope, where coal-fired power stations are being phased out through acombination of air quality legislation and climate policy, such as the LargeCombustion Plants Directive and EU Emissions Trading Scheme, shale gaswill most likely displace conventional gas, nuclear or renewables and the netimpact is to increase CO2 emissions compared to a business-as-usual tra-jectory. Similarly, a study of the probable end-destination of shale gas ex-tracted in British Columbia, Canada (an area holding half the technicallyrecoverable shale gas resources in Canada,40 where the incumbent energysystem is dominated by hydro-electricity), showed the probable end-destination of shale gas was not to replace coal-fired electricity but for exportas LNG or to replace conventional gas for use in neighbouring Albertasenergy-intensive tar sand extraction, perpetuating a positive feedback cycleof fossil fuel emission production, clearly not a transition role. Theliquefaction and re-gasification of LNG, together with the transportrequirements to the end-user, require additional energy, increasing the life-cycle GHG emissions of the fuel source and diminishing potential savingsfrom replacing coal use and hence the potential role as a transition fuel. Inconclusion, there is insufficient evidence to date that condition (1) is beingmet. Shale gas is not displacing an equivalent amount of coal.The second condition (2) is that increases in energy demand must not

outpace the rate at which carbon intensity of energy supply is reduced. Todate, global energy statistics demonstrate the rate of decarbonisation hasbeen outpaced by growth in energy demand. On average a 0.3% annual rate ofdecarbonisation is observed compared to an increase in global energy use of2% annually since the industrial revolution and hence a net increase year-on-year of energy-related CO2.

41 A six-fold increase in the decarbonisation rate ofglobal energy demand would be needed to stabilise global energy-related CO2emissions, a twenty-four fold increase to begin to deliver the minimum rate ofdecarbonisation necessary to provide a reasonable chance of avoiding morethan a 2 1C temperature increase. Could shale gas play a part in acceleratingthe decarbonisation of the energy system? Much will depend on whether it isburnt as well as or instead of coal, as discussed above, and if it does displacecoal, the rate at which it does so. As the emissions intensity of shale gas isonly approximately one third to one half that of coal, its contribution to the


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long-term decarbonisation of global energy demand is limited. Given a globaltarget of approximately 90% reduction in CO2 from fossil-fuel use by 2050 andnet zero CO2 emissions by 2070, the time frame within which shale gas can beused unabated is limited.The third condition (3) for the use of shale gas within a transition pathway

is that it leads ultimately to a lower-carbon energy system. Thus, it shouldnot divert investment in the research, development and deployment ofenergy-demand reduction, renewables, carbon capture and storage, andnuclear technologies. Currently, however, economic analysis of shale-gasexploitation in the US suggests its continued development will delay theeconomic feasibility of nuclear energy in the USA by one or two decades,42

and similarly, without more stringent climate-change policy in the US, delaydeployment of renewables and carbon capture and storage by up to twodecades.43 Such delays are significant when set within the context of globalenergy scenarios that deliver emissions reductions consistent with avoiding2 1C warming; these rely on large-scale deployment of these technologies, allof which in practice take decades to build at such scale.It is also important to consider the time frames of shale gas exploitation in

considering its role as a transition fuel. Given the lifespan of gas infra-structure, 30 years for a modern Combined Cycle Gas Turbine (CCGT) powerstation for example, the window of opportunity for shale gas as a transitionfuel is time bound. Building new infrastructure post-2020 would run the riskof it not being used for its full design life and becoming a stranded assetwhere environmentally unsustainable assets suffer from unanticipated orpremature write-offs, downward revaluations, or are converted to liabil-ities.44 In the case of shale gas and, more broadly, fossil-fuel-dependentinfrastructure, this is an area of on-going research, particularly with refer-ence to investment-fund holders.45 Furthermore, if appropriate energy pol-icies are not in place, rather than creating stranded assets inconsistent witha low-carbon future, the continued development of fossil-fuel infrastructurecould lock countries into dependency on fossil fuels, creating higher costbarriers for alternative energy sources to compete with.How this plays out in other regions of the world will depend very much on

local markets and governance systems, but it appears that in the only countrywhere shale gas has been exploited to date, the US, it is thus far not acting as atransition fuel. Indeed, the IEA reported in their World Energy Outlook sup-plement Are We Entering a Golden Age of Gas? (2011)1 that a high-gas-usescenario probably would result in 3.5 1C warming, well beyond what is gen-erally regarded as dangerous climate change. Their Chief Economist, FatihBirol, therefore commented that We are not saying that it will be a golden agefor humanity we are saying it will be a golden age for gas.46

4.2 Future Opportunities?

So what role could shale gas have in a rapidly decarbonising world? For shalegas to be a true transition fuel, any displaced coal must effectively remain in


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the ground, growth in energy demand must not outpace carbon intensitysavings and it must be part of a pathway towards truly low carbon energysources. How could this be achieved? There are two plausible scenarios whereshale-gas exploitation could be consistent with climate change agreements.Firstly, if there were an introduction of a global climate regime with a capcommensurate with 2 1C and/or, secondly, if the associated CO2 were pre-vented from reaching the atmosphere via carbon capture and storage (CSS).To take the first scenario, an annual or periodic global limit on the

amount of CO2 that can be released into the atmosphere is set. Regulatedentities, nations, cities or industrial actors, must then be bound by somepermitting regime, which may or may not involve carbon trading or taxation.In this system, shale gas could be used within a system where CO2 release islimited to a set global cap. This avoids the indirect emissions implications ofthe national local measures. However, such a system would require a globalagreement, including both developed and developing countries alongsideglobally agreed administration systems. At present, global negotiations arenot sufficiently advanced for this to become a reality in the near- to medium-term future.The second scenario, perhaps in conjunction with the first, is to prevent

the majority of emissions associated with shale gas from reaching the at-mosphere. If shale gas is used for combustion, this requires carbon captureand storage technology and a socio-economic system that facilitates its de-ployment. The principle of CCS technology is ostensibly straightforward: theCO2 is removed from the exhaust stream of a large point source, pre- or post-combustion, and transported to a long-term storage site, such as an old oilor gas field or saline aquifer. The technology has significant potential asmany of the individual steps of the process are well established in differentindustries. The challenge is to assemble all steps together to ensure the long-term safe storage of CO2 and to do it at the gigawatt scale. The technology isperhaps most promising when allied with biomass combustion to deliver netnegative emissions.To date approximately eight large-scale carbon capture plants are in op-

eration, predominantly deployed to recycle the CO2 stripped during the pre-processing of natural gas for use in enhanced oil recovery.47 No carboncapture and storage (CCS) projects are as yet coupled to electricity generationplant, although two carbon capture plants are under construction (BoundaryDam, Canada, and Kemper County, USA) and intending to capture CO2 forenhanced oil recovery rather than for long-term storage.47 To put the worldon a track to a 2 1C future, the International Energy Agencys 450 Scenariorequires CCS technology to capture and provide long-term storage of 2.5 GtCO2 by 2035, or approximately 870 large-scale CCS plants attached to long-term storage: a build rate of approximately 40 per year between 2014 and2035.48 To realise this potential, the build rate of these plants needs to besignificantly accelerated, at a pace incompatible with delays for a decade ormore. Such a roll-out will require substantial economic incentives andregulatory support.


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However, a shale gas plus CCS energy pathway is unlikely to realise verylow or zero carbon emissions and so will be restricted in the ultimate po-tential scale of deployment. Upstream emissions may add a not insignificantpenalty of up to 20%, dependent upon the source and transport of thegas.14,49 This has particular implications for CCS where the capture processitself imposes an energy penalty, requiring more fuel and hence realisinggreater upstream emission, outside of the capture mechanism. Hammondet al. 49 estimate the final emissions intensity of electricity from gas CCS tobe approximately 80 g CO2e kWh

1, four-to-seven times more than nuclearpower.49,50 Depending upon future grid composition, these quantities ofemissions are still likely to be problematic, especially for developed econ-omies given the scale and level of decarbonisation required.In effect, shale gas exploitation without prerequisite controls is a gamble

with high stakes. It may be exploited with the intention of its unabated useand an assumption that the global community will renege on existingcommitments. In which case, we all, including the energy industry, sufferthe impacts of dangerous climate change. Alternatively, if it is assumed thatthe global community is serious about avoiding dangerous climate change,it is being exploited with the expectation that either a global carbon cap willbe in place in due course or with the concomitant support for mass de-ployment of CCS technology. Without either of these breakthroughs inpolicy and technology, investment in shale-gas exploration and associatedgas infrastructure is, in effect, an investment in a stranded asset. Without aglobal carbon cap, the unconstrained use of shale gas is inconsistent withthe carbon budgets necessary to avoid dangerous climate change.

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climate change impacts of shale gas production

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