bioenergySD.pdf

ANRV325-EG32-05 ARI 2 October 2007 13:6

Bioenergy and SustainableDevelopment?Ambuj D. Sagar1 and Sivan Kartha2

1Science, Technology, and Public Policy Program, John F. Kennedy School ofGovernment, Harvard University, Cambridge, Massachusetts 02139;email: [email protected] Environment Institute, Somerville, Massachusetts 02144;email: [email protected]

Annu. Rev. Environ. Resour. 2007. 32:131–67

First published online as a Review in Advance onAugust 23, 2007

The Annual Review of Environment and Resourcesis online at http://environ.annualreviews.org

This article’s doi:10.1146/annurev.energy.32.062706.132042

Copyright c© 2007 by Annual Reviews.All rights reserved

1543-5938/07/1121-0131$20.00

Key Words

biodiesel, bioethanol, biofuels, biomass, clean energy, cookstoves

AbstractTraditional biomass remains the dominant contributor to the energysupply of a large number of developing countries, where it serves thehousehold energy needs of over a third of humanity in traditionalcookstoves or open fires. Efforts to reduce the enormous humanhealth, socioeconomic, and environmental impacts by shifting tocleaner cookstoves and cleaner biomass-derived fuels have had somesuccess, but much more needs to be done, possibly including the ex-panded use of fossil-derived fuels. Concurrently, biomass is rapidlyexpanding as a commercial energy source, especially for transportfuels. Bioenergy can positively contribute to climate goals and rurallivelihoods; however, if not implemented carefully, it could exacer-bate degradation of land, water bodies, and ecosystems; reduce foodsecurity; and increase greenhouse gas (GHG) emissions. For large-scale commercial biofuels to contribute to sustainable developmentwill require agriculturally sustainable methods and markets that pro-vide enhanced livelihood opportunities and equitable terms of trade.The challenge lies in translating the opportunity into reality.

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Contents

1. INTRODUCTION . . . . . . . . . . . . . . 1322. ENERGY FOR POOR

HOUSEHOLDS . . . . . . . . . . . . . . . . 1332.1. Biomass Use in Households

and (Un)sustainableDevelopment . . . . . . . . . . . . . . . . . 134

2.2. Alternatives to Traditional Useof Biomass in Households . . . . . . 135

2.3. Prospects for Sustainable andClean Energy for the Poor . . . . . 137

3. LARGE-SCALE, COMMERCIALBIOENERGY . . . . . . . . . . . . . . . . . . . 1393.1. Technological Options for

Biofuels . . . . . . . . . . . . . . . . . . . . . . . 1403.2. Energy and Environmental

Aspects of Biofuels Productionand Use . . . . . . . . . . . . . . . . . . . . . . . 143

3.3. Biotechnology ControversiesRedux? . . . . . . . . . . . . . . . . . . . . . . . 150

3.4. Land Requirements and LandAvailability . . . . . . . . . . . . . . . . . . . . 150

3.5. Socioeconomic Issues . . . . . . . . . 1524. CONCLUSION. . . . . . . . . . . . . . . . . . 155

1. INTRODUCTION

Bioenergy has two faces. It is the domi-nant source of energy for more than a thirdof the world’s population (1), taking theform of dung, agricultural wastes, and woodfuel burned in generally inefficient and pol-luting cookstoves. At the same time, it isthe most rapidly growing modern renew-able energy source, yielding transport fu-els and power at industrial scales to delivermodern energy services. These two faces ofbioenergy—the traditional and the modern—present daunting sustainable developmentchallenges.

Traditional bioenergy is a challenge in thatit is deeply imbedded in the day-to-day livesof developing country poor and provides vi-tal energy services, but it does so at great hu-man, social, and environmental cost. The shift

away from traditional biomass and its replace-ment with cleaner and more benign energysources higher up the “energy ladder” are longoverdue. The UN Millennium Project1 hasdrawn attention to the deep connection be-tween access to clean household energy andsustainable development, calling for the num-ber of households using biomass as a cook-ing fuel to be halved by 2015. The shift awayfrom traditional biomass will require an evo-lution in technologies, fuel supply infrastruc-ture, energy and social policies, and even cul-tural practices.

Modern bioenergy, in contrast, is a chal-lenge insofar as it is poised to grow into amajor contributor to global energy supply,but whether it will do so in a manner thatis environmentally sound and socially bene-ficial is by no means guaranteed. Althoughit is true that bioenergy has many potentialvirtues, it has equally striking hazards, andthe wry aphorism “today’s solutions are to-morrow’s problems” must not be allowed tohold true for bioenergy. Indeed, one can eas-ily imagine biomass production systems thatare ideally suited to their environment andthat even contribute to improving the en-vironment by revegetating barren land, sta-bilizing and replenishing topsoil, protectingwatersheds, reclaiming waterlogged and sali-nated soils, providing habitat for local species,and sequestering carbon—all the while con-tributing to livelihoods of rural communities.However, an equally plausible vision is thatof biomass production systems that are fossil-fuel intensive, exhaust the soil of nutrients,exacerbate erosion, deplete or degrade wa-ter resources, reduce biodiversity by displac-ing habitat, increase greenhouse gas (GHG)emissions, compete with food production for

1The recommendation of the UN Millennium Project isto “Enable the use of modern fuels for 50% of those whoat present use traditional biomass for cooking. In addition,support (a) efforts to develop and adopt the use of improvedcookstoves, (b) measures to reduce the adverse health im-pacts from cooking with biomass, and (c) measures to in-crease sustainable biomass production” (2).

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arable land and water resources, and under-mine the livelihoods of rural communities.The sustainable development challenge is tofoster the growth of a modern biomass systemthat fulfils the promise and avoids the pitfalls.This chapter reviews the major elements ofthe sustainable development challenges cen-tral to traditional and modern biomass energy.

2. ENERGY FOR POORHOUSEHOLDS

Worldwide, biomass has held nearly steady asa fraction of total primary energy demand,edging down only slightly from 12% to 11%over the period from 1971 to 2004, evenwhile the absolute quantity consumed rose byabout 80% (3). In many parts of the devel-oping world, biomass continues to constitutea significant fraction of the primary energysupply—nearly half in the case of Africa andmore than 80% for many countries (such asNigeria, Tanzania, and Mozambique in Africaand Nepal in Asia), with the number of house-holds relying on traditional biomass projectedin a business-as-usual world to continue toincrease.

Although biomass has historically played akey role in the provision of energy services forhumankind, the last few decades have seen arange of efforts intended at expanding and im-proving energy services for the poor in devel-oping countries. This has been part of a largertrend in these countries to expand their en-ergy sectors more generally. While the globalprimary energy supply doubled between 1971and 2004, the rise in the energy supply in mostdeveloping countries has been faster. Africa,for example, almost tripled its energy supplyover this period, and non-Organisation forEconomic Co-operation and Development(OECD) Asia almost quadrupled its totalprimary energy supply (3).

The overall expansion of energy sectorsand their modernization have had some pos-itive impact on their poorer populations, butin many cases, much still needs to be done.Biomass continues to play a significant, even

Table 1 People relying on biomass as their primary cooking fuel,2004a

Totalpopulation Rural Urban

Million % Million % Million %Sub-SaharanAfrica

575 76 413 93 162 58

India 740 69 663 87 77 25China 480 37 428 55 52 10Indonesia 156 72 110 95 46 45Rest of Asia 489 65 455 93 92 35Latin America 83 19 75 60 33 8Global 2528 52 2147 83 461 23

aAdapted from Reference 1.

central, role in the human and economic fab-ric of developing countries, particularly intheir rural and periurban areas where a sig-nificant portion of their populations still re-side. In fact, even as developing countries haveexpanded their energy sectors over the pastfew decades, in many countries, energy sup-ply from biomass has grown almost as fast or,in some cases, even faster.

Almost 50% of the world’s population con-tinues to depend on biomass for its cook-ing needs (see Table 1). Furthermore, about40% of the global residential energy con-sumption comes from biomass, but the frac-tion in many developing countries is muchhigher. In Africa, biomass accounts for about85% of the residential energy use; in LatinAmerica, 40%; and in Asia, 75% (3). In manycountries, a majority of the rural and urbanhouseholds use solid fuels (primarily biomass)for their energy needs (4, 5).

Generally poorer countries and those witha greater fraction of poor populations tend torely more on biomass for the energy needs,as Figure 1 shows. The International EnergyAgency reference scenario indicates that thenumber of people dependent on biomass forcooking and heating will increase to 2.55 bil-lion by 2015 (1).

In the past few decades, there has beenan enormous amount of work on the de-velopment and dissemination of household

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or small-scale bioenergy technologies. Overtime, there have been refinements of thesetechnologies and numerous projects todemonstrate and/or disseminate these tech-nologies. At the same time, there has emergeda greater understanding of the ways in whichthese bioenergy technologies interact with thehuman, economic, and environmental dimen-sions of sustainable development. This sec-tion reviews some of the main developmentsin these areas.

2.1. Biomass Use in Households and(Un)sustainable Development

The traditional use of biomass in householdsentails its combustion in open fires or simplethree-stone or mud stoves for cooking, spaceheating, and lighting. Although some of theearlier concerns about this inefficient modeof biomass use centered around deforestationand energy security, over time, the wider andsignificant human, social, and environmentalcosts of this dependence on biomass becamemore apparent (7, 8):

� The burden of fuel collection fallsmainly upon women and children, whocan spend up to 3–4 hours gatheringfuel resources every day (9, 10). In manycases, people may have to travel 5–10 kmper day gathering fuelwood and end upcarrying heavy loads (1, 9). The involve-ment of children in this activity can alsohave an adverse effect on their schooling(7).

� The use of biomass for cooking andother energy services such as space heat-ing is a major contributor to indoor airpollution. The smoke from the com-bustion of wood and other biomasssuch as dung is a veritable cocktailof harmful pollutants, including car-bon monoxide, nitrogen oxides, alde-hydes, benzene, other polycyclic aro-matic hydrocarbons, and particulatematter, with adverse health impacts thatslowly have become better understood

[for examples of early discussions of thistopic, see (11–13)]. There is strong ev-idence of correlations between such in-door air pollution and acute lower res-piratory infections and chronic obstruc-tive pulmonary disease; there is alsosome evidence for a host of other healthoutcomes, including lung cancer, tuber-culosis, asthma, and cataracts (4, 14).Despite the importance of this healthissue, it remains under studied (15, 16).Women and children are at highest riskbecause they have the highest exposure,given women’s proximity to the stoveand their children’s proximity to them.It has been estimated that indoor airpollution leads to annual excess mor-tality of 400,000–550,000 in India (17),∼420,000 in China (18),2 ∼390,000 inAfrica (14), and about 1.6 million world-wide (14, 19). The World Health Or-ganization (19) estimates that indoorair pollution from these fuels is thesixth largest health risk factor in devel-oping countries, responsible for about38 million disability-adjusted lost years(DALYs) in developing countries withthe attendant and significant social andeconomic costs.

� Fuelwood in rural areas comes from avariety of sources and therefore oftenputs only limited pressure on forests(20). It now has become apparent thatthe use of fuelwood is not leadingto large-scale deforestation, primarilybecause rural households use biomassfrom a variety of sources rather than justfrom forests; furthermore, most usersalso have a range of responses that allowthem to adjust to local changes in fuel-wood availability (20). However, urbandemand for charcoal does have a dele-terious effect on surrounding forests,leading to local deforestation (1). In

2In the case of China, the widespread use of coal as a house-hold fuel is also a major contributor to the adverse healtheffects.

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some locales, shortages of fuelwood forsubsistence users are becoming morepronounced particularly for the landlessand those with little land.

� The products of incomplete combus-tion (PICs) that result from the waybiomass is burned in traditional stoves(and even in some “improved” stoves)have recently been shown to have signif-icant global warming implications (21,22). In fact, the global warming com-mitment of these PICs can be highenough to exceed the global warmingcontribution of fossil-based [keroseneor liquefied petroleum gas (LPG)]stoves (on a per-meal-equivalent basis)(21). On a cumulative basis, the green-house implications of biomass combus-tion can be substantial; it is estimatedthat the greenhouse impact (on a 20-year time-frame) of PICs from biofu-els in 1990 was almost a quarter of thatfrom energy use in Asia, even if thebiomass was harvested sustainably (23).Biomass combustion also results in theemissions of carbonaceous aerosols (24),with residential biofuels accounting fora significant fraction of the emissions inIndia and Asia (25). These aerosols canhave significant regional and global cli-mate impacts (26–28).

� Poorer people generally spend a greaterfraction of their income on householdfuels than their richer counterparts (1,8, 29). Furthermore, they often end uppaying a greater amount for the sameamount of useful energy services, giventheir inefficient energy-conversion ap-pliances and the higher transaction costsof their energy purchases (because theyoften buy wood fuel or other energysources in smaller quantities, whichmakes it more expensive) (29). Thepoorest generally get most (or all) oftheir energy services from biomass; aspeople’s incomes grow, they move upthe energy ladder toward more mod-ern and cleaner fuels (but even as they

do that, they may continue to use somebiomass) (29, 30).

Thus, it is increasingly clear that alterna-tive and better ways of satisfying the energyneeds of this large fraction of humanity are anessential part of the sustainable developmentagenda. This has been further re-emphasizedrecently through the connections between thehousehold-level solid biomass use and theMillennium Development Goals (2, 5).

2.2. Alternatives to Traditional Useof Biomass in Households

There is a range of alternative approaches toreducing the adverse impacts resulting fromthe use of biomass in households, which in-clude (31)

� Emission-reducing cooking options,such as improved cookstoves (using tra-ditional or processed biomass includingbriquettes and charcoal), as well as bet-ter maintenance and operation of cook-ing equipment, other biomass-basedenergy services (such as biogas), otherrenewables-based energy services (suchas solar cookers and water heaters), fos-sil fuels (such as kerosene and LPG), andelectricity

� Living environment options, such asimproved ventilation in households orredesign of kitchen and cooking spacesto reduce exposure from cooking forother members of the households

� Behavior-modification options, such asavoiding smoke.

Ideally, approaches that intend to makea serious contribution to the sustainable de-velopment of this large fraction of humanityshould try to make headway on the whole hostof issues that are highlighted in the previoussection. That is to say, desirable approacheswould be those that offer as many of the fol-lowing benefits as possible (31):

� Reduced levels of indoor (as well as lo-cal and global) pollution and humanexposure


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� Increased fuel efficiency� Reduced time for fuel collection and

cooking� Reduced stress on the local environ-

ment� Contribute positively to the overall

home and working environment, espe-cially for women

Historically, much of the attention in theexploration for alternatives to traditional useof biomass for residential energy has beenon improved cookstoves. Some of the earli-est programs to develop and disseminate im-proved cookstoves were motivated by a per-ceived fuelwood crisis [for example, (32–34)]anticipated from a widespread and tradition-ally inefficient use of biomass for cooking (33).Thus, increasing energy efficiency was theprimary initial motive of most of the early im-proved cookstove programs (33, 35, 36), in-cluding the Chinese and the Indian programs(12, 37), which are the largest in the world. Itwas hoped that the development and dissem-ination of advanced designs that had a greatlyincreased efficiency would avoid deforestationand wood fuel shortages, while also reducingthe drudgery of women who had to spendhours collecting firewood or other biomassfor their households’ cooking and other en-ergy needs.

Most of the early efforts to develop and dis-seminate improved cookstoves had only lim-ited success. Many of the improved designsdid not lead to the hoped for gains in actualuse. Although initial predictions had been thatdesign changes could lead to a three- to sixfoldimprovement in efficiency, realization set inthat a 25% to 50% reduction in fuel consump-tion was a more realistic expectation, partlybecause of the traditional stoves were not asinefficient as initially believed and because thenew designs did not function as effectivelyin the field as in controlled/laboratory con-ditions (33, 35). Traditional cookstoves alsohad a variety of other benefits to households,such as space heating, protection from insects,and flexibility (35). In many cases, fuelwoodwas easy to gather and therefore reduced fuel

consumption was not a priority, and the rela-tively high costs of the stoves acted as a bar-rier to dissemination. There were also ma-terial and reliability problems with many ofthe earlier stoves. Such gaps between assump-tions/expectations and reality, coupled withpoorly designed dissemination programs, ini-tially led to the limited success with improvedstove programs (33, 35, 36).3

Over time, though, there has been somelearning from these early efforts. In the pasttwo decades, a great deal of effort has beendevoted worldwide to improving cookstovedesigns, with an enormous number of or-ganizations in various countries involved inthe development and dissemination of vari-ous designs (some are based on clay, metal,or concrete/masonry and also use other fu-els such as charcoal) intended to meet localneeds. There are an estimated 220 million im-proved stoves in use worldwide (including 180million in China that cover 95% of the rele-vant households and 34 million in India thatrepresent about 25% of the relevant house-holds) (39). Although there are some doubtson the accuracy of these estimates and aboutthe longevity and performance of the dissemi-nated stoves (38, 40–42), there is no doubt thatenormous numbers of these stoves have beendiffused. Furthermore, these cookstove (andrelated fuel) interventions have shown successin that they have led to the reduction in indoor

3One notable exception was the Chinese stove programwhich has had remarkable success, in large part due to thedesign of the dissemination program. In the first phase, thestrategy engendered competition among counties and thenfocused on counties that were ready for intensive efforts(the main criteria being fuel deficiency, sound managerialsetup, availability of appropriate financial resources, and aguaranteed supply of raw materials). Rather than providesubsidies (other than for the poorest households), a rangeof incentives and disincentives were provided to users andvillage leaders, local materials suppliers, and stove manu-facturers. Other key steps included the promotion of localrural energy manufacturing and service companies, train-ing of local workers, and independent review of county-level program performance. At the same time, the researchand design (R&D) program explicitly took into accountthe local conditions of fuel and cooking/heating needs andinnovative activities, such as national competitions, led topublicity and incentive for new designs (12, 38).

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air pollution (38) as well as health benefits(18).

Even though designs aimed at higher over-all fuel stove efficiency can result in increasedPIC emissions (43), there now are emerg-ing designs such as gasifier cookstoves thatmay in the future yield high-efficiency use ofbiomass as well as clean combustion (throughthermo-chemical gasification to yield a clean-combusting gas).

The other large-scale use of biomass toprovide household energy services in a moresustainable manner has involved the diffu-sion of biogas digesters. Biogas, a combustiblegas composed primarily of methane and car-bon dioxide, derives from the anaerobic di-gestion of biomass (generally manure, agricul-tural waste, or other biomass feedstock). Thecombustion of biogas is very clean, allowingfor delivery of energy services with almost noemissions of PICs (and no net emission of car-bon dioxide because the feedstock generallywill be renewably harvested, although theremay be leakage of methane). Biogas digestershave been used in developing countries forover a century as a way of providing energy, es-pecially in rural areas. In China, for example,there was an effort to promote biogas plantsin the 1930s to reduce the consumption ofkerosene (44). In recent years, there have beenprograms in a number of developing countriesto disseminate biogas digesters. As of 2005,there were an estimated 21 million householdsworldwide that used biogas for their cook-ing and lighting needs, including 17 millionin China and 3.8 million in India (45).

The Millennium Gelfuel Initiative (MGI)4

takes another approach to providing a mod-ern energy carrier—one that is based onethanol—to rural households. Ethanol gel canbe cost competitive with other modern (and

4The Millennium Gelfuel Initiative (MGI) was launchedas a public-private partnership between the RegionalProgram for the Traditional Energy Sector and theDevelopment Marketplace Program of the World Bankand Greenheat South Africa, with the aim of develop-ing and disseminating an ethanol-based gel for Africanhouseholds.

clean-burning) energy sources such as LPGand kerosene, and can in principle be derivedfrom biomass, offering climate benefits (46).Furthermore, the ethanol route offers the pos-sibility of local production of the fuel, which inturn can lead to generation of local economicopportunities (46). The MGI has developedtechnically suitable cookstoves, demonstratedthe commercial feasibility of using ethanol gel(and direct ethanol), and has helped set up afew ethanol production plants in Africa (46).Others have proposed the use of dimethylether (DME), another clean-burning fuel,that also may be derived from biomass (eventhough current efforts focus on DME produc-tion from coal) as another to route to ame-liorating the problems associated with tradi-tional biomass use (47) while also contributingto the sustainable development goals of localincome and employment generation.

In many cases, countries have put in placeprograms to bring clean fossil fuels to theirpoor. Brazil has had significant success with its“Auxilio-Gas” program that gave subsidizedaccess to LPG for users with a monthly in-come below half that of minimum wage (48).The subsidy program in India designed to en-hance access to kerosene for the poor, in con-trast, has been problematic (49), indicatingsubsidy regimes must be designed carefully.

Globally, although the percentage of peo-ple depending on solid fuels declined from58% to 52% between 1990 and 2003, in abso-lute terms, the number of people using solidfuels (mainly biomass) actually went up overthis period (10).

2.3. Prospects for Sustainable andClean Energy for the Poor

It is clear that provision of modern and cleanenergy services is an essential part of the over-all sustainable development agenda for thepoor in developing countries, which wouldinclude access to clean fuels for householdneeds. LPG has ideal characteristics in termsof ease of use and clean combustion, yet op-tions such as biogas, ethanol, and DME also


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work quite well. In fact, Goldemberg et al. (50)have suggested a Global Clean Cooking FuelInitiative to promote the provision of cleanenergy for the 2.5 billion people who still de-pend on biofuels for their household energyneeds as a way to meet the Millennium De-velopment Goals as well as the Plan of Imple-mentation of the World Summit on Sustain-able Development. Biomass certainly couldplay a major role through its conversion intoclean energy carriers with near zero net GHGemissions, although relying instead on LPG(or coal-derived DME) would not greatly in-crease global GHG emissions (50–52).

What are the chances of moving to such afuture in the near term? The costs of provid-ing clean energy to the world’s poor are notlow, even though moving people to cleaneralternatives (improved cookstoves or cleanerfuels such as kerosene or LPG) has a very fa-vorable cost-benefit ratio. It is estimated thathalving the number of people cooking withsolid fuels by moving them to LPG will costabout US$13 billion per year, and the gainswould be US$31–$91 billion/year (depend-ing on the value attributed to time savingsfrom reduced illness, avoided deaths, shorterfuel collection and cooking times) (10). At thesame time, an improvement in health will alsolead to gains in economic productivity. Large-scale deployment of liquid-fuel-based optionssuch as ethanol (or ethanol gel) and DME willdepend on the scale-up of production tech-nologies for these fuels. (In the case of ethanol,the most promising option is biomass-derivedethanol, and in the case of DME, it would bethrough biomass- or coal-to-liquid produc-tion routes.) This adds complexity and cost tothe large-scale deployment of these options.Targeted programs such as the MGI and theUN Development Programme’s LP Gas Ru-ral Energy Challenge5 should help make someheadway in moving selected groups, wherever

5The LP Gas Rural Energy Challenge is a public-privatepartnership between the World Liquid Petroleum Gas As-sociation and the UN that aims to create viable and sustain-able markets for LPG delivery and consumption in selecteddeveloping countries.

possible, further up the energy ladder, butthe progress toward raising the level of fund-ing needed to make a rapid and major globalshift toward these modern fuels seems slow atthis point, despite all the sustainable develop-ment gains that might be realized from such atransition.

In the meanwhile, the reality remains thattraditional biomass fuel is going to maintainits role as a primary energy supplier for a sig-nificant portion of humanity. In such a case,continued and concerted efforts will be re-quired to build on the progress of recent yearsto reduce the unsustainable aspects of biomassuse through the continued development ofimproved devices, programs, and policies thatreduce (though do not eliminate) the adverseimpacts of biomass use. The economics ofsuch activities are actually very favorable. Ithas been estimated, for example, that the costsof introducing improved cookstoves to thehalf the number of people cooking with solidfuels worldwide would lead to negative costsof $34 billion owing to fuel savings from theuse of more efficient stoves (10). As a health in-tervention, a move toward improved stoves orcleaner fuels is also very cost-effective. A pro-gram introducing improved cookstoves to halfthe biomass-dependent population in SouthAsia would lead to a gain of one healthy yearfor a mere $15 and for $20 in sub-SaharanAfrica. A similar program for kerosene wouldbe more expensive—$63 and $84, respectively(31).

Improved cookstove programs have alsobuilt on the lessons from the early programsand experiences (38, 53), which have included

� An understanding of the need to engagewith users in the initial stages of the pro-cess so as to help program implementersbetter understand the conditions of use(for example, the mix of biomass usedand the characteristics of the cookingprocess) and to make users aware of theadverse effects of solid biomass use aswell as the benefits of switching to im-proved designs

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� Technical training for stove manufac-turers with an emphasis on quality con-trol (especially of key components) sothat stoves maintain their combustioncharacteristics

� Designs that are amenable to mass pro-duction (54)

� Movement toward certification andstandardization

� Well-designed monitoring systems� The promotion of entrepreneurship-

based dissemination approaches (37, 55)

There are also a range of efforts toadvance information sharing about existingprograms, technologies, and approaches.These include a number of excellent Web-accessible resources, including the HouseholdEnergy Network (http://www.hedon.info),BioenergyLists (http://www.bioenergylists.org), the International Network on Gen-der and Sustainable Energy (http://www.energia.org), Practical Action’s BoilingPoint journal (http://practicalaction.org/?id=boiling point), the Shell Foundation’sBreathing Space program (http://www.shellfoundation.org/index.php?menuID=3&smenuID=10&bmenuID=5 and http://www.pciaonline.org/assets/SF-HEH-Strategy.pdf ) and the Partnership for CleanIndoor Air (http://pciaonline.org), whichwas launched at the World Summit forSustainable Development in Johannesburg inSeptember 2002. The latter two specificallyfocus on scaling up deployment by improv-ing processes for technology design, pilotprojects for product deployment, trainingand capacity building, as well as evaluationof interventions and their impacts. Therecognition of the GHG impacts of biomasscombustion may provide further impetus tothe shift toward improved cookstoves becausethese could offer a reduction in indoor, aswell as global, air pollution. Notably, asa complement to such programs that arefocused on the provision and disseminationof improved cookstoves, it is also critical tofocus on forest and biomass management

policies to make sure that the landless haveaccess to wood fuel (20).

In the end, it must be emphasized that, al-though improved cookstoves certainly ame-liorate many of the aspects of unsustainabilityassociated with the use of biomass for house-hold energy needs, they must be recognizedas being only the next step in the move to-ward the transition to a clean and sustainableenergy future for the world’s poor, relying onLPG and other energy carriers such as DMEor ethanol (50). Whether these energy carriersare derived from petroleum (as in the case ofLPG), coal (as in the case of DME), or biomass(as in the case of DME or ethanol), their pro-vision to the world’s poor will require signif-icant resources (even if these offer favorablecost-benefit ratios). It has been suggested thatanother way to view the relationship betweenthis segment of humanity and the climate is-sue is not to focus on the GHG emission fromtheir use of biomass but on the GHGs not be-ing emitted by them as a consequence of theirlow-energy use in relation to the global av-erages (52, 56). Such a perspective suggeststhat the UN Framework Convention on Cli-mate Change must consider ways to provideresources to transition this group to a sustain-able energy future as a way of compensatingthem for their (involuntary) contribution tothe goals of the climate convention—not onlydoes such an idea make sense from an equityperspective, but it also is very much in linewith the notion of paying people for environ-mental services (57).

3. LARGE-SCALE, COMMERCIALBIOENERGY

The growing interest in industrial-scale com-mercial biofuels arises for four reasons. First,there are rising concerns about the finitenessof the world’s conventional petroleum sup-ply amid continuing growth in demand. Ref-erence forecasts project global demand forpetroleum to increase by roughly 50% by2030 to 118 million barrels per day to fuela growing global transport sector, with the


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United States, Europe, and China projectedto lead global consumption [at 28 million bar-rels per day (mbd), 16 mbd, and 15 mbd, re-spectively] (58). Although there is no consen-sus about whether the peak in production ofconventional oil will occur in the next decadeor several decades hence, the topic has beenthe focus of increasing attention (59), as hasbeen the lack of slack in the global petroleumproduction and refining system and the re-sultant increases in prices and price volatility.These concerns are driving a shift to explorealternative sources of energy.

Second, many nations are increasinglyconcerned about energy security. As remain-ing petroleum reserves grow increasingly con-centrated, the import dependence of import-ing regions is expected to steadily rise andthe non-Organization of the Petroleum Ex-porting Countries share of global crude oilsupply is expected to steadily decline (60).Various nations have taken steps explicitlyaimed at increasing energy security by invest-ing in domestic resources or diversifying in-ternational sources (61, 62). Potential avail-ability of biomass resources is more evenlydistributed geographically than is the distri-bution of petroleum resources (63, 64).

Third, addressing the climate problem willrequire a shift to nonpetroleum fuels, whichpresently account for one fifth of the world’sfossil carbon dioxide emissions and are risingat a rate of roughly 2.5%/yr (60). Several anal-yses conclude that bioenergy could play a ma-jor role in low-carbon energy futures (1, 65–67). This is especially true in scenarios aimedat stabilizing atmospheric concentrations ofGHGs at very low levels, which may rely ondeploying bioenergy with carbon capture andsequestration as a negative-carbon energy op-tion capable of extracting carbon dioxide fromthe atmosphere (68–70).

The fourth motivation for promotingbioenergy derives from its potential to supportdevelopment in rural areas of both industrial-ized nations (71, 72), where governments areunder increasing pressure to eliminate subsi-dies to the agricultural sector, and developing

nations (73, 74), where creating viable liveli-hood alternatives for rural communities is anabiding challenge.

3.1. Technological Options forBiofuels

Technological options for using biomass en-ergy on a large scale can be divided into twocategories: biofuels and biopower. Biofuelsrefer to fluid fuels produced from biomass,primarily for transport. Biopower refers toelectricity produced from biomass, either forgrid or nongrid use. This section focuseson biofuels, because of the high presentlevel of interest in rapidly expanding the useof biomass-based fuels as an alternative topetroleum-based fuels for transport.6

Indeed, biofuels are a small but rapidlygrowing contributor to the transport fuelsmarket. In 2005, global fuel ethanol pro-duction was approximately 36,000 millionliters (75), and biodiesel was approximately4000 million liters (76, 77). This is sufficientto displace roughly 2% of global gasoline con-sumption and 0.3% of global diesel consump-tion. These amounts are modest but grow-ing rapidly; ethanol grew at more than 10%per year and biodiesel at more than 25% peryear over the period 2000 to 2004 (39). In

6In addition to biofuels, two other alternatives topetroleum-based transport fuels that can potentially helpto address the above problems are electricity and hydrogen.As these are not energy sources, but rather energy carri-ers, the degree to which they would be sensible solutionsdepends on the energy sources from which they would bederived. If renewable sources or coal (coupled with car-bon capture and sequestration) were the source of energy,then electricity or hydrogen could potentially be a long-term secure option with low life cycle carbon emissionsthat contributes to rural development. Biofuels are some-what advantaged in this three-way contest for the futuretransport fuel market in that they do not require any ma-jor advances in vehicle technologies, whereas both electricvehicles and hydrogen vehicles (specifically, hydrogen fuelcell vehicles) are in precommercial stages and need furthertechnological development. Hydrogen vehicles also wouldrequire a new fueling infrastructure, ultimately requiringa dedicated hydrogen pipeline network, whereas the fuel-ing infrastructure for biofuel vehicles (or electric vehicles)could largely evolve from existing infrastructures.

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the United States between 2005 and 2006,for example, biodiesel production tripled, andethanol production increased by 25% (76, 78).

This review focuses on ethanol andbiodiesel, but there are also various emerg-ing biofuel options including synthetic mid-dle distillates, DME, methanol, and hydro-gen, which may ultimately be competitiveeconomically and in terms of environmentalbenefits.

Emerging Biofuel Options

Aside from ethanol and biodiesel, thermo-chemical gasification of biomass provides analternate route to produce fuels from biomass.Thermochemical gasification entails partialcombustion of a feedstock, which decomposesinto a gas consisting primarily of hydrogenand carbon monoxide—the building blocksfor synthesis of many chemicals—along withcarbon dioxide, water vapor, nitrogen (unlessgasified in oxygen rather than air), and smallquantities of methane and higher hydrocar-bons. This synthesis gas (or “syngas”) can thenbe cleaned and used as a chemical feedstockin a manner very similar to the use of petro-chemical feedstocks. Recent research has fo-cused on gasification methods that can tol-erate heterogeneous biomass feedstocks andcleanup technologies that produce a syngasclean enough for the downstream chemicalprocessing stages. Particular challenges haveincluded avoiding the production of tars andremoving particulates and alkalis, which canfoul catalysts.

Thermochemical gasification is an attrac-tive route to producing biofuels because itgreatly broadens the range of potential bio-fuel feedstocks well beyond food crops, i.e.,the starch, sugar, or oil crops that are the ba-sis of ethanol and biodiesel today. It can makeuse of the cellulosic fraction of biomass, aswell as the lignin fraction (unlike cellulosicethanol approaches), which typically com-prises 20% to 30% woody biomass feedstocks.Thermochemical gasification makes potentialenergy sources of waste streams, agricultural

residues, and dedicated energy crops that canbe grown on less valuable land than annualfood crops.

Four biofuel options undergoing develop-ment that are produced via the thermochemi-cal gasification route are methanol, hydrogen,Fischer-Tropsch liquids, and DME (60, 64,79, 80).

Methanol. Methanol is a familiar fuel. It hasbeen amply demonstrated to function sat-isfactorily as a high-octane fuel in gasoline(spark-ignition) engines, although interest inwide-scale use has been somewhat muted byconcerns about its safety and possible ad-verse health effects. It can be produced frombiomass via a chemical process analogous tothe process by which methanol is currentlyproduced from coal in commercial, industrial-scale facilities at a volume greater than threemillion tonnes per year. It can be reformedinto a hydrogen-rich gas and has been demon-strated as a suitable liquid fuel for fuel cell ve-hicles with onboard reforming (81–84).

Fischer-Tropsch fuels. The Fischer-Tropsch process has been in use since the1920s, primarily for converting natural gasand gasified coal into synthetic gasoline,diesel, and other fuels that resemble crudeoil–derived products. Production of Fischer-Tropsch fuels from coal is well established inSouth Africa and still being employed today(85).

Hydrogen. Hydrogen has received attentionlately more so for its potential as a fuel for fuelcells than as a fuel for internal combustion en-gine vehicles. Fuel cell vehicles offer a largepotential for improved vehicle efficiencies andimproved pollutant emissions; however, vehi-cle technology, hydrogen storage technology,and distribution infrastructure are still in needof significant advancement before commer-cialization will be feasible. The processes forproducing hydrogen from biomass and coalare similar (81, 86, 87).


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Dimethyl ether. DME is used today primar-ily as a propellant but is well suited as a fuel indiesel (compression ignition) engines owingto its high cetane rating. It is also clean burn-ing because of its high oxygen content andlack of carbon-carbon bonds. Like methanol,it can also be reformed into a hydrogen-richgas and thus may be a suitable liquid fuel forfuel cell vehicles. Because DME is gaseousat atmospheric pressure, it would need to bestored in slightly pressurized (∼5 bar) con-tainers (somewhat like LPG). There are nobiomass-to-DME facilities operating, but twolarge-scale plants, conceptually analogous tocoal-to-DME in design, will be built in Chinafor operation in 2009 (82, 83).

Ethanol can be produced from a varietyof biomass crops, including sugar-laden crops(e.g., sugarcane and sugar beet), starch-ladencrops (e.g., corn and cassava), or cellulosicfeedstocks (e.g., wood, grasses, and agricul-tural residues). Production of ethanol fromsugar-laden crops is the simplest route; themain steps are milling, pressing, fermentation,and distillation. Production from starch-ladencrops requires the additional steps of liquefac-tion and saccharification (conversion to sugar)of the starch. Production from cellulosic cropsis similar, although it is significantly more dif-ficult and costly to convert cellulose and hemi-cellulose into their component sugars (glucoseand xylose, respectively) than is the case forstarches.

The key to improving the efficiency ofethanol production depends on advanced sci-ence and engineering.7 Much of the progressin recent years in cellulosic ethanol technol-ogy was related to the development of more

7The Brazilian success in ethanol, for example, drewupon a substantial scientific and technological effort. Atthe Centro de Tecnologia Canavieira (Cane TechnologyCenter), an R&D facility funded largely by the sugar-cane industry, the genome of sugarcane has been decodedand was used to select varieties that are more resistant todrought and pests and that yield higher sugar content. TheCenter has developed some 140 varieties of sugar, whichhas helped to drive costs down by 1% a year and has al-lowed the country to avoid the pests and diseases that canravage a monoculture (88).

efficient and less costly enzymes for break-ing down cellulose and hemicellulose into fer-mentable sugars and to the optimization ofyeast and bacteria for fermentation. The keyefficiency-increasing advances are expectedto involve (a) advanced biological and ge-netic engineering techniques to understandthe basis for, and reduce, the recalcitranceof biomass to its breakdown by enzymes andmicrobes (89), (b) the identification (or engi-neering) of enzymes and microbes to increasethe efficiency of these breakdown processes(90), and (c) improvements in the distillationprocess (90).8

Presently, roughly 60% of ethanol pro-duction is sugar based and 40% starch based(primarily produced from corn in the UnitedStates) (92). Production from cellulosic feed-stocks is not yet practiced at a commercialscale, although there are dozens of test-scaleplants in operation; at least 15 large-scalecellulosic ethanol plants are planned for op-eration by the end of 2008 to produce ap-proximately 800 million liters of ethanol intotal from a variety of feedstocks includingbagasse, straw, wood residues, and municipalwaste (93). Like the emerging biofuels op-tions discussed above, cellulosic ethanol de-rives its appeal from the fact that it broad-ens the scope of potential feedstocks beyondstarch- and sugar-based food crops.

Ethanol can be marketed as either hydrous(containing approximately 5% water) or an-hydrous (free of water). Hydrous ethanol canbe used as a “neat” unblended fuel in ded-icated spark-ignition engines that have mi-nor modifications relative to gasoline engines.As ethanol has a higher octane number thangasoline, dedicated ethanol engines can oper-ate at a higher compression ratio and achieveslightly higher fuel economies. Anhydrousethanol can be blended with gasoline up toat least 24% (by volume) without any engine

8For example, a recent news report suggests that a redesignof the distillation process by using a multicolumn systemtogether with a network for energy recovery could reducethe costs of manufacturing ethanol from corn by 11% (91).

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modifications (94). In blends with gasoline,ethanol acts as an octane enhancer (an an-tiknock agent) and an oxygenate (to reduceemissions of carbon monoxide and unburnedhydrocarbons). Blended with diesel, ethanolrequires an emulsifier or cosolvent to preventseparation at low temperatures and, becauseethanol has a lower cetane number than diesel,requires the addition of an ignition improverthat would enable compression ignition of themixture (95).

The world’s top producers of ethanol areBrazil and the United States, each produc-ing approximately 16 billion liters per year in2005 (Figure 2). In the United States, this vol-ume corresponds to less than 2% of transportfuel, whereas in Brazil this amounts to morethan one third of transport fuel. Brazil allo-cates roughly three million hectares to sugar-cane for ethanol, a bit more than half of itssugarcane crop. Brazil’s program was startedin the late 1970s for the purpose of reduc-ing oil imports and can be credited with ma-jor advances in sugarcane ethanol technology(96–98).

In the United States, approximately 95%of the ethanol is produced from corn. TheUnited States ethanol initiative, like theBrazilian one, is a subsidized program, drivenby the objectives of providing support to theagricultural sector and reducing demand forimported oil. The elimination of tetraethyllead, and then MTBE, as an octane enhancerand oxygenate, respectively, has contributedto boosting the market for ethanol (93).

Biodiesel is the common term for a clean-burning diesel fuel and heating oil substitutethat can be produced from vegetable oils oranimal fat. Chemically, it is a mono alkyl ester(C19H36O2) derived via the catalyzed transes-terification of lipid sources. It is also knownas soydiesel, methyl soyate, rapeseed methylester, or methyl tallowate (99, 100). The mostcommon feedstocks for biodiesel are soy oiland rapeseed oil, although it has also beenproduced from sunflower seed, cottonseed, ja-tropha, used frying oil, and, increasingly, palmoil. Its chemical properties and performance

characteristics are very similar to petroleum-based diesel fuel. It can readily replace or beblended with diesel fuel or heating oil in stan-dard diesel engines and boilers, requiring veryfew, if any, equipment modifications. It canbe produced fairly inexpensively from a vari-ety of biomass feedstocks in large oil refinery-sized plants or at the village level using simpletechnology.

Biofuels are positioned to continue theirrapid expansion. Several countries have putin place policies to that provide a long-termimpetus for biofuels. In the European Union(EU), the 2003/30/EC Directive dated May8, 2003, stipulates that fuels sold in memberstates should contain 2% of biofuels in 2005,stepping up to 5.75% in 2010, and EUleaders further resolved to increase targets to8% in 2015, corresponding to an estimated17 million tons of biodiesel and 12 milliontons of bioethanol (101). In the United States,the Energy Policy Act of 2005 (http://www.doi.gov/iepa/EnergyPolicyActof2005.pdf )created a national Renewable Fuels Standard(RFS) that will increase national biofuel con-sumption from 15 billion liters per year (gaso-line equivalent) in 2006 to 28 billion liters by2012, plus a requirement that after 2013 theRFS is to be met in part with 0.95 billion litersof cellulosic ethanol (93). In part promptedby this policy, investment in ethanol pro-duction facilities has rapidly accelerated, andthe U.S. Environmental Protection Agencyreports that fuel volumes already exceed theRFS requirements and that 2012 volumes areprojected to exceed 40 billion liters. India alsohas an ambitious ethanol policy, requiring10% blending across the country by the endof 2007, which will be met primarily fromdomestic sugarcane production.

3.2. Energy and EnvironmentalAspects of Biofuels Productionand Use

Although biomass is frequently labeled a“renewable” source of energy, this term isused loosely, as biomass production requires


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nonrenewable inputs, including fossil fuels,and ties up other finite resources such as landand water.

3.2.1. Energy. The degree to which a bio-fuel is in fact a renewable energy source de-pends on the amount of nonrenewable energyinputs relative to the energy outputs of thebiofuel cycle. Analysts have presented variousmethods for making this comparison: Somehave used the net energy balance (the energyoutputs of the biofuel cycle minus the energyinputs); some have used the energy ratio (en-ergy outputs of the biofuel cycle divided bythe energy inputs; and some have used the in-verse). Some have added the energy embodiedin the coproducts to the biofuel energy; othershave subtracted it from the energy inputs. [Seethe Supporting Material section in Farrellet al. (102) for a useful discussion of energymetrics.]

Energy inputs vary considerably amongbiomass options owing to the different agri-cultural production systems and biofuel con-version processes. Life cycle inputs include,for example, fuels consumed by farm machin-ery in land preparation, planting, tending, ir-rigation, harvesting, storage, and transport;fossil feedstocks used to produce chemical in-puts such as herbicides, pesticides, and espe-cially fertilizers (which tend to be energy in-tensive); and energy required for processingof the biomass feedstock into a biofuel.

Energy characteristics are generally bet-ter for perennial crops than for annual crops,which involve greater use of farm machin-ery and a higher level of chemical inputs.For example, some perennial crops (poplar,sorghum, and switchgrass) grown in a temper-ate climate have energy ratios (energy frombiomass divided by energy inputs) of 12 to16. In tropical climates with good rainfall,these ratios could be considerably higher, ow-ing to both higher yields and less energy-intensive (i.e., more labor-intensive) agricul-tural practices. Energy characteristics can bemuch poorer for annual row crops that requireboth a high level of inputs and a high level of

mechanization but yield a relatively small pro-portion of usable bioenergy feedstock per unitof plant matter produced. Some annual foodcrops in industrialized countries, for example,have energy ratios of less than one. Many agri-cultural or forestry residues can be consideredessentially renewable because negligible fos-sil fuel is consumed to obtain the residues inaddition to what is required to produce theprimary crop (103, 104).

The net energy balance and carbon dioxideimpacts of biofuels are issues of great interest,given the growing scale of their use as a GHGmitigation option, and have been reported ex-tensively (102, 105–110; and, for a compre-hensive review of reviews, see Reference 111).Here, we report results of studies for five fu-els that have been extensively studied: cornethanol, cellulosic ethanol, sugarcane ethanol,soy biodiesel, and rape biodiesel. The energyratio is defined as energy outputs in biofueland coproducts divided by energy inputs.

Figure 3 provides the results of reviewsof some recent life cycle energy studies forbiofuels. The studies considered the life cy-cle fossil-fuel inputs and compared them tothe energy contained in the biofuel outputas well as coproduct (including, for example,distillers’ dry grain and corn oil for ethanol,or soybean meal and glycerine for biodiesel).For corn ethanol, the estimates in the liter-ature range from roughly 0.75 to 1.35 (102,106, 108). The lower end of the range im-plies a corn ethanol process for which the fos-sil energy inputs exceed the energy contentof the biofuel plus coproduct outputs. At thehigher end of the range, the energy output ismodestly (up to 35%) greater than the en-ergy inputs. In contrast, estimates of cellu-losic (102) and sugarcane ethanol (112) en-ergy ratios range from 4 to 11. For biodiesel,estimates range from 1.2 to 3.0 (102, 106,108). The variation for a given fuel reflects therange of assumptions regarding factors suchas the mix of fossil fuels use for process en-ergy inputs, the energy value of the coprod-ucts, and the amount and nature of fertilizerrequired.

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The biofuel pathways with energy ratiosat the high end of the range (cellulosic, sug-arcane, with energy ratios >∼6) correspondto pathways for which photosynthesis servesunequivocally as the primary energy source.The biofuel pathways at the low end of therange (corn ethanol, certain biodiesel path-ways, with energy ratios <2) are pathways inwhich photosynthesis modestly augments fos-sil energy, which is the primary input. Biofuelswith energy ratios this low do not obviouslymerit the term “renewable.”

3.2.2. GHG emissions. Biofuels are regu-larly invoked as an important GHG reductionoption owing to the claim that they are zero-carbon energy sources because the amount ofcarbon dioxide emitted during combustion isno greater than was absorbed from the at-mosphere by photosynthesis during growth.Obviously, this is a facile claim. Given thevarious fossil energy inputs required to pro-duce biofuels, a thorough analysis of life cy-cle GHG emissions is needed to determinea given biofuel’s net climate benefits. In ad-dition to the GHG emissions correspondingto upstream fossil-fuel consumption, severalother elements of the life cycle have beenfound to have significant positive or neg-ative GHG impacts: land-use change [e.g.,from conversion from peatlands to palmoil plantation (116)], methane leakage [e.g.,emissions from biogas systems and removalsfrom diverted waste streams (117)], below-ground biomass [e.g., from high-diversitygrasslands (118)], fertilizer use [e.g., for soy-beans (107)], biomass handling [e.g., fromemissions arising from chipping of forestresidues (119)], coproduction of energy [e.g.,from use of lignin as an energy source in cellu-losic ethanol production (120)], storage [e.g.,from wood chip storage (121)], and displace-ment of coproduct energy [e.g., animal feed(102)].

Several factors lead to important differ-ences in estimates of net GHG reductionsfrom biofuels. [Larson (111) provides a use-ful discussion of the major uncertain factors

that lead to variation in life cycle conclusionsfor a given biofuel path.]

� Emissions from land use: Assumptionsregarding the prior use of the landare critical because the loss of exist-ing stocks of carbon (in the soil andaboveground plants) can give rise tohuge emissions. Delucchi (107) reportsa high net GHG emissions figure inpart because of his assumption thatundisturbed native vegetation is clearedfor soy production. Delucchi arguesthat the latter assumption is appropriateonce the rising soy demand for biodieselleads to a net increase in soy acreage.The same applies to palm oil biodiesel,which generates GHG emissions manytimes greater than petroleum diesel itdisplaces if it is obtained from planta-tions that are established on cleared anddrained peatlands (116).

� Yields: Especially for the not-yet-commercial biofuels pathways, such asthose using cellulosic biomass for whichlittle effort has yet gone into opti-mizing biomass crop production, yieldsare uncertain. Yields affect both theupstream fossil energy requirements(higher yields might require less use offarm machinery that scales with area,but higher rates of chemical inputs)as well as the per hectare output ofbiofuels.

� Emissions of nitrous oxide9 (N2O):Emissions of N2O, which derive largelyfrom use of nitrogen fertilizers, can con-tribute significantly to net GHG emis-sions yet are highly uncertain for manycrops. For example, Delucchi (107) re-ports a much higher figure for life cy-cle GHG emissions from soy biodiesel(leading to a net 50% increase in emis-sions compared to petroleum diesel),

9Nitrous oxide is a potent GHG with a global warmingpotential relative to carbon dioxide of 296 for a 100-yeartime horizon (122).


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driven in large part by higher assump-tions about N2O emissions from fertil-izer use.

� Coproducts energy can be significantand poorly specified: There are sev-eral ways of allocating energy associ-ated with coproducts. Hill (108, Table 9in the Supplementary Material) demon-strates the significant impact of differentallocation methods for corn ethanol andsoy biodiesel. Even for a given alloca-tion method, the contribution from co-products can also be expected to changeover time. Because biofuels are amongthe commodities with the largest poten-tial demand, the market for biofuel co-products may become quickly saturated.For example, as conventional glyc-erin markets become saturated, glycerinmight instead be used as an energy in-put in the soy biodiesel production pro-cess. Then, the lower-value secondarymarkets that emerge could be associatedwith either a higher or lower displacedenergy demand, and the net impact onthe biofuel energy ratio could go eitherway.

� National differences: There can be non-trivial difference in life cycle emissionsof biofuels across countries. For exam-ple, Delucchi (107) found that the GHGbenefits of cellulosic ethanol varies froma roughly one-half improvement rel-ative to gasoline fuel cycle emissions(e.g., United States, India, South Africa,

Chile) to a one-third improvement (e.g.,China). This is due primarily to differ-ences in land use and cultivation prac-tices as well as fertilizer application andproduction methods. The vast majorityof life cycle analyses have been done inindustrialized countries, leaving a con-siderable knowledge gap in energy andGHG impacts in the case of variousfeedstocks, such as jatropha, palm, andcassava.

Table 2 presents some recent studies cal-culating or reviewing net GHG impacts ofvarious biofuels. These are fairly typical esti-mates, although, as with the energy ratio stud-ies, various studies have presented results in arange around these figures. The main conclu-sions are robust: Cellulosic ethanol and sugar-cane ethanol are more effective at displacingGHG emissions (∼90% reduction) than soyor rape biodiesel (∼50% reduction), whichare in turn more effective at displacing GHGemissions than corn ethanol, which is itselfonly marginally lower in GHG emissions thangasoline (<20% reduction).

It is important to note that an alternativeto displacing petroleum-based fuels withbiofuels is to displace fossil-based electricitywith biopower. As Larson (111) has noted, afew studies have explicitly compared biofuelto biopower options on comparable basis.Tilman et al. (118) find that using switchgrassto displace coal-based electricity would pro-duce 2.8 times greater GHG reductions thanconverting it to ethanol and using it to displace

Table 2 Estimates of net GHG reductions and land requirements for various biofuel options

Source (for GHGreductions and yields)

GHG reductionsrelative to gasoline/

diesel vehicle

Yield perhectare

(liters fuel/ha)

Hectares requiredto fuel one car

(ha/car)Ethanol (corn) Farrell et al., 2006 (102) 14% 3463 1.1Ethanol (cellulosic) Farrell et al., 2006 (102) 88% 5135 0.7Ethanol (sugarcane) Macedo et al., 2004 (112) 91% 6307 0.6Biodiesel (soya) Hill et al., 2006 (113) 40% 544 4.3Biodiesel (rape) IEA, 2005 (106) 50% 1200 2.0

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gasoline. [Tilman et al. (118, Table S3 inonline Supporting Material at http://www.sciencemag.org/cgi/content/full/314/5805/1598/DC1) also calculate the sequesteredcarbon in soil and switchgrass roots. Takingcredit for this sequestration adds considerablyto the GHG reductions of both options andchanges the ratio between them to 1.6.] Green(123) also found that displacing coal-basedelectricity would produce greater GHGreductions than converting it to ethanol anddisplacing gasoline. The displacement ofcoal provides greater GHG benefits than thedisplacement of gasoline because (a) there isno need to incur the inefficiencies associatedwith converting biomass feedstock into ahigh-quality fluid transportation fuel, and(b) coal has higher carbon intensity per unitof energy than gasoline. This suggests that ifGHG mitigation is a major objective, then amore effective strategy may be to prioritizethe use of biomass to displace coal-basedpower over the use of biomass to displacetransport fuels.

3.2.3. Pollutant emission from biofuels. Inaddition to the GHG impacts of displacingfossil fuels with biofuels, there are significantchanges in other pollutants. The main pollu-tants of interest are particulate matter, carbonmonoxide, volatile organic compounds, andnitrogen oxides, and sulfur oxides.

Ethanol in blends with gasoline reduce car-bon monoxide (by acting as an oxygenate).In a 10% blend, ethanol can reduce carbonmonoxide emissions by 25% (106). Owing tothe relatively high vapor pressure of ethanol,it tends to increase the emission of volatileorganic compounds in blends with gaso-line. This effect can be offset by blendingwith gasoline formulated to have lower va-por pressure (106). Nitrogen oxide emis-sions are not significantly changed by blend-ing ethanol with gasoline; however, upstreamemissions from fertilizer usage can signifi-cantly raise life cycle nitrogen oxide emissions(106).

Pure biodiesel and biodiesel in blends withdiesel have better overall emissions character-istics than pure diesel. A recent review studyfound that in heavy-duty highway vehicles,pure biodiesel decreased carbon monoxideand particulate matter by about 45%, hydro-carbons by about 65%, and sulfur oxides by100% while increasing nitrogen oxide emis-sions relative to diesel by about 10%. [Morerecent analyses have suggested that nitrogenoxide emissions may be lower than previouslyreported (124).] The emissions impacts scaleapproximately linearly with the proportion ofbiodiesel blended into diesel (125).

3.2.4. Agro-environmental concerns.Agriculture is a land-intensive, environmen-tally high-impact undertaking. Whether theexpansion of biomass energy will exacerbatethe deleterious effects of the agriculturesector or mitigate those impacts is of cen-tral concern. Currently, the predominantbiomass crops—sugarcane, maize, rape, andsoybeans—are grown using the intensivemethods of modern agriculture. Thus, anunderstanding of the potential environmentalimpacts of scaling up the production of suchbiomass for energy feedstock requires an as-sessment of the environmental performanceof current agriculture methods and of the op-portunities for improving that performance.

The main features of modern intensiveagriculture are the control of crops (throughgenetics), of soil fertility via chemical fertil-ization and irrigation, and of pests (weeds, in-sects, and pathogens) via chemical pesticides(126). At the same time, cropping practiceshave moved toward monocultures, intensivetillage, and irrigation.

Agricultural food production doubled be-tween 1961 and 1996 with only a 10% in-crease in the land under cultivation [althoughirrigated cropland has gone up by about70% in the past four decades (127)], and themove toward resource-intensive agriculturalproduction models led to 6.9-fold and 3.5-fold increases in nitrogen and phosphorus


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fertilization, respectively, during this period(126). Total global fertilizer consumption in2002 was 142 million tons (of which nitrogenfertilizers were about 84 million tons) (128).In fact, the use of nitrogen fertilizers andnitrogen-fixing legumes in agriculture con-tributes as much to the terrestrial nitrogencycle as the natural (preindustrial) rate of ad-dition (129). Annually, about 2 million tons ofpesticides are used in agriculture worldwide(130); in the United States, insecticide use in-creased 10-fold between 1945 and 1989 (131).

As a result, modern agriculture is alreadyhaving enormous impacts on ecosystems andtheir properties. Agriculture is the largestsource of excess nitrogen and phosphorus towaterways and coastal areas, leading to eu-trophication and nitrification of many waterbodies (127). The loss of nitrogen (as nitrousoxide) from croplands also contributes sig-nificantly to GHG emissions (129, 132). Inaddition, over 40 million hectares worldwidewere estimated in 1990 to be suffering frommoderate or strong salinization (133), whichrepresented about one sixth of the worldwideirrigated cropland at that time (128). It isestimated that about 1.5 million hectares ofarable land and $11 billion in production arelost to salinization every year, representingabout 1% of the global irrigated area and an-nual value of production, respectively (134).Up to 40% of global croplands may also beexperiencing some degree of soil erosion orreduced fertility (127); agricultural misman-agement was estimated to be responsible forsoil degradation on 552 million hectares in1990 (133), which is nearly a third of theglobal cropland. Monocultures also lead toimpacts on biological components of ecosys-tems such as the pest complex (which may be-come less diverse but more abundant) and soilbiota (135); at the same time, agricultural sys-tems may have impacts on nearby or even dis-tant ecosystems (135). Cropping and tillagepractices also have an effect on soil organicmatter—conversion of native vegetation tocropland under intensive tilling practices, forexample, contributes to reduction in soil or-

ganic matter through disruption of soil aggre-gates, increased microbial activity, and erosion(136).10 It is estimated that about 1 millionpoisonings and 20,000 deaths occur from pes-ticides each year through occupational expo-sure among agricultural works, with pesticidesafety being a particular problem in develop-ing countries (139). The long-term effects ofpesticides are still not fully understood but arenow believed to include elevated cancer risksand disruption of the body’s reproductive, im-mune, endocrine, and nervous systems (140).Agriculture accounts for an estimated 70% to80% of the global use of water (128, 141),although for many countries the number iseven higher. The water requirements asso-ciated with large-scale bioenergy crops mayincrease the water stress in many countries(142).

Even though it is not possible to assessthe overall costs in economic terms of current“unsustainable” agriculture, analyses suggestthat these costs are substantial. In the caseof the United States, annual environmentaland health costs associated with agricultureare estimated to be $5.7–16.9 billion (143).[Pimentel (144) concludes that the environ-mental and social costs of pesticide use alonein the United States exceed $8 billion.] A morecomprehensive estimate for the United King-dom suggested that the total annual externalcosts and subsidies are 8.95 billion, whichworks out to an 11% addition to the foodprices paid by consumers (145).

It is, of course, possible to modify agricul-tural practices so as to reduce the ecologicalimpacts of biomass production by increasingnutrient- and water-use efficiency, maintain-ing and restoring soil fertility, and using

10As the demand for ethanol increases, crop choices offarmers will change. For example, the recent policy initia-tives that aim to increase the use of ethanol in vehicles arealready leading farmers to move to corn from soybean—it was expected that the area under corn will go up 15%and that under soybean will decline 11% from 2006 to2007 (137). However, moving from the dominant maizeand soybean rotation in the northern corn/soybean belt tocontinuous maize may reduce soil quality and yield (138).

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improved methods of disease and pest control(146). Such a move toward sustainable agricul-ture should be broadly based on the agroeco-logical principles of “balanced environments,sustained yields, biologically-mediated soilfertility and natural pest regulation throughthe design of diversified agroecosystems andthe use of low-input technologies” (147). Itwould entail complementary and interrelatedpractices such as integrated pest management,which allows for pest control through a judi-cious application of pesticides in combinationwith other pest-management approaches suchas more diverse cropping systems and targetedcropping practices (148); precision farming,which is based on applying nutrients in theright amount at the right place at the righttime (146); and improved cropping practices,such as polycultures, crop rotation, reduced(or no) tillage, cover crops, and fallow periods,which can help maintain and restore soil fertil-ity (146, 149).11 To be successful, sustainableagriculture must be tailored to local needs, re-sources, and ecologies. It will be most effec-tive if it combines traditional knowledge andcropping practices with modern techniques.In fact, sustainable agriculture is knowledgeintensive rather than input intensive (147).

Despite interest in sustainable agriculturefor some decades now,12 progress has beenwoefully slow [as it has also been in sustain-able forestry (151)]. Current incentives, infact, favor increases in agricultural productionwithout paying sufficient attention to preserv-ing ecosystems services (146). A review of theOECD’s experience in the 1990s shows mixedresults in protecting the environment, partlybecause of conflicting policies (152); further-more, it is not easy to measure agriculture’s

11There is some controversy, however, about the amountof soil carbon sequestered by no-till practices, especiallywhen the whole soil profile is considered (136).12According to (150), the term “sustainable agriculture”first appeared in the literature in 1978 but was formallyintroduced into policy in 1985 through the Food SecurityAct, with a Low-Input Sustainable Agriculture programaimed to help farmers use resources more efficiently, pro-tect the environment, and preserve rural communities.

environmental performance (152). Similarly,there has been progress in integrated pestmanagement worldwide, but it would be fairto say that the “rate of adoption has been dis-appointingly slow” (150).

One cannot assume that the expansion ofbioenergy would be environmentally benign.As recently seen in the case of palm oil (abiodiesel feedstock), an increase in biodieseldemand was a major contributor to defor-estation and drainage of peatlands in South-east Asia—an estimated 40% of the clearingof peatlands is attributable to palm oil plan-tations. The total annual emissions (throughpeat oxidation as well as fires) from South-east Asian peatlands are estimated to be about2 billion tons of carbon dioxide, which is about8% of the global carbon dioxide emissionsfrom fossil-fuel burning (116). New palm oilplantations are estimated to be responsible for87% of the deforestation in Malaysia between1985 to 2000 (153).

Thus, the large-scale use of biofuels de-rived from corn, soybeans, or sugarcane willbe convergent with sustainable developmentonly if there are coherent policies and incen-tives to move away from intensive agricultureand toward sustainable agriculture. The re-cent introduction of the concept of multifunc-tionality into agricultural policy discussionsshould help advance the cause of sustainableagriculture by explicitly recognizing that agri-culture may further several social objectivessimultaneously.13

The cellulosic ethanol route offers the po-tential to use a greater variety of feedstocks(including woody and herbaceous biomass)and a larger portion of the crop. Recent workwith prairie grasses in particular suggest thatthese might be an attractive source of biomassin temperate areas; these could be grown ondegraded lands, need little or no fertilizer,

13Multifunctionality recognizes that agriculture has multi-ple commodity and noncommodity outputs (such as such asenvironmental and rural amenities, food security and con-tribution to rural viability) and that some of the noncom-modity outputs exhibit the characteristics of externalitiesor public goods (154).


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need no pesticides, and may actually offer anet GHG reduction through the sequestra-tion of carbon below the ground (118). Ul-timately, realizing the sustainability gains ofbioenergy will depend on the commercializa-tion of cellulosic ethanol or thermochemicalgasification technologies that could convertbiomass grown in an ecologically sustainablemanner to useful energy (118, 155).

However, even though certain feedstocksand fuel cycles may provide the option oflower environmental impact through low-input farming, intensive agriculture may stillend up being employed (108). Whether ornot long-term options for the sustainable pro-duction of biofuels are taken up will de-pend on the policy and market context inwhich biofuels are emerging. Explicit, con-certed policy efforts would be needed to guideemerging biofuels markets toward sustainablesolutions.

3.3. Biotechnology ControversiesRedux?

Another issue that is likely to take onsome prominence is the role of biotech-nology. Biotechnology is being consideredto advance the production of biofuels frombiomass through the development of plants(with increased yield and reduced biomassrecalcitrance) and biological organisms to fa-cilitate the conversion processes (89, 156).Already soybeans that are genetically mod-ified for glyphosate resistance are widelyplanted (with significant environmental gainsfrom reduced tillage and reduced herbicideuse) (108). This is likely to set up a tensionbetween concerns about the possible (and stillnot fully understood) consequences of the useof genetically engineered crops (157) and theconcerns over climate change and energy se-curity.14 For example, some concerns about

14In some sense, this would be an extension of the ongo-ing debate on genetically engineered food crops that oftenreflects a tension between environmental protection andmeeting the needs of developing countries [see, for exam-ple, (158)].

genetic engineering of woody biomass cropshas been expressed (in that lignin modifica-tion may have unanticipated ecological appli-cations such as impacts on soil structure andfertility) (159). Uncertainties in the environ-mental risks of the widespread introduction ofgenetically modified organisms warrant im-proved understanding and cautious regula-tory approaches (160). But the “gap betweenadvocates and critics” remains on this issue(161), partly because it feeds into a wider de-bate about biotechnology and a range of pub-lic concerns spanning economic development,ethics, equity, and power (162) that are an in-tegral part of sustainable development. Thus,it is very likely that there will continue tobe widely differing viewpoints on the role ofbiotechnology in sustainable biofuels [see, forexample, (156, 163)] with the potential forcontroversy.

3.4. Land Requirements and LandAvailability

As pointed out by Larson (111), it is useful tocompare biofuel options on a per hectare basis(as opposed to per unit of fuel basis) becauseland is the basic primary resource for biofuelproduction. Table 2 and Figure 4 presentthe land intensity of various biofuel cyclesin terms of the amount of land that wouldbe required to displace the GHG emissionsfrom one light-duty passenger vehicle.15 It isa useful metric of the land intensity of bio-fuel production because it combines the threecritical component factors: (a) biomass yieldin terms of quantity of feedstock generatedper hectare, (b) the biofuel conversion effi-ciency in terms of quantity of biofuel gener-ated per unit of biomass feedstock, and (c) thelife cycle GHG reductions achieved relativeto a conventional vehicle using gasoline or

15The vehicle characteristics assumed for this calcula-tion are those corresponding to a typical North Americangasoline-fueled passenger vehicle: an annual mileage of24,000 km and a fuel economy of approximately 10 km/literor 23 miles per gallon.

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diesel.16 As can be seen from Table 2, the rele-vant parameters vary considerably across bio-fuels. The biofuel yield per hectare varies fromthe low end for soy biodiesel, which requiresmore than four hectares to fuel one vehicle,to the high end for sugarcane ethanol, whichrequires somewhat more than half a hectare tofuel one vehicle.17 This biofuel yield is com-bined with the effectiveness with which a fueldisplaces life cycle GHG emissions, whichranges from a low of ∼14% for corn ethanolto a high of ∼90% for sugarcane and cellu-losic ethanol. [For cellulosic ethanol, this fig-ure could exceed 100% if the feedstock werenative grassland perennials capable of seques-tering carbon in soils and generating a netcarbon-negative biofuel cycle (118).]

The result is that displacing one passen-ger vehicle’s worth of GHG emissions wouldrequire between 0.7 hectares (if fuelled withsugarcane ethanol) to more than 10 hectares(if fuelled with soy biodiesel). For compari-son, Figure 4 shows the current global crop-land of 0.24 hectares per person (or 1.5 bil-lion hectares total). Although it is a technicaland agronomic matter to calculate how land-intensive biofuel production is, it is a matter ofpolicy and societal choice to choose whetherthis is an appropriate use of land resources,and if so, how much land to thus use.

There are various measures that can betaken to reduce the land intensity of biofuelrequirements. First, considerable increases infuel economy can be made on the basis ofvehicle technologies such as hybrid engines,light-weight materials, and smaller vehicles.Second, annual vehicle mileage can be re-duced through greater access to public tran-sit along with transit-oriented urban design.

16This comparison does not, however, account for any dif-ferences in the quality of land used. Cellulosic crops, for ex-ample, can in principle be produced on lower-quality landthan annual food crops.17For cellulosic ethanol derived from biomass feedstocksconsisting of forestry or agricultural residues or other mu-nicipal waste streams, there would be no incremental de-mand for land.

Third, yields of biomass crops can possibly beincreased beyond the assumptions containedin the studies cited in Table 2. Fourth, in-creases in efficiencies of conversion from feed-stock to biofuel may be obtained beyond theassumptions in the cited studies.

The land intensity of biofuels production(corn ethanol and soy biodiesel in particular)is reflected in the scale of the current biofu-els program in the United States. After Hill(108), one can calculate that the 14.3% ofthe U.S. corn harvest that was converted toethanol in 2005 was able to displace about0.25% of GHG emissions arising from U.S.gasoline consumption. Devoting the entireU.S. corn harvest to ethanol and soy harvest tosoy biodiesel would allow the United States todisplace roughly 1.7% of the emissions aris-ing from its gasoline consumption and about2.4% of the GHG emissions arising from itsdiesel consumption.

Given the land intensity of biofuel path-ways, it is useful to look at some of the esti-mates that have been made of the supply ofbiomass feedstocks for energy that might betechnically available in the future. As it hap-pens, there is a staggering range of estimatesin the literature, some of which are summa-rized in Table 3.

There are also various analysts who ques-tion whether there will be sufficient landresources for biomass energy at all, aftersatisfying both food demand and the require-ments for land for natural ecosystem function-ing (166–168). The uncertainty in the aboveestimates and the major difference in opinionsrelate to the following issues:

� There are some fundamental demo-graphic and socioeconomic uncertain-ties relating to the future demand forfood, including uncertainty in futurepopulation and especially in future di-etary preferences. A shift to more an-imal products that often accompaniesrising affluence will significantly in-crease total land requirements for live-stock feed (169, 170).


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Table 3 Estimates of bioenergy potential

ReferenceBioenergy

Potential (EJ/yr) Feedstocks YearBerndes et al. (164) 206 Residues and energy crops 2050De Vries et al. (165) 80–300 End use biofuels 2050Moomaw et al. (65) 441 2050Hall et al. (103) 31 + 266 Residues + energy crops None specifiedHoogwijk et al. (63) 240–850 + 35–265 From excess cropland +

from savannah/grasslands2100

Sims et al. (104) 2–25 Energy crops 2025

� There are uncertainties about the fu-ture potential for yield increases bothfor food and energy crops. On theone hand, there are prospects forbiotechnology-driven improvements incrop characteristics and, on the otherhand, the possibility of yield declinesdue to the long-term impacts of inten-sive agriculture.

� Related to the above, there are uncer-tainties about the availability of excess,abandoned agricultural lands, whichmany biomass projections find to be themain source of land for energy crops.There are also uncertainties about theavailability and suitability of marginaland degraded lands, which are unlikelyto be completely free of other claims.

3.5. Socioeconomic Issues

Although there have been suggestions thatgrowing bioenergy markets could contributeto socioeconomic development in developingcountries (72–74, 171), capturing these ben-efits will not happen by default (172, 173).There are two major ways in which bioenergyintersects with socioeconomic welfare.

The first relates to the potential for bioen-ergy markets to influence food markets andaffect food security. Today’s major biofuelsare based on food crops (corn, cane, soy,rape, palm oil), which leads to direct competi-tion between biofuel processing facilities andfood processing facilities for the same food

commodities. The normal market responseto such a situation is a rise in prices. Evenif biofuels were derived from nonfood crops(e.g., cellulosic feedstocks or inedible oils),they could still place an additional demandon agricultural resources, specifically land andwater, and lead to a rise in food prices.

Human beings can only consume a cer-tain maximum amount of food, which putsan upper bound on the demand for agricul-tural products. But the demand for energyservices is essentially unlimited. As capturedin Figure 4, an individual’s demand for foodtranslates into a demand for land that is lim-ited to a fraction of a hectare of cropland,whereas an individual’s demand for trans-portation can translate into a demand for sev-eral hectares. The emergence of a biofuelmarket thus introduces a fundamentally newdynamic to agricultural markets. All else be-ing equal, this dynamic will lead to a rise infood prices.

With the recent boom in biofuel produc-tion, such a rise in food prices is indeed be-ing seen. The increasing demand for cornfor ethanol production in the United Stateshas escalated the price of corn in Mexico(more than doubling and even almost triplingin some parts between 2006 and 2007) andhas led to a tortilla crisis in that country.This is an issue beyond just culinary or cul-tural overtones because poor Mexicans getmore than 40% of their protein from tortillas(174). At the same time, chicken feed costs inthe United States increased 40% between the

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summer of 2006 and early 2007 because ofrising corn prices (137). Rises have also beennoted in other major biofuel feedstock mar-kets, including sugar, rapeseed oil, palm oil,and soybean (175). The prospect that this ismore than a transient effect is supported bya recent projections comparing the price ofcertain staples in an aggressive biofuels sce-narios (in which 20% of transportation fu-els are displaced by biofuels by 2020, includ-ing cellulosic ethanol starting in 2015) to areference scenario (176). The prices of sugarbeets, wheat, maize, sugarcane, oilseeds, andcassava were 10%, 16%, 23%, 43%, and 54%higher, respectively, than their baseline 2020prices. In a scenario where cellulosic ethanoldoes not become commercial, and food cropyields stay constant at today’s levels, the pricesrises for these crops are on the order of twiceas great. A recent study of the U.S. agri-cultural sector came to similar conclusions(177).

A rise in food prices is a double-edgedsword. It can benefit countries and householdsthat are net producers of food, including therural poor whose livelihoods are closely tiedto the agricultural economy. But, at the sametime, it can hurt those who are net consumers,including the urban poor—the caloric con-sumption among the poor is estimated to de-cline by 0.5% for every 1% rise in the priceof major food staples (178).

Biofuels do not need to adversely affectfood security. In principle, biofuels could relyon lower-quality land and not compete forprime cropland. To the degree that it increasesrural incomes, it can in principle enable in-vestment in productivity enhancements. Andbiofuels can help provide energy services thatenhance food security, such as transportationof food commodities from farms to markets.However, these measures cannot be assumedto be inevitable outcomes of the expansionof bioenergy markets. Concerted steps wouldbe needed to ensure that the policy contextand market environment in which bioenergywas expanding are structured so as to pre-vent food security from being compromised.

It cannot be assumed that this is the defaultscenario.

The second way in which bioenergy in-tersects with socioeconomic welfare relates toits potential contribution to sustainable liveli-hoods. To make a substantive contribution tosustainable development, bioenergy marketswould need to benefit small farmers in de-veloping countries. The Food and Agricul-ture Organization estimates that there were815 million chronically undernourished peo-ple in developing countries in 2000–2002,with attendant enormous human, social, andeconomic costs (179). About three quartersof these are extremely poor rural inhabi-tants, mainly practically landless small farm-ers living in difficult regions, underemployedagricultural laborers, and other artisans andtraders who rely on these groups for a living(180). The situation of these groups has be-come worse in many instances as the pricesof agricultural commodities have shown notonly a decline over the long term but alsoshort-term volatility (181); the decline in foodprices often does not help this group sincethey are not purchasers of food (180). Withthe continuing decline in prices of their prod-ucts (and often increases in input prices), evenincreased output may still lead to reduced sur-pluses, leading to what has been termed asdistress-inducing growth (182) and a need fornonagricultural income for making ends meet(183). Small farmers already have low cap-ital stock in primary agriculture (184), andby not being able to stay above the eco-nomic renewal threshold, they are unable torenew farm tools and inputs needed, leadingto declining agricultural stock in real terms(180). Thus, it is imperative that any effort touse bioenergy markets to promote sustainabledevelopment must find ways to include thisgroup.

The trend toward large-scale, verticallyintegrated corporations that have greatercontrol over agricultural commodity chainsmakes it difficult for small-scale producers tobenefit from the market for agricultural prod-ucts (181, 185), and bioenergy markets may


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well follow the same trend.18 It is possible thatcertification systems to promote sustainabil-ity (186) may help ensure that benefits accrueto small-scale producers, although some havepointed out the onerous burden certificationcan impose on small farmers (181, 187).

Agricultural subsidies in developed coun-tries can greatly distort the global agricul-ture markets and depress commodity prices(181)—producer support in OECD countrieswas estimated to be 280 billion dollars in 2005(188). Some have argued that the U.S. cornethanol program is following the same path,driven by political economy and corporate in-terests rather than sound science (189, 190).There is increasing agreement that, in or-der for trade in agricultural commodities tohelp poor countries, OECD countries willbe required to end the modes of support fortheir agriculture sectors that harm developingcountries. It will also require more effectivemanagement of risks caused by negative com-modity price shocks, better market access fordeveloping countries, and enhanced South-South cooperation in the field of trade andinvestment (184, 191–194). These measuresapply to bioenergy markets just as they applyto conventional agricultural markets.

Analogous to many agricultural commodi-ties,19 most of the value addition in biofuelswill come from the processing of the biomassfeedstock to the final biofuel (with the priceof the biofuels unlikely to decline much ow-ing to limits in production coupled with in-creasing demand and some linkage to theprice of petroleum-based fuels). In this case,the prices of biomass may remain relativelylow. Given the increasing sophistication of

18In Kenya, for example, even as its horticultural ex-ports have grown, the share of smallholders has been re-duced. Smallholders produced 70% of vegetables and fruitsshipped from Kenya before the horticultural export boom.But by the end of the 1990s, 40% of the produce was grownon farms owned or leased directly by importers in the devel-oped countries and 42% on large commercial farms, whilesmallholders produced just 18% (179).19Growers generally get only a small fraction of the priceof finished agricultural products, ranging from as low as4% for raw cotton to 28% for cocoa (181).

the biochemical conversion technologies forcellulosic ethanol, many developing countriesmay not yet have the technological capacityto build or operate these plants indigenously,making it difficult to move up the value chainin the biofuels market [paralleling the tradi-tional agricultural world, where the lack ofagroprocessing capabilities severely hobblesthe returns farmers receive from their pro-duce (195)]. Tariff escalation, i.e., the impo-sition of higher tariffs for goods that haveundergone greater processing, by developedcountries also hinders developing countries intheir attempts to establish processing indus-tries for exports at origin (181, 184, 185).20

Still, at least some developing countries mightbe able to develop a biofuels industry, whichcould then serve as a foundation for broaderindustrial development (88).

Yet, the integration of small farmers intoa bioenergy strategy does in principle offera worthwhile opportunity to advance thesustainable development agenda. It mustbegin by focusing on the multifunctionalnature of small farms, which are alreadyoften quite efficient and productive (even ifyields are low by the metric of single crops),can contribute to economic developmentwhere it is most needed, and can help sustainrural communities (196). They may alsobecome model implementers of sustainableagriculture—recent work has shown that12.6 million small farmers across 57 poorcountries cropping 37 million hectares (rep-resenting 3% of the cropland in developingcountries) have successfully adopted a varietyof resource-conserving technologies andpractices that led to a 79% average increase inyield while improving critical environmentalservices (including carbon sequestrationof 0.35 t C ha−1 year−1) (197). But suchincreases in yield while conserving resourcesand maintaining environmental services

20The share of developing countries in global exports ofprocessed agricultural products decreased from 27% forthe period from 1981 to 1990 to 25% in the period from1991 to 2000, and the share of less-developed countries fellfrom a 0.7% to 0.3% during the same 20 years (181).

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depend not just on technological approachesbut also social processes that value commu-nity involvement and empowerment (147);social and human capital can help agriculturalproductivity and natural capital grow (197,198). The development of cooperativesand other efforts by producers to organizecommercially can counteract the marketdominance of transnational corporations inagricultural markets and improve their marketaccess and returns (179, 181).

Lastly, it should be mentioned that a movetoward biofuels can help reduce the depen-dence on fossil fuels, but biofuels must be seenas part of a larger portfolio of approaches to-ward this end. The technical fix of biofuelsis a supply-side solution and must not dis-place efforts to enhance efficiency (throughfuel-efficiency standards for automobiles, forexample) and reduce vehicle travel (throughchanges in settlement patterns and consumerbehavior as well as modal shifts), which mustbe regarded as cornerstones of a sustainabletransportation policy.

Clearly, biomass energy is now of a largeenough scale to consume a significant amountof arable land and affect markets for agricul-tural products. In addition, it is being enlistedto play a major role in combating climatechange and meet countries’ energy securityneeds. And it is a rapidly expanding agro-industrial venture that affects the lives of in-creasing numbers of rural laborers. But, as thischapter has hopefully shown, biomass energycan no longer be treated as an idealized re-newable energy solution that will by defaultcontribute positively to sustainable develop-ment. The potential to do so still exists, butthe experience demonstrates that this cannotbe taken for granted.

4. CONCLUSION

There is little doubt that biomass is goingto remain an important part of the noncom-mercial energy arena for some years to comeand to evolve into a major contributor to thecommercial energy arena. As with other po-

tentially attractive renewable energy sources,biomass energy has a definite contribution tomake to sustainable development. The abilityof this energy source to further the sustain-able development agenda, though, depends onhow it is produced, converted, and used. This,in turn, requires a broad view that encom-passes the many dimensions of environmentalsustainability—carbon balances (comprehen-sively defined), air pollution, water and soilresources, and biodiversity—and also recog-nizes the human and socioeconomic dimen-sions of sustainability: health, gender equity,food and energy security, and livelihoods.

Exploiting bioenergy while taking thiscomprehensive, sustainability-centered viewat modest scales is easy. But the real challengecomes in scaling up implementation so that itmakes a significant contribution toward satis-fying a significant portion of the unmet needfor clean energy services. It is at these largerscales that the various challenges and conflictsdiscussed in this chapter become more prob-lematic. We emphasize some specific conclu-sions in this regard.

In the case of household bioenergy, themagnitude of the problem remains absolutelyenormous. Although an ideal world mightbe one in which there are adequate, clean,and affordable energy services that are basedon sustainably harvested biomass (or otherrenewables) for poor households, the envi-ronmentally sustainable nature of the energysource is not necessarily the most impor-tant factor. The most urgent concerns arisefrom the welfare and health impacts of thelabor-intensive and highly polluting nature oftraditional biomass use. Thus, certain clean-burning fossil fuels such as LPG must alsobe considered as part of the overall effort toexpand clean energy supplies rather than fo-cus only on biomass-derived supplies. Regard-less of the approach (improved cookstoves,biomass-derived or fossil-based clean fuels),providing cleaner energy to poor householdswill certainly require concerted efforts andgreater resources. One way to generate moreresources is by acknowledging this group’s


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relatively minor contributions to the climateproblem and exploring policies to compen-sate them for providing atmospheric space toother GHG emitters.

On the commercial biofuels front, therehas been a recent explosion in interest in in-dustrialized and developing countries. The re-sulting policy developments have been drivenby climate concerns, energy security con-cerns, as well as opportunities to benefit agri-cultural enterprises and contribute to ruraldevelopment. As commercial biomass energyexpands at this rapid rate, a number of issuesarise that were not particularly relevant at asmaller scale but must be considered in detailfor the future.

� The energy and GHG implicationsof biofuels cannot be properly as-sessed without a whole-system viewof their production, conversion, anduse, which greatly influence these en-ergy and GHG balances. Corn-basedethanol offers only marginal benefitson both fronts, calling into question itsrole as a suitable clean energy source.Soy and rapeseed biodiesel offer mod-est gains, but sugarcane and cellulosicethanol are better. In fact, some biofu-els that look reasonable at first blush canhave unequivocally negative climate im-pacts, as demonstrated by the ongoingproduction of biodiesel from palm oil oncleared forest lands in Southeast Asia.

As a GHG mitigation option, biofu-els should be seen in the context ofthe wider range of mitigation oppor-tunities. In particular, as long as thereare opportunities to significantly re-duce emissions from coal-based power,this may well be a more effective useof biomass resources than displacingpetroleum-based transport fuels. Andreducing transportation-related GHGemissions from increased fuel economyor reduced use of vehicles should notbe neglected in favor of fuel substitu-tion. These latter measures are just as

effective with regard to enhancing en-ergy security, which for most countriesrefers to reducing dependence on im-ported petroleum.

� The potential for conflict between foodand biofuels has long been raised be-cause biofuel production is an intrin-sically land-intensive undertaking. Therecent empirical observations of risingfood prices owing to the ongoing bio-fuels boom have heightened consider-ably these concerns for the future. Theyhave also brought into sharper focusthe polarization on this issue. Someanalysts have concluded that there isenough land to meet food needs as wellas provide a large amounts of bioen-ergy feedstocks and that these bioen-ergy markets can contribute to farmer’slivelihood opportunities and food se-curity. Others maintain that large-scalebioenergy will necessarily shift land, la-bor, and capital resources away fromfood production in a manner that un-dermines food security and degrades theenvironment. The resolution of this de-bate hinges in part on technical argu-ments relating to food and fuel pro-duction systems (such as land resourceestimates, yield projections, conversionefficiency assumptions). More impor-tantly, though, it will depend on theshape and nature of the food and fuelmarkets, how they interact, and the pol-icy regimes under which they operate.Insofar as the biofuel markets are un-derpinned by relatively wealthy con-sumers of transportation fuels, a purelymarket-driven allocation of global oreven national land resources could haveadverse consequences for the environ-ment and for food availability and ac-cess for poor consumers. Thus, the ex-tent to which commercial biofuels canhelp further the sustainable develop-ment agenda ultimately depends on thepolicies we put in place as safeguards to

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ensure that biomass feedstocks are pro-duced in an environmentally sustainablemanner and that bioenergy markets en-hance rather than undercut food secu-rity and livelihoods for the poor.

Thus, in both cases discussed here, the fea-sibility of employing bioenergy as an instru-ment of sustainable development depends notjust on the technical potential of the options,but also as much (if not more) on policies toensure that potential is exploited in a fashionthat gives due consideration to all dimensionsof the sustainable development agenda. His-tory has shown that this can only be done if

the views of all stakeholders are given consid-eration. It also requires a willingness to learnfrom our experiences and to move forward in adeliberate and thoughtful manner. Most of all,it means putting the needs of the poor and dis-advantaged front and center and making surethat they are sharing in the broad gains thatmay result from the continued or expandeduse of biomass.

To sum up, there is no doubt that biomassdoes offer the opportunity to further thebroad sustainable development agenda. Thechallenge lies in translating that opportunityinto reality. Whether we can rise adequatelyto this challenge remains to be seen.

SUMMARY POINTS

1. Traditional bioenergy is the dominant contributor to household energy supplies formuch of the world’s population but comes at high cost in terms of health and welfare.Expanding access to clean energy services is a critical development issue, yet progresshas been slow.

2. Modern bioenergy has rapidly expanded over the past decade and is poised to becomea major contributor to global commercial energy supplies. This is largely in responseto policy mandates driven by concerns about energy (oil) security and climate change.

3. Bioenergy has the potential to contribute to sustainable development both at thehousehold and commercial levels in the future. It can serve as a renewable sourceof energy that provides environmental and agronomic benefits while enhancing foodsecurity and supporting rural livelihoods.

4. The fulfillment of this potential cannot be presumed. Equally plausible futures fea-ture bioenergy as a land-intensive undertaking that is environmentally burdensome,adversely affects food security, and undermines rural livelihoods. Recent experiencewith the rapid expansion of biofuels markets has elevated anxieties about such futures.

5. The difference between these futures hinges primarily on the policy and marketenvironments in which bioenergy emerges. If sustainable development is an objectiveof a bioenergy economy, then it will need to be deliberately pursued via proactivepolicies.

DISCLOSURE STATEMENT

The authors are not aware of any biases that might be perceived as affecting the objectivity ofthis review.

ACKNOWLEDGMENT

The authors are grateful to an anonymous reviewer for useful comments that helped improvethe paper.


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Figure 1

Poverty and reliance on biomass for residential energy needs. The energy data are from 2004; thepoverty data are from 2000–2004 (from latest year available, if multiple years are available) (3, 6).Abbreviation: PPP, purchasing-power parity.

HI-RES-EG32-05-Sagar.qxd 9/15/07 17:42 Page C-1

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Top ethanol producers (2005)

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Figure 2

Top producers of biofuels (2005) (75–77).


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Farrell et al., 2006 (102)

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*** Soy biodiesel

Hill et al., 2006 (113)

Delucchi, 2003 (114)

*** Rape biodiesel

IEA, 2005 (106)

*** Sugarcane ethanol

Macedo et al., 2004 (112)

de Oliveira, 2006 (115)

*** Cellulosic ethanol

Farrell et al., 2006 (102)

Wu et al., 2006 (110)

Cornethanol

Soy biodiesel

Cellulosicethanol

Sugarcane ethanol

Rape biodiesel

Figure 3

Energy ratios of biofuel cycles (102, 106, 110, 112–115).


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Figure 4

Estimated hectares per car required to displace vehicle GHG emissions (data from sources in Table 2).


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AR325-FM ARI 21 September 2007 16:39

Annual Review ofEnvironmentand Resources

Volume 32, 2007Contents

I. Earth’s Life Support Systems

Feedbacks of Terrestrial Ecosystems to Climate ChangeChristopher B. Field, David B. Lobell, Halton A. Peters, and Nona R. Chiariello � � � � � �1

Carbon and Climate System Coupling on Timescales from thePrecambrian to the AnthropoceneScott C. Doney and David S. Schimel � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 31

The Nature and Value of Ecosystem Services: An OverviewHighlighting Hydrologic ServicesKate A. Brauman, Gretchen C. Daily, T. Ka’eo Duarte, and Harold A. Mooney � � � � � 67

Soils: A Contemporary PerspectiveCheryl Palm, Pedro Sanchez, Sonya Ahamed, and Alex Awiti � � � � � � � � � � � � � � � � � � � � � � � � � 99

II. Human Use of Environment and Resources

Bioenergy and Sustainable Development?Ambuj D. Sagar and Sivan Kartha � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �131

Models of Decision Making and Residential Energy UseCharlie Wilson and Hadi Dowlatabadi � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �169

Renewable Energy Futures: Targets, Scenarios, and PathwaysEric Martinot, Carmen Dienst, Liu Weiliang, and Chai Qimin � � � � � � � � � � � � � � � � � � � � � �205

Shared Waters: Conflict and CooperationAaron T. Wolf � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �241

The Role of Livestock Production in Carbon and Nitrogen CyclesHenning Steinfeld and Tom Wassenaar � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �271

Global Environmental Standards for IndustryDavid P. Angel, Trina Hamilton, and Matthew T. Huber � � � � � � � � � � � � � � � � � � � � � � � � � � � � �295

Industry, Environmental Policy, and Environmental OutcomesDaniel Press � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �317

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Population and EnvironmentAlex de Sherbinin, David Carr, Susan Cassels, and Leiwen Jiang � � � � � � � � � � � � � � � � � � � �345

III. Management, Guidance, and Governance of Resources and Environment

Carbon Trading: A Review of the Kyoto MechanismsCameron Hepburn � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �375

Adaptation to Environmental Change: Contributionsof a Resilience FrameworkDonald R. Nelson, W. Neil Adger, and Katrina Brown � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �395

IV. Integrative Themes

Women, Water, and DevelopmentIsha Ray � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �421

Indexes

Cumulative Index of Contributing Authors, Volumes 23–32 � � � � � � � � � � � � � � � � � � � � � � � �451

Cumulative Index of Chapter Titles, Volumes 23–32 � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �455

Errata

An online log of corrections to Annual Review of Environment and Resources articlesmay be found at http://environ.annualreviews.org

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