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OUP UNCORRECTED PROOFS


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A N D R E W T. G U Z M A N

1

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3Oxord Universiy Press is a deparmen o he Universiy o Oxord.

I urhers he Universiys objecive o excellence in research, scholarship,and educaion by publishing worldwide.

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Oxord is a regisered rademark o Oxord Universiy Pressin he UK and cerain oher counries.

Published in he Unied Saes o America by

Oxord Universiy Press198 Madison Avenue, New York, NY 10016

Andrew . Guzman 2013

Al l righs reserved. No par o h is publicaion may be reproduced, sored in arerieval sysem, or ransmited, in any orm or by any means, wihou he prior

permission in wriing o Oxord Universiy Press, or as expressly permited by law,by license, or under erms agreed wih he appropriae reproduc ion r ighs organ iza ion.

Inquiries concerning reproducion ouside he scope o he above should be sen o he Rig hsDeparmen, Oxord Universiy Press, a he address above.

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v

Foreword vii

1.KerPlunk!and Plane Earh 1

2. A Message rom Climae Scieniss 19

3. Deeper Waers 54

4. A Tirsy World 97

5. Climae Wars: A Shower o Sparks 132

6. Climae Change Is Bad or Your Healh 172

7. Where Do We Go rom Here? 211

Notes 231Index 251

C O N T E N T S

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vi i

Climae change is a subjec ha is a once amiliar and myserious. I would behard o nd an adul who is unaware o he issue, ye discussions o he subjecare so ull o misinormaion and uncerainy ha mos o us are no sure whao believe. Scieniss who sudy he climae know a grea deal more han hepublic realizes, and heir quesions abou climae change are no a all he onesha seem o make he news or ge included in poliical debaes.

Some o he conusion surrounding climae change can be explained by hecomplexiy o he science involved. Undersanding he workings o he earhsclimae is a massive ask ha remains a work in progress in even he mossophisicaed scienic circles. Ta said, public debaes abou climae and cli-mae change ofen do an excepionally poor job o presening and consideringwha we do know abou he science. Tis means ha while climae change is acriical subjec or scieniss, hey are no he only ones who should be, or musbe, alking abou i.

I am cerainly no a scienis. I am rained as an economis and a lawyer,and I work as a law proessor. Much o my career has been spen hinking andwriing abou how he inernaional legal and poliical sysems work (or, some-imes, don work). A ew years ago, I sared o hink abou climae change,in par because i is perhaps he single greaes inernaional challenge o hiscenury and beyond. How could I be a suden o he inernaional sysemwihou examining his criical issue? Tis seemed a litle like being an experon errorism in 2001 and ye ignoring Al-Qaeda.

When I sared working on climae change, I had no inenion o wriinghis book. Te plan was o produce academic aricles, which are, ulimaely, hemain currency by which hose in my proession are evaluaed. Bu as I workedon he subjec, I became more and more convinced ha he mos imporanhurdle o meaningul acion on climae change is he ac ha people have nocome o accep how serious i is. A grea deal has been writen and discussed

F O R E W O R D

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Foreword vi ii

abou he subjec, bu he basic message o how changes in he worlds climaewill affec virually every human being on he plane has no been commu-nicaed effecively. Unless and unil regular people undersand he serious-

ness o he hrea, i is unlikely ha our poliicians will make serious efforso respond.

Tis pushed me o invesigae more specically how climae change willaffec all o us. Raher han ocusing on debaes abou wheher climae changeis real or geting disraced by he (imporan) deails o wheher emperaureswill rise by 2 C or 3 C or 4 C, I ried o undersand more clearly wha wouldhappen o people on he ground. Over ime, I ound mysel puting ogehera sory abou how a seemingly modes increase in emperaure o a couple odegrees is enough o make he seas rise, ood producion collapse, naions go

o war, and disease spread virually unchecked. I was becoming clear, in a wayha I el was no widely appreciaed, ha he consequences o hese changeswill be measured in he hundreds o millions o lives, i we are lucky. I we areunlucky, perhaps billions.

Tis book, hen, is an atemp o ell his sory. I represens a gahering o awide range o scienic inormaion and sudy o human sysems and humanbeings. I am orunae o work in an insiuion and a conex ha no onlyallow me o do his work bu also encourage i. o alk sensibly abou howclimae change will affec human beings requires an inerdisciplinary excur-

sion ino climae science, economics, poliics, inernaional relaions, andmuch more. Nobody can be an exper in everyhing, so i ineviably requiresworking ouside ones comor zone. In many pars o a research universiy,his sor o cross-cuting work is discouraged and branded as diletanism. Inairness, his relucance o work across disciplines or o venure ino opics inwhich one is no exper is par o wha makes he bes scieniss good a heirjobs. I also offers a parial explanaion or why climae scieniss, who knowmore abou climae change han anyone else, ofen rerain rom explaining heconnecions beween heir own research and human well-being. A similar, i

perhaps more exible, se o norms makes i diffi cul or social scieniss suchas economiss and poliical scieniss o use he predicions o climae scien-iss as a saring poin o explain how people will be affeced. Te connec-ion beween he scienic oupus and he real-lie impacs are oo complexo analyze ully wihou exposing onesel o he charge o being overly specu-laive. Tere are good reasons or his commimen o academic rigor, and Iam cerainly no rying o criicize hem here. Te problem o climae change,however, is a once scienic, economic, poliical, social, and insiuional.I canno be ully undersood wihou going beyond he normal boundaries

o individual academic disciplines and wihou acceping a cerain degree oinormaliy in he discussion.

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Foreword ix

In wriing he book, I developed an ever deeper appreciaion or hecomplexiy o he climae-change challenge. Te ask o presening an accu-rae and reasonably general accoun o how humans will be affeced by climae

change was even more diffi cul han I anicipaed. I relied on my experience inwriing abou and sudying human and legal insiuions and sysems. I urnedo my raining in economics o undersand he consequences o climae changeor resources issues such as he ood supply or access o waer. Perhaps morehan anyhing, I drew on years o academic work spen evaluaing and challeng-ing heories and argumens as I ried o exrac rom he enormous amouns oavailable maerial he mos reliable predicions abou he earhs naural andhuman sysems. Even wih my bes effors, I am cerain ha I have only scrachedhe surace. Te implicaions o a changing climae are ar-reaching, and I have

ye o nd a eld o human endeavor ha wil l no be affeced. Perhaps ha is hemos imporan message o he book. Climae change will urn he world as weknow i upside-down. Each chaper o he book presens one way in which i willdo so and considers some o he consequences or he human race.

I canno imagine compleing a projec o his size and scope wihou assis-ance rom many people. From he very earlies sages, when wriing a bookwas no more han a disan possibiliy, I have had he bene o ousandinghelp. Working wih young, energeic, and brillian sudens is one o he greajoys o an academic job, and his projec gave me he opporuniy o do so in a

more concenraed way han a any oher ime in my career. Law sudens andundergraduaes who made major conribuions o he book include Brenda Au,Leslie Bryan, Sarah Cohen, Jalle Daa, Mat DalSano, Earh Duare-ratner,Karis Anne Gong, Ryan Lincoln, Scot Lindlaw, Holly Mariella, ElaineMeckensock, Andrew Roberson, Sabrina Solange, Sophie urell, LindsayWaler, and Andrew Wang. I also received valuable ediing assisance romChrisine Sinnot.

For nancial assisance, I am graeul o Berkeley Law School; he Ceneror Law, Energy, and he Environmen; and he Undergraduae Research

Apprenice Program a he Universiy o Caliornia, Berkeley.My academic colleagues endured many hours o discussions and ques-

ions, including ime spen educaing me on issues I knew litle abou. Teyalso provided invaluable commens on earlier drafs and an academic commu-niy wihou which his work would have been impossible. I canno name allo hose who were o help, bu a ew o he mos imporan were Jeff Aik, EricBiber, Dan Farber, Jody Freeman, Deborah Lambe, Kaerina Linos, imohyMeyer, and John Yoo. For his and every projec I have underaken or manyyears, I am indebed o my assisan, Jennier Zahgkuni, who no only makes

he enire enerprise run smoohly bu also serves as he las line o deense orprooreading and ediing.

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Foreword x

Oxord Universiy Press and David McBride have provided wonderulsuppor hroughou he process. My agen, Susan Schulman, has guided mehrough he publishing hicke wih grace and effeciveness.

My greaes debs are personal ones: o my parens, Danilo A nonio Guzmanand Carole Guzman, whose inuence is palpable in anyhing I accomplish; omy wie, Jeannie Sears, whose riendship and love are he oundaion o all omy achievemens; and o my children, Nicholas and Daniel, who inspire me ohink abou he uure and who will always be he greaes hing I have done.

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1

1

KerPlunk!and Planet Earth

We have already shot ourselves in the foot. Our immediate problem is

not to shoot ourselves in the head.Rober Srom, Hot House1

Tis books lesson is easy o sae and is worh making explici up ron. Aswe make decisions abou how o respond o climae change, we mus no losesigh o he very real possibiliy ha i will have a caaclysmic impac on heway we live. I do no mean ha here will be serious economic effecs or hahere wil l be modes numbers o addiional deahshese impacs are alreadyhappening. I mean ha we should be worried ha climae change may kill ens

o millions or hundreds o millions and severely disrup he lives o perhapsbillions.Tis al l sounds alarmis, and I suppose i is. Bu ha is because we should be

alarmed. Nobody knows wih cerainy (or wih grea condence, or ha ma-er) exacly wha he impac o climae change will be, and I am no excepion.We do know some hings, however, and hey are no comoring. We know hahe expeced changes in our climae are signican, and he projecions seemo grow more dire wih each passing year. We know ha he oceans are risingand wil l coninue o do so or a leas he nex cenury, causing deadly ooding

in some pars o he world. We know ha agriculure will be disruped as em-peraure and precipiaion paterns change and as mounain glaciers mel. Weknow ha he sresses generaed by climae change will increase ensions inmany pars o he world and are likely o rigger violen conic. We know harising emperaures will increase he incidence o disease and illness aroundhe world. We know ha even i he changes urn ou o be on he mild end oexising projecions, here wil l be grea sufferingand ha is i we are lucky. Iae is unkind and climae change is on he severe end o our bes predicions,hen we are all in deep, deep rouble.

Wheher or no we are lucky, he consequences o climae change willbe el by billions o people around he world. Tis is obvious, bu i is also

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ofen ignored in our public debaes. We alk abou environmenal changes,scienic evidence, ice shees, ocean levels, and droughs, bu we do noalways ge around o alking abou people. In wriing his book, I have ried

hard no o all ino his amil iar rap. I have writen i wih he human impaco climae change in mind. Te book is abou how people will be affeced byclimae change, raher han how science and climae inerac.

A ocus on he human cos o climae change is criical, because ha is whawill persuade people o ac. Scienic debaes are imporan, bu acknowl-edging he science is no, by isel, enough o ge our poliical sysems oreac. Discussing possible policy responses o climae is imporan, bu heseresponses will happen only i people are persuaded ha somehing mus bedone. I am convinced ha he mos imporan barrier o a sensible and deer-

mined response o climae change is a lack o public undersanding abou heways in which our lives and he lives o our children will be affeced. Hearingha global average emperaures will increase by a couple o degrees is noenough or mos people o suppor aggressive governmen acion in response.Recognizing ha his change in climae will lead o ens o millions or hun-dreds o millions o deahs and ha i will harm billions o people, on he oherhand, may moivae people o demand acion rom heir poliical leaders.

Tere is no way o avoid a discussion abou science enirely, bu I have riedo keep ha maerial o a minimum. I ask ha you bear wih me or a ew pages

in his inroducion as I address he predicions o scieniss jus enough o gehe ball rolling. Chaper 2 hen explains he basic science o climae change,because some undersanding o he science is necessary o appreciae he con-sequences or humans. Te remainder o he book, however, is ocused on howhuman beings, our communiies, and our social srucures ace a hrea unlikeany we have ever seen beore.

Tere is no way o hink abou he uure wihou predicions, and so hereis no way o hink abou he challenge o climae change wihou predicionsabou he worlds uure climae and is consequences. You can hink o scien-

iss making predicions abou he likely impac o climae change he sameway you hink o making bes on he roll o wo six-sided dice. I you have obe on he oucome o a roll o he dice, you should be ha hey will add upo seven. Tis is he mos likely o all oucomes. You will, however, be wrongmuch more ofen han you are righ. Tere is one chance in six ha he roll wil lbe a seven, so you will be wrong ve ou o six imes. W hen climae scienissmake a predicionor example, when hey predic ha he earh will warmby 2 C during his cenur yhey are making a predicion he same way youare when you are beting on he dice. Ta is, hey are offering heir bes guess,

even hough hey are more likely o be wrong han righ. Tis is no a crii-cism o he science or he scieniss bu raher a reecion o he complexiy o




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K e r P l u n k !a n d P l a n e t E a r t h 3

he earhs climae sysem. Te bes scieniss are no he ones who ge i righall he imehere are no scieniss like habu raher he ones who havehe bes undersanding o he probabiliies involved. Tese scieniss will ge i

righ more ofen han anyone else, bu hey will sill be wrong a lo.Te ac ha we do no know exacly wha he uure holds does no, unor-

unaely, relieve us o he need o make policy decisions. Should we ax carbonemissions? Implemen a cap-and-rade scheme? Ener ino an inernaionalagreemen on miigaing greenhouse-gas emissions? Inves in geoengineeringprojecs o ry o cool he earh? o alk sensibly abou any o hese opionsorany o he dozens o oher issues relevan o climae changewe need o akeour bes guess abou wha he uure holds, even i our bes guess is wrongmore ofen han i is righ.

Forunaely, we have some ools or making policy in areas, such as climaechange, where here is a lo o uncerainy. Knowing ha a seven is he moslikely resul when you roll he dice is useul or gamblers, even hough hapredicion is wrong more ofen han i is righ. In a similar way, he bes guesso scieniss abou wha climae change will bring is useul or poliical leadersdeciding wha policies o implemen.

Human conduc is causing he earh o warm, and we have o decide wha odo abou i. We are locked ino playing a game o dice wih he world and wihhumaniy. I here was ever a ime when we could have chosen no o play, i is long

pas. Te challenge we ace, hen, is no deciding wheher or no o play bu, raher,how o place our bes. Should we enac policies ha are a litle less expensive bucause more warming in he uure, or should we op or policies ha cos moreoday and cause less warming laer? Eiher way, we are placing a be on how heclimae will reac o our acions and how wehumaniywill be affeced by hechanges in he climae. And we are playing wih he highes possible sakes.

Tese quesions always bring us back o he scieniss or answers. Scienisscan ell us which oucome is, in heir view, mos likely. Tere are, o course,disagreemens wihin he scienic communiy. Disagreemen is a he very

hear o scienic inquiry. Bu despie he ever-presen debaes and compeingclaims, scieniss have reached a broad consensus on climae change ha issuffi cien o le us make sensible decisions.

So, jus as he gambler knows ha he mos likely roll o he dice is a seven,scienic research has given us some sense o he mos likely changes o heearhs climae. We also know a lo abou he likelihood ha he changes willbe greaer or less han expeced and abou how serious he impacs will be iexising climae predicions prove o be wrong. Tis is essenial inormaion iwe are o make responsible choices abou how o respond o a warming world.

Given wha we know abou how he climae is likely o change, and evenwih he uncerainy surrounding ha inormaion, we need o consider how




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hose changes o our climae will affec he way we live. o undersand howour lives will be affeced, i is no enough simply o noe he ways in which heclimae will change or even how hose changes will affec he naural world

around us. We need o have some appreciaion or how we, ourselves, will beaffeced. How will our lives be changed? How will we acually eel he con-sequences o climae change? Climae scieniss can ell us only a small paro ha sory. Tey know somehing abou how our environmen will change,bu we also wan o know how humaniy will reac, how our inrasrucurewill hold up, how ood supplies will be affeced, how our healh will be com-promised, and more. In shor, we need a sense o how our way o lie will bechanged along wih he climae.

Ideally, we would no only wan o know how our lives will be affeced by he

mos likely consequences or he mos likely changes o he climae. We wouldalso wan o know how we will be affeced by all o he possible oucomes and,o course, have a sense o how likely each one is. Te chances o even he moslikely impacs, afer all, may be no greaer han he likelihood ha a seven willappear when you roll wo dice. In ligh o he subsanial uncerainy involved,we do no have he luxury o assuming ha he mos probable oucome willacually come abou. Te gambler cerainly wans o know wha happens whena seven is rolled, bu he also needs o know wha happens i some oher numbercomes up.

Despie he desire o know abou all possibiliies, I have chosen o look ajus one o he poenial oucomes, because doing so helps o make my messageclearer. I means ha you do no have o ry o keep rack o a whole range opossibiliies as you read his book. In addiion, ocusing on jus one scenarioallows me o discuss he coming challenges in more deph, somehing ha isnecessary o ge a sense o how human lives wil l be affeced.

Te quesion, hen, is wha degree o climaic change I should ocus on. II assume a relaively large change, I risk exaggeraing he effecs o climaechange. Te book would be a cauionary ale bu would no describe he mos

likely se o evens. I I assume oo modes a change in he climae, I will beundersaing he likely harms and providing an overly, and perhaps naively,opimisic picure o wha he uure holds. You migh hink ha he bes hingo do would be o pick he mos likely oucome. Tis presens wo problems.Firs, alhough i is he mos likely, ha predicion is also quie likely o bewrongjus as predicing a seven on he roll o wo dice is l ikely o be wrong.More imporan, nobody knows jus wha he mos likely oucome is.

Wih all o ha in mind, I have chosen o ocus on an oucome ha is wihinhe range o likely oucomes based on curren predicions bu ha lies near

he botom o ha range. Te book will operae on he assumpion ha wecan expec an increase in emperaure o 2 C by he end o his cenury. Tis




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is a very conservaive choice, as I explain more ully in chaper 2. I oped ora airly low esimae or a couple o reasons. Firs, as I already menioned, mygoal wih his book is o convey he seriousness o wha climae change will

do o humaniy. I urns ou ha even i we make a airly opimisic assump-ion abou how he climae will change, he effecs will sill be enormouscerainly large enough or me o make my poin. Second, one o he hingsI mos wan o avoid is making an overly pessimisic assumpion abou heclimae. Doing so would undermine he orce o he book. I do no wan odiscuss uure evens ha are merely possible. I wan o discuss evens ha arelikely. Assuming a rise in average emperaures o 2 C allows me o do so.

Even wih a conservaive assumpion abou how he climae will change,here is, o course, some chance ha he acual oucome will be somehing

less. I is possible ha he aes will smile upon us and hings will urn ouo be beter han I have assumed. I cerainly hope ha is he case. No onlyha, bu I will be he rs o admi ha when we hink abou how o respond,we have o ake ino accoun boh good and bad oucomes. Les reurn o heexample o rolling wo dice. Assuming an increase in emperaures o 2 C isa litle like invesigaing wha will happen i we roll a six. A six is possible, bulos o higher oucomes (analogous o larger changes in emperaure) are alsopossible. Some lower oucomes are also possible, bu hey are less likely. Techances o roll ing a six or higher are abou 72 percen, so by choosing a number

a litle less han he mos likely, i is possible o capure mos o he possibleoucomes.

By making a conservaive predicion, hen, I have rigged he game againsmysel. Te oucomes I describe are less severe han wha I hink is mos likely.As he res o he book shows, however, hey are sill enormous. Choosing anincrease o 2 C does no, o course, eliminae he uncerainy surroundingclimae change. I is sill possible ha we will see less han 2 C o warming.I would be a misake, however, o ake much comor rom his ac. In addi-ion o my inenional choice o a modes emperaure increase over he nex

cenury, here are wo reasons i would be oolish simply o hope or a bi ounlikely good orune wihou aking acion in response o he more likely andmore righening alernaive oucomes.

Firs, our experience o dae has been ha he scienic communiy hasconsisenly underesimaed he speed o climae change. In 2008, or exam-ple, climae-change exper Nicholas Sern saed ha emissions are growingmuch aser han wed hough, he absorpive capaciy o he plane is less hanwed hough, he risks o greenhouse gases are poenially bigger han morecauious esimaes, and he speed o climae change seems o be aser.2A di-

eren sudy ound ha carbon-cycle eedbacks could signicanly acceleraeclimae change over he weny-rs cenury.3 Alhough pas perormance




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does no guaranee uure resuls, as nancial advisers say, one canno help buge he sense ha scieniss are playing cach-up in he climae-change game.Humaniy has never winessed such rapid changes o our climae, so here is

no preceden o guide science. Add o his he ac ha he climae is a sag-geringly complex sysem wih a seemingly endless number o inuences allineracing wih one anoher. o give jus one simple example, because cloudscan boh rap hea and reec sunligh back ino space, hey cause warming ohe plane in some circumsances bu cooling in ohers. Furhermore, we dono undersand how clouds orm and dissipae. You can see how diffi cul i is oincorporae his one variable ino climae models. Overall, I hink i is amaz-ing ha science has done as well as i has in coming o grips wih he problem.Neverheless, I canno help hinking ha here remain so many orces push-

ing us oward a warmer world ha we may sill be underesimaing wha iscoming.

Second (and more imporan), he climae-change cos curve is, aseconomiss pu i, convex. In plain English, his means ha coss rise morequickly as he earh warms. So i a emperaure increase o 1 C causes a cer-ain amoun o harm, an increase o 2 C wil l cause more han wice as muchharmperhaps a lo more han wice as much. Tis is imporan because,even i we conclude ha, or example, we can manage no only an increaseo 1 C, bu harm ha is wice as much, i does no necessarily ollow ha

we can handle an increase o 2 C. Te later may be much more han wiceas bad.

Tere are a lo o insances in everyday li e in which we encouner coss harise a an ever-increasing pace. Anyone who runs, swims, cycles, or paricipaesin any oher ype o exercise wih an endurance componen has experiencedhis siuaion. Suppose you go or a jog. As long as you do no choose oo as apace, running is iniially almos efforless. Afer a ime, however, you sar oeel some srain. I is no longer quie so easy, bu i is sill possible o mainainyour pace. As you keep running, he effor you have o exer increases. Te

rs en minues is easier han he second en minues, which is easier han hehird en minues, and so on. Unless you are an experienced disance runner(even or hese runners, he same holds rue, bu i may ake longer or hemo wear down), i will evenually become almos impossible o mainain yourpace or ye anoher en minues. And even i you succeed, he en minuesafer ha will be harder sill. A some poin, you will simply have o slow down;your body will be incapable o coninuing a your pace. I you keep running,even his slower pace will become oo diffi cul. Evenually, you will have osop; anoher en minues will simply no be possible. One can describe he

effor required o coninue running as a convex cos curve: as you run, i gesharder and harder o coninue.




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Figure 1.1 illusraes how he impac o climae change rises a an acceler-aing pace as emperaures increase. Suppose, or example, ha he expecedincrease in emperaure is 2 C. As indicaed in he gure, his corresponds

o a cerain level o impacs. Tese include impacs on he economy, healh,naional securiy, agriculure, and more. I he warming we acually experi-ence is somewha less han anicipaedi i is 1.5 C insead o 2 Cyoucan see ha he corresponding impacs are reduced. I, on he oher hand, cli-mae change is more severe han expeced and he change in emperaure is2.5 C, he impacs are greaer. Te key hing o noice is ha he differencebeween he impacs el a 1.5 C and a 2 C is much smaller han he differ-ence beween 2 C and 2.5 C.

Because he harm rom climae change increases a an acceleraing rae

as emperaure changes, he difference beween wha is prediced and whaacually happens is much bigger i we underesimae climae change han i weoveresimae i. Even a small underesimaion o he changes coming o ourclimae migh cause us o overlook enormous impacs. I is beter o ace herealiy now ha hese errible evens migh come o pass, while we sill havea chance o do somehing o avoid hem, han o seek he alse comor hacomes rom ignoring hem, only o realize in he uure ha hey have becomeineviable.

In Al Gores amous 2006 movie, An Inconvenient Truth, he ormer vice

presiden used he amiliar meaphor o boiling a rog o describe he crisiso climae change. Te sory, which you have likely heard many imes appliedin many insances, goes like his: I a rog is placed in a po o cold waer ha

Impac o a 2.5 Cemperaureincrease

Impac o a 2 Cemperaureincrease

Impac o a 1.5 Cemperaureincrease

emperaure Change

Impac

1.5 C 2 C 2.5 C

Figure 1.1 Impacs accelerae as emperaure increases.




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is hen gradually brough o a boil, he rog says pu. Te emperaure o hewaer increases so slowly ha he rog is unaware o he impending danger,whereas a sudden change in emperaure would have promped he rog o

jump ou o he po. By ailing o reac, he rog is boiled o deah (alhough inGores more humane version, he rog is rescued beore i is harmed).4

Alhough a rog placed in waer ha is slowly heaed apparenly will, in ac,jump ou (I have never ried i, bu ha is wha I am old), he use o he mea-phor is now so widespread ha i has a lie o is own, quie apar rom whaan acual rog would do in an acual po. I is a wonderully ap meaphor orclimae change or he obvious reason ha in boh he meaphor and he realworld, hings are geting hoter, and in boh he meaphor and he real world,he heaing migh go unnoiced unil i is oo lae. Te boiled-rog analogy is

effecive o make he poin ha i we wai oo long o ac, we will no be able opreven a variey o harms, including higher sea levels, increased sorm aciv-iy, drough, conics over environmenal resources, and so on. In ac, hemeaphor works so well ha i has become a amiliar par o climae-changediscussions.5

When I hink o climae change, however, I hink o a differen meaphor.As a child, I played a game called KerPlunk! A generaion laer, my childrenplayed i, oo. Te game consiss o a clear plasic ube wih hin sicks, likepick-up sicks, pushed hrough holes in he sides o he ube so ha hey sick

ou on boh sides. When all o he sicks are pu in, hey orm a kind o pla-orm. Marbles are hen dropped in rom he op o he ube and res on hesicks. Once he sicks and he marbles are in place, he game begins. Duringyour urn, you mus remove one sick. I any marbles all when you remove asick on your urn, you keep hem. Once all o he marbles have allen, he win-ner is he player who has colleced he ewes.

A he sar o a game oKerPlunk!hings are easy. You can pull ou jus abouany sick and be conden ha no marbles will all. Beore long, however, youhave o pay atenion and selec he sick you are pulling ou wih care. Even a

his poin, however, an examinaion o he posiion o he sicks usually allowsyou o pull one ou wihou collecing even a single marble. As he game pro-ceeds o he sage in which no player can avoid collecing some marbles, hesakes remain relaively low or a ew urns. Tere are a lo o marbles in hegame, and a ew marbles are unlikely o make a difference in he nal oucome.As long as he sicks sill creae some sor o serviceable plaorm, even i he pla-orm has small gaps, here is no cause or panic. Te game ges more serious asmore sicks are pulled ou and he plaorm erodes. Tis happens slowly a rs,bu hings ge progressively worse wih he removal o each sick. Evenually,

somebody pulls ou a sick and a whole bunch o marblessomeimes all haremaincome umbling down. Te loss o ha one sick causes a collapse.




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Someimes i is clear ha he nex sick o be removed will cause an avalancheo marbles. A oher imes, i seems as i a sick can be removed saely, bu his

urns ou o be an illusion as he marbles cascade down.Te dynamic o climae change resembles ha o he game o KerPlunk!

Tink o he marbles inKerPlunk!as represening he harm caused by climaechange and he removal o he sicks as represening he coninued emission ogreenhouse gases (GHGs) ino he amosphere. When one rs hinks aboua warming world, i seems as i here is nohing o worry abou. Jus as we canremove some sicks early in he game oKerPlunk!wihou much concern, add-ing GHGs iniially seems harmless. Even i we add enough o cause a change inhe concenraion o GHGs in he amosphere, he impac on he climae ini-

ially seems so small ha i is easy o ignore. Te plane was a his sage owardhe sar o he Indusrial Revoluion, when greenhouse gases sared beingreleased in dramaically higher quaniies. Indeed, we were also a his sagefy years ago, a which ime we had no ye experienced much o an increasein emperaures. By ha poin, human aciviy had raised he level o GHGs inhe amosphere bu wihou much consequence or he climae or he way welived our lives. Even i we had ully undersood he impac o sending GHGsino he amosphere, he impercepible effecs on emperaure and precipia-ion would no have seemed worh worrying abou.

By he lae 1970s and ino he 1980s, he siuaion was changing. By hisime, GHGs had accumulaed enough o sar warming he plane. Te changes

Figure 1.2 KerPlunk!




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were small and hard o measure, and heir cause (or even heir exisence) wasconroversial. Our limied undersanding o he climae sysem and how wewere affecing i made i diffi cul o consider wheher o resrain GHG emis-

sions. Even i we had undersood he rise in emperaure, he changes mighno have been large enough o cause much concern.

Like he ew marbles ha all in he middle o a game oKerPlunk!,he smallemperaure changes ha were aking place were perhaps no ideal bu did nocry ou or a dramaic response. While we would have preerred, or example,no o conribue o damaging weaher evens such as hurricanes, he worldran, as i coninues o do oday, on ossil uels and oher sources o GHGs, andi would have been boh diffi cul and expensive o change our ways. I was be-er o le a ew KerPlunk! marbles all han o underake large-scale changes in

how we lived.More recenly, however, i has become clear, and seems o become more so

wih each passing year, ha he laer sages in his global game o KerPlunk!are eiher as approaching or already upon us. We have added enough GHGso he amosphere ha he siuaion is now very much like he sage o a gameoKerPlunk!a which many sicks have already been removed. We are alreadyable o ideniy marbles ha have allen. Sea levels are higher, emperaureshave risen, and he requency o sorms has increased. Glaciers are disappear-ing rom mounains, and he ice in he Arcic is meling. Te eigh warmes

years since 1880 have all occurred since 1998, and he oureen warmes yearshave all occurred since 1990.6Tere has also been a oll in human suffering.Te bes esimae we have pus he deah oll rom climae change a 300,000per year, wih an even larger number o people made worse off in smal l or largeways.7

As we coninue o emi GHGs, more sicks rom his game o KerPlunk! willbe removed, and more marbles will al l. By 2030, i is expeced ha 500,000people will die each year as a resul o climae change, and 660 million peo-ple could be negaively affeced.8Tis represens a dramaic acceleraion o

he harms caused by global warming. Te marbles are saring o all morequickly.

Even hese esimaes assume a cerain coninuiy in he sysem; heyassume ha a small change in he acors ha affec he sysem will notlead oan abrup change in he magniude o heir effec. Bu in he game oKerPlunk!he marbles do no always all a a coninuous rae. Tere comes a poin awhich he removal o one more s ick will cause an avalanche o marbles. I hegame is indeed a good meaphor or our climae, i is his realiy ha shouldrighen us mos. A wha poin will a urher increase in GHGs (he removal o

one more sick) rigger a sudden increase in harm (he avalanche o marbles)?Te ruh is ha we simply do no know. We know ha he harms will increase




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more quickly as emperaures rise, which is bad enough. We do no know i weare heading oward a sor o ipping poin where here will be a very suddenand dramaic increase in consequences. We do no know, or example, wha

he risk is ha he meling o he permaros in he Arcic will release GHGssuffi cien o cause urher warming, mel more permaros, and release moreGHGscreaing a vicious cycle ha will accelerae warming.

We also do no know how humans will respond o he sresses o climaechange. Exising esimaes o he impac o climae change, including heone menioned above indicaing ha 500,000 people per year migh die asa resul o climae change by 2030, assume ha human and naural sysemswill coninue o work more or less as hey do now. On he conrary, here aremany ways in which hose sysems could break down, leading o much greaer

harms. Te already ragile coexisence o naions in he Middle Eas could col-lapse as saes in he region compee or limied and shrinking waer resources.Agriculural producion is likely o be slashed by drough or he meling omounain glaciers whose summer runoff is currenly used o irrigae crops.Rising seas will ood major populaion ceners and displace millions. As hesehings happen and as oher hreas maerialize, he deah rae rom climaechange wil l shoo up in much he same way he marbles inKerPlunk!all downwhen he wrong sick is removed.

Wih so much uncerainy, i is essenial o reurn o wha we do know.

We have reasonable esimaes o how much emperaures will increase in heuure, or example. My assumpion o 2 C may no seem like very much, buas I discuss hroughou his book, such an increase will cause immense dam-age. I we are unlucky and he change is larger, however, he damage will bemuch greaer.

We also know somehing abou where we are. Tere is no doub ha we area he sage in he game where marbles have sared o all, and we have alreadybegun o eel he consequences o cl imae change. Worse si ll, we are ndingi diffi cul o sop playing or even o slow he game down. As we coninue o

emi GHGs, we are sill pulling sicks ou o he game. Humans emi GHGswih virually everyhing we do, making dramaic reducions in emissions anenormous challenge. Even wih global recogniion o he ac ha a reducionin emissions is imperaive, he rend is in he opposie direcion: humans aresending more GHGs ino he amosphere each year. o dae, neiher domesicnor inernaional effors have done much o reduce emissions. I we ail o slowhe rae a which GHGs are released ino he amosphere, we will coninue opull sicks rom he game, and he pace a which marbles all will coninue oincrease.

We ace a rea l ri sk o he col lapse o human insiuions ha we akeor granedagriculural sysems, waer-disribuion sysems, healh-care




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sysems, naional borders, and inernaional peace, o name a ew. hiswould have seemed impossible jus a ew decades ago, bu i we do no reacproperly o climae change, i i s a genuine possibiliy. his ac has become

clearer as he concenraion o GHGs in he amosphere has increased.Once a cerain number o sicks are removed inKerPlunk! players can seeha he plaorm o sicks is eroding badly and will soon ail. In a similarway, we have seen he early signs o how climae cha nge wil l a ec us, andi is no encouraging. I we coninue o pull ou sicks, sooner or laer (andhere is mouning evidence ha i will be sooner), we will see marbles all-ing much more quickly. Unorunaely, in our game o global KerPlunk!insead o paying he price in alling marbles, we will see human lives cushor or upended and enire ways o lie los. No only ha, bu jus as

he removal o a ew key sicks can ransorm wha was once a plaormino a ew sray s icks, unable o suppor more han a ew leover marbles,we may ind ha cl imae cha nge hreaens o dismanle he physical andsocial srucures ha orm he plaorms o our sociey. I we do no ind away o reduce he rae o GHG emissions, we may ind our very way o l ieransormed.

Tis book explains how ha migh happen and why i migh happen aserhan many people realize. I considers he poenial impac o climae changeand asks how imporan aspecs o he lives o bil lions o people who share he

plane migh be affeced.We are so used o he way our sysems and insiuions work ha we orge

ha hey have no always been here. In my own sae o Caliornia, or exam-ple, we recognize ha here are droughs and waer issues, bu we do no ofenconsider ha i our children wan o live in Caliornia as aduls, here may nolonger be enough waer o suppor hem. By his, I mean ha here may no beenough even i he populaion does no grow. Fuure populaion growh willmake he challenge much greaer.

In oher pars o he world, he problems are someimes easier o grasp. For

many small island naions (e.g., uvalu, he Maldives), climae change maycause he enire counry o disappear beneah he waves. In oher places, risingseas will ood large racs o land, displace people, and inerere wih exis-ing inrasrucure. In Bangladesh, or example, i is likely ha millions will bedisplaced rom heir homes, very possibly creaing he larges humaniariancrisis he world has ever aced. Wih nowhere else o go, hey will no doub ryo move o already overcrowded ciies. Some will ry o leave he counry insearch o a beter exisence, creaing inernaional ensions. Makeshif campsmay crop up o house some o hese displaced persons, creaing a permanen

class o people living on he edge o subsisence. Rising seas will also inererewih ood producion, making i diffi cul or some naions o eed hemselves.




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Even in rich naions such as he Unied Saes, he inrasrucure is no in placeo deal wih seas ha are a meer or more higher han oday.

Te ood problem creaed by rising seas will be exacerbaed by oher

changes. Bill ions o people around he world rely on mounain glaciers o serveas massive waer-sorage aciliies. Rain ha alls in he mounains reezes oorm glaciers. In he summer, some o his sored waer mels, and he runoffis used o grow crops and suppor human exisence. When hese mounainglaciers melas hey are already doinghere wil l be no naural sorage sys-em. When rain alls, i will immediaely run down he mounains, creaingooding during he rainy season and drough during he dry season. Exisingirrigaion and agriculural sysems ha rely on he runoff rom glaciers wil l nowork properly, and agriculural yields will al lin some places caasrophi-

cally. While waer-sorage issues creae crises in some pars o he world, hesimple absence o waer will be he problem elsewhere. A changing climaemeans changing paterns o precipiaion, and some pars o he world willexperience much less rainall in he uure. Tis is a problem because humanbeings have come o rely on exising paterns. Populaion ceners have beenbuil up based on where waer is available. When drough and oher disrup-ions o waer availabiliy come o pass, he bes we can hope or is an expen-sive adapaion process, and he wors is a major crisis.

Unorunaely, he impac o climae change will no be limied o naural

sysems. Humans are consanly ineracing wih one anoher, and changesin our environmen have an effec on hose ineracions. Tere is already amajor effor under way wihin American naional-securiy circles o considerhow climae change will affec he securiy and ineress o he counry. Temain concern is ha climae change creaes addiional ensions among andwihin counries. Where ensions already exis wihin or beween counries,climae change may ip he relaionship ino violence. We have already seenhis in Darur, where exising ensions were managed in a peaceul way unila drough ipped he siuaion ino violence and, ulimaely, genocide. I does

no require an overly acive imaginaion o see ha srains in oher areasincluding he Middle Eas, he India-Pakisan region, and various pars oAricacould descend ino war and violence.

Alhough here is a lo we canno say or sure abou climae change, one ohe effecs ha can be prediced is a worsening o human healh. I is viruallycerain ha more people will ge sick a a younger age, alhough here is no wayo know precisely how bad he impac wil l be. Healh may also be affeced in adifferen and more righening way. Climae change will generae condiionsha are ideal or he spread o conagious disease. Expers can esiy ha hey

are always concerned abou he poenial or a large-scale oubreak o a deadlydisease. I we decided we waned o rigger such an oubreak, we could hardly




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do beter han wha climae change promises. A combinaion o rising seas,higher emperaures, changing precipiaion paterns, and lack o access owaer will displace enormous numbers o people. Tese people will nd heir

way o already crowded ciies or perhaps be housed in reugee camps. In eihercase, very large numbers o people will live in cramped and unsaniary spaceswihou proper inrasrucure such as sewage sysems or access o clean waer.Tey will live in precisely he condiions ha are suiable o he oubreak andspread o disease. Te combinaion o a lack o proper prevenion sraegies, ashorage o medical care, and he requen movemen o people rom one placeo anoher (rom camps o ciies, rom one camp o anoher, rom counry ocounry) will make i easy or disease o ravel and nd new vicims.

Te rs sep o undersanding he hrea o climae change is adjusing

your mind o appreciae he meaning o an increase in global average empera-ures o 2 C, 4 C, or 6 C. Alhough I now live in Oakland, Caliornia, I grewup in Otawa, he capial o Canada. Compared wih where I live now and,indeed, compared wih mos places, Otawa has real weaher. Winers arecolder and summers are hoter han in Oakland. Te average high emperaurein July is a litle more han 26 C (79 F), and he average low in January is 15(5 F). Te record high is 38 C (100 F), and he record low is 36 C (33 F).In he conex o hese exreme emperaure swings, a change o wo or evenour degrees can seem like a rie. Afer al l, i people can happily go abou heir

lives in places where he emperaure can change by more han 40 C over hecourse o a year, why would a global increase o a ew degrees mater?

Tis misconcepion is undersandable. A ew degrees cerainly does noseem like much. Mos people in he world experience larger shifs han harom morning o afernoon in heir daily lives. And in many pars o he coun-ry, he local weaher will vary by more han 2 C rom one place o anoher.Tis is rue in he San Francisco Bay Area, where here are bizarre microcli-maes. Places wihin hiry minues o each oher by car migh differ in em-peraure by 10 C (18 F) or more. When I rs moved o Oakland, here was

more han one warm summer day when I hopped ino my car and ook heweny-minue drive ino San Francisco wihou realizing ha, while shorsand a -shir suied he weaher in Oakland, I needed, and had ailed o bring,long pans and a jacke or San Francisco. Our everyday experiences wihchanges in he weaher shape how we hink o changes in emperaure andmake a global shif o a ew degrees seem rivial.

Te problem is ha we are used o hinking in erms o weaher, heday-o-day variaion in emperaure or precipiaion. Climae is somehingdifferen. A paricular climae will experience changes in weaher rom

day o day, and boh humans and naure are able o adap o hese changes.Bu a change in he climae isel affecs us much more. Humans, human




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sysems, and naura l sysems are much less able o adap o climaic changes,a leas when hey happen quickly enough. Wha sound like small changes ohe climae can urn ou o have enormous consequences.

For example, he difference in average emperaure rom he las ice age onow is abou 5 C.9I an average decrease o 5 C means he difference beweenhe world we live in oday and an ice age, i is suddenly much easier o believeha an increase in average emperaures o 5 C could lead o dramaic changes,including he meling o mounain glaciers, rising sea levels, and so on.

In realiy, we don need a emperaure increase anywhere near 5 C o rig-ger major changes. Looking arher back, ino prehisory now, an increase inaverage global emperaures o 2 C would make he earh as warm as i was 3million years ago. Tis seemingly modes difference in emperaure is enough

o explain why sea levels were abou 25 meers higher a ha ime han heyare oday.

Tis disconnec beween our inuiion and he realiy o global empera-ure changes comes abou in par because he changes we are alking abouare averages. I he average emperaure goes up by 2 C or 3 C, he empera-ures ha we experience may vary by considerably more. Our insincs abouclimaic change are also misleading because he world is much more sensiiveo changes in climae han our everyday experiences sugges. Even beore heinvenion o many o he echnologies ha make our lives comorable oday,

humans were able o live in many differen climaes around he world, givinghe impression ha small changes in climae do no cause problems. Summeremperaures in Por Sudan, Sudan, or example, reach ino he mid-o-high40s C, wih an average in he summer o 41 C (106 F). In conras, wineremperaures in Yakusk, Russia, are below 30 C (22 F) rom December oFebruar y, and i is no unusual or emperaures o all below 40 C (40 F).Tese wo places have wildly differen climaes, ye humans are able o live inboh places.

Conrary o our insincs, however, a change o jus a ew degrees can have a

major impac on a number o criical sysems on our plane. Tese include, orexample, he level o he oceans, when and where waer is available or humanso use, and he ypes o ora and auna ha exis. Nor is i only emperaureha is a sake when GHGs cause changes o he climae. Precipiaion paternsalso change, posing challenges o all manner o human aciviy, rom agricul-ure o energy o human healh. Even he small changes we have already seenhave been aal or many species. Jus one example is ha a leas 70 species orogs, mosly mounain-dwellers ha had nowhere o go o escape he creep-ing hea, have gone exinc because o climae change. . . . Beween 100 and 200

oher cold-dependen animal species, such as penguins and polar bears, are indeep rouble.10




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Te realiy is ha even modes changes o he climae can have majorimpacs on our lives and our world. Because o his, climae change hreaenshe very abric o our global sysem. I has he poenial o cause loss o pros-

periy, calamiy, and dramaic suffering on a scale humaniy has never seen.Beore moving on o he hear o his book, I need o commen on he con-

inuing debaes abou wheher climae change is real and wheher i is he resulo human acion. I have more o say abou his in he nex chaper, bu I musacknowledge he quesion here. I one lisens o he popular media, i ofenseems as i here are wo imporan and opposing views abou climae change.Te rs is ha he earh is warming and is doing so as a resul o human aciv-iy. Te second, ofen porrayed as a minoriy scienic view, is ha climaechange is no a serious hrea.

Tese opposing views rame and dominae many books and aricles onhe subjec and ofen rame he way he media presen he issue. Believers inclimae change argue ha here is a widespread consensus among scienisso suppor heir view, and hey lobby or one orm o governmen acion oranoher. Skepics claim ha he consensus among scieniss is more illusoryhan real and ha we are in he grip o climae-change hyseria.

Presening he issue o climae change in his way is misleading. I is sim-ply no he case ha climae-change debaes eaure wo comparable groups,each wih is own srong argumens. Tose o us who are persuaded ha he

hrea rom climae change is real do no simply differ rom deniers in our viewo he science involved. Many o us, mysel included, nd i diffi cul even obelieve ha anyone is persuaded by he argumens o skepics. Te skepics iback and orh beween claims ha he scienic communiy agrees wih heirposiion and complains ha science isel canno possibly give us answers.Tey claim o wan a sober and raional debae bu hen reuse o engage, in aserious way, he mounains o evidence ha climae scieniss have provided(some o which is presened in chaper 2). When one examines he argumenso deniers, hey urn ou o be litle more han a mix o conspiracy heories,

misrepresenaions o he science, and unounded asserions.Alhough I believe ha climae-change deniers are dangerous and under-

mine effors o underake a serious discussion abou how o respond oclimae change, my objecive is no o engage in a debae wih his group.I rmly believe ha climae change is real. Indeed, I am among hose whobelieve ha a good-aih examinaion o he evidence canno lead o anyoher conclusion. I will spend some ime (mosly in chaper 2) laying ou hereasons or my views and he reasons scieniss are abou as unanimous onhis quesion as hey ever are on any issue. Chaper 2 also explains why he

argumens o deniers are so deeply awed. Bu I am under no illusion hahe conens o ha chaper will conver any rue climae-change skepics.




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Alhough our undersanding o climae change seems o be growing by heday, he mos imporan evidence is well known. As ar as I am concerned, weare well pas he poin where here is serious doub abou wheher humans

are causing he globe o hea up. I do no deny ha he argumens o skepicsmus be challenged o prove ha hey are misleading and wihou scienicbasis so ha criical policy decisions can be made wihou he conusion cre-aed by deniers. For his reason, I applaud hose who ake on hese skepicsin public and who gh o make discussions o climae change as ransparenand hones as possible.

As imporan as i is o explain he science o climae change and o con-vince he public and poliical leaders o he realiy o his hrea, i is equallyimporan o examine wha will happen i our response is inadequae. We can-

no le deniers hijack his mos imporan debae. A some poin, we have oignore he unounded claims o skepics and urn o he evidence so ha wecan undersand, as well as possible, wha he consequences o inacion arelikely o be. Tis book does ha, explaining in clear and sraighorward lan-guage wha we need o worry abou as we make decisions on climae policy,boh domesically and inernaionally.

Alhough I do no inend o ge bogged down in a skirmish wih climae-changedeniers over heir all-oo-successul atemps o manuacure conroversy, I can-no ignore he real uncerainy ha exiss in our undersanding o global warm-

ing. Te ac ha he earh is warming is clear, bu here remains subsanialuncerainy wih respec o many imporan quesions: he rae a which humanswill coninue o pu GHGs ino he amosphere, he precise way in which he cli-mae will respond o hose GHGs, how naural sysems will respond o a chang-ing climae, how human insiuions and pracices will respond, and how all ohese changes will affec he well-being o humans. Despie his uncerainy, wehave o do our bes o look orward so ha we can decide wha o do oday.

Predicions abou he uure are essenial, ye geting such predicions righis almos impossible. As Mark wain once said, Te ar o prophecy is very

diffi cul, especially abou he uure. Forunaely, he problem is no quie soserious i you remember he earlier discussion abou predicing wha numberwill come up when you roll wo dice. I is impossible o predic wha he dicewill do on a given roll, bu we have a good sense o wha is likely. I is in haspiri ha his book considers he poenial impacs o climae change.

I do no and canno claim ha all o he evens I describe here are inevi-able. I do no aspire o ha level o precision. Troughou he book, I ry o beclear abou which evens are virually cerain (e.g., he loss o some low-lyingisland saes o rising seas, an increase in exreme weaher evens, major chal-

lenges or agriculural sysems ha rely on mounain glaciers or waer sorage,increased securiy hreas, and more); hose ha are likely i climae change




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is as bad as (or worse han) wha mos expers predic (e.g., major populaiondisplacemens, dramaic ood shorages, deadly hea waves); and hose hamigh be caused by climae change and would be so errible ha we need o

keep hem in mind even i hey may no happen (e.g., worldwide spread o adeadly disease, exreme increases in sea level).

Te ac ha I canno avoid he uncerainy associaed wih climae changemakes i impossible or me o anicipae precisely wha we have o look or-ward o. I am no he only one who has o deal wih his uncerainy, however.Policy makers who have he power o decide how we will respond o climaechange ace he same problem, as do he voers who pu hose policy makersino posiions o power. We have no choice bu o make decisions in he ace ohis uncerainy.

o decide wha o do in he ace o uncerainy, however, we have o knowwha migh happen. Tis book presens a picure o wha is likely o be waiingor us in he warmer world ha we are creaing.




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19

2

A Message from Climate Scientists

Te debate on the authenticity of global warming and the role played by

human activity is largely nonexistent among those who understand thenuances and scientic basis of long-term climate processes.

Peer . Doran and Maggie Kendal l Zimmerman,Examining he Scienic Consensus on Climae Change1

I you eel ha he subjec o climae change coninues o provoke anapparenly endless debae, you are no alone. Someimes here is so much con-radicory and angr y dialogue ha i is diffi cul o undersand he key issuesand evaluae how much evidence here is on each side. Mos o us are ed upwih over-he-op rheoric ha seems o be more abou scoring poins han

geting o he acs. Tis realiy makes he enire issue unnecessarily hard oundersand and makes rying o learn abou i rusraing and off-puting.You should no need a Ph.D. o undersand he basics o cl imae change, andlearning abou he relevan issues should no require ha you wade hrougha never-ending sream o inormaion. Furhermore, deciding wha youhink abou he issue should no be a poliical ac o eiher loyaly or berayal.Climae change is an imporan public-policy issue, bu i is one ha can bealked abou calmly and sensibly. Doing so, however, requires some under-sanding o wha we know, including he relevan scienic inormaion.

Tis chaper is writen or hose who are ineresed in climae change (i youare reading his book, you qualiy) bu who are no specialiss in i. You canhink o i as a simple our o wha we know abou climae change. Te idea iso help us undersand he undamenal scienic orces a work and wha heyare doing. I have no ried o include everyhing we know, because he goal is okeep he discussion as sraighorward as possible. On he oher hand, I believeha I have included he key inormaion you need and ha, afer reading hechaper, you will have an accurae and pracical sense o he science o climaechange and how scieniss view he problem.

Te chaper has ve pars. In he rs par, I explain he remarkable degreeo consensus ha exiss in he scienic communiy. I you pay only casual




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atenion o climae-change repors and sories, i is easy o ge he impressionha he scienic world is in he mids o a batle abou wheher climae changeis happening and how humans are conribuing o ha change. In ac, here

is almos no disagreemen among climae scieniss ha i is happening andha humans have conribued o i. Tis is imporan o undersand, because ipus a differen ligh on he debae. Tose who deny climae change are asser-ing ha virually he enire scienic communiy has goten i wrong. Deniers,hen, mus explain how he observed acs lead hem o a conrary view andwhy so very ew scieniss agree wih hem. Despie a broad consensus wihinhe scienic communiy, he general public remains much more skepicalabou climae change. Te rs secion o he chaper also addresses he publicdiscussions o climae change and how I hink hose should be viewed.

Te second par o he chaper explains wha we know abou pas climaicchanges and considers wha migh happen in he uure. I use he projecionso climae scieniss o ge a sense o wha he climae migh look like decadesrom now.

Te hird par presens he science ha explains why he world is warm-ing. Basically, as human aciviy emis increasing amouns o greenhouse gases(GHGs), he concenraion o hose gases in he amosphere increases. GHGsreduce he amoun o energy ha escapes ino space, so adding more o hemo he amosphere leads o more energy in he earhs sysem, causing empera-

ures o rise.In he ourh par o he chaper, I address he mos common argumens o

climae-change skepics. As I said in chaper 1, I hink i is imporan o avoid ge-ing bogged down in a batle wih skepics. Te science on he subjec is compelling,and he skepics argumens have been addressed many imes over. Te consensusamong climae scieniss illusraes ha when people look careully a he relevanscience, he realiy o climae change is clear. Neverheless, I wan o spend a litleime addressing he claims made by skepics or wo reasons. Firs, i is helpul oge a sense o why skepics coninue o advance heir claims and why hey have

reused o be convinced by he exising evidence. Second, I wan o presen hemos common claims made by skepics so ha you can undersand he weaknesseso he claims and he ways in which hose claims have been disproved.

In he las par o he chaper, I explain why even someone who is skepicalabou climae change should suppor effors o address he issue.

I. As Much Consensus as a Poliical Issue Can Ge

Climae change can be a polarizing poliical opic, especially in he UniedSaes. Many o hose who speak abou i have a poliical ax o grind, and i can




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A M e s s a g e f r o m C l i m a t e S c i e n t i s t s 21

be hard o know wha o believe. Climae change remains par o he culurewars in he Unied Saes. o believe ha human behavior is causing warmingis o beray one side o he poliical divide, and o rejec ha noion is o beray

he oher.o pick an admitedly exreme example, Melanie Phillips, a columnis a

BriainsDaily Mail, wroe in 2006: Te heor y ha global warming is all heaul o mankind is a massive scam based on awed compuer modeling, badscience and an ani-wesern ideology. . . . Te majoriy o well-meaning opinionin he Wesern world believes a pack o lies and propaganda.2Similarly, SevenMilloy, a Fox News commenaor, described he very idea o ghing climaechange as an atack on our sandard o living.3Tese commens raise hesakes: apparenly, we are no simply rying o decide i he climae is chang-

ing, bu we are also deciding wheher o be ani-wesern, o believe a pack olies, and o join an atack on our sandard o living.

Tose who believe ha man-made climae change is a serious problemhave no been immune o using exreme rheoric. Al Gore, or example, hassaid, Te people who dispue he inernaional consensus on global warm-ing are in he same caegory now wih he people who hink he moon land-ing was saged on a movie lo in Arizona. 4Ohers make Gores commensseem downrigh chariable. Te Unied Naions special climae envoy, GroHarlem Brundland, declared in 2007 ha is compleely immoral, even,

o quesion . . . wheher we need o move or ward a a much sronger pace ashumankind o address he issues.5No o be oudone, he execuive secre-ary o he Framework Convenion on Climae Change, Yvo de Boer, saedha i would be criminally irresponsible o ignore he urgency o climaechange.6Here again, a scienic and policy issue is suddenly somehing abouwhich we canno even ask quesions wihou invoking immoraliy and crimi-nal irresponsibiliy.

Te poliical drama surrounding climae change has also leaked ino hemedia and general public discussions. I you pay atenion o discussions o

climae change in he media, i is easy o ge he impression ha here is a sig-nican and widespread debae on he quesion o wheher climae change isacually happening and, i i is happening, wheher i is he resul o humanaciviy. However, i you lisen o hese debaes careully, and especially i youinvesigae hem on your own, i soon becomes clear ha believers in climaechange make heir case by rying o poin o he science ha is involved, whiledeniers spend much more ime criicizing he views o believers. I is diffi culo nd denials ha involve heir own scienic invesigaion and analysis.

Te debae akes his orm because he scienic evidence or man-made

climae change is overwhelming. I is so overwhelming ha believers coninueo poin o i as i o say, Look, here i is, clear scienic evidence ha we are




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22

righ. Wha else do you need beore you believe us? Because he science isairly clear, deniers rerea o a rheorical sraegy o poking holes in he believ-ers claims. Tis is essenially he same acic used o resis he scienic evi-

dence ha obacco and asbesos were dangerous. Science works because peopleask hard quesions. Tey challenge one anohers ndings and ake nohing orgraned. Ta is all good and erribly imporan. Bu i is equally imporan noo ignore where he evidence poins. Te evidence on climae change poinsclearly and consisenly in he direcion o a hoter uure.

Alhough climae-change deniers do no believe ha he world is heaing up(or do no believe ha i is heaing up very much), hey do agree ha he issueis ulimaely a scienic quesion. I is no somehing ha can be deerminedby poliical ideology, economic ineress, popular opinion, or, as comedian

Sephen Colber would say, gu. I is eiher a scienic ac ha he earh iswarming, or i is a scienic ac ha i is no. Tis poin o agreemenhow-ever limiedis a good place o sar he conversaion.

I you had some indicaion ha here was a problem wih your cars rans-mission, you would ake i o a mechanic. You would hope ha nohing waswrong, bu i would be a bad idea simply o rely on ha hope. You migh evenhave a riend who, despie a lack o auomoive experise, opines ha he rans-mission is ne. Even so, you would wan o hear rom a mechanic, because he isan exper on his quesion. I he mechanic gave you bad news, explaining ha

in his opinion he ransmission would give ou wihin he nex housand miles,you would be wise o ake ha opinion seriously. O course, i you had doubsabou he abiliy or he honesy o he mechanic, you migh seek a second opin-ion beore spending he money o x he ransmission. I a second mechanicsaid he same hing, you would be prety sure ha you had a problem. I a hird,and hen a ourh, also agreed, you would presumably accep ha your rans-mission was sho. I you had hundreds, or even housands, o mechanics allagree ha you had a problem, hough perhaps disagreeing on he quesion owheher you had ve hundred, one housand, or wo housand miles lef beore

he ransmission ailed, i would seem sel-eviden ha you should accep heac ha your ransmission was in rouble. I your riend coninued o insisha here was no problem, you would be wise o dismiss or a leas discounhis opinion, since he does no know anyhing abou cars. You would also nole your own hopes abou he ransmission override he inormaion you weregeting rom hese many mechanics.

For he same reason you would ask a mechanic abou your car, we shouldseek ou expers o ell us wha is happening o our climae. Tese expers areclimae scieniss.

Beore examining wha scieniss say, I wan o acknowledge ha climaescieniss disagree on many issues. Tis is wha scieniss dohey debae he




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available evidence. Trough his process, hey reach more reliable conclusions.Jus because hey disagree on some hings, however, does no mean ha heydisagree on everyhing. Tere are areas o srong agreemen among scieniss,

and when ha is he case, we are wise o lisen o hem, much as you would bewise o lisen o wha mechanics believe abou your car. Invesigaing whascieniss believe can be diffi cul, because each individual researcher has hisor her own views. Forunaely, we are ineresed in a relaively simple quesionha allows us o ge a good sense o wha he communiy o scieniss believes.We wan o know i he earh is warming and, i so, i humans are causing io do so.

Despie he many uncerainies and disagreemens abou he climae andclimae change, we have a very clear answer o his quesion. Tere is no longer

any serious doub ha he earh is, indeed, geting warmer and ha humanaciviy is a major conribuor. Tese are acs ha scieniss know. When Isay ha scieniss know ha man-made climae change is real, I mean i in hesame way ha we say scieniss know ha cigaretes and asbesos cause cancer.I mean ha here is no serious dispue wihin he communiy o climae sci-eniss.7Tese are quesions ha were once he subjec o scienic debae buare now setled.

Te bes way o ge a sense o wha scieniss believe is o look a scienicwriings. Te currency o science is he publicaion o research in peer-reviewed

journals, where scieniss evaluae submissions and selec he bes ones or pub-licaion. Tese journals are where scieniss ell he world abou heir researchand heir discoveries. Tey are he gold sandard o scienic inquir y.

In 2004, Naomi Oreskes rom he Universiy o Caliornia, San Diego, wenlooking or climae-change skepicism in he American scienic communiy.She was unable o nd any. She examined more han nine hundred scienicaricles abou climae change published in peer-reviewed journals beween1992 and 2003. O hese, exacly zero dispued he noion ha climae changewas real and was caused by humans.8

Tis is a sunning resul, especially when conrased wih he public debaeabou climae change. Te peer-review sysem o publicaion, used by all aca-demic disciplines, ensures ha only he highes-qualiy work ges published.I is also a sysem ha encourages debae, because a researcher can becomeamous by successully challenging or debunking a well-esablished heory. Ihe claim ha he earh is warming as a resul o human aciviy were ull oholes, here would be a rush o scieniss eager o make he opposie case. Tais how careers are made in he academic world. Wha Oreskes ound, however,is a complee lack o disagreemen on his mos undamenal poin. Unanimiy

o his sor is jus abou he bes evidence one can imagine in suppor o henoion ha humans are causing a change in he worlds climae.




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Oreskes also ound ha all major scienic bodies in he Unied Saeswhose members experise bears direcly on he mater have issued . . . sae-mens concurring wih he message ha humans are causing he earh o

warm.9A more recen sudy, released in 2010, examined he work o 1,372 climae

researchers and ound ha abou 97 percen o hose mos acively publishingin he eld believed ha human aciviy was causing climae change.10 Tissurvey does no quie allow us o say ha lierally every climae researcherbelieves ha man-made climae change is happening, bu i comes awullyclose. Te old elevision commercial or sugarless chewing gum used o sayha our ou o ve deniss recommend sugarless gum. Well, i urns ou haclimae scieniss share a much sronger agreemen on climae change han

deniss do abou sugarless gum. Tere are ar more deniss (a leas accordingo he commercial) who recommend gum wih sugar han here are climaescieniss who doub climae change.

When we add up he scienic evidence, hen, i is hard o imagine a clearersignal coming rom he scienic communiy. Te relevan scienic bodies allagree ha climae change is real and is man-made, he peer-reviewed scien-ic lieraure has ully acceped he same conclusion, and virually al l climaescieniss agree. Whaever debae exiss ouside he scienic communiy, hescieniss hemselves are in agreemen.

You migh hink ha i he scieniss agree ha human aciviy is conribu-ing o climae change, everyone else would believe hem. Tis migh be how ishould workwho beter o judge he scienic quesion han scieniss rainedo do so? Bu ha is no he world we live in. In his book Denialism, MichaelSpecer reminds us ha he general public, or a leas signican porions o i,ofen reuses o believe wha science has shown o be rue. Te experise o sci-eniss and researchers is someimes dismissed in avor o views and opinionsha have no basis in science and/or can be shown o be alse.

Te lack o aih in science is aggravaed by he ac ha scieniss are no

always good a explaining science o he public. When he conversaion urns oemissions models, radiaive characerisics, or hermohaline circulaion,many o us une ou. Even when he problem is presened clearly, he realiy oclimae change is no uplifing. A genuine crisis is looming, and someimes i iseasier o avoid ocusing on bad news. All o us, afer all, have pleny o do in oureveryday lives as we sudy or school, work or a promoion, sruggle o akecare o our kids, worry abou paying bills, and so on. Te las hing we wanis somehing else o re abouespecially a problem as big as changes o heearhs climae ha no single person, or even a group o people, can solve.

Any serious response o climae change will ineviably cos money andwill involve a reducion in GHG emissions. I is hardly surprising, hen, ha




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people and businesses ha sand o lose as a resul o sensible climae-changepolicies will look or ways o delay acion as long as possible. Gore makes hispoin wih a quoe rom Upon Sinclair ha has become almos a manra o

advocaes or sronger climae-change policies: I is diffi cul o ge a man oundersand somehing when his job depends on him no undersanding i.

In shor, here are many powerul economic and poliical orces ha have anineres in denying climae changes exisence, regardless o wha he evidencesays. Prominen members o his camp are he oil, coal, and auo indusries,all o which sand o lose i governmens ge serious abou addressing climaechange. Money has poured ino sysemaic campaigns aimed a promoing heviews o skepics. Despie he absence o scienic suppor, hese groups havepu ou he message ha climae change is no happening, is no caused by

humans, is no a hrea, is no worh ghing, or all o hese hings. Tis hasbeen a anasically successul effor, as i has prevened he public rom recog-nizing he deep agreemen among climae scieniss.

All o he above reasons explain why skepics have had an inuence on heclimae-change debae wihin he general public ha is ar greaer han heinuence hey have had in he scienic communiy.

Te disconnec beween scienic and popular opinion creaes a challengeor his book, and or any book on climae change. I wan o emphasize hahe science o climae change is clear, bu o do so in a comprehensive way

would ake up so much space ha here would be no room lef o discuss hehuman impacs o global warming. Forunaely, here have already been sev-eral careul effors o presen wha we know on he subjec and o debunk heskepics argumens. Tese oher books and aricles persuasively demonsraeha climae change is, indeed, real, man-made, and hreaening.11

I will no, hereore, review he debae abou he exisence o climae changein ull deail. I will no chase down every skepics claim abou why he scienceand scieniss are wrong or why he evidence is imperec. And I will no ryo respond o all o he asserions o deniers or he conspiracy heories used o

explain why virually all op scieniss are convinced ha our world is warm-ing. Insead, I ry o presen he key scienic evidence we have in an accessibleand even-handed way.

I is also worh noing ha while he public debae has nohing like heconsensus ha can be ound in he scienic communiy, skepicism does norun nearly as deep as i someimes seems. Alhough skepics are ofen givena voice in he media, or example, he usual sance o major media oules iso accep ha humans are causing climae change. Te Economist magazine,hardly a basion o lef-leaning hinking, pu climae change on is cover in

March 2010. Te reamen ocused on he ambiguiies in he science, bu ireaed he quesion o wheher humans have caused he plane o warm as




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a setled one. In ac, i wen even urher, recommending serious acion ocomba he hrea.

Te Economist is a Briish publicaion. Wha abou American media on

he righ o he poliical specrum, where doubs abou climae change endo be more common? Here, oo, ediorial views are clear: climae change ishappening, and i is man-made. o be sure, he media cover he claims oskepics. For example, no oo long ago, he Wall Street Journal publishedan op-ed piece by well-known climae-change skepic Parick Michaels, inwhich he quesioned he science o climae change along wih he characero climae-change scieniss12bu he newspaper isel recognizes ha heworld is warming. Such examples illusrae ha while i is easy o nd peoplewih some doubs abou wheher he world is warming , hose doubs are no

credible enough or common enough o be reeced in mos major media ou-les (Fox News being a possible excepion). Alhough he media undersand-ably ocus on areas o disagreemen, we should no lose sigh o he ac hahere, oo, here ends o be an accepance o he idea ha humans are causinghe plane o warm.

How does all o his reec isel in he atiudes o he general public?While here are cerainly people wi h doubs abou climae change, here isless serious skepicism among he public han i may seem. In 2009, a Galluppoll ound ha 41 percen o Americans polled el ha he seriousness o

global warming was exaggeraed in he news. Fify-seven percen houghhe news go i abou righ or underesimaed he danger. So by his mea-sure, abou wo in every ve Americans could be couned as skepical. Buwe should be careul in inerpreing polls. Tis is no skepicism abou heac ha he world is warming. R aher, i is skepicism abou he seriousnesso he issue. Many people believe ha human aciviy is, indeed, causing heearh o warm bu are no convinced ha a small increase in emperaureis somehing o worry abou. Ta group is also included in he above 41percen.

In he rs chaper o his book, I discussed why an increase o a couple odegrees seems so modes. Te mos imporan message o his book is ha, inac, a change o ha magniude will have devasaing impacs. I do no expeco convince hard-core climae-change deniers who reuse o accep he clearscienic evidence. I do no hink any evidence would convince hem. I dohope o demonsrae how caasrophic a warming o a couple o degrees wouldbe. I wan o speak boh o hose who recognize he hrea we ace and hosewho accep he science bu wonder why wo degrees is so dangerous. Many ohose people are among he 41 percen who say he news oversaes he danger.

My hope is ha when someone in ha group reads his book, he or she will beconvinced ha he problem really is deadly serious.




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urning rom popular opinion o he opinions o poliicians, viewson climae change have been unsable recenly. he science o climaechange has no undergone a revoluion in he las ew years, bu here has

neverheless been a grea increase in he voice o climae-change deniersamong naional poliical igures. A he ime o he 2008 presidenial elec-ion, boh major poliical par ies in he Unied Saes had come o he con-clusion ha climae change was happening. O he wo par ies, here is nodoub ha he Democraic Pary has hisorical ly been less skepical abouclimae change han has he Republican Par y. Indeed, i is easy o ge heimpression ha he Republican Pary does no believe climae change ishappening a all. his impression, however, is wrongor a leas, i waswrong in 2008. Jus he opposie was r ue a he ime. I one judges rom

heir oicial pary plaorms, he Republicans and he Democras hadboh come o he conclusion ha human aciviy was causing our pla neo warm.

During he 2008 presidenial campaign, Senaor John McCain, heRepublican candidae, was on he record as believing ha climae change wasindeed man-made. Wihin his pary, McCain was hardly alone. Te offi cialpary plaorm saed:

Te same human economic aciviy ha has brough reedom and

opporuniy o billions has also increased he amoun o carbon in heamosphere. While he scope and long-erm consequences o his arehe subjec o ongoing scienic research, common sense dicaes hahe Unied Saes should ake measured and reasonable seps odayo reduce any impac on he environmen. Tose seps, i consisenwih our global compeiiveness, will also be good or our naionalsecuriy, our energy independence, and our economy. Any policiesshould be global in naure, based on sound science and echnology,and should no harm he economy.

As par o a global climae change sraegy, Republicans supporechnology-driven, marke-based soluions ha will decrease emis-sions, reduce excess greenhouse gases in he amosphere, increaseenergy effi ciency, miigae he impac o cl imae change where ioccurs, and maximize any ancillary benes climae change mighoffer or he economy.13

Alhough i is couched in economic raher han environmenal erms, his lan-guage acceps he realiy o man-made climae change.

Pary plaorms are poliical documens raher han scienic ones. Teyare inended o atrac voers during an elecion campaign. Tis means hey




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are a good place o ge a sense o wha each pary and is supporers believe.Tey can be viewed as a sor o poliical weahervane. My poin here is ha in2008, he Republican Parys plaorm saed ha climae change posed a real

hrea (hough perhaps no a serious enough one o jusiy acions ha comewih signican economic coss). So while here were sill voices ha dispuedhe very exisence o climae change, including he voices o some poliicians,boh poliical paries could be couned as believers.14

Jus a ew years laer, hings have changed. Deniers in Congress have beenmore ouspoken o lae, and Republican poliicians appear much more hesiano acknowledge publicly he realiy o climae change. o be sure, here havealways been doubers in Congress. In 2003, or example, Senaor James Inhoerom Oklahoma, anoher prominen skepic, saed ha he claim ha global

warming is caused by man-made emissions is simply unrue and no based onsound science. . . . Wih all o he hyseria, al l o he ear, al l o he phony science,could i be ha man-made global warming is he greaes hoax ever perperaedon he American people? I sure sounds like i. 15Speaking on he oor o heU.S. Senae on March 15, 2010, he conrmed ha he ever-mouning evidencedemonsraing ha he climae is changing has no alered his view. In ac, heutered almos exacly he same words (hough wih apparenly a litle morecondence): Te noion ha anhropogenic gases are causing global warm-ing is he greaes hoax ever perperaed on he American people.16

Te apparen increase in he number o skepics in Washingon may behe ineviable resul o an economy in recession; nobody wans o alk aboulong-erm problems ha may cos money when he economy is on he skids.Whaever he reason, boh individual poliicians and congressional hear-ings have eaured srong saemens by deniers. On March 25, 2009, orinsance, during hearings on climae change beore he House Subcommiteeon Energy and he Environmen, Lord Chrisopher Monckon, a prominenclimae-change skepic wih no scienic raining, esied ha he plane wascarbon sarved and answered in he affi rmaive when asked by Represenaive

John Shimkus, I we decrease he use o carbon dioxide, are we no akingaway plan ood rom he amosphere? . . . We could be doing he opposie owha he people who wan o save he world are saying. Even i one were skep-ical o climae change, here is absoluely no evidence ha reducing emissionso carbon dioxide would be harmul because i would be aking away planood.17Te exchange had no preense o rying o bring serious science o bearon policy making. I is an embarrassing indicmen o our decision-makingprocess ha his sor o poliical posuring, wihou a shred o scienic oun-daion, is carried ou a he highes levels o governmen.

On June 26, 2009, during debae on a climae-change bill in he Houseo Represenaives, Represenaive Paul Broun rom Georgia saed ha




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climae change is nohing bu a hoax ha has been perperaed ou o hescienic communiy.18 Tese saemens demonsrae eiher a willingnesso make claims ha he speakers know o be alse or a wildly exaggeraed

sense o he scienic communiys capaciy o perperae a hoax. Srange

clima overheated

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