Comments Submitted to Harvard Workshop on SolarRadiation Management Using Stratospheric Aerosols

Harvard UniversityCambridge, MA

Alvia Gaskill, Jr.Environmental Reference Materials, Inc.

Research Triangle Park, N.C.November 8, 2007

1. Introduction. I have limited my comments and recommendations to onesnot already covered at the November 2006 NASA Workshop Report onManaging Solar Radiation (1) to which I also submitted material, but did notattend.

2. Distraction Problem. One of the major objections to solar radiationmanagement (SRM) with aerosols or other means is that if successful orthought to be successful (global temperatures are reduced enough to limitmost harmful effects of climate change, even though ocean acidificationwould still occur), its apparent success and low cost will serve as adisincentive for nations to reduce their greenhouse gas emissions.

The perceived low cost of carrying out the stratospheric aerosol strategy andpossibly the marine cloud albedo enhancement strategy, on the order of afew billion dollars per year vs. that of the emissions reductions strategiesthat have estimated costs in the trillions of dollars is often cited as theprimary reason for the disincentive. This is also a major factor often cited aswhy geo-engineering research is not funded or there is reluctance on the partof scientists and policymakers to discuss it as an option.

To address the cost disparity issue, before any plan is adopted to employSRM of the kind described above, I propose that a mega fund be created intowhich nations would contribute money each year equivalent to their annualgreenhouse gas emissions. The total global contribution per year would be

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at least $250 billion. This figure is based on global greenhouse gasemissions of around 8 billion metric tons of carbon valued at around $31/tonof carbon or $114/ton of CO2 about 10X the current market price forcertified carbon emission reduction credits under the Clean DevelopmentMechanism (2). In this scenario, the U.S. and China, each responsible forroughly 25% of emissions would each contribute $63 billion. The UNwould administer the fund, either as a separate project or as part of a followon to Kyoto.

Given the large amount of money and the lack of suitable projects in whichto invest, rather than throw money at the problems, the money should beallocated as needed to cover worthwhile projects. If the quality of identifiedprojects only justify that some of the money can be spent, the remainingmoney stays in the fund and accrues interest, like any other investmentaccount.

The money can be collected by taxes on producers or consumers or simplyappropriated by the respective governments. In the case of the U.S., a 50-cents per gal gas tax at the pump, based on 141 billion gallons of gasolinesold per year would cover the $62 billion (3). More equitably, apportioningthe tax among petroleum, coal and natural gas producers or consumerswould achieve the same outcome without adversely impacting markets orthe global economy.

One can argue that this is simply another get out of jail free card for theproducers and users of fossil fuels with a modest fee required to continueBAU. However, $250 billion is not a small amount of money and could go along way towards funding the kinds of renewable energy projects that willultimately solve the climate problem.

Note that the Bush Administration has funded global warming work at nomore than $6 billion annually (their numbers) with most estimates, includingmy own far less, especially when only technology development isconsidered. For example, in the area of carbon capture and sequestration,the U.S. only funds a handful of actual carbon capture and sequestrationprojects, with a total value of a few hundred million dollars and much of thatthrough cost shares with industry. The proposed plan would result in at leasta 20-fold increase in spending in technology development, although the UNwould decide where the money would be spent.

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As the world economy grows, the amount collected each year can beincreased. I chose $250 billion somewhat arbitrarily and higher and loweramounts should also be considered in a formal analysis of how to price thisplan. The thought of having to give $250 billion to the UN every yearshould be a considerable incentive for countries to proceed withimplementing greenhouse gas emissions reductions, even with SRM inplace.

3. Definition of Emergency. Most discussions of when to use SRM,including those at the NASA Workshop, either talk about using it now as apreventative measure or holding it in reserve once a suitable technology isdeveloped, for use in a climate emergency. Generally, this is framed assome kind of abrupt climate change that requires immediate action.However, no one has to my knowledge adequately defined abrupt climatechange. Even more importantly, I believe, before there would be any abruptclimate shift, there would also be gradual climate change as we are seeingtoday.

Some of the impacts of gradual climate change such as loss of Arctic sea icecould be reversed by SRM, but others such as sea level rise cannot bereversed and there are no credible technologies available for replacing landbased ice nor do models indicate significant increases in precipitation in thepolar regions that could offset the melting. The Mt. Pinatubo eruptionreduced sea level by a puny 5mm, but did delay its full recovery for about adecade (4). So there was some mitigating impact. However, a sea level riseof several feet would not be correctable or delayed by SRM, whetherreached gradually or all at once.

Likewise, changes in and loss of animal and plant species and ecosystemscannot expect to be corrected by SRM, at least in the short term which isdecades or in some cases, ever.

So, the question is, how much permanent damage is required before it’s anemergency?

4. Actual Risks vs. Perceived Risks. Most reviews of the Mt. Pinatubo andsimilar volcanic eruptions that serve as models for stratospheric aerosolSRM treat ozone depletion, acid rain and regional warming, reduction inbeam radiation, and global and regional droughts and floods associated withthe eruptions as having caused harm to humans and the environment.

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However, there is little confirmed or anecdotal evidence that the Pinatuboeruption harmed humans or ecosystems in these ways.

For example, loss of stratospheric ozone and damage to the environmentfrom loss of ozone are not necessarily the same thing. Some ozonedepletion may be tolerable. The level of aerosol loading at which this occursshould be determined. There is also no evidence that the 6MT of aerosolfrom the Pinatubo eruption caused any acid rain from the stratosphericfallout of particles/droplets.

The harm from northern hemisphere winter warming has also not beendocumented. Reduction in beam radiation may have some affect on solarcollectors, but the ones affected in 1992 may not be as efficient as the onesin service today. I also could not find any evidence that Pinatubo producedan excessive number of cirrus clouds which it is said could warm thetroposphere. Pinatubo cooled the troposphere in general, so how couldcirrus clouds be a problem with a man-made program?

There does appear to be a relationship between the Pinatubo eruption andreduced global precipitation that makes sense (5, 6). However, the extent ofthe impact is in dispute. Trenberth and Dai (5) found a significant reductionin rainfall globally and especially in the tropics due to the eruption, but Gu etal. also recently (6) calculated that the volcanic impact was much less, withabout one third of the estimated 9 inches per year maximal reduction duringthe time of the aerosol clouds existence due to Pinatubo, one third due to aconcurrent ENSO event and one third due to other unknown factors. Seeslide at end of references.

Lower beam radiation reduces evaporation of water and thus fewer cloudsare produced, leading to less rain. But how much less rain and howdamaging were the effects due to Pinatubo alone? And would there be acombined effect from the aerosol program on top of the droughts alreadypredicted for global warming or would the aerosol driven droughts justreplace the ones that were going to occur anyway?

Modeling done by Matthews and Caldeira (7) seems to suggest that reducingsolar radiation from outside the atmosphere would reduce precipitation inthe tropics by about 14 inches per year in 2100 when the SRM is applied toreduce all anthropogenic forcing from 1700-2100. However, their modelingalso shows that unmitigated global warming will itself reduce precipitationby about 7 inches per year in the same region by 2100.

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So the SRM would only reduce precipitation by about 7 inches more than ifnothing were done. Of course, this is in the year 2100. What would be theimpact of offsetting the forcing added since 1700 or 2000 until 2050?Would the additional reduction in precipitation be 3-4 inches? What aboutoffsetting just the 21st century forcing, or that required to prevent a 2 degreeC rise in temperature, etc? Note also that SRM from outside the atmospheremight have different impacts than from within the stratosphere and thedifferences need to be determined. Also, volcanic eruptions are transientevents. SRM carried out over long periods of time may have differenteffects on precipitation.

El Chichon did not produce any global droughts or reduction in precipitationand was about one third the magnitude of Pinatubo in terms of aerosolproduced. It may have reduced precipitation in the tropics, however byabout the equivalent of one inch per year (6). Because its spread was largelyconfined to the northern hemisphere, one cannot assume a threshold forglobal or tropical droughts of 2MT. What is needed is modeling at lowerlevels of aerosol loading to see if there is a threshold and if so, what it is. Ifit is 2MT that is not enough to offset all the past and future warmingexpected, but it could certainly help out and especially in delaying the mostdamaging consequences of global warming.

In general, what are the real risks and let’s not get hung up on what a onePinatubo equivalent can do for us. Some fractional Pinatubo equivalent mayyield significant benefits without creating negative impacts.

4. Perpetual Program. Because of the long lifetime of CO2 in theatmosphere with about half gone in 1 year, 75% gone in 150-300 years andthe remainder lasting for up to thousands of years (8), critics of geo-engineering have seized upon this and said that SRM if adopted involves acommitment of centuries or millennia, similar to the argument made aboutdisposal of high level nuclear waste and that wars or economicconsiderations could disrupt the program, leading to a rapid rise intemperature (7).

This is unrealistic, since it assumes no advances in technology to reduceemissions or remove CO2 from the atmosphere. A more realistic viewpointis that SRM may be required for from 50 years to the end of the century.Economic concerns are also not important, since the cost of the aerosol

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treatment is judged to be quite low. Any global conflict would probablyinvolve nuclear weapons and thus the aftermath of that would probably befar worse than global warming. Ironically, the most likely event to createsufficient disruption that a global SRM program could be negativelyimpacted would be the kind of disruption that unmitigated global warmingwould cause. As for saddling future generations with even carrying out aSRM program for 100 years, I would rather saddle them with this than a 15-ft sea level rise.

5. Delivery Systems and Precursor Chemicals. The NASA Workshop, byits own agenda did not address how the aerosol would be delivered to thestratosphere. However, delivery systems and implementation in generalcannot be ignored as they define what is possible and affect the modeling.For example, in a global program, most of the models assume that theaerosol will be transported to 25Km or thereabouts, around 82,000 ft andthat balloons, artillery guns, rockets, airplanes or some kind of tetheredballoon/blimp/hose system is or will soon be available as OTS equipment. Ithas been suggested that a combustor be built on a mountain to facilitate thedelivery of SO2 to the stratosphere.

I am in the process of evaluating delivery systems for a global stratosphericaerosol program and have concluded that artillery guns and rockets are outof the question for lack of capability and other practical considerations (9-11). Rocket payloads are also too expensive to be justified. Also unsuitableare subsonic passenger, cargo and military jet aircraft and unmanned aerialvehicles. The tethered balloon/blimp/hose idea has not been tested and notethered blimp or balloon has exceeded 15,000 ft. Proposals to increase thesulfur content of jet fuel are also ruled out due to engine performance limitsand inadequate flight areas and altitudes.

The mountain combustor idea fails to consider that just like with Pinatubo, agreat deal of the SO2 wound up in the troposphere, as acid rain downwind,creating a zone of death. It is also highly unlikely that the plume wouldefficiently rise an additional 70,000 ft from a 10,000 ft mountaintop.

Of course, future technology developments in the area of delivery systemsalso cannot be ignored. But for 2007 or the next few years, I have concludedthat only two delivery systems are practical: military fighter jets (F/15c andMIG-31) capable of combat ceilings of around 70,000ft and stratospheric

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balloons containing hydrogen as the lifting gas and hydrogen sulfide as theprecursor chemical. The jets carry the H2S as a liquid in under the wingtanks and release the liquid as a gas at 70,000ft. Hydrogen sulfide isconverted into sulfuric acid aerosol in about 40 days. The use of H2S andhydrogen reduce the payloads compared to SO2 and helium.

There are sufficient planes available to carry out a program that offsets allpast and 21st century forcing by incrementally adding the precursor to thestratosphere daily. The 70,000ft ceiling may not be optimal for aerosollifetimes of 2 years as the models based on Pinatubo assume. However itmay work for some shorter lifetime of say 1 year and my estimates use the1-year lifetime. The stratospheric balloons could be used to achieve higheraltitudes of up to 100,000 ft and could be used along with the planes to stageprecursor releases at different altitudes and latitudes in a way that woulddamp out some or all of the drought producing effects of a tropicalstratosphere release mimicking Pinatubo. The cost of such a program wouldbe around 5 billion dollars per year, far less than some of the estimates given(12).

There has also been some discussion about optimizing droplet sizes tomaximize scattering (1, 12). The assumption is that the Pinatubo aerosolswere less than optimal for some reason related to the quantity produced.That may well be true. It is also the case that much of the Pinatubo aerosolstayed within the tropics and was pulsed out seasonally towards the poles.The concentrated layer there may have led to larger particles or perhaps itwas due to the higher loading of dust from the eruption, some of whichprobably did reach the upper stratosphere and stay there long enough toserve as aerosol condensation nuclei.

With a man-made release of precursor gas only, the only particles that canform nuclei are the ones naturally present from dust and other sources andmay result in smaller aerosol droplets than from Pinatubo for that reason.Not concentrating all the releases in the tropics may also reduce the aerosoldroplet size. Particles that are specially engineered, if such a thing is everpossible, may be too small and due to Brownian motion, clump togethermore rapidly than the larger droplets that are naturally formed and have ashorter lifetime.

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Whatever improvements can be made in engineering precursor chemicals ordelivery systems, it is important to consider that these may not be necessarynow and that we can use existing technology in a stratospheric aerosol SRMversion 1.0 to be improved upon later.

Thus, realistic delivery systems need to be given consideration in modelingand in analyses of outcomes.

6. References

1. Workshop Report on Managing Solar Radiation, L. Lane, K. Caldeira, R.Chatfield and S. Langhoff, NASA Ames Research Center and CarnegieInstitution of Washington Department of Global Ecology, Ames ResearchCenter, Moffett Field, California, November 18-19, 2006, NASA/CP-2007-214558, April 2007,event.arc.nasa.gov/main/home/reports/SolarRadiationCP.pdf

2. State and Trends of the Carbon Market 2007, The World Bank,Washington, D.C., May 2007,http://carbonfinance.org/docs/Carbon_Trends_2007-_FINAL_-_May_2.pdf

3. Gasoline Usage and Pricing, Wikipedia, October 22, 2007,http://en.wikipedia.org/wiki/Gasoline_usage_and_pricing

4. Significant Decadal-Scale Impact of Volcanic Eruptions on Sea Level andOcean Heat Content, Church J.A, N.J. White and J.M. Arblaster, Nature,438, 74-77, doi:10.1038/nature04237, 2005.

5. Effect of Mount Pinatubo Volcanic Eruption on the Hydrological Cycle asan Analog of Geoengineering, K.E. Trenberth and A. Dai, GeophysicalResearch Letters, Vol. 34, L15702, doi:10.1029/2007/GL030524, 2007.

6. Tropical Rainfall Variability on Interannual-to-Interdecadal/Longer TimeScales Derived from the GPCP Monthly Product, G. Gu, R. Adler, G.Huffman and S. Curtis, J. Climate (in press) 2007, http://www.nasa-news.org/resources/2007highlights/May05/Adler_Why_NEWS_highlight_050507.ppt.

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7. Transient Climate-Carbon Simulations of Planetary Geoengineering,Proceedings of the National Academy of Sciences, H.D. Matthews and K.Caldeira, published online before print June 4, 2007,10.1073/pnas.0700419104,http://www.pnas.org/cgi/content/abstract/0700419104v1?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=Ken+Caldeira&searchid=1&FIRSTINDEX=0&resourcetype=HWCIT

8. Fate of Fossil Fuel in Geologic Time, D. Archer, J. Geophysical Research,Vol. 110, C09S05, doi:10/1029/2004JC002625, 2005,http://geosci.uchicago.edu/~archer/reprints/archer.2005.fate_co2.pdf

9. Not All Geoengineering is Science Fiction, Commentary on the Status ofClimate Engineering and Discussion of Options for Reflecting SunlightUsing Soot and Sulfate Aerosols Delivered to the Stratosphere by JetAircraft, A. Gaskill, Jr., Environmental Reference Materials, Inc., ResearchTriangle Park, N.C., October 22, 2006.

10. The Aerosol Air Force: Halting Global Warming by Reflecting SunlightUsing Sulfur Dioxide (SO2) or Hydrogen Sulfide (H2S) Deliverred to theStratosphere by the USAF KC-135R Stratotanker, A. Gaskill, Jr.,Environmental Reference Materials, Inc., Research Triangle Park, N.C.,November 18, 2006.

11. The International Aerosol Air Force: Slowing, Halting or ReversingGlobal Warming by Scattering Sunlight Back into Space Using SulfuricAcid Aerosol Produced by Sulfur Dioxide (SO2) or Hydrogen Sulfide (H2S)Delivered to the Stratosphere at 60,000-70,000 Feet by USAF F-15 and 16and Russian MIG-29 and 31 Fighter Aircraft and by Stratospheric Balloonsat 80,000-100,000 Feet, A. Gaskill, Jr., Environmental Reference Materials,Inc., Research Triangle Park, N.C. (in preparation).

12. Geo-engineering Climate Change with Sulfate Aerosol, P. Rasch, P.Crutzen and D.B. Coleman, in http://calamar.univ-ag.fr/uag/physique/lpat/lpat-new/colloque/PRESENTATIONS/Latham/LathamGuadaloupeLong.ppt.

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From Reference 6:

Impact of ENSO and Volcanoes on Tropical Precipitation

Original MonthlySeries

Derived ENSOocean and landsignals

Derived volcanoimpact-up to 5%

Derived data setwith ENSO andvolcanic signals“removed”-notereduced amplitudeof variations

Gu et al. (2007) J. Clim (in press)NEWS PI: Adler

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Table 5. H2S and SO2 Required to Obtain Forcing Offsets from 1700 to2100 with and without Including Tropospheric Aerosol Decrease; 2010Increase Offsets All Net Pre-2000 Forcing, Tg (from Reference 11).

Year Without Trop. Decreasea With Trop. Decreaseb

H2S SO2 H2S SO22000 0.056 0.105 0.095 0.1792001 0.112 0.211 0.190 0.3592002 0.168 0.316 0.285 0.5382007 0.448 0.843 0.760 1.4352010 4.186 7.878 2.599 4.8982015 4.466 8.405 3.074 5.7952020 4.746 8.932 3.549 6.6922030 5.306 9.986 4.499 8.4862040 5.866 11.040 5.449 10.2802050 6.426 12.094 6.399 12.0742060 6.986 13.148 6.959 13.1282070 7.546 14.202 7.519 14.1822080 8.106 15.256 8.079 15.2362090 8.666 16.310 8.639 16.2902100 9.226 17.364 9.199 17.344

1700-2100 forcing based on 6.5W/m2 total anthropogenic forcing, increasingby 0.0396W/m2 each year from 2000-2100 with the 2.5W/m2 already inplace in 2000 reduced to 0 starting in 2010 and kept at 0 thereafter.Tabulated values represent quantities present in stratosphere at end of yearshown. Tropospheric decrease based on -1.4W/m2 maximum in 2000 goingto 0 in 2050 in annual decrements of 0.0275W/m2. 1Tg = 1 Million Metric

Tons (2205 lbs per metric ton).aassumes no tropospheric aerosol impact,

bassumes -1.4W/m2 maximum tropospheric aerosol impact,

c1700-2000

forcing of 1.1W/m2 based on 2.5W/m2 greenhouse gas forcing - 1.4W/m2

tropospheric aerosol forcing. Results after 2040 differ due to roundingerrors. Example: H2S in 2060 with or without tropospheric aerosol decreaseis the same.

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USAF F-15C Eagle from 1st Fighter Wing, Langley AFB, VA

The conformal fuel tanks under each wing could be replaced with tanksholding around 800 gals each of H2S, allowing 6 tons of H2S to be releasedper flight. From Reference 11.

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