- -^'ISi;^

^ " • • " ^ i k _ ' "

SOLVING THECLIMATE PROBLEMTechnologies Available to Curb COp Emissions

by Robert Socobw, Roberta Hotinski,Jeffery B. Greenblatt, and Stephen Pacala

BEYOND

KYOTO

The atmosphere's concentration of car-bon dioxide (CO-,) has increased bymore than 30 percent over the last 250

years, largely due to human activity. Two-thirdsof that rise has occurred in the past 50 years.'Unless there is a change, the world will seemuch higher CO, levels in the future—levelsthat are predicted to lead to damaging climatechange. Fortunately, many carbon mitigationstrategies are available to set the world on a newpath, one that leads to a lower rate of CO, emis-sions than is currently expected.

The environmental community is currentlyplaying a prominent role in the developmentof the CO, policies that will elicit these strate-gies. Until a few years ago, the environmentalcommunity was almost exclusively interestedin policies that promote renewable energy,conservation, and natural sinks. More recently,it has begun to explore alliances with tradi-tional energy supply industries on the groundsthat to establish the pace required to achieveenvironmental goals, parallel action on manyfronts is required.

Charting a New Path

Comparing the carbon mitigation potential ofdifferent strategies requires a fixed time frame.

A 50-year perspective may be best: It is longenough to allow changes in infrastructure andconsumption patterns but short enough to beheavily influenced by decisions made today.

If the world continues on its currently pre-dicted path for 50 years—relegating significantaction on global carbon to a later time—-manymodels of this future show CO, emissions fromhuman activities roughly doubling by 2054relative to today (see Figure la on page U,dashed line).- This path is likely to lead to atleast a tripling of the preindustrial (circa 1750)level of CO, in the atmosphere—280 parts permillion (ppm)—by the middle of the next cen-tury. Such a high concentration is likely to beaccompanied by significant global warming,rising sea level, increased threats to humanhealth, more frequent extreme weather events,and serious ecological disruption.^

An alternate 50-year future is a world in whichemissions stay roughly flat (Figure la, solidline). Assuming natural sinks of carbon in theocean and on land continue to function as theyhave in the past (see the box on pages 14 and 15),such a world can avoid a doubling (550 ppm) ofthe preindustrial CO, concentration if furtheremissions cuts are made after 2054. Avoiding adoubling of CO, levels is predicted to reducesubstantially the likelihood of the most dramaticconsequences of climate change, such as shut-

ENVIRONMENT DECEMBER 2004

down of the ocean's thermohaline circula-tion (which transprorts heat from the equa-tor to northern climes) and disintegrationof the West Antarctic Ice Sheet.

However, keeping global emissions attheir current level will require a monu-mental effort. As seen in Figure la, com-mitting to an emissions trajectory approx-imating the flat path entails an amount ofCO, emissions reduction in 2054 roughlyequal to all CO., emissions today.

In 2000. about 6.2 billion tons of car-bon were emitted into the atmosphere asCOj. Approximately 40 percent wasemitted during the production of elec-tricity and 60 percent when fuels wereused directly in vehicles, homes, com-mercial buildings, and in industries.Approximately 55 percent was emittedin the 30 member countries of theOrganisation for Economic Co-opera-tion and Development (one quarter ofthe world's total in the United States),10 percent in transitional economies(Russia and other formerly Communistcountries), and 35 percent in developingcountries.''To achieve the flat trajectory,therefore, no-carbon and low-carbonenergy strategies must be implementedon a massive scale across all sectors ofthe economy and in countries at allstages of economic development.

The Scale of the Problem:Stahilization Wedges

To assess the potential of various car-bon mitigation strategies, the concept of"stabilization wedges" is useful. The dif-ference between the currently predictedpath and the flat path from the present to2054 gives a triangle of emissions to beavoided (see Figure la), a total of nearly200 billion tons of carbon. This "stabi-lization triangle" can be divided intoseven triangles—or "wedges"—of equalarea (see Figure lb on page II). Eachwedge results in a reduction in the rate ofcarbon emission of 1 billion tons of car-bon per year by 2054, or 25 billion tonsover 50 years.

Fifteen carbon-reduction strategieshave been examined, each of which is

based on known technology, is beingimplemented somewhere at an industrialscale, and has the potential to contribute afull wedge to carbon mitigation.^ Scalingup from present capacity to an entirewedge would be challenging but plausiblein each of the 15 cases. Each wedgewould entail environmental and socialcosts that need to be carefully considered.

Expressing various strategies in termsof the amount of activity required to fillone wedge allows for comparisons acrossstrategies: area of forest plantation versusnumber of fuel-efficient cars versus num-ber of coal plants where carbon emissionsare captured and stored (sequestered fromthe atmosphere), for example. The strate-gies may be grouped into five categories:energy conservation, renewable energy,enhanced natural sinks, nuclear energy,and fossil carbon management.

Energy Conservation

History leads one to expect substantialincreases in energy efficiency in thefuture, even without an emphasis on cut-ting carbon emissions. Over the past 30years, advances in efficiency, in conjunc-tion with changes in the sources of energysupply, have led carbon emissions to growonly half as fast as the gross wodd prod-uct (1.5 versus 3 percent per year).^ As aresult, global carbon intensity—the ratioof global carbon emissions to gross worldproduct—has been steadily falling. If thepatterns of the past 30 years continue foranother half century, the world carbonintensity will fall by half, relative to today.This reduction is already taken intoaccount in the currently predicted path inFigures la and lb. To count toward anywedge, changes in efficiency and all otherstrategies will need to result in an evenlower carbon intensity than that expectedfrom historical trends.

Global CO., emissions come fromthree broad end-use sectors: power gener-ation (which in 2000 made up 42 percentof emissions), transportation (22 per-cent), and direct uses of fuel in industryand buildings (36 percent).'' There areopportunities everywhere: in power

plants and household apphances, in air-plane engines and city planning, in steelmills and materials recycling. In a worldfocused on carbon, all three sectors willbecome targets of more intense efforts toimprove energy efficiency.'"

For example, a conspicuous source of awedge is increased efficiency for theworld's light-duty vehicles—cars, vans,sports utility vehicles (SUVs), and lighttrucks. A recent study by the global autoindustry, the Sustainable Mobility Project(SMP)," reports that the worid's light-duty vehicles emitted 0.8 billion tons ofcarbon as CO., in 2000, one-eighth of allglobal emissions. SMP predicts that theseemissions will double in 2050, to 1.6 bil-lion tons of carbon per year. In this sce-nario, while miles driven by light-dutyvehicles increases 123 percent (1.52 per-cent per year), average fuel economy(miles per gallon) increases by only 22percent {0,4 percent per year). Represen-tative values yielding such carbon emis-sions in 2054, for example, are 1.6 billionlight-duty vehicles (versus about 600 mil-lion today), 10,000 miles per year of dri-ving per vehicle (about the same as today)and 30 miles per gallon average fuel econ-omy (versus somewhat more than 20miles per gallon today).

Almost a whole wedge is achieved(actually, 0.8 wedges) if 2054 fuel econ-omy doubles, relative to what SMP pro-jects, or if total distance driven in 2054 ishalf as much as SMP projects.'- Such areduction in driving could be accom-plished by increased reliance on masstransit and telecommuting, if urban plan-ning makes these options convenient andeconomical relative to travel in a privatevehicle. Achieving a wedge here isapproximately equivalent to keeping thetotal CO., emissions rate from theworld's light-duty vehicles in 2054 nohigher than today's instead of letting itroughly double.

Another route to wedges of energy effi-ciency is adding a carbon focus to capitalformation (such as new power plants,steel mills, and apartment buildings).Decisions that determine the energy effi-ciency of the world's capital stock are par-ticularly important, because they lock in a

10 ENVIRONMENT DECEMBER 2004

particular level of energy efficiency formany decades.

For example, the details of the con-struction of an apartment building can dic-tate its future CO, emissions for a centu-ry; of a power plant, for a half century; ofa truck, for a decade. Retrofitting an itemof capital stock after construction is gen-erally far more costly than making theitem energy efficient in the first place.

At present, much of the world's addi-tion to its capital stock is taking place indeveloping countries, a trend that isexpected to remain true throughout thenext 50 years. More aggressive pro-grams to demonstrate low-carbon capita!facilities—such as advanced powerplants—in industrialized countries mayreduce the reluctance of developingcountries to build their own low-carboncapital facilities in parallel. New finan-cial mechanisms that encourage globallycoordinated demonstration of new low-carbon technologies are justified,because wherever capital facilities arebuilt that are inappropriate for a futurewhere global carbon emissions are con-strained, the world bears the costs oftheir future emissions.

It is impossible to decide whichimprovements in energy efficiency willarrive only in a world focused on globalcarbon management and which will arriveregardless. For example, installing themost efficient lighting and appliancesavailable, along with improved insulation,could supply two wedges of emissionsreductions if applied in all new and exist-ing residential and commercial buildingsby 2054, provided one assumes that nosuch improvements would be installedwithout a carbon constraint. An Intergov-ernmental Panel on Climate Change(IPCC) report expects half of these reduc-tions to arrive without climate policy, so itis conservative to expect energy efficiencyimprovements in buildings to yield atmost one wedge, rather than two.'^ Simi-larly, compact fluorescent bulbs alonecould provide one-fourth of a wedge overthe next 50 years if used instead of incan-descent bulbs^which are four times lessefficient—for all the lighting projected for2054.'"' Energy efficiency also carries

Figure la. Historical carbon emissions with twopotential pathways for the future

•7 _

Towardtripling

Stabilizationtriangle

Historicalemissions

doubling

1954 2004

Year

2054

NOTE: Our currently predicted path (dotted black line) will probably lead to at least atripling of atmospheric carbon dioxide (CO^) relative to its preindustrial concentration,while keeping emissions flat (solid line) would put us on track to avoid a doubling ofCO,.

SOURCE: R. Socolow, R, Hotinski, J, B. Greenblatt. and S. Pacala.

- Figure 1b. Stabilization wedges

OQ

7- -

7 wedges

2004

Flat path

Year

1 wedge

avoicJs 1 billiontons of carbon

.^emissions per yearby 2054

2054

NOTE: The stabilization triangle in Figure la can be divided into seven equal "wedges"that represent activities capable of reducing one billion tons of carbon per year by 2054.

SOURCE: R. Socolow, R. Hotinski, J, B- Greenblatt, and S. Pacala.

VOLUME 46 NUMBER 10 ENVIRONMEMr I I

intangible benefits in addition to financialsavings: It fosters elegant design, qualityconstruction, and careful maintenancethat result in more satisfying products.

Energy efficiency does not have to dothe whole job of keeping global carbonemissions constant for the next 50 years.There is room for energy use to grow,even when carbon emissions are constant,as long as the growth is in the fonn ot no-carbon and low-carbon energy. In particu-lar, the prospect of a future much morefully powered and fueled by renewableenergy is tantalizing.

Renewable Energy

A useful division of CO, emissionsdistinguishes those arising at powerplants and those arising where fuels areused directly. The introduction ofrenewable energy can reduce emissionsin both settings.

Renewable Electridty

Electricity can be produced by manyrenewable energy sources. Hydropow-er was the first renewable energy

base, is also growing 30 percent peryear globally.

A wedge from renewable electricityreplacing coal-based power is avail-able from a 50-fold expansion of windby 2054 or a 700-fold expansion of PVrelative to today. The expansion factorfor geothermal energy is about 100.Tidal energy and wave energy areprobably too untested at a large scalefor a claim to be made for a wedgebased on existing technology.

A 50-fold expansion of wind amountsto deploying two million wind turbines(of the one-megawatt size that is cur-rently typical).'^ The land demands areconsiderable: A wedge of wind requiresdeployment on at least 30 millionhectares (the area of the state ofWyoming or nearly the area of Ger-many). Because wind turbines slowdown the wind, the wind turbines on awind farm are typically separated by 5 to10 rotor diameters to make room for thewind speed to recover from one windturbine to the next. Current rotor diame-ters are approaching 100 meters, so oneshould expect perhaps two wind tur-bines per square kilometer, or five persquare mile. The spaces between tur-

NIMBY (not in my backyard) reactions.In response, wind farms in Europe,where wind power is expanding mostrapidly, are being taken to offshore loca-tions—recently, far enough to be invisi-ble from the shore."'

For a renewable energy technology,land demands for PV are relatively lowbecause the efficiency of conversion ofsunlight to PV is relatively high: An entirewedge of PV electricity will require anestimated two million hectares (the areaof New Jersey).^'' Some of this area can besupplied by the roofs and walls of build-ings. The only technology comparable inefficiency of conversion of sunlight is thesolar engine running on high-temperatureheat, produced by a solar concentrator (afocusing trough or dish). This technologywas commercialized for a brief time notvery long ago with the help of subsidiesand will probably return.

Wind, PV, and solar thermal energy allhave the obvious problem of intermitten-cy. The output of wind turbines is highlydependent on the strength of the wind,and solar cells and solar troughs provideelectricity only when the sun shines. Thisproblem grows more acute as these inter-mittent technologies gain market share.

Alrlioui>h the land demands associated with a wedge from wind power are considerable (30 million hectares—the area of Wyoming I.land between turbines can be used for agriculture, grazing, and other purposes.

source to gain a large market share.Now, wind power—growing globallyfor the past decade at about 30 percentper year—is playing a substantial rolein several countries, notably Germanyand Denmark. Solar photovoltaic elec-tricity (FV). from a much smaller

bines on land can be used in many ways,including for agriculture and grazing.

Nonetheless, because modern windturbines are so tall (as tall as all but thevei"y tallest skyscrapers) and thereforevisible from far away, the expansion ofwind fartns is already provoking strong

To be practical for large-scale use in elec-trical grids, intermittent renewable energysources are best combined with energystorage technologies as well as energysupply technologies that can fluctuate inoutput yet can also operate a large fractionof the time. Natural gas turbines are well

12 ENVIRONMENT DECEMBER 2004

matched to intermittent renewables, as ishydropower.

Renewable Fuels

There are fewer routes to low-carbonfuels than to low-carbon electricity.Renewable biofuels can be producedfrom vegetation, and hydrogen—a no-carbon fuel—can be produced fromrenewable electricity.

Because plant matter is created by pho-tosynthesis using C0^ from the atmos-phere, combustion of "biofuels" simplyreturns borrowed carbon to the atmos-phere. Renewability requires that theplants are grown sustainably—that is.planting must keep pace with harvest-ing—so that there is no net effect on theCOT concentration of the atmosphere.Renewability also requires that very littlefossil fuel is used in harve.sting and pro-cessing. Renewable biofuels can displacethe gasoline for a car or the cooking fuelfor a stove.

Tlie world's two largest biofuels pro-grams today are the Brazilian program toproduce ethanol from sugar cane and theU.S. program to produce ethanol fromcom. Between them, the two programsmake a total of 22 billion liters of ethanolper year.'* If the world's ethanol produc-tion could be increased by a factor ofabout 50, with much less associated fossilfuel use, this strategy could provideenough renewable fuel to account for onewedge of the stabilization triangle,assuming that ethanol displaces gasoline.The land demands, however, would bemuch greater for a wedge of biofuel thanfor a wedge of PV or even a wedge ofwind—about 250 million hectares.''' anarea almost the size of India and one-sixthof the area now used globally for allcrops. Bioengineering might increase theefficiency of plant photosynthesis, butlarge-scale production of biofuels willalways be a land-intensive proposition.

Wind and PV can also be used to pro-duce hydrogen fuel, enabling an economywhere hydrogen is the dominant fuel (the"hydrogen economy"). The attractivenessof a hydrogen economy, from a globalcarbon perspective, stems from the simple

fact that hydrogen (HO, unlike almostevery other combustible gas or liquidtoday considered a usable fuel, does notcontain carbon. When conventional fuelsare used in individual cars, trucks, orbuildings. CO-, is produced at such smallscale that recovery of CO, is, if not hope-less, then extremely costly. Substantiallyreducing the CO, emissions associatedwith energy use in vehicles and buildings,therefore, requires replacing carbon-containing fuels either with hydrogen or,in some cases, electricity.

For hydrogen fuels to contribute awedge, they cannot be produced byprocesses that emit as much CO, as wouldfossil fuels with the same energy content.Producing hydrogen by electrolysis afterproducing electricity from wind emits noCO,, while producing hydrogen from nat-ural gas or coal—the principal primaryfuels used to make hydrogen today—ordinarily emits such large amounts ofCO, as to defeat the emissions-reductionobjective. Producing hydrogen from fos-sil fuels can lead to substantially reducedCO, emissions (relative to the emissionsfrom the hydrocarbon fuel displaced)only if the CO, emissions can be capturedand stored (discussed below).

One can compare the relative impact oncarbon emissions of using a given amountof renewable electricity to back out con-ventional coal-based electricity or to backout gasoline via the intermediate step ofhydrogen production by electrolysis.Because the production of hydrogenrequires extra energy, and because thecarbon content of coal is high, displacingcoal-based electricity with wind electrici-ty provides emissions reductions roughlytwice as great as displacing gasoline withwind-produced hydrogen fuel.-" Thus,from a climate perspective, the optimaluse of wind may not be as a primary ener-gy source for hydrogen.

Enhanced Natural Sinks

The strategy of compensating ior CO,emissions by deliberately enhancing nat-ural sinks challenges our capacity to uselarge areas of land in ways that are not

damaging to biodiversity. (See the box onpages 14 and 15 for futher discussion ofnatural sinks,) Enhancing natural sinksentails fostering the biological absorptionof carbon and increasing its storage aboveand below the ground by, for example,reducing deforestation, creating new for-est plantations on non-forested land, orexpanding conservation tillage.

Current deforestation is transferringcarbon from forests to the atmosphere at arate of approximately one billion tons ofcarbon per year (a rate that is still veryuncertain). If we arbitrarily assume thattoday's deforestation rate declines by 50percent over the next 50 years in a worldthat does not pay attention to carbonissues, a half-wedge could be provided byhalting deforestation completely in thattime. Another half-wedge could be pro-vided by establishing plantations on 300million hectares of non-forested landworldwide—about the same area neededto supply a whole wedge of biofuels (seeabove) and five times the land area now intropical plantations.-^'

Conversion of natural vegetation toannually tilled cropland has resulted inthe loss of more than 50 billion tons ofcarbon from the world's soils over his-

Natural carbon sinks tern he enlumccd bycreating forest planlariims. such as thispine stand in Angus. Scotland.

torical time.-^ Conservation tillage, bywhich farmers avoid aeration of the soilto promote retention of carbon, couldprovide a full wedge, if used on allcropland around the globe; today, lessthan one-tenth of agricultural produc-

VouiME 46 NUMBER 10 ENVIRONMENT 13

tion uses conservation tillage.-^ Theincreased need for weed control thataccompanies conservation tillage cangenerate its own environmental prob-lems. However, conservation tillagecan be implemented in many ways.ranging from heavy use of chemicalherbicides to planting cover crops

immediately after harvest, with little orno herbicide use.

Nuclear Energy

Those hoping for a revival of nuclear

power see support coming their way if

carbon management becomes a higher

societal priority. Yet in environmental

discourse, nuclear power is quite often

not mentioned.

The connection between nuclear

power and reduced carbon emissions is

likely to become an important part of

the debate about the extension of the

OCEAN AND LAND SINKS

,' ocearis anil lenes jcction ior the iK-vt iwo L-L'iiturii."s IIKII SI;I-bili/os atiiio'-plkTR- CO, al 5tHt p;u(s |vi'niillitui (ppiii), Vhc Ihit palh -iluiwii jii

(.'iiiiUL'i! into itk' Litniosplk'iv MIKV IIK' l;l tol ilu" lni,lu>itri;il Ri'Milution. I'IK' iVjurcholtm dcpiLls fii'isil lik'l L'missii>ns.iitninspliLTii: growth, and tlio tKvaii ;iiulILHUI Miiivs (or till" past .' O \i';ir>. ;iiiil a [>ro-

\L-ars :iH)4 :il54.The future cnntrihutions ot (IK' lami aikl

iK\';iii sinks, himc\or. will bo aUcclai Inchanges in LliniLik- and olhor tacttHs,Chanecs in Itk'sc nalura! sinks tonki

Where does the carbon go?

Fossil fuel emissions

NOTE: Shown are total fossil fuel emissions (thick black line), atmospheric increase(light blue), land uptake (green), and ocean uptake (dark blue). The atmosphericincrease is the difference between fossil-fuel emissions and ocean and land sinks. Theocean sink is calculated with a simple model (see source below), and the land sink isheld constant after 2004 al 0,5 billion tons of carbon per year. Fossil-fuel emissionsare prescribed by a 500 parts per million stabilization path with the following fourcomponents: 1954-2004: historical emissions; 2004-2054: flat path emissions, as inFigures 1a and 1b; 2054-2104: linear descent to stabilization: after 2104: stabilization,"Stabilization" means there is no further build-up of CO^ in the atmosphere, becauseemissions are balanced by land and ocean sinks.

SOURCE: R. Socolow, R, Hotinski, J. B. Greenblatt, and S. Pacaia,The ocean sink iscalculated using a model described in U, Siegenthaler and F, Joos, "Use of a SimpleModel for Studying Oceanic Tracer Distributions and the Global Carbon Cycle," Tellus44B (1992): 186-207,

ik'aio<l lor slalirli/.ilion In up to (lirivuciiiii-s Ml oillk'r diivilioii.

OceansOver Ilk' p;ist luo ci-nturk's. ilk- o^\-;ms

haw abs(ii'lH\l rousililv hall ol ttk' 250 itiiiion tons olcartnin that ha\o Ivoii cmiUi'itIrtMn lossil IUL'I conihiisiinn,' I-or the past^0 \L'ars. the oceans lia\e Iveii absorbingainiosi iwo hiliion tons nl L-ar!io!i \x-r \c:nas CO,, ami \\w raU' is sii\uiil\ nk-roasnii;,fonipk'k' oecan nnxni;; Iain's inori- than a(housanii vears. sn [he i.-oiiliiiiialiipwollnii: ol i.\ccp waler w ilh prL-iniiiisirial CO. concL'iilriilitms will i\\\o\\ [heocc.m to he u siiinillcanl sniiv ol alnios-plk-rii.- CO, lor si-vvial (.-I'liltinos, In thefitiiiiv al tiMl. the oee.m sink is sinmn loiik-roLise inUit 2OS4 aikl lik-n lo tali !:railiiali\ uikier iho itopitloil lossii lik'l emis-sions scenario,

rik- 5O-\oar luuire o\ Ilk- ivi-an sink isuncertain In about luo wcdyes >0 hil-lion Ions ot carlum mcr 50 xcars -ineither liiieetiun. The inkertaiiil\ is thfresult ol iiinitatioiis ui Ihe aeeiirLk-\ ofhisioik-.ii tt.ua. niojelm ;: ol' uileiaiiTuialiKvan \:iriahilil\. inler.ktit'ns ol niariili,'oi'jianisnis wuh (he earlton ..u-le. andregionai inixiiis:. |iariieiiiari\ in lik- SiHithem Ocean-'

Ciiniatc-ciiaiiiie icedixick etinipiMindsliiis uncertain^. H omissions are ilal

uill aiinosi eerlainh eontinne lo nk-roaM-ils earKm uptake Irorn lik' almospliere.ilo\\e\er. there is a tliaike (iiat climalceiianiie wili weaken tik' ocean sink, snh-stantiall\ increasinjz tiie CO.eniissiunsleducEiuns needed for stabili/atiim at 5(X)ppm. While the ocean's response towarrnini; is nol weli uiklorstoi)d. tiie lactthai tik- soliibilit\ o! CO, in the oL-eandecreases as the ocean temperalure

14 ENVIRONMENr DECEMBER 2004

plant life of existing reactors. If, over

the next 50 years, all of today's nuclear

power plants were to be phased out in

favor of modern coal plants, about half

a wedge of additional CO., emissions

reductions would be required to com-

pensate. This half-wedge would not be

required if current nuclear reactors were

replaced with new ones, one-for-one.

Similarly, building a wedge with new

nuclear power requires tripling the cur-

rent nuclear electricity production,

assuming the new plants displace coal.

This would mean building about 700

new 1,000-megawatt nuclear plants

around the world.-"'

The expansion of nuclear power is, of

course, a politically charged issue. Much

of the debate has focused on plant safety

and waste management. The nuclear

power community would welcome the

opportunity to build a new generation of

advanced nuclear reactors whose designs

incorporate intrinsic safety features that

iiicrciiscs poiiils U> a wciikcning ol Ilk-sink. This cftcLt. nni iiichiclcil in thonioik'l Ivhiiui Ihf lii;inv. L-oiild ho ;is

;is oiiL' vvctii;!.'.' liirllk-r. il'i'.li)li;ilL; Irigiiurs a slowiiuwn ol' (IK-

iH;i.';in's "(.•niui-\nr lull" Ilk- llii.Tinoli;ilitK" liauhiliiin lh;il li.instL'is cokl ('(),-rich siii'l:iLO walors In ihc ticcp niv;inlliis could luilhor ivducc carhim uplaki.'.pfiluips siyiiilkanlly. Hinvc\or. such aslowdown wcmlil ivi|uiiv waiiniiiL! ol SL'\cral dctjrt'L's CL-ISJUS lh:i[ is iiiilikL'l> li>occur In 2054.'

'I JK" L'i)iiijiiuL-il inlliix oTCd . lo llieiK-can will chantrL' UCLMII Llii-inisliy. Addi-liun iifC't), lo tho iw-oan niiikcs il moreiicidic. Anlhnt|io<;i:iiic CO, emissinns haveiilroad) liivivascil smraLL'-otiMii pll b\ap|>in\iniak'l\ II. I iiiiil !:loh:ill\. foni[iLn"iibk" (lln>ii!;h oppoMli" in sijjii) Ut Ihi.- pllchanyi' diiriiis: Ilk' hisl ILL- a^i-.^ lTiLiv;isiiiy

ma\ aiKiTsi-K allL'cl iiiariin."U'iiis :iEid alUT llu' halaiiLL' oldis-

.M>lval miiK'iak.'' Adililinn til 'CO, to llu*HLi.Mii also reduces llie eiHiL'eiilralion nlearlmnalo. llie iiLVaii's main biillerin^ayenl. aiul u ill atleel Ihe tKeaii\ ahilih loahsoih CO, on lonji lime scales.

Land

The loneslri;il bios[)lieiv. in emilrasi ioIhe ocenii. has bet-ii almost neutral wiihrespect lo carhon excliaiiiie. neilher asijinillcaiil nel carhon source nur sink.when averajjeti o\er ihe pasi iwo cen-turies.^ Prior to almut h'>ll il was a nelsource iliie to u idespteati laikl cleatiiis:for aiiriculture. hul il has siiice hectmie anel sink due lo a vaiiely ol factors.These include rcgrowlh on the pre\ioiislycleared land, fire suppression (whichincreases Ihe amounl ol carbon in slaiid-in^ wood), eiilomhiiieiil ol caibon in sed-imenls nl' reservoirs and oilier boi.lies olwater, the buildup ol woot.1 producis in

i s and landlills. a^ricullural soileonser\atioii, and. possibi), fertilizationol veyelalion by llie incivasod CO. in iheainiosphere or iiilroiien in MV pollution.Data show lliat lor the past hall ceritur\these lactors ha\e been lakini; more car-bon oui or Ihe atiiuv-phere ihan has beeneiiiiited lo the atmosphere by tho massixeloiesl clearing in Ihe tropies. 'Tho nellorrestrial sink over iho pasl two docadoshas been soinew hal less ihaii half asslroni; as ihe net ocean sink.'"

The future laikl Nink depends on iherelali\e im|>orta!k\' ot sikli nieebanisms,which are siiil uncertain, i-or example, itllie sink is caused piimaril) by reurowlhon previously cleared land and Ike sup-pression, then it will probably decreaseover time as reyrouth iiears completionami as laikls uikler fire suppression com-plele theii Jidiustnk-nt to the new comli-lions." This decrease, aloiii; wiih tilherpossible ncyalixe impacts on the landsink due to changes in temperature iindprccipilation. could mean another iwowedues ol emissions reductions would helequired tor slabili/alion at 5(10 pptiiCO,. Sonk' modeK preilicl that reL:ii>nalsliitts to holler and ilrier cliiiiales w iltdoniinaie the lutme of the lerrestrial sinkami cause a catastrophic loss ot iilohalbiodi\eisily and carbon.'

In contrast, if the sink is caused priniarily by CO, leitili/ation. ihen il willincrease with the buildup of alnkts|ilieiicCO, lo absorb Ihree billion Ions or moreof carl-mn per \eai In mid-cenlur>,' 'Tliislasl inecliaiiisin represeiils the sinyle-laryesi unceilanit) lor carbon manayc-nieiil in Ihe .S()-\ear time Iraino—3wediies' worlh of uptake ihal could sig-nificantly reduce emissions cuts needed.The liLUire on page 14 is hased on theassumption that the net taiul sink willreiiiain appro\irnLitel\ the sank- si/e as ithas heen o\er the last two decades, at

half a hiilion tons ot carhon per year, tortho indetinite future.

All these eonsiderations nk'an the liitureof the laiul sink is L|uite uneerlain. rangingIroni uptake surpassini; that ol the oceanto a si>;nificant loss of earbon.

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n . J L. Diilr tMnri ' lat . "Onitii.- Nrit'niunti.-ol hisi-li\i.' l'i.vilh;iL'k tviwfL'n Inriiro Ctiniak' Chaiiyi' JIH! itio

make minor events far less likely to esca-late into major releases of radioactivity.Workable long-term nuclear waste man-agement probably requires the develop-ment of a political consensus in favor ofchanging the objective from managementby passive barriers to management active-ly and indefinitely.

Even more challenging than wastemanagement, however, are the problemsfor international relations generated bythe linkages between the military atomand the civilian atom. A climate strategybased on the expansion of nuclear powermust contend with the need to reduce CO^emissions all over the world. Is the worldready to permit nuclear power develop-ment in all countries? Currently, thenuclear power program in Iran is a sourceof international tension; Although Iranclaims its nuclear program is for peacefulpurposes only and is willing to acceptintemational safeguards, it appears deter-mined to build a uranium-enrichment

only the 40 percent of CO^ emissionsassociated with electricity production.(Someday, perhaps, nuclear reactors willalso produce hydrogen fuel.) To decar-bonize electricity, there are many alterna-tives. As providers of low-carbon electric-ity, wedges of nuclear power compete withwedges of wind and PV, and. as well, withwedges from the fossil energy strategies.

Fossil-Carbon Management

In the flat trajectory of Figures 1 a andlb. fossil fuels hardly disappear in thenext 50 years; rather, their CO-, emissionsstay constant. In that same period, howev-er, global energy demand is predicted togrow even faster than global CO, emis-sions, more than doubling. If the flat tra-jectory is followed, the fossil fuel indus-try's share of the global energy system in2054 will be much less than its 85 percentshare today. How much less will be deter-

formidable implications for the future.Each fossil fuel has its own ratio of hydro-gen to carbon. Carbon emissions perunit of energy content are highest forhydrogen-poor coal and lowest forhydrogen-rich natural gas. (Carbon emis-sions per unit of energy content areapproximately in the ratio of 5 to 4 to 3 forcoal, oil, and natural gas, respectively.)Carbon concems, as they come into play,will therefore favor natural gas and thwartcoal. Greatcr-than-expected expansion inthe global use of natural gas, which emitshalf as much CO, as coal for the sameamount of electricity production, is a pos-sible consequence of a carbon constraint.

Any major expansion of natural gas usewill require transporting large amountsover long distances, either in liquefiedform or in pipelines. A wedge's worth ofpower from natural gas instead of coal ismatched to 50 large liquefied natural gas(LNG) tankers docking and unloadingevery day or building the equivalent of the

Acid-gas injection wellsin Alberta. Canada

(near right), as a sulfurdisposal strategy, co-

store hydrogen sulfideand carbon dioxide.

Studying cement sealsin old wells (far right)clarifies risks of CO^

leakage underground.

capability that would put it very close tonuclear weapons if it chose to go thatroute. Entirely new intemational arrange-ments that make unprecedented demandson the sovereignty of all countries areprobably required for wedges of nuclearpower to materialize.

The "mutual hostage" relationshipamong nuclear power plants creates yetanother obstacle to the creation of awedge of nuclear fwwer. A reactor acci-dent at any power plant generates politicalpressure for the shutdown of all powerplants, to an extent not present elsewherein the energy system.

Nuclear power does not have to play amajor role in reducing global CO, emis-sions. Nuclear power addresses, for now.

mined by the extent to which the CO-,emissions to the atmosphere associatedwith fossil fuels can be reduced.

Fossil fuel CO, emissions can bereduced in two ways. The first strategy isto change the relative market shares ofcoal, oil, and gas. The second strategy isto interfere with the CO, emissionprocess, preventing the CO, from reach-ing the atmosphere.

Changing the Mix ofFossii fuels

Shifts in the market shares of coal, oil,and natural gas have been a feature of fos-sil fuels throughout their history. Carbonconcems have had only a minute role thusfar in these shifts, but such concems have

Alaskan natural gas pipeline, currentlyunder negotiation, every year.-^

Oabon Capture and Storage

The second principal strategy forreducing the CO, emissions associatedwith fossil fuel use—interfering with CO^emissions—requires a two-step processknown as "carbon capture and storage."The first step, carbon capture, typicallycreates a pure, concentrated stream ofCO,, separated from the other products ofcombustion. The second step, carbon stor-age, sends the concentrated CO, to a des-tination other than the atmosphere.

Opportunities for CO, capture are abun-dant. The natural gas industry routinely

16 ENVIRONMENT DECEMBER 2004

generates capturable streams of CO-, whennatural gas, after coming out of theground, is stripped of CO, before ship-ment by pipeline or tanker. Refineriesmaking hydrogen for internal use are gen-erating, as a byproduct, capturable streamsof CO,; refinery hydrogen requirements,in turn, are increasing to process heaviercrude oils and to remove more sulfur. Cap-turabte streams of CO, will also be gener-ated where technologies are deployed toconvert coal or natural gas into liquidfuels, and the geopolitics and economicsof oil are nearly certain to increase the useof these technologies. In a world focusedon the reduction of CO, emissions, allthese streams are candidates for capture,instead of venting to the atmosphere.

The most promising storage idea is "geo-logical storage." in which the CO, is placedin deep sedimentary fomiations. (Alternatecarbon storage ideas include storage of CO.,deep in the ocean and storage of carbon insolid form as carbonates.) Carbon captureand storage has the potential to be imple-mented wherever there are large pointsources of CO-,, such as at power plants andrefineries. The storage space availablebelow ground is probably large enough tomake carbon capture and storage a com-pelling carbon mitigation option.

For decades, oil companies have beeninjecting CO, underground to scrubhydrocarbons from oil reservoirs in lalestages of production, a tactic calledenhanced oil recovery (EOR). Storing awedge's worth of CO, would require scal-ing up the current global rate of injectionof CO. in EOR by a factor of about 100.-"Because EOR projects to date have nothad the explicit objective of long-termCO, storage, little is known about thelong-iemi fate of the CO^ injected.

If waste carbon can be captured andstored, hydrogen production from coaland natural gas could provide an alter-nate route to the "hydrogen economy."And in all situations where CO, captureand storage is under consideration, theremay be opportunities to "co-capture andco-store" other pollutants, like sulfur,with the CO,. With co-capture, the costsof above-ground pollution control willbe reduced, and perhaps pollution con-

trol costs and total environmental emis-sions will as well.

At this time, via demonstration proj-ects, the carbon capture and storagestrategy is undergoing its first testing(see the box on page 18). The environ-mental community is being asked to helpestablish the criteria—such as the condi-tions under which permits would begiven for CO, storage below ground—toensure that the strategy is effective andsafe. Some in the environmental com-munity want to keep their distance, call-ing carbon capture and storage an"addict's response" to climate change.-^^Others recognize the importance of tak-ing part in setting the ground rules forcarbon capture and storage to increasethe at-tention paid to its environmentalperformance. Still others see benefit inengaging in coalition politics, leading topolicies that advance several CO, miti-gation strategies at once—to the benefitof technologies they prefer.

Getting Started with Wedges:The Next 10 Years

The challenges of carixin mitigation aredaunting. Unless campaigns to reducecarbon emissions are launched in theimmediate future across all sectors of theeconomy and in countries at every stageof economic development, there will belittle hope of avoiding a doubling ofatmospheric CO,.

To clarify the scale of the effort, it ishelpful to consider the emissions reduc-tions needed over the next 10 years to stayon the flat path of Figures la and lb.assuming the alternative is the currentlypredicted path. By 2014, as a point of ref-erence, one might implement 20 percent

of each of 7 wedges. There are manyways to do this.

• Addressing demand, to reduce elec-tricity emissions, the world could accom-plish the first 20 percent of a buildingsefficiency wedge by replacing everyburnt-out incandescent bulb with a com-pact fiuorescent bulb. Addressing supply,the world could develop the first 20 per-cent of a wind wedge by completing400.000 new wind turbines, or of anuclear power wedge by building 140new nuclear plants. It could implementCO, storage projects with 700 times thecapacity of the Sleipner project (see thebox on carbon capture and storage onpage 18). As part of an augmented strate-gy to displace coal with natural gas inpower plants, it could build 10 natural gaspipelines having the capacity of the Alas-ka pipeline now under discussion.

• To reduce transport emissions, againaddressing demand, the world couldimprove average vehicle fuel economy

Replacing hurm-outIncandescent hiilhswith fluorescentones could he oneof a handfulof significantbeginning stepstoward reducedCO emissions.

by 25 percent with the assumption thatthe amount of driving also increases by25 percent. Addressing supply, the worldcould convert 50 million hectares(200,000 square miles) to crops likesugar cane that can be converted toethanol with modest fossil fuel inputs. Itcould accelerate the arrival of hydrogen-powered vehicles and the production oflow-carbon hydrogen.

• To reduce emissions from the space-heating and -cooling of buildings, the worldcould embark on a campaign of imple-menting best-available design and construc-tion practices, especially for new buildingsbut also for the retrofit of buildings.

• The world could take some pressureoff the eneigy system by modifying the

VOLUME 46 NUMBER 10 ENVIRONMENT 17

agricultural practices on nearly one-fifthof all cropland to bring about conservationtillage. It could create 60 million hectaresof sustainable plantations on nonforestedland and set a new course to eliminatetropical deforestation within 50 years.

It is hard not to feel overwhelmed hythis menu. Are there ways out? Perhaps anoptimum pace for a 50-year campaignwould result in bringing some of thesewedges forward more slowly, accomplish-ing less than 20 percent of the job in thefirst 10 years. But how much more slow-ly? Perhaps the number of parallel effortscan be reduced by getting two or threewedges from a single strategy; energy effi-ciency is the most likely area. But formany of the other strategies, bringing ontwo wedges is more than twice as hard asbringing on one because cheap and easyopportunities will be used up early on.

Perhaps the stabilization triangle willturn out to be smaller: The world econo-my might grow more slowly, and greenplants, in response to elevated CO., levels.might store more carbon than predicted.But the stabilization triangle could just as

easily be larger (see the box on pages 14and 15). In this case, getting onto a paththat avoids doubling the preindustrialCO, concentration might require morethan seven wedges.

The Road Ahead

Advocates of any one wedge shouldtake a clear-eyed look at the difficultiesinherent in cutting one billion tons of car-bon enussions per year using that strategy.Deep patterns in the energy system limitthe rate of introduction of energy efficien-cy. Land-use constraints limit the roles ofrenewable energy and natural sinks. Deepfear and distrust, as well as nuclearweapons proliferation, hobble nuclearpower. The long record of resistance topro-environment initiatives by the fossilfuel industries compromises their credi-bility. Aesthetic considerations limit thepenetration of several renewable options,including wind and hydropower.

Advocates of one kind of wedgeshould also not minimize its potential to

attract the support of other interestgroups who can help advance its adop-tion. The widespread use and economiccompetitiveness of natural gas andnuclear electricity mean they might beimplemented within the existing energysystem relatively quickly, bringing repre-sentatives from those industries to thetable. Coal used with carbon capture andstorage reduces not only CO^ emissionsbut conventional pollution as well, a ben-efit attractive to public health advocates.Photovoltaics are bringing electricity toremote areas, including poor villages farfrom any electricity grid, and appeal toadvocates for the developing world.Wind energy should engage rural com-munities, as it brings income to ruralareas and may slow migration to cities.Biofuels and plantations can helpreclaim degraded land, enhancingecosystem services. The pursuit of ener-gy efficiency will cut costs for business-es, providing joint environmental andeconomic gains. Attention to energy effi-ciency brings broad support from all whotake pleasure in well-made goods.

Environmental groups and others havecalled iittcntit)n to the riLvd to est;ihlishIhe loni^-lerni clfectivcncss ol uiidL-r-grounJ storagL- Lind its safely. AllhctughCO, is not tlaniniablc or explosive, largeCO, releases into low-lying depressionscould lead lo ha/ardous concentrations.CO, pereokiliiig upward from deep stor-age could also increase ihc acidity ofground wiiler ;ind soil.

Two iiidjor projects are under way tostudy geological CO. storage, each cur-rciilly injecting one inilliim tons of CO,per year. In Ihe Weyhurn project inSaskatchewan. Canada. CO. captured ala synlhetie fuels plant in North Dakoiaand transported norlh to Saskatchewanby pi|x.'linc is used lor enhanced oilrecovery (HOR) in the aging Weyhurnoil tlelds. In the Sleipner project in theNorth Sea off the coasi of Norw;iy.exces.s CO, in the natural gas being pro-duced from one foniialion below the seaHoor is stripped away and then reinject-ed into another reservoir, as opposed loIhe ciisloniary praclice of venting il lo

CO2 STORAGE PROJFXTS

the atmosphere. A third major project,the In Salah project in Algeria, is jusistarting. Like the Sleipner projeel, il willship excess CO, rr()ni natural gas. and ilwill also store a CO, stream of aboutone million Ions of CO, per year. In thisprojecl. the CO, will be iiijccled inlo thefomialioii from which the gas was ini-tially recovered, aiding in gas recovery.This is in coittrasl lo the Sleipner proj-eel, in which CO, is injected inlo a non-h)'drocarbi>ii-beariiig foriiialinn.

This approach lo carbon mitigation isvery young and i.s slill being reviewed bythe iiilernalional community. Next year.

the Intergovenimenlal Panel on ClimateChange (IPCC) will release a specialreport on carbon dioxide capture andstorage (CCS) Ihat will suiiimari/e eur-rent knowledge. If these initial liiidingsand CCS pilol projects suggest that long-term storage will be sate and elfeclive.and it adequate permitting procedurescan be established, over Ihe next 50 yearsCCS could provide one or more wedgesof emissions reductions. For each CCSwedge, slorage programs equivalent to70 of Ihe Sleipner, Weyburn. or In Salahprojects would have lo be crealed cveiyyear and mainlained through 2054.

At this facility in Algeria, excess CO, is removed from natural gas for injeitinnunderground.

1 8 ENVIflONMENT DECEMBER 2004

A multiple-wedge approach to CO,policy will provide common ground andfoster consensus on mitigation policy.Most advocates of particular wedgesagree that it is too early now to settle onjust a few "winner" strategies, that therelative attractiveness of strategies willdiifer from one region to another, thatenvironmental problems associated withscale-up ought to be investigated, thatsubsidy of early stages is often merited,and that choices among mature alterna-tives should be determined mostly bymarket mechanisms. Framing the climateproblem as one requiring ihe parallelexploration of many stabilization wedgesmay help broaden the political consensusfor early action.

Robert Sotiilow is a profess«r in the Department ofMechanical and .•Aerospace Engineering at PrincetonUiiiversiiy. New Jersey, and eti-directiir ol" the CarbiiiiIniliaiive. a lO-year. universiiy-widc research programwithin the Princeion Fnvimnmenial Institute, The ini-tiative, spunsered hy BP and Ford, explores the sci-ence, technology, and poliey dimensions of global car-bon mitigation, .Socotow's current research focuses onglobal carbon management and mitigation and energyand environmental technology and policy. He is aconiributing editor of Emironmem and may bereached at iocolowt^prlnceton.edu. Roberta Hotinskiis an informaiion officer for the Carhon MiiigationInitiative. She oversees communiealion of the initia-tive's research results lo corporate spongers, theresearch community, the media, and the general pub-lic. Her previous research focused on paleoceanogra-phy and ocean biogeochemical cycles. She may bereached at (609) 2.'!8-7253 or via e-mail at hotinski©princeion.eiiu. Jeflery B. Greenblatt is a research staffmember at Princeton University. His research interestsinelude mixieiing of global energy systems, windenergy, ihe ocean carbon eyele. and population. Hemay be reached at 1609) 258-7442 or via e-mail atjgreenhl@princeton.edu, Stephen Pacala is the PetrieProfessor of Biology ai Prineeton's Department ofEcology and Evolutionary Biology and co-direcior ofthe Carbon Mitigaiion Initiative. Hi.s research focuseson the processes ihat govern ecological communities.the interplay between communiiy and eeosystem-level processes, and ihe interactions between theglobal biosphere and climaic. Pacala is currentlyworking on a new model of the terrestrial biosphere.He may be reached at pacala@princeton.edu. Detailsof calculations given here and more complete refer-ences can be found in the paper S. Pacala and R.Socolow, "Stabilization Wedges: Solving the ClimaieProblem for the Next .W Years with Current Technolo-gies." Science, 13 August 2004, 968-72. available atthe Carbon Mitigaiion Initiative Web site,http://www.pri nceton.edu/-cnii.

NOTES

I. C. D, Keeling and T. P. Whorf. "AtmosphericCO, Records from Sites in the SIO Air Sampling Nei-work," in Carbon Dioxide Information Analysis Cen-ter. Trends: A Compendium tifDutii on Global Change{Oak Ridge. TN: Ridge National Laboratory, 2000),

2. S. Pacala and R. Soeolow, "Stabilization Wedges:Solving ihe Climate Problem for the Next 50 Yearswith Current Technologies." Science. 13 August 2004.96K-72.

3. R, Socolow. S. Pacala. and J. Creenblatt."Wedges: Early Mitigaiion with Familiar Technology."to be pubh-shed in the Proceedings ofGHCT-7. the lihtnieniuiiimal Cunfererice on Greenhouse Gcif ConlmlTechnology, Vancouver, Canada. September 5-9. 2004(forthcoming, 2004),

4. U, Cubasch ei al., "Piojeclions of Future ClimateChange." in J, T. Houghton ei al.. eds., Climaie Change2t)l)l: The Scieniific Biisi.\ (Cambridge. UK: Cam-bridge University Press. 2001). 525-82; and J, Anile etal,. "Ecosystems and their Goods and Services." in J. J.McCanhy et a!,, eds.. Climaie Change 2001: Impacts.Adaptation, and Viihiembility iCiunbridge. UK; Cam-bridge University Press, 2(^)11, 235-342.

5. B. C. O'Neill and M. Oppenheinier, '"DangerousClimate Impacfi and the Kyoto Protocol," Science. 14June 2(K)2. 1971-72.

6. Inteniational Energy Agency (IEA), World Ener-gy OuiliHik 2(X)2 I Paris: Organisation for EconomicCo-operation and Development/IEA. 2002), http://library.iea.org/dtitw-wpd/Texibase/nppdf/siud/02/weo2002^1.pdf,

7. Pacala and Soeolow, note 2 above,

8. IEA, note 6 above,

9. IEA. note 6 above.

10. H. Gcller. Energy Revolution: PolUii".for u Sus-tainable fi((«n: (Washington. DC: Island Press. 2003);and M. A. Brown, M. D. Levine. J. P. Romm, A. H.Rosenfeld, and J. G. Kwimey, "Engineering-EconomicSludies of Energy Technologies to Reduce GreenhouseGas Emissions: Opportunities and Challenges," Annu-al Review of Energy and ihe Emininment 23 (1998):2 87-385.

11. World Business Council for SustainaWe Devel-opmeni. Mobility 2030: Meeting the Challenges toSustainability-. Full Report 2004 (Geneva. Switzerland;World Business Council for Sustainable Developtnent.2004), http;//www, wbcsd.org,

12. Pacala and Socolow. note 2 above.

13. K. Blok et al., "Technological and EconomicPotential of Greenhouse Gas Emissions Redueiion," inB. Metz, O, Davidson. R. Swan, and J. Pan, eds.. Cli-mate Change 2001: Mitigaiion (Cambridge. UK: Cam-bridge University Press. 2001), 167-299,

14. Paeala and Soeoiow, note 2 above.

15. Pacala and Socolow. note 2 above.

16. See M. J. Pastjualetti, "Wind Power: Obstaclesand Opportunities," Envinmment, September 2004,22-38.

17. Pacala and Socolow. note 2 above.

18. IEA, Biofuels for Transport: An InternationalPerspective (Paris: IEA, 2004).

19. Pacala and Socolow; note 2 above,

20. Paeala and Soeolow. note 2 above,

21. Kauppi et a!,, "Technological and EconomicPotential of Options to Enhance. Maintain, and Man-age Biological Carbon Reservoirs and Geo-engineer-ing." in Met/. Davidson. Swart, and Pan. noie 13above, pages 3Oi-^3.

22. Pacala and Socolow, note 2 above.

23. World Resourees Institute. Building a Safe Cli-imite iWashingion. DC: World Resources' Institute.I9K8).

24. Pacala and Socolow. note 2 above.

25. Pacala and Socolow: note 2 above.

26. Paeala and Socolow, note 2 above.

27. G. Mutiiti and B, Diss, "Carbon Injection: AnAddict's Response lo Climate Change," The Ecologtsi.22Oe!ober200l.

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HP Statistical Review of World

Energy, by Hiilish IVlrolcuni;

stibsL'ct ion ,du .Vaicgory ld=95&ui)nlcntld=2(H)648()

Internalional tJiergy Annual 2(Hil.

by the HiKTgy Inlbmiation

Adniiiiistnlidii; http://www.ci;i.di)c

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by the Kncrgy Inlumialiun Agency;

iiidex.htnil

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Conference on Greenhouse Gas Con-

tivl Technologies: 14 October. 2002.

Kyoto, Ja/Hiu. edited by Johti Gale and

Yuiclii Kaya; hltp://www.ieagiren.org

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by the liiletnalicinal Energy Agency;

littp://librar>'.iej,()rg/dblw-wpd/

TcxI basc/n|ipd t/stud/l)2/

wco2t)()2_l,pdi'(by subsLTiplion)

Key World Energy Statistics, by llie

lnlemalional Energy Agency;

hUp://www,ic;i.(H"g/dbtw-wpd/htK»kshop/add.aspx .'id= 144

hind Use, Ixmd Use Change and

Forestry, edited hy RttK'rt T, Wjt.snn

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i |x;c/land_iisc/iiidcx Jit in

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mate Change 2fH)l, by the Intergnv-

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ios, by Ihe lnlci"goveniinenlal Panel on

Climate Chirngo; htlp;//www.grid:i.tn)/

Lliinale/i|x:c/L'inissioii/iiide\.hlni

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ties. Costs. Barriers, and HAD Needs.

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VOLUME 46 NUMBER 10 ENVIRONMENT 19