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Stratospheric aerosol injection

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Main articles: Geoengineering and Stratospheric sulfur aerosols
Military jets or tanker aircraft have been suggested to deliver aerosol precursors to the stratosphere, to reduce the amount of sunlight reaching the Earth's surface.[1]

The ability of stratospheric sulfate aerosols to create a global dimming effect has made them a possible candidate for use in geoengineering projects[2] to limit the effect and impact of climate change due to rising levels of greenhouse gases.[3] Delivery of precursor sulfide gases such as hydrogen sulfide (H2S) or sulfur dioxide (SO2) by artillery, aircraft[1] and balloons has been proposed.[4]

Tom Wigley calculated the impact of injecting sulfate particles, or aerosols, every one to four years into the stratosphere in amounts equal to those lofted by the volcanic eruption of Mount Pinatubo in 1991,[5] but did not address the many technical and political challenges involved in potential geoengineering efforts.[6] If found to be economically, environmentally and technologically viable, such injections could provide a "grace period" of up to 20 years before major cutbacks in greenhouse gas emissions would be required, he concludes.

Direct delivery of precursors is proposed by Paul Crutzen.[1] This would typically be achieved using sulfide gases such as dimethyl sulfide, sulfur dioxide (SO2), carbonyl sulfide, or hydrogen sulfide (H2S).[4] These compounds would be delivered using artillery, aircraft (such as the high-flying F15C)[1] or balloons, and result in the formation of compounds with the sulfate anion SO42-.[4]

According to estimates by the Council on Foreign Relations, "one kilogram of well placed sulfur in the stratosphere would roughly offset the warming effect of several hundred thousand kilograms of carbon dioxide."[7]

Aerosol formation

Primary aerosol formation, also known as homogeneous aerosol formation results when gaseous SO2 combines with water to form aqueous sulfuric acid (H2SO4). This acidic liquid solution is in the form of a vapor and condenses onto particles of solid matter, either meteoritic in origin or from dust carried from the surface to the stratosphere. Secondary or heterogeneous aerosol formation occurs when H2SO4 vapor condenses onto existing aerosol particles. Existing aerosol particles or droplets also run into each other, creating larger particles or droplets in a process known as coagulation. Warmer atmospheric temperatures also lead to larger particles. These larger particles would be less effective at scattering sunlight because the peak light scattering is achieved by particles with a diameter of 0.3 μm.[8]

Arguments for the technique

The arguments in favour of this approach are:

  • Natural process[9] — Stratospheric sulfur aerosols are created by existing atmospheric processes (especially volcanoes), the behaviour of which has been studied observationally.[10] Other, more speculative geoengineering schemes, do not have natural analogs (e.g. space sunshade).
  • Speed of action[11] — Solar radiation management works quickly, in contrast to carbon sequestration projects such as carbon dioxide air capture which would take longer to have an effect, as the latter relies on removing large amounts of carbon dioxide before they become effective;[5] however, gaps in understanding of these processes exist (e.g. the effect on stratospheric climate and on rainfall patterns)[12] and further research is needed.[13]
  • Technological feasibility — In contrast to other geoengineering schemes, such as space sunshade, the technology required is pre-existing: chemical manufacturing, artillery shells, fighter aircraft, weather balloons, etc.[4]
  • Cost — The low-tech nature of this approach has led commentators to suggest it will cost less than many other interventions. Costs cannot be derived in a wholly objective fashion, as pricing can only be roughly estimated at an early stage. However, an assessment reported in Newscientist suggests it would be cheap relative to cutting emissions.[14] According to Paul Crutzen annual cost of enough stratospheric sulfur injections to counteract effects of doubling CO2 concentrations would be $25–50 billion a year.[3] This is over 100 times cheaper than producing the same temperature change by reducing CO2 emissions.[15]
  • Efficacy — Most geoengineering schemes can only provide a limited intervention in the climate - one cannot reduce the temperature by more than a certain amount with each technique. New research by Lenton and Vaughan suggests that this technique may have a high radiative 'forcing potential'.[16]
  • Tipping points — Application of this technique may prevent climate tipping elements, such as the loss of the Greenland ice sheet[17]

Efficacy problems

All geoengineering schemes have potential efficacy problems, due to the difficulty of modelling their impact and the inherently complex nature of the global climate system. Nevertheless, certain efficacy issues are specific to the use of this particular technique.

  • Lifespan of aerosols — Tropospheric sulfur aerosols are short lived.[18] Delivery of particles into the lower stratosphere will typically ensure that they remain aloft only for a few weeks or months.[19] To ensure endurance, high-level delivery is needed, ensuring a typical endurance of several years. Further, sizing of particles is crucial to their endurance.[20]
  • Aerosol delivery — Even discounting the challenges of lifting, there are still significant challenges in designing a delivery system that is capable of delivering the precursor gases in the right manner to encourage effective aerosol formation. For example, it is unclear whether aerial shells should be designed to leak slowly or burst suddenly. The size of aerosol particles is also crucial, and efforts must be made to ensure optimal delivery.[20]
  • Distribution — It is logistically difficult to deliver aerosols evenly around the globe. Challenges therefore exist in creating a network of delivery points sufficient to allow viable geoengineering from a limited number of launching sites.

Possible side effects

Geoengineering in general is a controversial technique, and carries problems and risks, such as weaponisation.[citation needed] However, certain problems are specific to, or more pronounced with this particular technique.[21]

  • Drought, particularly monsoon failure in Asia and Africa is a major risk.[22]
  • Ozone depletion is a potential side effect of sulfur aerosols;[23][24] and these concerns have been supported by modelling.[25]
  • Tarnishing of the sky: Aerosols will noticeably affect the appearance of the sky, resulting in a potential "whitening" effect, and altered sunsets.[26]
  • Tropopause warming and the humidification of the stratosphere.[24]
  • Effect on clouds: Cloud formation may be affected, notably cirrus clouds and polar stratospheric clouds.
  • Effect on ecosystems: The diffusion of sunlight may affect plant growth.[27][28][29]
  • Effect on solar energy: Incident sunlight will be lower,[30] which may affect solar power systems both directly and disproportionately, especially in the case that such systems rely on direct radiation.[31]
  • Deposition effects: Although predicted to be insignificant,[32] there is nevertheless a risk of direct environmental damage from falling particles.
  • Uneven effects: Aerosols are reflective, making them more effective during the day. Greenhouse gases block outbound radiation at all times of day.[33]

Further, the delivery methods may cause significant problems, notably climate change[34] and possible ozone depletion[35] in the case of aircraft, and litter in the case of untethered balloons.

Delivery methods

Various techniques have been proposed for delivering the aerosol precursor gases (H2S and SO2).[3] The required altitude to enter the stratosphere is the height of the tropopause, which varies from 11 km (6.8 miles/36,000 feet) at the poles to 17 km (11 miles/58,000 feet) at the equator.

See also

Further reading

  • Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1007/s10584-006-9101-y, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1007/s10584-006-9101-y instead.

References

  1. ^ a b c d e Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1029/2009GL039209, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1029/2009GL039209 instead.
  2. ^ Launder B. and J.M.T. Thompson (2008). "Global and Arctic climate engineering: numerical model studies". Phil. Trans. R. Soc. A. 366 (1882): 4039–4056. doi:10.1098/rsta.2008.0132. PMID 18757275. {{cite journal}}: More than one of |number= and |issue= specified (help)
  3. ^ a b c Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1007/s10584-006-9101-y, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1007/s10584-006-9101-y instead.
  4. ^ a b c d Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1098/rsta.2008.0131, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1098/rsta.2008.0131 instead.
  5. ^ a b Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1126/science.1131728, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1126/science.1131728 instead.
  6. ^ http://www.ucar.edu/news/releases/2006/injections.shtml
  7. ^ "The Geoengineering Option:A Last Resort Against Global Warming?". Geoengineering. Council on Foreign Affairs. March/April 2009. Retrieved 2009-08-19. {{cite web}}: Check date values in: |date= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  8. ^ Keith, David W. (2010). "Photophoretic Levitation of Engineered Aerosols for Geoengineering". Proceedings of the National Academy of Sciences of the United States of America. 107 (38): 16428–16431. doi:10.1073/pnas.1009519107. ISSN 0027-8424. {{cite journal}}: |access-date= requires |url= (help)
  9. ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1007/BF00115242, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1007/BF00115242 instead.
  10. ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1029/94JD03325, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1029/94JD03325 instead.
  11. ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1073/pnas.0700419104, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1073/pnas.0700419104 instead.
  12. ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1073/pnas.0711648105, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1073/pnas.0711648105 instead.
  13. ^ Andrew Charlton-Perez and Eleanor Highwood. "Costs and benefits of geo-engineering in the Stratosphere" (PDF). Retrieved 17 February 2009.
  14. ^ Brahic, Catherine (25 February 2009). "Hacking the planet: The only climate solution left? (NB cost data in accompanying image)". Reed Business Information Ltd. Retrieved 28 February 2009.
  15. ^ "Research on Global Sun Block Needed Now". Nature. 463 (7280). Nature Publishing Group: 426–427. 28 January 2010. doi:10.1038/463426a. ISSN 0028-0836. {{cite journal}}: |access-date= requires |url= (help)
  16. ^ Lenton, Tim. "Radiative forcing potential of climate geoengineering" (PDF). Retrieved 28 February 2009. {{cite web}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  17. ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1088/1748-9326/4/4/045109, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1088/1748-9326/4/4/045109 instead.
  18. ^ Monastersky, Richard (1992). "Haze clouds the greenhouse - sulfur pollution slows global warming - includes related article". Science News.
  19. ^ http://www.crosswalk.com/news/11572945/
  20. ^ a b Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1029/2007GL032179, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1029/2007GL032179 instead.
  21. ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.2968/064002006, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.2968/064002006 instead.
  22. ^ http://climate.envsci.rutgers.edu/pdf/2008JD010050small.pdf
  23. ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1073/pnas.052518199, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1073/pnas.052518199 instead.
  24. ^ a b http://www.cosis.net/abstracts/EGU2008/10823/EGU2008-A-10823.pdf
  25. ^ Heckendorn, P; Weisenstein, D; Fueglistaler, S; Luo, B P; Rozanov, E; Schraner, M; Thomason, L W; Peter, T (2009). "The impact of geoengineering aerosols on stratospheric temperature and ozone". Environmental Research Letters. 4 (4): 045108. doi:10.1088/1748-9326/4/4/045108.
  26. ^ Olson, D. W., R. L. Doescher, and M. S. Olson (2004). "When the Sky Ran Red: The Story Behind The Scream". Sky & Telescope: 29–35. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
  27. ^ L. Gu; et al. (1999). "Responses of Net Ecosystem Exchanges of Carbon Dioxide to Changes in Cloudiness: Results from Two North American Deciduous Forests". Journal of Geophysical Research. 104 (31): 421–31, 434. {{cite journal}}: Explicit use of et al. in: |author= (help)
  28. ^ L. Gu; et al. (2002). "Advantages of Diffuse Radiation for Terrestrial Ecosystem Productivity". Journal of Geophysical Research. 107. Bibcode:2002JGRD.107f.ACL2G. {{cite journal}}: Explicit use of et al. in: |author= (help)
  29. ^ L. Gu; et al. (2003). "Response of a Deciduous Forest to the Mount Pinatubo Eruption: Enhanced Photosynthesis". Science. 299 (5615): 2035–38. doi:10.1126/science.1078366. PMID 12663919. {{cite journal}}: Explicit use of et al. in: |author= (help)
  30. ^ Balan Govindasamy, Ken Caldeira (2000). "Geoengineering Earth's Radiation Balance to Mitigate CO2-Induced Climate Change". Geophysical Research Letters. 27 (14): 2141–4. Bibcode:2000GeoRL..27.2141G. doi:10.1029/1999GL006086.
  31. ^ Michael C. MacCracken (2006). "Geoengineering: Worthy of Cautious Evaluation?". Climatic Change. 77 (3–4): 235–43. doi:10.1007/s10584-006-9130-6.
  32. ^ http://climate.envsci.rutgers.edu/pdf/aciddeposition7.pdf
  33. ^ "Sulfate Aerosol and Global Warming". University of Washington.
  34. ^ "Chapter 6: Potential Climate Change from Aviation". Aviation and the Global Atmosphere. Intergovernmental Panel on Climate Change.
  35. ^ Robert Parson. "Will commercial supersonic aircraft damage the ozone layer?". Ozone Depletion FAQ.
  36. ^ PICATINNY ARSENAL DOVER N J. "PARAMETRIC STUDIES ON USE OF BOOSTED ARTILLERY PROJECTILES FOR HIGH ALTITUDE RESEARCH PROBES, PROJECT HARP,". Retrieved 25 February 2009.
  • US 5003186  "Stratospheric Welsbach seeding for reduction of global warming"

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