The Econmist - USA (2021-10-30)

26 Special report Stabilising the climate The Economist October 30th 2021

soughtcarbon­removalprojectstomeettheirnet­zeropledges,

theyfoundthatnature­basedprojectswerepricedat$5­50per

tonne.Buttherearethreeproblems.Oneisthatnotalloffsetting

schemesarewellrunorwellsupervised.InChilegovernmentsub­

sidieshelpedestablish1.3mhectares oftree plantationssince

1986—buta rulerequiringthatthisexpansionshouldnothappen

attheexpenseofnativeforestswasnotenforced.Asa resultthe

programme actuallyreducedtheamount ofstoredcarbonby

some50,000tonnes.

Asecondisthatoffsettingisunlikelytosolvedeeperissues.

Theairlineindustryhasstrongeconomicincentivestousefuelef­

ficiently,buttheyhavenotmadethewrenchingtechnological

shiftsrequiredtostopbuyingkerosene.Iftheindustrybuysoff­

setstomakeitsplanes“carbon­neutral”,asitplansthrougha

schemecalledcorsia, theefficiencyincentiveswillincreasefur­

ther.Butthatwillnotofitselfmakea post­keroseneworldmore

likely.ThatisonereasonwhytheScienceBasedTargetsInitiative,

a standard­settingcoalition,doesnotacceptoffsettingasa pathto

emissionreduction.

Thethirddrawbackislimitedcapacity.Thisfeelssurprising,

sinceinprinciplethescopefornature­basedsolutionscouldbe

verylarge.AteamofresearchersledbyCécileGirardinofOxford

Universityestimatesthata radicalcommitmenttotheideacould

seetheamountofCO 2 fromhumanemissionsabsorbedbythe

biospheremoreorlessdoubledby2025,from 10 gt a yearto 20 gt a

year,makinga realdifference.Evenmorewouldbepossible.Add

themeasuresdescribedbytheresearcherstoa trajectorywhich

wouldotherwiseleadto2°Cofwarmingandyouget1.8°C;a 3°Ctra­

jectorycomesdownto2.7°C.

Suchmassiveeffectscannotbeachievedthroughexpansionof

currentoffsettingschemes.TheOxfordplanwouldentailagricul­

turaltransformationaroundtheworld,anendtodeforestation

andtherestorationofnaturalecosystemsacrossroughly7mkm^2

ofEarth’ssurface—twicetheareaofIndia.Italsorequiresforests

and other ecosystemsto stay healthy. Unfortunatelyclimate

changeismakingthismuchharderbyincreasingtheriskoffire

andothernasties,suchasinsectinfestations.Ifnature­basedsol­

utionsweretogoaheadwithouta simultaneousefforttocurb

emissions,leavingtheworldtogoonwarmingregardless,carbon

storedinwoodandsoilcouldfinditswaybacktotheatmosphere.

Anotherprocessthatcouldbeco­optedismineralweather­

ing—reactionswithrocksthatuseupCO 2 dissolvedinwater.What

isgoingoninthebasaltunderHellisheiðiisa formofweathering

whichproducescalciumandcarbonateionsthatgoontoprecip­

itateoutascalcite.Rockweatheringalreadysoaksupa billion

tonnesofCO 2 a year.Increasetheareaavailableforitbygrinding

suitablerocksintodustandyouwillgetmore.DavidBeerling,a re­

searcherattheUniversityofSheffield,andhiscolleagueshavecal­

culatedthatspreading3.5bntonnesoffinelygroundbasaltover

700,000km^2 offarmlandeveryyear—that’s 50 tonnesperhectare

overanarearoughlyasbigasTexas—coulddoubletheweathering

rate,drawingdownanotherbilliontonnes.

Finda way

For weathering to work on a really large scale, though, turn to the

oceans, where geochemical manipulation could in principle store

trillions of tonnes of CO 2 . Increase the alkalinity of seawater—eg,

by  adding  lime,  an  oxide  of  calcium  used  in  cement—and  the

amount  of  carbon  dissolved  in  it  as  carbonate  atoms  increases.

That  shift  provides  room  for  more  CO 2 to  be  absorbed.  Unfortu­

nately  it  takes  some  700m  tonnes  of  lime  for  1gt  of  CO 2 —and  to

make the lime requires putting a lot of energy into heating lime­

stone in kilns which have to be fitted with ccs, since the process it­

self  gives  off  CO 2.  The  sheer  scale  of  the  carbon  drawdown  that

ocean alkalinisation offers makes such schemes worth consider­

ing. But they are at best a long­term possibility. Their costs would

be enormous, their effects on ocean ecosystems would need care­

ful monitoring and they would require international laws govern­

ing marine pollution to be renegotiated from the bottom up. 

A more plausible near­term approach to sucking down CO 2 in­

dustrially  is  to  fit  ccsto  power  stations  which  burn  recently

cropped  plants.  Because  the  carbon  in  those  photosynthesising

plants  was  recently  CO 2 in  the  air,  putting  what  is  released  by

burning  them  underground  is  in  effect  a  transfer  from  atmo­

sphere to crust. And because biomass energy with ccs(beccs) pro­

vides electricity as well as negative emissions it can be used to dis­

place fossil fuels, further reducing emissions. 

When  the  climate­and­economics  models  used  to  analyse

emission  pathways  first  began  to  be  applied  to  negative  emis­

sions, it was by adding beccsto them. This gave the technology a

first­mover advantage in subsequent discussion in theipcc, at the

Paris summit and elsewhere. That it has been more discussed than

other approaches, though, does not make beccsbetter. Its large­

scale deployment requires vast amounts of land be turned over to

growing energy crops; in some estimates an area equivalent to up

to 80% of that now used for food crops would be needed. 

This is what gives purely technological dacschemes like Orca

their  appeal.  The  installation  is  designed  to  tuck  away  48,000

tonnes of CO 2 over its 12­year life. A tree plantation in a temperate

climate  capable  of  soaking  up  that  much  would  have  to  cover

about 400 hectares. Orca is just a small hangar and four pairs of

shipping­container­sized collector units on stilts; a plant the size

of a small school doing the work of a forest

as  big  as  a  fair­sized  town.  And  not  only

does  dacrequire  less  land  than  beccs.  It

can  also  use  land  that  agriculture  can’t:

witness  Hellisheiði’s  barren  boulders  and

moss.  Sunny  deserts  far  from  anywhere

where  the  process  can  be  powered  by

cheap solar panels would do fine.

The problem is cost. Climeworks says it

costs between $600 and $800 to separate a

tonne  of  CO 2 from  the  Icelandic  air  and

store  it  away,  though  it  may  do  better  in

larger plants. It sells customers the assurance that a tonne of CO 2

has  been  turned  to  stone  at  their  behest  for  over  $1,100.  Because

Orca is exciting and its capacity small, these offsets have more or

less sold out. But when non­novelty offsets sell for a hundredth of

the price it doesn’t look like a very scalable business. One serious

rival, a Canadian firm called Carbon Engineering, says it can offer

offsets at $300 a tonne when it gets its 1m­tonne­a­year plant oper­

ating in Texas by 2025. That fits with an analysis in an academic

journal by the company’s founder, David Keith, that puts the costs

of the technology it is using in the $90­240/tonne range. 

Neither company focuses on offsetting as a core business. Car­

bon Engineering, which is partnered with Occidental Petroleum,

an oil firm, plans to pump the CO 2 it isolates in Texas into oilfields

to squeeze out oil that is otherwise reluctant to flow. Because the

CO 2 stays  underground,  the  oil  will  count  as  a  low­carbon  fuel

which can be sold at a premium, thanks to regulations in Califor­

nia. It is also looking at combining the CO 2 it captures with hydro­

gen to make synthetic fuels—a business Climeworks is keen on. A

startup called Prometheus Fuels claims to be able to do this profit­

ably with a cheaper form of dac, but has yet to provide details. 

Such fuels may help with decarbonisation in some of the plac­

es electricity cannot reach, such as aircraft flying over oceans. But

the greatest potential for daclies in changing the overall carbon

budget. If applied on a scale close to that of today’s natural­gas in­

dustry  it  could  in  principle  create  space  in  the  atmosphere  for

hundreds of billions of tonnes of further emissions as the world

A dac plant the

size of a small

school can do the

work of a forest

as big as a fair-

sized town