Stratoshield White Paper

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IntroductionMassive shis are underway in he global energy sysem as hu-maniy atemps o curail he release o he gases responsibleor greenhouse warming. Ye relaively litle progress has beenmade so ar in reducing global emissions o greenhouse gases;concenraions o carbon dioxide (CO), mehane, and oherconribuors o he warming coninue o increase in earhsamosphere [Homann 2009, Raupach e al. 2007]. A hesame ime, scienic projecions o he possible uure warmingand associaed changes o precipiaion, hea waves, and majorsorms have generally grown more alarming[IPCC 2007].

A number o leading scieniss have voiced concern haour bes eors o reduce emissions hrough conservaion, im-provemens o energy eciencies, and shis o cleaner sourceso energy may no be sucienly as o preven inolerable cli-mae change. Tey have proposed a variey o echnologiescommonly called geoengineeringha could reverse globalwarming emporarily, buying ime or he global economyo complee is move o a more susainable energy sysem[Cruzen 2006, Cicerone 2006, Royal Sociey 2008].

Tese proposals have generaed a lively and ruiul debae

wihin he scienic communiy and he public a large abouhe cos and pracicaliy o various geoengineering echnolo-gies, as well as possible uninended side eecs o heir use.Inellecual Venures hopes o play a consrucive role in hisdebae as a source o innovaive echnical ideas or solvingsome o hese issues. We have unded research in his areaand are encouraging ohers o do so as wellbecause i wouldbe irresponsible or he echnical communiy o pospone suchwork unil a climae emergency was acually underway. Inel-lecual Venures does no advocae consrucion or deploy-men o geoengineering sysems now, and we hope hey will

never be needed. Bu he pruden course is o begin sudyingopions immediaely. (See Climae Science and Engineeringa Inellecual Venures or urher discussion abou he roleo geoengineering.)

A Global Cooling SystemScieniss have proposed a wide variey o approaches orcooling par or all o he Earh [Blacksock e al. 2009]. Oneapproach has received more atenion han he ohers, how-ever: he idea o increasing he amoun o sulur-bearingaerosols in he sraosphere and hereby decreasing slighly amoun o sunligh ha reaches he earh [Kunzig 2009]. (Tsraosphere is he weaher-ree porion o he amosphere aaliudes beween abou 10 kilomeers and 50 kilomeers, or33,000 o 165,000 ee.)

Te atraciveness o his approach sems largely rom he

ac ha i happens naurally during large volcanic erupionssuch as he erupion o Moun Pinaubo in he Philippinesin 1991. Inensive scienic sudy o he Pinaubo erupionshowed ha sulur dioxide aerosols injeced high in he amosphere cooled he plane by refecing more incoming sunlig

back ino space [Robock 2002]. An even larger erupion in1815 o Moun ambora in Indonesia led o he second-coldes year in he norhern hemisphere in our cenuries, he y

wihou a summer [Bria e al. 1998].Imporanly, he cooling eec begins immediaely, bu is

shor-lived: unlike carbon dioxide emissions, which persis ihe upper amosphere, warming he earh or cenuries [Mahews and Caldeira 2008], sulur dioxide aerosols appear oremain in he sraosphere or only a year or wo aer injeci

beore alling back o Earh [Caldeira and Wood 2008]. Anygeoengineering sysem should ideally be no only quick-aci

bu also quickly reversible, so ha he climae reurns o isprevious sae soon aer he sysem is urned o. Tis provida measure o saey in case any damaging side eecs appear

when he sysem is deployed.Also imporan is he ac ha aerosols in he sraospher

end o migrae oward he poles. Tus aerosols injeced a hArcic Circle would be expeced o cool he Arcic bu o havlitle or no eec on sunligh received by he emperae andropical pars o he Earh. Aerosols injeced ino he amo-sphere above Anarcica will similarly end o disperse graduly oward he Souh Pole. o cover he enire plane, he spra

would have o be released a a variey o laiudes, includingsies near he equaor.

Te general poleward migraion o high-aliude aerosols

The Stratospheric ShieldA practical, low-cost way to reverse catastrophicwarming o the Arcticor the entire planet

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is useul or wo reasons. Firs, i allows small-scale esing o ageoengineering sysem. A pilo projec could be se up in norh-ern Alaska or norhern Europe, or example.

Second, he polar regions have so ar experienced ar greaerwarming han has he res o he plane, and climae modelsprojec ha his rend will coninue [IPCC 2007]. I a climaeemergency does occur ha would warran use o geoengineer-

ing, i seems probable ha i will aec he Arcic or Anarcicice caps rs and more severelyindeed, an abrup shi inclimae may already be underway in he Arcic [Kerr 2007]. Sys-ems ha can concenrae heir cooling eecs o he norhern-mos or souhernmos pars o he plane are hus more useulhan hose ha only work uniormly on he enire Earh a once.

o esimae how much sunligh would need o be refecedo ose greenhouse warming o he Arcic or o he enireplane, scieniss have urned o he same compuer modelsha hey use o projec climae change scenarios [Caldeiraand Wood 2008]. Tese models sugges ha reducing incom-

ing solar radiaion by abou 1.8% worldwide would ose hegreenhouse warming caused by he doubling o CO concenra-ion rom is level in preindusrial imes. (Te CO concenra-ion is currenly abou 1.4 imes is preindusrial level and risingseadily. [Homan 2009])

Such a small change in solar radiaion would almos cerainlybe impercepible o our eyes. Because incoming sunligh wouldbe more diuse, scieniss believe ha sraospheric aerosolswould increase plan growh, boosing agriculural produciv-iy and increasing he rae a which carbon dioxide is absorbed

ou o he amosphere [Robock e al. 2009]. More sudies areneeded o undersand he magniude o his eec and wheheri could help o alleviae oher consequences o high CO levels,such as changes o he pH o he oceans.

Preliminary modeling sudies sugges ha wo million ove million meric ons o sulur dioxide aerosols (carrying onemillion o 2.5 million ons o sulur), injeced ino he srao-sphere each year, would reverse global warming due o a dou-bling o CO, i he aerosol paricles are sucienly small andwell dispersed [Rasch e al. 2008]. wo million ons may soundlike a lo, bu i equaes o roughly 2% o he SO ha now rises

ino he amosphere each year, abou hal o i rom manmadesources [Caldeira and Wood 2008], and ar less han he 20 mil-lion ons o sulur dioxide released over he course o a ew daysby he 1991 erupion o Moun Pinaubo [Robok e al. 2009].Scienic sudies published so ar conclude ha any increase inhe acidiy o rain and snow as several million addiional ons ayear o SO precipiae ou o he amosphere would be minus-cule and would no disrup ecosysems [Kraviz e al. 2009].

A more limied geoengineering sysem designed o rescue

RESCUING ARCTIC SUMMER SEA ICE may be necessaryan possiblei

CO levels continue to rise, accoring to computer moels o the global clima

The extent o ice cover on the Arctic Ocean at the en o September is shown

top or a worl with preinustrial CO levels (pink). The raction covere by ic

is much smaller i CO levels ouble (middle). Moels inicate that i a strato-

spheric aerosol shiel reuce sunlight over latitues north o 60N by 10%, t

ice cap woul be restore to its ormer extent each summer (bottom).

CREdIT: Maps by Wayt Gibbs; ata courtesy o Ken Caleira, Carnegie Institute o Washington


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he Arcic ice cap and undra rom caasrophic warming (wihmuch less cooling o he res o he plane) would aim o atenu-ae he solar radiaion hiting he Arcic and sub-Arcic laiudeso 60N and higher by abou 10%. Climae models indicaeha his would lead o average emperaures in he region be-ing abou 2.8 C (5 F) lower han hey would be wihou hesysemenough o resore sea ice in he Arcic o is preindus-

rial exen. Snow deph migh acually increase a bi over whai was beore global warming began [Caldeira and Wood 2008].Because abou 10% o he plane lies norh o 60N

which is roughly he laiude o Anchorage, Alaska or Oslo,Norwaya rough rs-order esimae is ha injecion o as litleas 200,000 meric ons a year o sulur dioxide aerosol ino hesraosphere above his region could ose warming wihin heArcic. A phenomena peculiar o he polar amosphere, he po-lar sraospheric vorex, adds uncerainy o his esimae, how-ever. Te vorex causes mixing beween sraospheric air and helower par o he amosphere o occur more rapidly in he Arcic

han a lower laiudes. As a resul, aerosol paricles injeced inohe sraosphere a laiudes above 60N will probably all backo Earh in less han a year, on average. o compensae or hiseecand because he aerosols serve no purpose during hedark polar wineri would hus make sense o concenrae heinjecion period o jus he spring, so ha he cooling eec is amaximum srengh during he summer meling season.

Cutting the Cost: A Hose is Better than BombsLiing large masses o aerosolsor o anyhing, or ha ma-

erup o he sraosphere poses a subsanial engineering chal-lenge. One o he principal criicisms o geoengineering propos-als so ar has been cos: published esimaes o he consrucioncoss o delivery sysems o various kinds have run rom $784million o $6.6 billion, wih esimaed operaing coss rangingrom $225 million o $30 billion a year, depending on wheheraircra, arillery, or sulur-lled exploding balloons were envi-sioned as vehicles or he aerosols [Robock e al. 2009].

In a series o invenion sessions over he pas several years,scieniss and engineers a Inellecual Venures have feshed ouideas or a geoengineering sysem ha could be ar less expen-

sive and more pracical han ohers proposed o dae. Calleda Sraospheric Shield, or SraoShield or shor, he sysemwould deliver sulur dioxide o an aliude o 30 kilomeers inliquid orm, hrough a very long hose suppored by large, long-duraion balloons. A he op o he hose, a series o aomizerswould disperse he liquid ino a ne mis o aerosol paricles,each abou 100 nanomeers in diameer.

In he calculaions we perormed o validae his approach(described below), we ocused on an insallaion capable o

HIGH-FLYING BLIMPS, base on existing protoypes, coul support a hose

thicker than a ire hose (above) to carry sulur ioxie as a clear liqui up

the stratosphere, where one or more nozzles (below) woul atomize it into

ine mist o nanometer-scale aerosol particles. CREdIT: davi Fie


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pumping 100,000 meric ons a year (abou 3.2 kilograms asecond) o liquid sulur dioxide up o he sraosphere, where iwould be dispersed by aomizers ino a ne mis. Several insalla-ions o his sizeor one larger insallaion wih several hosesmigh be needed o save he Arcic rom runaway warming, ihey were operaed only in he spring raher han year-round.

I a some poin world leaders decided ha a climae emer-

gency warraned deploymen o Sraospheric Shields on aglobal scale, a dozen or more insallaions o he size skechedou here could be se up around he world, wih mos o hem aropical and emperae laiudes, o erec an invisible refeciveshield ha could counerac greenhouse warming worldwide.

Our work so ar, which represens subsanial inveniveaciviy bu is sill quie preliminary, suggess ha he cos oconsruc a Sraospheric Shield wih a pumping capaciy o100,000 ons a year would be roughly $24 million, includingransporaion and assembly. Annual operaing coss wouldrun approximaely $10 million. Te sysem would use only

echnologies and maerials ha already exisalhough someimprovemens may be needed o exising aomizer echnol-ogy in order o achieve wide sprays o nanomeer-scale sulurdioxide paricles and o preven he paricles rom coalescingino larger droples.

Even i hese cos esimaes are o by a acor o 10 (and wehink ha is unlikely), his work appears o remove cos as anobsacle o cooling an overheaed plane by echnological means.

Te Sraospheric Shield, and geoengineering in general,mus sill clear many oher obsacles, however, beore such

sysems can reasonably be considered or deploymen. Aconcered, well-unded, long-erm research eor is neededo answer he many quesions ha remain. Wha eec wouldcooling by sraospheric aerosols have on shis in precipiaion,increasing acidicaion o he oceans, and oher environmenalchanges driven by rising levels o CO? How would addiionalSO in he sraosphere inerac wih he ozone layer? Are herecompounds ha would perorm beter han sulur dioxide asrefecors, ha would be even less expensive, or ha would beligher and hus easier o li?

Now is he ime or he science and engineering communiy

o engage ully in he research needed o answer such quesions.Tere currenly is no business model or geoengineering hawould encourage creaive rms such as Inellecual Venureso ramp up and mainain a serious research eor. Bu i is ooimporan a opic o leave or he indenie uure.

In he ollowing secions, we presen more deails on heSraospheric Shield in he hope ha i will inorm and inspireohers o rene he idea and o generae oher invenions orcoping wih he dening problem o he 21s cenury.

References and Further ReadingJ. J. Blackstock, D. S. Battisti, K. Caldeira, D. M. Eardley, J. I. Katz, D. W.

Keith, A. A. N. Patrinos, D. P. Schrag, R. H. Socolow and S. E. Koonin,

Climate Engineering Responses to Climate Emergencies, Novim, 2009.

K. R. Bria, P. D. Jones, F. H. Schweingruber, and T. J. Osborn. Inuence

volcanic eruptions on Northern Hemisphere summer temperature ov

600 years. Nature393, pp. 450455, 4 June 1998.

K. Caldeira and L. Wood. Global and Arctic climate engineering: numer

model studies. Philosophical Transactions o the Royal Society A, 366,pp. 40394056, 2008.

R. J. Cicerone. Geoengineering: Encouraging research and overseeing

implementation. Climatic Change77, pp. 221226, 2006.

P. J. Crutzen. Albedo enhancement by stratospheric sulur injections: a

contribution to resolve a policy dilemma?Climatic Change 77, pp. 211

220, 2006.

D. J. Homann. The NOAA Annual Greenhouse Gas Index. NOAA, 20

Intellectual Ventures. Climate Science and Engineering at Intellectual

Ventures. White paper, 2009.

IPCC. Climate Change 2007: The Physical Science Basis. Cambridge

University Press, 2007.

R. A. Kerr. Is Battered Arctic Sea Ice Down or the Count? Science 318,

pp. 3334, 5 October 2007.

B. Kravitz, A. Robock, L. Oman, G. Stenchikov, and A. B. Marquardt.

Suluric acid deposition rom stratospheric geoengineering with sula

aerosols.Journal o Geophysical Research114, D14109, 2009.

R. Kunzig. A Sunshade or Planet Earth. Scientifc American, pp. 4655,

November 2008.

H.D. Matthews and K. Caldeira. Stabilizing climate requires near-zero

emissions. Geophysical Research Letters35, L04705, 2008.

P. J. Rasch, S. Tilmes, R. P. Turco, A. Robock, L. Oman, C. C. Chen, G. L.

Stenchikov, and R. R. Garcia. An overview o geoengineering o clima

using stratospheric sulphate aerosols. Philosophical Transactions o th

Royal Society A366, pp. 40074027, September 2008.

M. R. Raupach, G. Marland, P. Ciais, C. Le Quere, J. G. Canadell, G.

Klepper, and C. B. Field. Global and regional drivers o accelerating C

emissions. Proceedings o the National Academy o Sciences o the U.S.A

104: 24, 2007.

A. Robock. The Climatic Atermath. Science295, pp. 12421243,

15 February 2002.

A. Robock, A. Marquardt, B. Kravitz, and G. Stenchikov. Benefts, risks,

costs o stratospheric geoengineering. Geophysical Research Letters3

L19703, 2009.

The Royal Society o London. Special issue on geoengineering.

Philosophical Transactions o the Royal Society A366, September 2008
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Pumping to the Stratosphere

o undersand some o he imporan design parameers andengineering rade-os or a Sraospheric Shield, we analyzeda sysem ha could raise 100,000 ons o liquid a year rom heground o an elevaion o 30 kilomeers (100,000 ee). Delay-ing or a momen he quesion o how o suppor he hose, lesconcenrae rs on he fuid fow, which or he purposes ohis exercise we assume will be consan.

Alhough 100,000 ons a year sounds like a lo o liquid,when pumped coninuously hrough a hose, ha amouns ojus 3.2 kilograms per second and, a a liquid SO densiy o

1.46 grams per cubic cenimeer, a mere 34 gallons (150 liers)per minue. A garden hose wih a -inch inner diameer candeliver liquid ha as.

I akes quie a bi o energy o li maerial ino he srao-sphere: abou 30 rillion Joules o poenial energy, in ac,o li 100,000 ons o a heigh o 30 kilomeers. I he workis spread ou over he course o a year, however, ha energyranslaes o a required power o jus 1,000 kilowats. Ine-ciencies and oher pracical consideraions will increase hisamoun, possibly by several imes; noneheless, he power

levels are no dauning by indusrial sandards.o pump 34 gallons a minue up a 30-kilomeer-long hose,he sysem mus overcome boh he graviaional head andhe fow resisance. Te graviaional head, which is simplyanoher way o alking abou he poenial energy consideredpreviously, would amoun o a pressure o 4,300 bar (62,000p.s.i.) i he liquid has a consan densiy o 1.46 g/cmnoaking ino accoun he small atenuaion in he srengh ograviy wih increasing aliude.

Te densiy o he SO does no remain consan during isjourney hrough he hose, however. Ta ransi akes enough

ime ha a any poin in lengh o he hose, he emperaureo he liquid inside he hose is no oo ar rom he empera-ure o he air ouside i, alhough ricion rom he fow willimpar some hea o he fuid. Air emperaure drops wihaliude, and so will he emperaure o he SO; he densiyo he liquid hus increases wih aliude. Te magniude ohe densiy change will vary depending on he sie o heSraoShield as well as he season and ime o day, bu wecan use he hermal prole o he Sandard Amosphere o

esimae a ypical value: beween 1.40 g/cm and 1.57 g/cmTis densiy range rom botom o op produces an overallgraviaional head o 4,520 bar. Tere isn much we can doabou graviy excep gh i wih pumping power.

We have more conrol over he second kind o impedi-men, fow resisance. Tis pressure arises rom drag orcesimposed on he fuid by he walls o he pipe. By selecing diameer o he hose and oher design characerisics, we cachoose wheher he fow resisance pressure is much greaehan he graviaional head or much less han i. A lower fo

resisance migh seem always preerable, bu i comes a aprice: a larger diameer hose, which means more mass or h

balloons o suppor.Te weigh o boh he hose isel and he fuid i conain

increase quickly as hose diameer expands. Consider wodesigns, one using a hose wih a diameer o inch (1.6 cmhe oher a hose 1 inches (3.8 cm) in diameer. Te -inchhose has a cross-secional area o 1.98 cm, which means hahe fow velociy a he ground mus be 11.4 m/s o achievehe required 34 gallons per minue delivery rae. (Te fow

velociy or his hose drops o 10.2 m/s a higher aliudes, do cooling o he SO.)o calculae he resuling fow resisance, we need o

acor in he fows Reynolds number and also he eec opipe roughness. Well assume a wall roughness o mil (13micron). Te Reynolds number, like densiy, is a uncion oemperaure and hus aliude. I changes along he hose bymore han a acor o worom 320,000 o 810,000dueo he emperaure-induced gradiens in densiy, viscosiy,and velociy.

Forunaely, his variaion in he Reynolds number has

very litle eec. Te fow resisance remains esseniallyconsan along he hose, ranging rom 1,000 o 1,100 bar/kTe oal fow-induced pressure head or he -inch hose ishus 30,800 bar, much larger han he 4,500 bar graviaionhead. For a -inch hose, drag orces hus largely deermineour pumping power.

In conras, a 1-inch hose can deliver he payload a a forae under 2 m/s, which generaes a markedly smaller fowresisance o jus 360 bar. Te price or his huge reducion in

The Stratospheric Shielddigging into the details

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pumping requiremens is, o course, he need o generae moreli o suppor a heavier hose. Te SO alone in he -inch hoseweighs 9.1 ons, whereas he liquid in he 1-inch hose comeso a whopping 52.5 ons. Te larger-bore hose will also weighmore han he hin hose, o course, bu ha dierence is a leasparially ose by he need o insall more pumps (and elecri-cal cable o run hem) along he lengh o he hin hose. Te

choice o he opimum hose diameer hus requires a complexse o design rade-os; one canno simply peg he fow resis-ance o some percenage o he graviaional pressure head.

Option 1: A Big Pump on the GroundRaising he fuid up he enire lengh o he hose wih a singlepump on he ground may seem impracical. A more easiblealernaive, we hough, would be o disribue a series osmall pumps a inervals along he hose. Each pump couldhen be o lower power, because i would only have o raisehe liquid as ar as he nex pump. In eec, his does an end-

run around graviy.Wih urher hough, however, we recognized ha pump-

ing rom he ground, eiher using one large pump or a se opumps in series, oers a number o advanages. Mainenanceand replacemen would be signicanly easier, or example.Keeping he pumps on he ground would reduce he size ohe balloons required and could eliminae he need o run elec-rical wiring up he hose.

Anoher imporan, bu less obvious, advanage o pumpingrom he ground is ha in such a sysem he pump can suppor

he mass o he SO liquid, hrough he pressure i delivers.Flow resisance will acually push up on he hose maerial andcan be used o suppor par o is mass as well. Tese eecsgrealy reduce he li necessary o raise he hose o aliude.

Unorunaely, however, a hose suppored his way wouldbe unsable o sideways wind orces, which can impose laeralmomenum ar greaer han he upward momenum deliveredby he fow o SO. Supporing mos o he sysem weighwih ground pressure is also ill-advised because o he pos-sibiliy ha a disrupion o pump operaion could cause heSraoShield o all precipiously. A sysem pumped rom he

ground would hus probably need enough exernal suppor ohandle wind orces and pump ailures saely.

Suppor issues aside, an obvious drawback o pumpingonly rom he ground is ha he resuling pressures insidehe hose mus be exremely large. Te hose wall mus behickened o wihsand he high pressure, and he densiy ohe SO (which is a compressible fuid) will increase. Temagniude o his later eec is no compleely clear. Ex-perimenal daa on he compressibiliy o liquid SO exends

only up o abou 350 bar, which is no even a enh o hegraviaional head in he SraoShield. Wha daa here areshow ha SO has compressibiliy a 0 C o 1.1 x 10 -9/Pa

(1.1 x 10-4/bar), a value abou wice ha o waer. Using hexising daa o an expression or he linear-secan modulus, we expec a 20% densiy increase a 4,500 bar and 0 C

A he lower emperaures encounered hroughou moso he hose, he SO is sier. We esimae ha he inegraedpressure head, aking ino accoun he pressure and emperaure dependence o he compressibiliy, is abou 5,000 bar.So, or a relaively a hose, where he pressure is dominaed

by graviaional head, compressibiliy is no a major concerneven i we are pumping solely rom a ground saion. Com-

pressibiliy becomes a much larger issue i he hose is narrowdue o he addiive eec o fow resisance.Hoses capable o conaining pressures above 5,000 bar

are already available commercially, so his does no seem opresen a dicul echnical challenge. High-pressure hosesare heavier, however. Te quesion is wheher he hose maerial and hickness required is compaible wih a SraoShieldsysem. Consider a hose made rom a composie (possiblymulilayered) maerial 10 mil (254 micron) hick wih a mao 400 g/m. A layer o high-srengh Zylon bers woven inhe hose wall conain he high fuid pressure and are designe

o reduce he operaing sress rom 800,000+ psi o a long-erm creep-resisan value o 340,000 psi.

Te hose mass required o conne a pressure o 5,000 bascales wih he mass o he fuid and he raio o pressure ober srengh. For mos o he hoses lengh, he pressure-resan mass dominaes, requiring a hose mass o abou 40% ho he SO. Tis penaly is highes a he base and decreases

wih heigh as he pressure requiremen alls. Te hose, inoher words, need no be as srong and heavy a he op as i

Hose

diameter

(cm)

Gravitational

head

(bar)

Flow

resistance

(bar)

Total

pressure

(bar)

SOmass

(metric

tons)

Mass o

uid-flle

hose(metric ton

2.0 5,470 15,600 21,060 17.5 31.7

2.5 5,280 6,480 11,760 26.5 39.0

3.0 5,170 3,160 8,330 37.3 50.2

3.5 5,100 1,720 6,830 50.1 64.5

4.0 5,070 1,020 6,090 65.0 81.6

4.5 5,050 640 5,690 81.9 101.5

TABLE 1. Hose Options or a Stratospheric Shiel

Pumpe rom the Groun


7/18

a he botom, i all he pumping is done on he ground.For large diameer hoses, he pressure is dominaed by

he graviaional head, and he hose weigh is dominaed by

he large diameer o he hose raher han he hickness o hewall. For narrow hoses, fow resisance increases he pressure,he compressibiliy o he fuid, and hence he weigh penalyimposed by hose wall hickness. On he oher hand, he overallmass can be lower or a narrow hose simply because i enclosesa smaller volume.

Option 2: Smaller Pumps in the AirInsead o relying solely on a big pump on he ground, wecould place a series o pumps a inervals along he hose. Large

pressures and fuid compressibiliy hen cease o be concerns,and he hose can be ligher and have hinner walls. Each pumpneed deliver only modes pressure, and we could build exrasino he chain so ha he sysem can olerae occasional pumpailures. Te oal mass requiring suppor will be greaer hanwha is shown in able 2, however, because i will include headdiional weigh o he pumps hemselves as well as he elec-rical cables ha power hem.

Te oal pumping power required or he disribued ap-proach is, o course, very similar o ha or a ground-basedpump, bu here are small dierences. Te absence o com-

pressibiliy reduces he graviaional head, bu or low diam-eer hoses his eec is more han ose by he ac ha denserfuid requires lower fow velociies and hence incurs less fowresisance.

Up, Up, and AwayLe us urn now o he quesion o how o raise he hose o hesky and hold i here. Ohers have suggesed building enor-mous owers o suppor a hose, bu his seems unnecessarily

expensive and risky. A more pracical way o suppor a hose he sky is o harness amospheric orces, eiher buoyancy oraerodynamic li.

Balloons and blimps are well developed echnologies,and are quie capable o loing he hose weighs presenedin ables 1 and 2. As wih pumping, we can choose amongseveral sraegies. One exreme is o li only rom he op o

he hose, using a single long-duraion balloon o 200 meersor more in diameer, fying a an aliude o abou 30 kilomeers. (A cluser o 100-meer-diameer balloons could workas well.) Te hose maerial mus hen have sucien ensilesrengh o suppor he enire sysem, or mus be assised byaddiional suppor cables. Because amospheric densiy is loin he sraosphere, he balloon would have o be enormous develop enough buoyancy.

A he opposie end o he range o sraegies is an approain which he hose isel is buoyan, so ha every poin alongis lengh carries is own weigh. (For a preliminary analysis o

his opion, see Blacksocket al. 2009.) In beween hese woexremes are inermediae sraegies ha use muliple ballooneach o which suppors one segmen o he hose. Tis approaallows he balloons o fy a lower aliudes and hus o besmaller (see illustration on next page). Te hose isel need havminimal ensile srengh, which ranslaes o ligher weigh.

One benchmark ha is useul is considering hese opionis NASAs long-sanding projec o develop and demonsralarge, high-aliude balloons ha are superpressurized wih hlium. A mission in December 2008 few one such balloon h

was 80 meers in diameer (200,000 m volume) o an aliuo 33 kilomeers. NASA plans o fy even larger balloons, oover 600,000 m volume, in uure missions.

Te NASA balloons are no spherical, bu raher are pumkin-shaped or greaer srucural eciency. Te envelope haan isoensoid meridional prole and a muli-lobed, azimuhshape. A hin-walled plasic maerial boh conains he heliuand ransers he inernal gas pressure azimuhally o he meridional borders o each lobe. Global pressure loads are henhandled by srong bers running along each meridional cusp

able 3 shows he liing capaciy o such balloons as a

uncion o heir size and o aliude along he hose (see pa9). Tese gures show ha a series o small balloons, each20 o 30 meers in diameer and spaced roughly a kilomeerom he nex, should easily suppor ypical hose weighs o1 o 2 on/km along he lower hal o he hose. Near he oo he hose, however, larger balloons o 60 o 70 meers indiameer would be needed (or alernaively more small balloons spaced closer ogeher).

Te disribued suppor sraegy oers us considerable d

Hose

diameter

(cm)

Gravitational

head

(bar)

Flow

resistance

(bar)

Total

pressure

(bar)

SOmass

(metric

tons)

Mass o

uid-flled

hose(metric tons)

2.0 4,520 18,810 23,330 14.5 15.4

2.5 4,520 7,550 12,070 22.6 23.8

3.0 4,520 3,610 8,130 32.6 34.0

3.5 4,520 1,940 6,460 44.3 46.0

4.0 4,520 1,140 5,660 57.9 59.9

4.5 4,520 720 5,240 73.3 75.6

TABLE 2. Hose Options or a Stratospheric Shiel

with Airborne Pumps


8/18

8

sign reedom, because balloons need no be equal in size or a equal inervals. Nor, given he ensile carrying capabiliy ohe hose, do li and weigh have o be balanced o close oleances a each locaion. We could, or insance, elec o devo0.2 on/km o he hose mass o he srong Zylon bers previously discussed; his sraegy would yield a hose wih a 30-ocarrying capaciy, allowing very large oses o li o weigh

Blowing in the WindGiven all hese opions, a suppor sysem would be sraigh-orward o designi only here were no wind. Unorunae

winds a aliude are srong, oen blow in dieren direciona dieren aliudes, and can change speed and direcionrapidly. Te need o deal wih he saic and dynamic orcesimposed by wind will grealy infuence he design o he hosaerial suppor.

Te exisence o winds preven he quesion o op-hungvs. disribued suppor rom being he open-and-shu case

i would oherwise be. Te mos ecien way srucurallyo help a long, hin objec such as he hose resis sidewaysdefecion by he wind is o draw i auexacly wha a gian

balloon a he op would do. Moreover, he sronges and movariable winds do no occur in he sraosphere, bu a iner-mediae aliudes o around 10 kilomeers (33,000 ee)aliudes where one migh disribue smaller suppor ballooLoing balloons in he windies par o he amosphere willexpose he sysem o more wind sress.

Wind speeds generally increase in aliude, reaching val-

ues around 60 m/s a heighs o 10 o 15 kilomeers. Whenconvolved wih he amospheric densiy prole, he dynamipressures generaed by he wind peak a roughly 1,000 Pa inhe viciniy o 10 km aliude.

Te wind pushes boh he balloons and he hose isel.Tese should be hus designed o minimize drag and o preen he smalles cross-secion o he wind achievable (parilarly or segmens near 10 km aliude, where he wind orcare highes).

Te balloons pose he greaer challenge because o heirlarger laeral area: a single spherical balloon 35 meers in dia

eer presens abou 1,000 m o area o he wind, or examplwhich is abou he same laeral area as he enire lengh o ahose 3 cenimeers wide and 30 km long. Omiting balloonsrom he hose in he region around 10 km aliude wouldreduce he dynamic pressure on he sysem. Bu i he hoseis denuded o balloons in is middle, he balloons a higheraliudes mus be correspondingly larger.

o illusrae he rade-o, les compare wo designs orsupporing a SraoShield ha includes a hose 3 cm in diame

Supporting a StratoShield with Multiple V-shaped Balloons

There are many possible ways

to support a 30-kilometer-

long hose to the stratosphere.

Illustrate here is a series o

11 V-shape blimps o three

istinct sizes. The balloons are

numbere rom top to bottom.

Balloon altitude:

Balloons 15 Arm length: 330 m

X-sectional diameter: 22 m





For the entire setEstimated wind drag: 170 kN

Estimated lift: 1,000 kN

Lift-to-drag ratio: 6:1

Est. slant angle:


9/18

er, pumped solely rom he ground. For saey, les assume heballoons mus suppor he ull 50 ons o he loed srucureplus he SO payload, no jus he weigh o he empy hose.

Te rs design balances li and weigh locally, as hey varyalong he hose, by placing balloons o appropriae size everyhal kilomeer. Te balloons range in diameer rom 15 meersa he base o 56 meers a he op. Alogeher, he balloonspresen an aggregae laeral area o 30,000 m o he wind30

imes he area o he hose isel. When convolved wih he

dynamic wind pressure, he aggregae side orce (or a dragcoecien o 1) is 3.3 MNw, which is more han six imes

weigh o he hose.Te second design balances li and weigh globally, by pl

ing balloons only near he op o he hose, a a spacing o a hkilomeer beween he aliudes o 20 and 30 km. Te ballooin his design are larger, ranging in diameer rom 50 meerso 85 meers. Alogeher, heir aggregae laeral area is 45,00m, 50% larger han in he rs case. When convolved wihhe dynamic wind pressure, however, he aggregae side orc

(again or a uni drag coecien) is only 2.5 MNw, abouone quarer lower han in he rs design. Te side orce is smuch greaer han he weigh o he hose, however. Clearly wmus nd some way o drasically reduce he wind load.

One redeeming eaure o wind orces is ha hey can provide aerodynamic li as well as drag. We could ake advanago his by using kies or oher liing airoils o help suppor hose. Alhough hey wouldn uncion all he ime, hey wouprovide li a precisely he imes i is mos neededwhen

wind is severe and pushing he hose sideways.An even beter soluion may be o use buoyan liing

bodies, such as elongaed balloons shaped like aerodynamicblimps raher han squa pumpkins. Te balloons hemselvecan hen combine he uncions o saic and dynamic li.

Tis approach oers hree major advanages. Firs, an elogaed shape presens a much smaller ronal area o he windor any given inerior volume. Second, and even more imporan, is a reducion o he drag coecien: or a ypical blimphis is abou 0.05, 1/20h ha o a pumpkin-shaped balloonFinally, blimps can be designed o generae aerodynamic li

Diameter

Altitude(km) 20 m 40 m 60 m 80 m 100 m

0 2.65 21.4 72.3 171.6 335.4

3 1.96 15.9 53.7 127.5 249.3

6 1.42 11.5 39.1 92.8 181.5

9 0.99 8.12 27.6 65.6 128.3

12 0.65 5.38 18.3 43.7 85.6

15 0.39 3.30 11.3 27.1 53.1

18 0.23 2.01 6.95 16.7 32.8

21 0.13 1.18 4.18 10.1 20.0

24 0.064 0.67 2.45 6.02 12.0

27 0.025 0.36 1.39 3.52 7.12

30 0.001 0.17 0.74 1.97 4.10

TABLE 3. Liting Capacity, in metric tons,o Pumpkin-shape Balloons

V-SHAPEd BLIMPS large enough to be use in a StratoShiel system have been

constructe by JP Aerospace in Rancho Corova, Caliornia.

CREdIT: Courtesy o JP Aerospace


10/18

10

ha grealy exceeds he drag orce. JP Aerospace has designedlarge V-shaped blimps ha reporedly can generae 20 imesas much li orce as he drag imposed by inciden wind. Tecompany has even consruced prooypes. Alhough a highraio o li o drag doesn acually reduce he laeral orce im-posed by he wind, i would increase he hose ension, herebyreducing he defecion caused by he wind.

Te one clear disadvanage o using blimp-like balloons isha hey are less srucurally ecien han pumpkin-shapeddesigns. Ta is, hey have more wall mass per uni o buoy-an li, so hey mus be larger and made rom more envelopemaerial. Tese are aordable penalies, however, paricularlysince he gains in aerodynamic li more han ose he lossesin buoyancy.

We can similarly reduce he drag coecien o he hoseby giving i a sreamlined shape or by surrounding i wih alow-mass aerodynamic sheah. In eiher case, he wind willauomaically wis he hose ino he proper, drag-minimiz-

ing, orienaion.I seems clear ha sensible use o well undersood srae-

gies or producing aerodynamic li and reducing aerodynamicdrag can enable a SraoShield sysem o olerae wind orceswih only modes (albei highly dynamic) defecion o hehose.

Intead of a Hose, an Elevator?An elevaor is anoher alernaive or liing mass o hesraosphere. Like he hose, i would use one or more ligher-

han-air srucures ehered o he ground and a dispersal sys-em a he op o he eher, nominally a 30 km aliude. Teelevaor, however, would carry he payload liquid in discreeanks carried by vehicles (climbers), which crawl up heeher cable.

Te main advanage ha an elevaor oers over a hose ishe eliminaion o fow resisance. In principal, an elevaorcould ranspor liquids much more quickly han a hose oequivalen saic capaciy. I is cerainly reasonable o imaginedesigning a vehicle ha climbs a cable a ens o meers persecond, in conras o he ew meers per second envisioned

above or a 1-inch (3.8-cenimeer) hose.We could consider many design opions or a sraospheric

elevaor sysem. Moive power could be delivered mechani-cally by a coninuous loop o moving cable (similar o a skili) or by a winch; or via elecric racion, using exernal powerrom he cable or beamed rom he ground; or by sel-poweredmoors on he vehicles hemselves.

Te sysem could use jus one large-capaciy climber or

several smaller vehicles. A single-car sysem is simpler. In-creasing he number o cars keeps he load on he cable closo consan, however, as well as more evenly disribued.Muliple vehicles could ravel on a single cable i sidings

were placed o allow up- and down-raveling vehicles o pasone anoher.

Oher opions include:

vehicles ha simply drop rom he op o he cable an

all or glide back o Earh when empy;separae cables going up and coming down. A challen

wih his approach would keeping cables rom anglior vehicles rom colliding, unless he cables were very

widely space a he ground.Te simples opion is probably o send a single sel-pow

ered climber up and down a single saionary cable. Te moecien opion is likely a conveyor bel wih an endless loo cable carrying many small anks. Te later would requirelarge amoun o engineering developmen, however.

Te rs choice o power plan or a sel-powered climbewould be a urbosha engineor perhaps a lighweigh,urbocharged pison enginedriving he vehicle mechani-cally. Unorunaely, he upper porion o he cable is, a 25 30 km, oo high or exising air-breahing engine designs; hPerseus-B used a riple urbocharger o run a 18 km (62,00.) aliude, he curren record. (See www.aurora.aero ordeails.)

We have considered oher opions ha migh work orshor-duraion climbs wih minimal polluion ino he srao

sphere, including:a monopropellan or bipropellan urbogeneraor, e.gusing hydrogen peroxide plus a small amoun o hydrcarbon uel;an air-breahing urbogeneraor ha operaes rom selevel o 1518 km, a which poin high-specic-enerlihium bateries provide main propulsive power;high-eciency elecric moors driven exclusively by

batery power.A climber powered solely by bateries, i i is reasonably e

cien, could climb o 30 km wih abou 50% payload racio

(~200 Wh/kg = 720 kJ/kg = 2.4 kg lied o 30 km per 1 kg obatery). Outed wih a lighweigh moor o provide poweor he rs 15 km, i could have a payload racion o abou70%. For long-erm use o a batery-powered climber, howev

bateries would have o endure many more han 1,000 chargedischarge cycles. I such opions were no available, hen a lasor microwave-beamed power sysem, or a moving cable, wouoer he nex mos atracive and cos-eecive approaches.


11/18

A Cable to the SkyFinally, les consider wha kind o cable would be requiredby a 30 km elevaor. Zylon or similar cable o 1 cm hicknessoers a usable ensile srengh (wih saey margins) o 2 GPaand a load raing o 20,000 kg a a cable mass o 156 kg/km (so4,700 kg or 30 km). I may be necessary o use muliple hin-ner cables inerconneced by webbing o provide boh proec-

ion rom single-poin breaks and addiional racion area.Indeed, his is he ribbon conguraion beloved o hose whoadvocae developmen o space elevaors.

I we assume a op saion (anks, ank swap mechanism,sprayer) ha weighs one meric on, hen he oal mass o belied is 15,700 kg. Ta is less han one hird o he weigh o ahose sysem pumped solely rom he ground.

A slighly more sophisicaed elevaor sysem capable omainaining climb speeds o 50 m/sor one ha includes arelay saion a around 15 km aliude so ha wo climbers canravel a oncecould subsanially reduce he cycle ime and

hus he sysem mass. A 6,000 kg vehicle and 10,000 kg oalsysem weigh would be a reasonable goal.

An elevaor could oer oher advanages over a hosebesides lower weigh. I would be easier o unload he sys-em quickly in he even o high winds alo or low-aliudesorms. Unloading a 30 km hose migh require more han anhour, compared o abou 15 minues or an elevaor. A relaedadvanage is he ease wih which he sysem could be unloadeda nigh in order o reduce load on he balloons and mainainconsan aliude. An elevaor sysem is also probably easier

o prooype a small scale (e.g. 10,000 ons per year deliveryraes), whereas fow resisance makes his dicul o do wih along hose.

ReferencesJ. J. Blackstock, D. S. Battisti, K. Caldeira, D. M. Eardley, J. I. Katz, D. W.


http://arxiv.org/pdf/0907.5140http://arxiv.org/pdf/0907.5140


12/18

12

CONTENTS

General

Wha is he SraoShield?

Where is he sraosphere?

How would he SraoShield pu aerosols ino he srao-sphere?

Why are you building his now?

Why did you choose his idea o sudy?

How much aerosol would he SraoShield pu ino he srao-sphere?

Why design a sysem ha can only do a racion o wha isneeded o sop global warming?

So wha would his rs-generaion SraoShield accomplish?

Wha is he aerosol made o?

Balloons an Blimps

How much does he aerosol loing sysem weigh?

Has anyone ever fown a high-aliude balloon capable o li-ing ha much mass?

How many blimps would here be?

How big would he blimps be?Is i really possible o eher a blimp (or blimps!) o heground rom ha aliude?

How hick would he eher need o be?

Win

Wha happens when heres a wind?

How much li could a blimp generae?

Won hose blimps and ha cable ac like a sail, puting oomuch side-load on he ground anchor? Won hey ac like akie, liing he anchor ou o he ground or breaking he cablea he ground?Wha abou dynamic loads? Won peak loads (eiher a heground due o sronger winds alo or a any place along hecable due o creaion o and hen sudden eliminae o slack inhe line) be greaer han he sysem can handle?

Hoses an Pumping

Skyscrapers need special sysems jus o pump waer up oheir op, which is generally less han 1,000 ee. How are ygoing o pump a fuid up o 100,000 ee?

Given how long and high he hose is, whas o preven i roreezing?

Maintaining Altitue

Wha happens when a balloon burss or develops a leak?

How would you replenish he helium in a blimp ha will belos due o normal leakage?

Won he cable or cables ge angled wih each oher and h

blimps + pumps, or a leas ge damaged by collisions?

Logistics

Won he cable presen a navigaional hazard or airplanes?

How much power does i ake o pump ha much mater alhe way o he op?

Electrical discharge

How will he sysem handle elecrical discharge? Won i bhe worlds larges lighning rod?

Alternative Approaches to Aerosol InjectionWhy no jus use airplanes o disperse he aerosols?

Why no jus use arillery shells?

Wha are some o he oher ideas or sraospheric aerosolenhancemen?

Aren here oher ways o achieving he same eec?

Atmospheric Science

How will he aerosols be scatered across he enire srao-sphere insead o jus clumping in a narrow band where

heyre ejeced?Wha is he lieime o he aerosols in he sraosphere?

Is radiaion damage o he saion componens a higher aludes a concern?

The Stratospheric ShieldFrequently Aske Questions


13/18

General

What is the StratoShiel?

Te SraoShield is one possible way o respond o a climae

emergency in which greenhouse warming becomes inolerable. Te

SraoShield would reverse greenhouse warming by slighly reduc-

ing he amoun o solar radiaion ha his he Earh. Te shield does

his by increasing he amoun o sulur aerosols injeced ino hesraosphere by abou 1%, a process ha happens naurally when-

ever volcanoes erup. Te aerosols refec incoming sunligh back

ino space. Alhough he change in sunligh would be impercepible

o human eyesand probably benecial or plansi would have a

subsanial cooling eec or he par o he Earh under he shield.

Where is the stratosphere?

Te sraosphere is a layer o he amosphere beween abou 10

kilomeers (33,000 ee) and 50 kilomeers (165,000 ee) aliude.

I lies above he roposphere, which is where mos weaher happens.

Te exac boundary beween he roposphere and he sraospherevaries wih laiiude.

How woul the StratoShiel put aerosols into the

stratosphere?

I would pump hem up in liquid orm hrough a very long hose,

suspended by one or more balloons. Aomizers a he op o he

hose would spray he clear liquid ou ino he air as a very ne mis,

which wind currens would hen spread around he circumerence

o he plane.

Why are you builing this now?

We are no building or even planning o build he SraoShield.

Inellecual Venures is simply urging ha research on geoengineer-

ing opions, including sraospheric aerosol enhancemen, begin in

earnes now. We share wih many ohers a concern ha he massive

scale o echnological developmen, deploymen, invesmen, and

liesyle changes required o bring greenhouse gas levels down o

susainable levels will ake more ime o implemen han we have

beore he climae sars changing in inolerable ways.

I ha happens, geoengineering opions could buy humaniy

addiional ime o complee he shi o a cleaner energy sysem. Tesoluion o he problem o climae change is new energy sysems,

no geoengineering. Bu we may nd ha we need geoengineering

echnologies as sop-gap responses i he ransiion o hese cleaner

energy sysems akes oo long, or i abrup changes in climae occur

unexpecedly.

Why i you choose this iea to stuy?

I he world decided ha i had o use geoengineering as a sop-ga

soluion, he goal would be o deploy i quickly bu also o phase

i ou relaively quickly. Ta leads us o preer geoengineering

approaches ha are less expensive and ha require litle or no new

echnology, so are easier o deploy quickly. I also leads us o preeapproaches whose cooling eecs are well undersood and readily

conrolled, and which dissipae quickly once he sysem is urned

down or urned o.

Te SraoShield is an example o a geoengineering sysem ha

draws on exising echnology and has deploymen and annual op

eraion coss amouning o millions o dollars, raher han billions

Alhough we have explored he general principles o how a sysem

like his would operae, many echnical deails would have o be

worked ou. Te deailed R&D is no somehing ha IV currenly

conemplaes doing, alhough i a responsible research program ogeoengineering is launched, we may paricipae and collaborae w

ohers in invening and rening a variey o echnical opions.

In concer wih echnical developmen, a grea deal o environ

menal science mus be done o ideniy possible side eecs. Te

may be work-arounds o avoid some side eecs, bu ohers could

be show-soppers. Much more inellecual eor needs o be appl

o his area so ha a body o scienic and engineering knowledge

exiss, should i ever be needed o address a climae emergency.

How much aerosol woul the StratoShiel put into the

stratosphere?Te reerence sysem were sudying would injec 100,000 meric

ons o sulur dioxide a year ino he sraosphere, which a a con-

san fow rae works ou o only abou 34 gallons (130 liers) a m

ue. Abou 100 million ons o sulur dioxide already rise ino he

sraosphere each year, abou hal rom manmade sources (such a

power plans) and hal rom naural processes (such as volcanoes)

One SraoShield insallaion would hus increase annual aerosol

inpu o he sraosphere by abou one par in 1,000.


14/18

14

Scienic sudies so ar have concluded ha a worldwide sysem

(which would require a dozen or more SraoShield insallaions)

would probably have o spread several million meric ons a year o

sulur dioxide hroughou he sraosphere o reduce solar radiaion

hiting he enire plane by abou 1.8% (4 W/m) globally. Climaol-

ogiss believe ha small reducion in sunligh would be adequae (i

i occurred equally around he globe) o couner all o he warming

caused by a doubling o CO over preindusrial levels.A SraoShield placing 100,000 meric ons o aerosol a year ino

he upper amosphere would be expeced o reduce incoming solar

radiaion by less han hal a wat per square meer, averaged over he

globe. More research is needed o conrm hese esimaes.

Why esign a system that can only o a raction o what is

neee to stop global warming?

Global warming is an exremely complicaed problem, and global

cooling echnologies should be approached gradually and wih

careul invesigaion o possible unwaned side eecs. Small-scale

esing will be a necessary par o his invesigaion.A small scale SraoShield could also have more han a small

impac. I deployed a an appropriae norhern laiude, jus a ew

insallaions o his size may be adequae (as a rs generaion

sysem) o proec he Arcic by cooling Arcic waers enough

o preven caasrophic loss o sea ice, as well as by making mos

precipiaion all as snow insead o rain. Saving he Arcic ice cover

could in urn hal posiive eedback cycles ha hreaen o acceler-

ae global warming.

I a some poin an inernaional consensus emerged ha a em-

porary planewide sysem was necessary, more and perhaps largerSraoShield insallaions could be deployed a a range o laiudes o

generae he aerosol cover necessary.

So what woul this rst-generation StratoShiel

accomplish?

Tree or our Sraoshield insallaions o he size we discuss here,

i deployed a a laiude beween 60N and 70N and operaed only

during he spring monhs, could help resore he shrinking ice cap

in he Arcic Ocean o is ull preindusrial exen. Mainaining sea

ice is imporan in he gh agains global warming, because ice has

a very high albedo (i refecs sunligh back ino space), whereassea waer has a very low albedo (i absorbs mos o he inciden

sunligh). Because o his dierence in albedo, once some o he sea

ice mels, he resuling waer absorbs much more sunligh, warming

he adjacen waer and causing more ice o mel, poenially resul-

ing in a disasrous eedback cycle. In ac, he dierence in albedo

can lead o a dierence o over 100 W/m, a much larger eec han

he aerosol isel. Combaing he loss o Arcic sea ice is hereore a

major ron in he gh agains global warming.

What is the aerosol mae o?

Te aerosol would likely be made o sulur dioxide (SO), a naur

componen o volcanic ash ha is presen in he air we all breahe

every day. Anoher possibiliy is o use SO3

insead. Engineered

aerosols, no ound naurally in he amosphere, could be more

ecien a refecing cerain pars o he solar specrum, bu heir

benes over SO migh no be worh he cos o developmen an

producionor he uncerainies abou heir environmenal eeScience has produced a good undersanding o boh he global

sulur cycle (which includes volcanic ash) and he saey o sulur

dioxide a he very low concenraions required or geoengineerin

A good deal more research would be required o esablish he sae

and environmenal lie cycle o cusomized aerosol paricles.

Why has Intellectual Ventures le or patents on the

StratoShiel?

Paens are he primary way ha I.V., as an invenion company,

communicaes is echnical ideas in deail o he global communi

o invenors and engineers. In he case o geoengineering, here ara leas wo addiional reasons ha invenors are well advised o

le or paens. Firs, hisory shows ha ideas are beter cared or

and more likely o be developed responsibly when someone owns

hem. Second and more imporan, a paen gives he invenor som

measure o conrol over howand wheherhe invenion is us

A geoengineering sysem would have eecs ha ranscend borde

and possibly generaions. I should be deployed only i absoluely

necessary, and even hen only aer a deliberae and inclusive ine

naional decision-making process. Paens usually remain in orce

or only 20 years aer he ime o applicaion, bu during ha imhey can give invenors some infuence in prevening he premau

use o heir invenions.

Balloons an Blimps

How much oes the aerosol loting system weigh?

Te weigh o he reerence sysem is in he range o 30 ons o10

ons, depending on design choices such as he number o pumps,

balloons, ec.

Has anyone ever own a high-altitue balloon capable o

liting that much mass?

High-aliude balloons capable o liing a ew ons have been fow

by NASA and ohers. A SraoShield could use muliple balloons

(or blimps) o disribue he weigh. Alernaively, exising blimp

echnology could be scaled up o a larger diameer i i was desirab

o use ewer blimps, or perhaps even only one.


15/18

o hold he ension rom he blimps. Tere is a rade-o beween

he pump pressure needed and he hose diameer, bu a hose wih

he capaciy o a large garden hose or a small re hose should be

sucien. Depending on he design, ension loads could likely be

handled by meal cable o less han a cenimeer in diameer.

Win

What happens when theres a win?

A many aliudes, here will always be a wind, oen very srong.

Wind will defec he enire sysem and hereby reduce he aliud

a he op. I he hose were defeced enirely in one direcion by 1

degrees, he release heigh would be lowered rom 30 kilomeers

29 kilomeers, sill well ino he sraosphere.

I he blimps are no spherical bu raher have an aerodynamic

shape, hey will have lower drag and could even generae li rom

he wind. Te more li we have available (eiher by making he

blimps bigger or by harnessing aerodynamic li), he less he cabwill be defeced in a wind.

How much lit coul a blimp generate?

I is easy o design blimp shapes whose li orce exceeds heir win

drag. Te V-shaped blimp we are examining should produce near

12 imes as much li as drag. Balloons o his sor would ensure h

he hose would no defec rom he verical much a all. A rough

baseline design, using 11 blimps, would generae nearly 100 mer

ons o li and would limi defecion o 10 degrees.

Wont those blimps an that cable act like a sail, putting t

much sie-loa on the groun anchor? Wont they act lik

a kite, liting the anchor out o the groun or breaking the

cable at the groun?

Alhough using muliple blimps would dramaically ease he ech

cal specicaions ha he hose, cable, and blimps mus mee, her

a downside o his approach: i can exacerbae he cumulaive win

eecs along he lengh o he cable. More aerodynamic designs (

cluding V-shaped blimps) should be able o limi average sideway

load a he anchor o 20 meric ons or less.

Any given cable segmen will have some low, nominal ensiona he botom, o pull agains whaever i is conneced o (generall

a blimp). As you move up he cable, he ension increases since an

poin along he cable needs o suppor he weigh o all o he cab

below i. Tereore he maximum ension in any cable segmen w

be a is op, where i is conneced o a blimp. Te 100 meric ons

li menioned above or maximum winds would simply require a

appropriaely-sized cable and anchor.

How many blimps woul there be?

As our whie paper discusses, he rade-os beween using more or

ewer balloons are complicaed, so more engineering sudies need o

be perormed o decide on he bes approach. A sysem wih ewer(one o en) blimps would use less helium, lowering coss. One wih

hundreds o blimps would have more redundancy in case o ailure,

which expands opions or he maerials used o make he balloons.

How big woul the blimps be?

Te size o he blimps depends on wheher hey are simple spheri-

cal balloons or more aerodynamically shaped blimps, as well as on

how many here are. We are currenly leaning owards a V-shaped

blimp conguraion, which provides low drag and a high li-o-drag

raio. For a sysem using 20 blimps, he balloons migh need o aver-age abou 30 meers in diameer (i hey are spherical). Numerous

rade-os can be made among blimp size, number, spacing, and

aliude. I here were only one single blimp a he very op, i would

need o be over 200 meers in diameer.

Is it really possible to tether a blimp (or blimps!) to the

groun rom that altitue?

ehered, high-aliude blimps are already being sold and oper-

aed. Aerosas, which are blimps direcly ehered o a saion

on he ground, are sold by a ew companies or communicaions,

surveillance, and oher purposes. Tey can carry signican weigh(approximaely a on) a aliudes greaer han our kilomeers.

More han 40 years ago, a V-shaped ehered blimp was fown o an

aliude o 20 km.

How thick woul the tether nee to be?

Te eher would have muliple componens. A a minimum, i

would need o have a hose or ranserring he liquid aerosol up.

I may also include a srucural componen (such as a seel cable)


16/18

16

What about ynamic loas? Wont peak loas (either at the

groun ue to stronger wins alot or at any place along the

cable ue to creation o an then suen eliminate o slack

in the line) be greater than the system can hanle?

One piece o research needed or he SraoShield is accurae inor-

maion on wind speed, direcion, and variabiliy a all aliudes rom

he ground up o 30 kilomeers. Wih ha inormaion, he blimps

and cables can be sized o accommodae he maximum expeced

winds. Te sysem can also be designed o minimize he possibiliyo slack in any o he cables.

Hoses an Pumping

Skyscrapers nee special systems just to pump water up to

their top, which is generally less than 1,000 eet. How are

you going to pump a ui up to 100,000 eet?

Sandard residenial pipes canno handle high pressuresgenerally,

hey are raed o jus 150 p.s.i. By using a specially designed hose

and one or more pumps a high pressure, we can boos he fuidall he way o he op o he SraoShield. I he SraoShield used

only a single pump, i would require more han 73,000 p.s.i. (nearly

5,000 imes amospheric pressure) o push aerosols all he way o 30

kilomeers. Tis pressure can be reduced by insead using muliple

pumps disribued along he lengh o he hose. I here were 40

pumps, or example, each one would need o generae abou 2,000

p.s.i., which reinorced hose can easily handle.

Tere is a rade-o beween a single pump a he anchor, requir-

ing a very hick and heavy hose on he one hand, and many pumps

disribued along he cables, increasing weigh hanging rom hosecables on he oher hand. In addiion o he weigh rade-os be-

ween cable size and number o pumps, here is also he imporan

consideraion o reliabiliy o he componens. Much esing will

need o be done in order o condenly undersand he durabiliy o

he sysem.

Given how long an high the hose is, whats to prevent it

rom reezing?

Te meling/reezing poin o sulur dioxide is -75 C (-103 F), so

i is unlikely o reeze. Alhough he air a cerain aliudes can occa-

sionally ge ha cold, ricion beween he fowing SO and he hosewall will provide enough hea o avoid reezing.

Maintaining Altitue

What happens when a balloon (blimp) bursts or evelops

leak?

Each blimp would have excess li so ha he sysem as a whole

can sill operae wih he loss o a single blimp. Te op would los

aliude, bu could sill coninue uncioning in he sraosphere. I

blimp were damaged, he enire sysem would be reeled in and hdamaged componens replaced.

How woul you replenish the helium in a blimp that will b

lost ue to normal leakage?

Tere are some ideas or using an exra hose o supply helium o

blimps. Bu i may be more pracical o reel he sysem down o h

Earh on a regular basis o change ou blimps, service pumps, ec.

Te amoun o pariculae mater ha needs o be sprayed ino h

sraosphere is deermined on a ime-averaged basis. Having a ew

days o down ime every couple o monhs can easily be handled b

sizing he sysem o pump a a slighly higher rae o compensae.High-aliude blimps can survive or 30-60 days on saion, and re

search on improving he robusness o he ouer blimp maerial (

proec i agains UV damage) could exend his lieime.

Wont the cable or cables get tangle with each other an

the blimps + pumps, or at least get amage by collisions

Te various cables (power or he pumps, he hose, he ensile rop

ec.) would likely be woven ogeher o preven exacly his probl

Te sysem will be designed o minimize he abiliy o one compo

nen o bump ino anoher, urher minimizing any damage.

Logistics

Wont the cable present a navigational hazar or airplane

Te blimps and hoses would use appropriae signaling echnolog

(e.g., fashing lighs) o warn airplanes o heir locaion. Addiion

ally, a noice abou he locaion and figh hazards o a SraoShie

could be added or all local fighs (a Noice o Airmen or

NOAM in he Unied Saes) so ha pilos are aware o he gen

eral locaion o avoid.

How much power oes it take to pump that much matter

the way to the top?

Te reerence sysem requires a ew housand kilowats o power

li he SO o he release poin. Te exac answer will depend on

energy eciencies o various pars o he sysem.


17/18

Electrical discharge

How will the system hanle electrical ischarge? Wont it

be the worls largest lightning ro?

Segmens beween blimps would likely be insulaed rom eachoher, and he ground anchor would also be elecrically insulaed, o

preven grounding. Isolaing segmens rom each oher should also

help reduce undesired curren fows hrough he hose.

Alhough in principle power could be generaed rom elecri-

cal fows beween layers o he amosphere, he hardware currenly

available o do his would add unwaned mass and complexiy.

Furher research ino his ype o power generaion migh urn up

lighweigh and ecien mehods.

Alternative Approaches to Aerosol Injection

Why not just use airplanes to isperse the aerosols?

Ohers have proposed his approach, we also gave i serious consid-

eraion. We concluded ha airplanes may no be he bes soluion.,

or a number o reasons. Some exising miliary aircra do fy

high enough o reach he sraosphere, and in principle could be

reasked o deliver sulur-bearing aerosols in he even o a climae

emergencywhich would aer all consiue a hrea o inerna-

ional securiy. Caclulaions so ar sugges he operaing coss o use

aircra could be quie high, however, and i he required aliude oraerosol injecion is beyond he botom o he sraosphere (due o

sraospheric wind paterns), he cos would go up dramaically.

A second concern wih using miliary aircra as delivery vehicles

is he emissions o carbon dioxide and oher greenhouse gases

ha hey would produce, exacerbaing he very problem hey were

deployed o solve. I gher jes were used, 167 jes would each have

o make hree fighs a day, 250 days a year o delivery he amoun o

aerosol required, according o one recen sudy [Robocket al. 2009]

A relaed, more promising idea is o adjus he uel mixure in

commercial airplanes o generae he needed aerosols in heir ex

haus (raher han fying a cargo hold ull o aerosols). Unorun

ly, his opion would reduce heir uel eciency and is no likely

be acceped by sakeholders in commercial airplane operaions.

Why not just use artillery shells?

Firing arillery shells ull o aerosols ino he sraosphere is unliko gain accepance or poliical, environmenal, and nancial rea-

sons. Poliically, we would expec here o be large opposiion o

idea o using large cannons ha would be shooing wo large shel

each per minue around he clock. Environmenally, he casings

rom each shell would presumably descend back o Earh, creain

localized problem wih debris. Financially, ring shells is esimae

o cos much more han oher opions.

What are some o the other ieas or stratospheric aeros

enhancement?

An idea, similar o he SraoShield, ha our invenors have explois he chimney o he sky. Te idea here is o creae a double-

walled, ubular balloon. Te ouer layer would be well insulaed o

keep he inner layer warm, enabling he enire srucure o be ligh

han air. Te balloon would be atached a one end o he ground,

wih he oher end foaing in he sraosphere. Te inner blimp

would be kep warm by injecing ho SO, which would rise up

he chimney o an exhaus por a he op. I needed, he op o h

chimney could be parially suppored by balloons.

I.V. invenors have begun prelimary calculaions on wha migh

be involved in consrucing an elevaor version o he SraoShieTis version would use a kind o elevaor on which climbers woul

carry liquid sulur dioxide o he sraosphere. Te elevaor would

no require pumps or hick-walled hose, so i would have less weig

o li. I migh also be able o deliver he payload more quickly.

Arent there other ways o achieving the same efect?

Tere are many oher ways o enhancing Earhs albedo o reduce

average global insolaion. I.V. has been collaboraing wih Proesso

John Laham and Sephen Saler on one very promising idea o he

o increase marine cloud cover by spraying saly sea waer ino he

air. Te small droples would serve o nucleae more clouds, whichincreases he albedo o ha area. U.S. Secreary o Energy Seven C

has advocaed paining roos whie o increase heir refeciviy. Ou

invenors have begun exploring ways o brighen ground cover suc

as asphal by, or example, incorporaing crushed glass ino he mix

Many o hese ideas will no doub prove ineecive or imprac

cal or one reason or anoher when hey are ully sudied, bu her

does seem o be a wide array o opions sill o explore. I is an are

ripe or invenion.


18/18

Atmospheric Science

How will the aerosols be scattere across the entire

stratosphere instea o just clumping in a narrow ban

where theyre ejecte?

Tere are wo scales o dispersal ha are relevan here. One is he

local densiy o aerosols (which will aec heir clumping rae), and

he oher is he degree o which aerosols migrae o oher laiudes.Localized dispersal (a he ejecion poin) o aerosols is one

area ha will require more research and developmen. Ideas or

enhancing dispersal include elecrosaically charging he aerosols o

encourage separaion or coaing hem o reduce heir abiliy o sick

o each oher.

Curren knowledge o sraospheric winds suggess ha aerosols

would mix a dieren aliudes and would migrae owards he

poles. Aerosols injeced a ropical and emperaure laiudes would

hus be expeced o,spread boh around he circumerence o he

plane and norhward or souhward oward he neares pole.

What is the lietime o the aerosols in the stratosphere?

Te erupion o M. Pinaubo in 1991 gave us an opporuniy o learn

many hings abou using sulur-based aerosols o cool he Earh. Te

aerosols i spewed ino he sraosphere remained here or an aver-

age o 1-2 years beore alling down hrough he roposphere.

Is raiation amage to the station components at higher

altitues a concern?

Te blimp maerial may be coaed o proec i rom UV damage.

Oher radiaion damage should be negligible or he relaively shorduraion ha he SraoShield would be deployed.

References and Further ReadingJ. J. Blackstock, D. S. Battisti, K. Caldeira, D. M. Eardley, J. I. Katz, D. W.



Intellectual Ventures. Climate Science and Engineering at Intellectual Ven-

tures. White paper, 2009.

A. Robock, A. Marquardt, B. Kravitz, and G. Stenchikov. Benefts, risks, and

costs o stratospheric geoengineering. Geophysical Research Letters36,

L19703, 2009.

The Royal Society o London. Special issue on geoengineering. Philosophical

Transactions o the Royal Society A366, September 2008.
http://arxiv.org/pdf/0907.5140http://publishing.royalsociety.org/index.cfm?page=1814http://publishing.royalsociety.org/index.cfm?page=1814http://arxiv.org/pdf/0907.5140

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