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Energy Policy 36 (2008) 1251–1256

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Mitigating greenhouse: Limited time, limited options

Patrick Moriartya,�, Damon Honneryb

aDepartment of Mechanical Engineering, Monash University, P.O. Box 197, Caulfield East, Vic. 3145, AustraliabDepartment of Mechanical Engineering, Monash University, P.O. Box 31, Vic. 3800, Australia

Received 23 November 2007; accepted 15 January 2008

Abstract

Most human-caused climate change comes from fossil fuel combustion emissions. To avoid the risk of serious climate change, very

recent research suggests that emission reductions will need to be both large and rapidly implemented. We argue that technical solutions—

improving energy efficiency, use of renewable and nuclear energy, and carbon capture and sequestration—can only be of minor

importance, mainly given the limited time available to take effective climate action. Only curbing energy use, perhaps through ‘social

efficiency’ gains, particularly in the high-energy consumption countries, can provide the rapid emissions reductions needed. The social

efficiency approach requires a basic rethinking in how we can satisfy our human needs with low environmental impacts. Large cuts in

emissions could then occur rapidly, but only if resistance to such changes can be overcome. Particularly in transport, there are also

serious potential conflicts between the technical and the social efficiency approaches, requiring a choice to be made.

r 2008 Elsevier Ltd. All rights reserved.

Keywords: Energy reductions; Global climate change; Social efficiency

1. Introduction: energy and climate change

In 2005, world primary energy use was around 496EJ(International Energy Agency (IEA); Moriarty and Honn-ery, 2007a). The UN projects the world population willgrow to 8.32 and 9.19 billion (median values) by 2030 and2050, respectively, compared with 6.465 billion in mid-2005(UN, 2006). In 2005, average per capita primary energy useglobally was thus about 77GJ. However, in the USA, theaverage was 332GJ (BP, 2007), with a number of countriesat even higher per capita use. If by 2030 all the world’speople enjoyed even present US per capita energy use, totalannual primary energy use would then be 2762EJ, and by2050, 3051EJ, over six times today’s level. For comparison,official estimates for global primary energy use for variousscenarios in 2030 are 659–786EJ (IEA, 2007) and668–816 EJ (Energy Information Administration (EIA),2007), and for 2050, 800–940EJ (European Commission,2006). Since all studies project continued energy growth forthe Organisation for Economic Cooperation and Develop-

e front matter r 2008 Elsevier Ltd. All rights reserved.

pol.2008.01.021

ing author. Tel.: +613 9903 2584; fax: +61 3 9903 2076.

ess: patrick.moriarty@eng.monash.edu.au (P. Moriarty).

ment (OECD) countries, they clearly expect global energyinequality to continue for many decades to come.The purpose of the present research is to establish

whether the threat of global warming will force the worldto reduce energy use, and if so, by what means. To avertdangerous climatic change, the European Union (EU)proposes limiting the global temperature rise to 2.0 1Cabove pre-industrial temperatures (Bows and Anderson,2007). The Intergovernmental Panel on Climate Change(IPCC) gives a ‘best estimate’ for climate sensitivity as 3 1Cwith a likely range of 2–4.5 1C (Solomon et al., 2007). TheIPCC survey of various model results (Fisher et al., 2007)suggests that global carbon dioxide equivalent (CO2-eq)emissions by 2050 will need to be reduced by up to 85% oftheir 2000 values for stabilisation at 445–490 ppm—a Category 1 stabilisation target in Fisher et al. (2007)—which would give a 2.0–2.4 1C temperature rise atequilibrium above pre-industrial levels. (Following Barkeret al. (2007a, b), ‘CO2-eq’ refers only to CO2, N2O, CH4

and fluorinated gases.) The corresponding peaking year forCO2 emissions alone is 2000–2015. Since CO2 levels arealready 380 ppm, and non-CO2 gases today total roughly100 ppm CO2-eq (Barker et al., 2007a), we are already near

ARTICLE IN PRESSP. Moriarty, D. Honnery / Energy Policy 36 (2008) 1251–12561252

the upper end of this 445–490 ppm range. Even490–535 ppm CO2-eq levels would need a 30–60% reduc-tion by 2050, with the CO2 peaking year 2000–2020, andthe resulting equilibrium temperature rise 2.4–2.8 1C. Thereport also considers much higher greenhouse gas (GHG)levels, but even 490–535 ppm level runs some risk ofequilibrium temperature increases of 4 1C above pre-industrial, with resulting serious consequences (Parryet al., 2007).

Studies of past climate have shown that abrupt climaticchange can occur over the course of a decade or even a fewyears. Overpeck and Cole (2006) state that ‘abrupt climatechange in the future is inevitable’, and that ‘continuedhuman forcing of climate change increases the probabilityof deleterious abrupt climate change’. This is important, asthe IPCC (Barker et al., 2007a) note that ‘if the damagecost curve increases steeply, or contains non-linearities (e.g.vulnerability thresholds or even small probabilities ofcatastrophic events), earlier and more stringent mitigationis economically justified’. Because of the risk of abruptclimate change, Shindell (2007) also cautions againstwaiting too long before acting forcefully.

An important effect of increased temperatures is itseffect on sea-level rise. The IPCC (Solomon et al., 2007)forecasts a sea-level rise of between 18 and 59 cm by theyear 2100. In contrast, NASA physicist James Hansen(2007) states: ‘I find it almost inconceivable that ‘‘businessas usual’’ climate change will not result in a rise in sea levelmeasured in metres by the end of the century’. He adds thatif the world warms by 2–3 1C, a rapid, non-linear andirreversible collapse of the Greenland and possibly theWest Antarctic ice sheets is inevitable. His findings aresupported by recent calculations suggesting that Green-land’s ice sheet collapse ‘could be triggered by temperatures1 1C warmer than today’s of which 0.7 1C is already ‘‘in thepipeline’’’ (Pearce, 2007).

A further uncertainty concerns the effect of any furtherclimate change on the natural carbon cycle, specifically, thecontinuing ability of the oceans and the biosphere tosequester about half of CO2 net annual emissions (ClimateInstitute, 2007). Because of continuing climate change,some coupled carbon-climate models indicate that carbonsequestration could reverse in a warming world, withforests and soils eventually becoming an atmosphericcarbon source (Jones et al., 2006). Their coupled modeltherefore indicates that for CO2-only stabilisation at450 ppm, allowable annual emissions would need to bereduced by a further 21% compared with models that donot incorporate this feedback. Because of these carboncycle feedbacks, the IPCC report similarly suggests that theneeded reductions levels discussed earlier may be under-estimated.

It is clear that two questions are important in attemptingto avert dangerous climatic change by emission reductions:by how much do we have to reduce GHG emissions, and inwhat time frame? Huesemann (2006) concludes that, giventhe high levels of uncertainty as discussed earlier, the

precautionary principle demands that we limit atmosphericGHGs to the lowest level possible, ideally at or near theirpresent levels, i.e. at near 100% reduction. Harvey (2007)likewise argues that we should accept only a lowprobability (at most 10%) of dangerous climatic change,and consequently that atmospheric GHGs should remainnear today’s levels. This urgency is underlined by a recentstudy (Climate Institute, 2007) which concluded that ‘thereexists evidence that the IPCC process may have led to anunderestimation of the risk of greater warming and that theimpacts of climate change are occurring more rapidly thanpreviously projected’.Delaying effective response may be politically easier in

the short term, but will entail higher overall costs and moreeventual disruption. The more—and the longer—we over-shoot, the greater is the risk of irreversible adverse change,and the harder it will be to reverse emission levels.Reductions will prove progressively more difficult if theindustrialising countries also get locked into high fossil fuelconsumption patterns, a process well under way in China.We therefore assume here that any rise above present CO2-eq levels carries a risk of serious adverse climate change,and that reductions in emission levels need to be made in avery few decades, not by the end of this century. Sincemean temperatures have already risen 0.74 1C on pre-industrial levels, and we are already committed to about a0.6 1C further rise from past emissions, it is likely that the2 1C EU limit is the best that can be hoped for (Riahi et al.,2006).Most of radiative forcing (about 77%) from the emission

of GHGs from all sources is from CO2, and 74% of thisCO2 is from fossil fuel combustion and industrial processes(Barker et al., 2007a). Hence, this paper will concentrate onoptions for CO2 reductions, particularly from fossil fueluse. We first evaluate the potential for technical mea-sures—carbon sequestration, non-carbon energy use andimproved energy efficiency—using the IPCC 2007 Mitiga-tion Report as a basis. We show that all these methodshave limited mitigation potential in the time frameavailable. Next, we outline an alternative approach, ‘socialefficiency’ improvement. Finally, we argue that because ofthe huge unmet demand for energy in the industrialisingworld, any technical energy efficiency gains made would besoon swamped by rising energy demand.

2. Mitigating climate change: technical measures

Although climate change is a serious challenge thatneeds to be tackled without delay, a focus on mitigatingclimate change should not blind us to the fact that we livein a divided world, one which also faces other seriousenvironmental, resource and political problems. All toooften, researchers forget the complexity and interconnect-edness of both the physical and social worlds. There areonly a limited number of realistic technical approaches formitigating the climate change effects of energy use. Thissection briefly examines the prospects for these mitigation

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options in a divided world, using the 2007 IPCC 4thAssessment Report as a basis.

The IPCC, in its Mitigation volume (Barker et al.,2007a), examined in detail the potential for carbon captureand sequestration (CCS), nuclear energy and renewableenergy (RE) to reduce emissions, as well as the scope forenergy efficiency in each energy-using sector. Reductionsboth in the short- and medium-term (to 2030) and in thelonger term (up to 2100) were considered. They found thatby 2030, the global economic potential for emissionreductions from all sectors (including those for land use,land use change and forestry) is from 16 to 31GtCO2-eqannually, for emission taxes of up to US$ 100/tCO2-eq atyear 2000 prices based on a ‘bottom-up’ approach(17–26GtCO2-eq annually for a ‘top-down’ approach).This range can be compared with the estimated 2004emissions from all sources of 49GtCO2-eq.

These potential reductions must also be compared withthe scenario emissions in 2030 (in the absence of specificemission reduction policies) to assess the likely remainingemissions in the year 2030. The reductions mentionedearlier are calculated relative to the Special Report onEmission Scenarios (SRES) B2 and the similar IEA WorldEnergy Outlook (WEO) 2004 baseline emissions. For theB2 scenario, 2030 emissions are projected at 49GtCO2-eq/year (Barker et al., 2007a, Table TS 15). So, even in the bestcase, 18GtCO2-eq/year would still be emitted in 2030, andin the worst case, 33GtCO2-eq/year. Other SRES scenariosgive even higher emissions—68GtCO2-eq/year for SRESA1 B—and as the report points out, all scenarios areequally likely to occur. It is likely that reduction potentialswill be higher for higher emission scenarios, but willprobably be a lower proportion of projected emissions.Although the emission reduction potential for transportefficiency could be expected to be roughly proportional tototal transport emissions, such is not the case for non-carbon energy sources, as many of these are resource- orcost-limited. But even if reductions are proportional,68GtCO2-eq/year would only be reduced by 22.2GtCO2-eq/year in the worst case.

Furthermore, emissions are now rising faster than in anyof the IPCC scenarios (Climate Institute, 2007). The IPCCreport also stresses that numerous non-economic barriersprevent the economic reduction potentials from beingachieved, so actual reductions achieved for a givenemissions tax will be less. Further, Hultman and Koomey(2007) point out that actual costs for new energytechnologies routinely exceed estimates. Indeed, so com-mon is this that they use the term ‘expected surprises’.

How are these modelled reductions distributed globally?The IPCC Mitigation Report divides the world into threecategories: the OECD; the economies in transition (EIT),which include the East European countries; and theremaining countries (non-OECD/EIT). Most of the eco-nomic potential for emission reductions by 2030 withoUS$ 100/tCO2-eq emissions tax is in the non-OECD/EITgroup of countries. Their overall economic reduction

potential in 2030 was estimated as 8.3–16.8 for GtCO2-eqavoided, compared with 15.8–31.1 global total. Only in thetransport sector was the potential in non-OECD/EITcountries a minor part of the total (Barker et al., 2007b,Table 11.3).The only acceptable policy for very deep cuts (85% of

year 2000 emissions by 2050, for example, as discussedearlier) will be roughly equal emissions per capita for allcountries, as advocated by the ‘contraction and conver-gence’ proposal (Bows and Anderson, 2007). It is improb-able that important industrialising countries such as Chinaor India will permanently accept per capita emissions lowerthan the already industrialised countries. It is also unlikelythat these poorer countries will be prepared to accept theincreased costs that reducing emissions will entail unlesseither OECD per capita emissions have been reduced to alevel not much above their own, or the increase in costs ispaid for by the OECD. OECD emissions/capita arepresently much greater; in 2002, the energy-related CO2

emissions of the USA/Canada, for example, were 5.3 timesthe world average (Sims et al., 2007; UN, 2006).Industrialising countries could go even further, anddemand parity in cumulative per capita emissions overthe past century for CO2 and other long-lived gases. Suchan approach would require the already industrialisedcountries to reduce emissions to near zero.The IPCC report projects nuclear power to increase its

share of global electricity from 16% today to at best 18%in 2030 for carbon prices up to US$ 100/tCO2-eq, butstresses that ‘safety, weapons proliferation and wasteremain as constraints’. Possible reductions from nuclearenergy were 1.88GtCO2-eq. The largest RE electricitypotential emission reductions in year 2030 were modelledto come from wind, hydro and bioenergy (0.93, 0.87 and1.22GtCO2-eq, respectively). Potential CCS reductionsfrom coal and gas electricity generation together weresmall at 0.81GtCO2-eq. All these reductions are foremission taxes of US$ 100/tCO2-eq or less, and refer tomaximum values (compared to the no-mitigation policybase scenario) for each option considered in isolation (Simset al., 2007, Table 4.19). As the IPCC report makes clear,these individual values cannot therefore be simply summed.Energy efficiency potential was seen as very large out to2030, with possible savings especially important in thebuildings and transport sectors (Barker et al., 2007b; KahnRibeiro et al., 2007).To be considered the solution to global warming,

technology must be able to provide the reduction inGtCO2-eq emissions needed. Assume that emissions fromall sources in 2030 will be 68GtCO2-eq, as in the SRES A1B scenario, in the absence of climate mitigation policies.This figure seems modest, given that, as already noted,growth in CO2 emissions now outpace all SRES emissionscenarios, and that the carbon intensity of the worldeconomy has stopped decreasing (Canadell et al., 2007).From the earlier discussion, reductions brought about bytechnical means might be below 22.2GtCO2-eq, especially

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if by 2030 most reductions must come from the high-emission OECD/EIT countries. Since the residual wouldroughly equal present emissions in this case, it follows thatthe technical solutions to global warming suggested by theIPCC and others cannot deliver anywhere near therequired reductions if temperature increases above pre-industrial are to be kept to around 2 1C.

We have identified a large potential gap between theemissions reductions needed and what the various technol-ogy-based approaches can deliver by 2030. For example,Table 4.20 in Sims et al. (2007) makes clear that potentialreductions from electricity production to 2030 depend notonly on much replacement of old plant but also on a largeexpansion of generating capacity worldwide. But if largeemission reductions are required, and can only be partlymet by low-carbon sources or CCS, then energy usereductions themselves, both primary and delivered, wouldhave to produce the remaining emission reductions. Thiswould adversely affect the introduction of low-carbonelectric power, which would then only make a significantcontribution in the longer term. Similarly, if few new coal-or gas-fired plants were built, any CCS would have to usemainly ‘add-on’ technology to older plants, which wouldboth increase electricity production costs and lower theefficiency (Kintisch, 2007). But on the positive side, largereductions in OECD/EIT power output would enable theearly closure of much carbon-intensive plant, and thus givedisproportionate emission cuts.

3. Mitigating climate change: social efficiency

The preceding discussion has shown that for the crucialenergy and industry sectors, emission reductions fromenergy efficiency, non-carbon energy and CCS will likelyfall far short of that needed to avert dangerous climaticchange. If so, the world will have to make do withsignificantly less energy use. Reductions could in principlebe achieved by energy pricing, but the large cost risesnecessary would be inequitable. An alternative approachwould be to improve the ‘social efficiency’ of energy use,that is, the effectiveness with which a given amount ofenergy is used to satisfy human needs. We have appro-priated the term ‘social efficiency’, because the morecommon term ‘energy conservation’ usually includesreductions through both technical efficiency gains as wellas less use of energy-using devices. Because of the heavyemphasis on technical solutions for both our energy andclimate change challenges, this approach has been seen ashaving only a minor role, as the IPCC report makes clear.We stress that any approach to large and rapid cuts inglobal energy use is likely to entail disruption—there seemsno easy solution.

If technical efficiency is a measure of how much outputthere is from a given input, social efficiency is concernedwith how much social value can be derived from thisoutput. This approach in general argues that energydemand analysis should focus on the basic needs all people

have, for example, for food, housing, access, sociality,exercise and new experiences, and devise new ways ofmeeting these demands with lowest environmental impact.Energy use is nearly always a derived demand; socialefficiency shifts the focus from the energy-using equipmentto the need that equipment is meant to satisfy. So, first wemust identify the basic human needs, and then determinehow the needs are to be met. Social efficiency would actdirectly to reduce final energy demand, and thus primaryenergy demand.We will illustrate how social efficiency might help by

considering transport and buildings. Transport is impor-tant not only because of its high and rising share of globalenergy use and CO2 emissions (IEA, 2006) but also becauseglobal oil depletion could soon make big cuts in the energyderived from oil necessary. Our previous research hasshown that large emission reductions for surface transportwill require not only a near-total shift from the private carto public transport but also large reductions in vehiculartravel itself. To obtain the greatest benefit, expansion inpublic transport systems will be needed. However, empha-sis must be placed on access rather than mobility, as well aspolicies to expand non-motorised transport, not reduce it(Moriarty and Honnery, 2005, 2007b). Indeed, for deepcuts, it is likely that non-motorised transport will need tohave a much larger share of total travel. In shifting to asocially efficient transport network, many of the benefits ofprivate travel would be lost, such as privacy and thepsychological benefits of driving. However, the changewould bring its own benefits, including increased exercise,lower air pollution and, particularly in lower incomecountries, lower traffic casualties. Drastic reductions in airtravel would also be needed, and might be achieved, forexample, by a shift to more local destinations for holidays.Energy use in the important buildings sector includes

energy for appliances, climate control and water heating.Effecting large reductions will require less ownership andduplication of electric appliances in households, longerlasting equipment, and, through recognition of the energycosts of absolute control of our interior environment,greatly reduced use of active cooling and heating. It willalso entail a partial replacement of machine energy use byhuman labour—not only for non-motorised travel—whichmay lead to some reversal of the trend established by theIndustrial Revolution. There is little scope for socialefficiency improvement in industry or electricity produc-tion; energy reductions in these sectors would flow fromlower industrial output (reduced manufacturing produc-tion and infrastructure) and lower power consumption ofhouseholds, businesses and industry.

4. Discussion and conclusions

We have seen that deep emission reductions, if requiredby 2030, would require large cuts in energy use, whether bytechnical or social efficiency measures. This in turn wouldreduce the scope for low-carbon sources or CCS in the

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electricity generation sector, although early retirement/lessuse of high-emission plant would partly offset this loss ofemission reduction potential. However, in the transportenergy sector, technical and social efficiency approachescould themselves work at cross-purposes. If both car andair travel were greatly reduced, sales of new vehicles andplanes would also decrease. Assuming worldwide reduc-tions, not only would fleet turnover be low but interest in,and funds for, developing radically new carbon-efficientdesigns would be lacking. Even if adopted for the greatlyreduced fleet, the savings in CO2-eq emissions would beminor. (On the other hand, sales of public transportvehicles would grow, allowing the share of more energy-efficient designs to rise more rapidly.) Thus, at least intransport, we may have to make a choice between socialefficiency and technical efficiency.

We have argued that if deep cuts are needed soon,technical solutions alone are unlikely to deliver anywherenear the reductions needed. As the IEA (2007) stresses, theprimary scarcity the world faces is time. The technicalenergy efficiency improvements discussed in Section 2 havea well-known ‘rebound effect’ on the resulting energysavings (Alcott, 2007); presumably, the model resultssurveyed by the IPCC Mitigation Report include thiseffect. But technical advances (in energy efficiency, non-carbon energy, CCS) also strengthen the belief—both inindustrial and industrialising countries—that for solutionswe need not look beyond technology. Since technicalsolutions to our problems are seen as just around thecorner, presently high-consumption OECD lifestyles can besustainably exported to the world outside the OECD. Theattempt to continue present consumption patterns in theOECD sends a strong signal to all other countries withpresently more modest consumption patterns to aim atOECD lifestyles.

There is today a huge imbalance in energy consumptionlevels worldwide, itself the result of similar imbalances inper capita incomes. By OECD standards, there is thus avast latent demand for energy-consuming goods andservices. For example, most people live in countries withless than 0.02 cars/capita, compared with 0.5 or moretypical of OECD countries (World Bank, 2006). Air travelshows similar imbalances. An even more extreme case isannual per capita electricity consumption: in 2004, therewas three orders of magnitude difference between Iceland(27.0MWh), and Norway (24.5MWh), on the one hand,and a dozen countries, mainly in tropical Africa, with0.01–0.04MWh, on the other. Even the world average isonly 10% of Norway’s per capita use (World Bank, 2006).

Unless these inequalities continue—and the rapid growthof the Chinese and Indian economies suggest that they willnot—any improvements in technical efficiency will soon beswamped by rise in the numbers and use of energy-usingequipment. Indeed, this phenomenon has already beingobserved: between 1990 and 2004, the energy intensity ofthe global economy fell, but both energy use and fossil fuelCO2 emissions continued to grow (Raupach et al., 2007).

Even the modest emission reductions from energy effi-ciency improvements projected by the IPCC will be lost, if,as a result of the ‘demonstration effect’, world primaryenergy use grows faster than in the IPCC scenarios. As wehave seen, the very recent global energy growth ratessupport this view.Our conclusion, that social efficiency must be the most

important part of the solution, is based both on thelimitations of available technical solutions to bring aboutlarge emission reductions in the short term, and therecognition that energy use is a derived demand. Technicalsolutions have an important place—once a lower con-sumption lifestyle based on social efficiency is accepted.Energy efficiency can then deliver absolute energy andemission reductions. And in the long term, the world willhave to move to renewable energy sources. Whether thelifestyle changes underpinning social efficiency can beimplemented in a couple of decades depends on howseriously the electorate and policy makers perceive theproblem to be. Given strong political support, thesechanges could be rapidly implemented: Shindell (2007)has stressed that sudden climate change could help producea more rapid positive response to the global climatechallenge, as happened earlier with the discovery of theAntarctic ozone hole. Since many of the needed changesmay prove unpopular with business leaders, or even thegeneral public, there is thus no guarantee that the measuresdiscussed here will be implemented by governmentsglobally in a timely manner.But if they are not, we argue that effective mitigation of

global climate change will not take place at all. We will beleft with adapting to climate change in a world where ourability to foresee such changes will progressively diminish,along with our ability to adapt to changes, which willbecome more severe as the decades pass. The costs ofadaptation will then fall most heavily on low-incomecountries least able to bear them—and who are leastresponsible for greenhouse emissions (Parry et al., 2007).

Acknowledgement

Patrick Moriarty would like to acknowledge thefinancial support of the Australasian Centre for the Gov-ernance and Management of Urban Transport (GAMUT)in the preparation of this paper.

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