The Econmist - USA (2021-10-30)

30 Special report Stabilising the climate TheEconomistOctober30th 2021

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pre­industriallevels—iftheystabiliseatall.

Thealternativetothisgameofchickenwouldbetomeetthe

Paristemperaturelimitsthroughothermeans.Solargeoengineer­

ingisanapproachtotheclimatethatconcentratesnotonmaking

iteasierfortheEarthtocoolitself,asremovingcarbondioxide

does,butstoppingit fromwarmingsomuchinthefirstplace.The

wayofdoingthiswhichhasbeenstudiedinmostdetail,albeital­

mostentirelyinmodels,istocreatea thinlayerofreflectivepart­

iclesinthestratospherethatreflectssunlightbackintospacebe­

foreit warmsthesurface.Studiessuggestthat,forgoodorill,such

a schemecouldbeimplementedbya relativelysmallfleetofpur­

pose­builtaircraft.

Theseideashave,forunderstandablereasons,longbeenmar­

ginalisedinpolicycircles.Theyreekofhubrisandthepotential

forunintendedconsequences.Andif,byprovidinganotherwayof

limitingtemperaturerises,theyreducetheperceivedurgencyof

curbingemissions,theymightweakenorevenstallthecommit­

menttoemissionsreduction.

Thatwouldbedisastrous.Thoughithastheoppositeeffecton

temperature,thecoolingofferedbysolargeoengineeringisnot,in

physicalterms,anexactcounterofthewarmingcreatedbygreen­

housegases.Onedifferenceisseenintheworld’shydrologicalcy­

cle;solargeoengineeringtendsto suppressprecipitation.The

moretheworldcametorelyonit,themorethisandothermis­

matcheswouldbecomeharmful.This,alongsidethefactthatit

doesnothingaboutoceanacidification,isa strongpartoftherea­

sonwhyresearcherslookingseriouslyatsolargeoengineering

neveradvocateusingit insteadofmitigation.Thosenotturnedoff

byit completelyseeit asa possiblecomplementtomitigation,not

asanalternative.

Inthisitisverylikenegativeemissions—onereasontheyare

sometimescalled“carbongeoengineering”.Thewaya solar­geo­

engineeringcapabilitymightreducetheincentivetocontinue

withemissionsreductionissimilartothewayexistingnegative­

emissionscapacitymightwork.Andinbothcasesthatreduced

ambitionmightwellcomeabouteveniftheproposedgeoengi­

neeringdidnot.

A crucialdifferencebetweenthetwo,though,isthecostofin­

stigatingthem.Itseemslikelythatputtinga veilintotheatmo­

spherewouldbecomparativelycheap(inthetensofbillionsof

dollarsa year,perhapsevenless),thoughtheexternalitiesnotin­

cludedinthecostmightbehigh.Anotherdifferenceisthatnega­

tiveemissionswouldaffecttheclimateinmoreorlessthesame

waywhoeverundertookthem;theworld’scarbon­dioxidelevelis

whatitis.Differentsortsofsolargeoengineering,though,would

havedistinctlydifferentregionaleffects.

Designforliving

If the world as a whole were able to design a solar­geoengineering

scheme, studies suggest it could come up with one that provided

climate  benefits  to  almost  everyone  and  serious  problems  to  al­

most  nobody.  A  plausible  way  to  use  such  an  optimal  scheme

might be to offset the temperature rise caused by overshooting the

carbon budget. That would provide a sort of breathing space to al­

low  the  excess  CO 2 to  be  drawn  down  more  slowly  and  cheaply

than would be necessary if its warming effects were actually being

felt. A comparatively gentle acceleration of chemical weathering,

rather  than  a  huge  investment  in  dacor  other  schemes,  might

prove  sufficient.  As  those  measures  slowly  wore  the  overshoot

down  the  solar  geoengineering  could  be  reduced.  When  the  CO 2

level was low enough it would  be phased out completely, leaving

behind a stable climate.

But  the  world  as  a  whole  might  not  get  to  choose  the  wisest

path. A small group of countries, or even a single large one, could

undertake  a  solar­geoengineering  scheme  unilaterally.  Such  a

club  would  be  likely  to  optimise  its  own  interests  rather  than

those  of  the  world.  It  might,  for  example,  choose  to  cool  some

places to a degree that, because of geoengineering’s effects on the

water cycle, risked desiccating others. That might lead to resent­

ment, rancour or reprisals.

Nor  would  any  given  set  of  solar  geoengineers  be  sure  to  get

things  their  own  way.  The  late  Marty  Weitzman,  a  pioneering

economist  of  climate  change,  pointed  out  that  though  emission

reductions  (and  by  implication  negative  emissions),  because  of

their  cost,  have  a  free­rider  problem,  solar  geoengineering,  be­

cause it looks cheap, has a “free­driver” problem. Where free­rider

problems lead to underprovision (countries are unwilling to com­

mit to cutting emissions when others do not, as 26 years of cops

has made clear) free­driver problems may lead to overprovision.

Solar geoengineering looks cheap enough that countries wanting

more of it can provide it unilaterally, whatever others think.

This  implies  that,  other  things  being  equal,  the  level  of  solar

geoengineering would be a trade­off between the amount that the

most enthusiastic countries wanted and the amount that the least

enthusiastic  would  endure  before  taking  decisive  action,  quite

possibly through force of arms. Another game of chicken. 

The  difficulties  involved  in  negative

emissions  and  solar  geoengineering  are

very different, and the second looks much

more unfamiliar and threatening than the

first. But in both cases the problem is fun­

damentally similar—and closely related to

the contradiction between global tempera­

ture  goals  and  national  emissions­reduc­

tion commitments at the heart of the Paris

agreement. The world has needs which can

be  agreed  on;  but  the  decisions  necessary

to meet those needs are made by countries

which differ in their interests, their capabilities and the amount of

persuasion  they  can  exert  or  resist.  The  responsibilities  may  be

common; the differentiation is endless.

Glasgow will show the degree to which national governments

are able to deliver progress in terms of the increased ambition of

their  ndcs,  the  realisation  of  long­promised  transfers  of  money

from north to south, and workable rules for the parts of the Paris

agreement  which  remain  sketchy.  The  progress  is  unlikely  to  be

spectacular, reinforcing the point that managing global issues like

the  climate  purely  through  national  lenses  is  impractical.  But

coming up with an alternative in which individual countries will

allow  the  interests  of  others  to  be  placed  above  their  own  is  im­

plausible. And if the world is to stabilise the climate at an accept­

able level, something will have to give. 

The climate crisis was brought about as part of the creation of a

new world economy. Coming throughitsuccessfully may well re­

quire a new world politics. Failingtodoso will be calamitous in

terms of politics and economics alike.n

It seems likely

that putting a veil

into the atmo-

sphere would be

comparatively

cheap