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definition - Solar_radiation_management

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Solar radiation management

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Removing trees from snowy landscapes can help reflect more sunlight into space

Solar radiation management[1] (SRM) projects are a type of geoengineering which seek to reflect sunlight and thus reduce global warming.[2] They do not reduce greenhouse gas concentrations in the atmosphere, and thus do not address problems such as ocean acidification caused by these gases. Their principle advantage as an approach to geoengineering is the speed with which they can be deployed and become fully active. By comparison, other geoengineering techniques based on greenhouse gas remediation, such as ocean iron fertilization need to sequester the anthropogenic carbon excess before they can arrest global warming. Solar radiation management projects can therefore be used as a geoengineering 'quick fix' while levels of greenhouse gases can be brought under control by greenhouse gas remediation techniques.

A study by Lenton and Vaughan suggest that marine cloud brightening and stratospheric sulfur aerosols are each capable of reversing the warming effect of a doubling of the level of CO2 in the atmosphere when compared to pre-industrial levels.[3]

Contents

Background

The phenomenon of global dimming is widely-known, and is not necessarily a geoengineering technique. It occurs in normal conditions, due to aerosols caused by pollution, or caused naturally as a result of volcanoes and major forest fires. However, its deliberate manipulation is a tool of the geoengineer. The majority of recent global dimming has been in the troposphere, except that resulting from volcanos, which affect mainly the stratosphere.

By intentionally changing the Earth's albedo, or reflectivity, scientists propose that we could reflect more heat back out into space, or intercept sunlight before it reaches the Earth through a literal shade built in space. A 0.5% albedo increase would roughly halve the effect of CO2 doubling.[4]

The idea goes back at least to Hoyle (1957)[5] and was expanded on by Kahle and Deirmendjian (1973) of Rand Corporation.[6]

As early as 1974, Russian expert Mikhail Budyko suggested that if global warming became a problem, we could cool down the planet by burning sulfur in the stratosphere, which would create a haze. Paul Crutzen suggests that this would cost 25 to 50 billion dollars per year. It would, however, increase the environmental problem of acid rain.[7][8][9] However, this is now believed to be a minor side effect.[10]

These geoengineering projects have been proposed in order to reduce global warming. The effect of rising greenhouse gas concentrations in the atmosphere on global climate is to create a warming effect on the planet. By modifying the albedo (whiteness) of the Earth's surface, or by preventing sunlight reaching the Earth by using a solar shade, this warming effect can be cancelled out - although it should be noted that the cancellation is imperfect, with time of day and regional discrepancies remaining[citation needed].

The applicability of many techniques listed here has not been comprehensively tested. Even if the effects of small-scale interventions are known, there may be cumulative problems such as ozone depletion, which only become apparent from large scale experiments.[citation needed]

Various small-scale experiments have been carried out on techniques such as cloud seeding, increasing the volume of stratospheric sulfur aerosols and implementing cool roof technology.

A preliminary study by Edward Teller and others in 2002 presented the pros and cons of various relatively "low-tech" proposals to mitigate global warming through scattering/reflecting sunlight away from the Earth via insertion of various materials in the upper stratosphere, low earth orbit, and L1 locations.[11]

Limitations

As well as the imperfect cancellation of the effect of greenhouse gases on global warming, there are other significant problems with solar radiation management as a from of geoengineering not least of these are effects on the global hydrological cycle[12] and the inability of such techniques to reduce ocean acidification.

Particular to solar radiation management, a risk of abrupt cessation exists. If SRM were to abruptly stop, the climate would rapidly warm.[13] This would cause a sudden rise in global temperatures towards levels which would have existed without the use of the geoengineering technique. The rapid rise in temperature may lead to more severe consequences than a gradual rise of the same magnitude.[14]

Atmospheric projects

These projects seek to modify the atmosphere, either by enhancing natural processes such as the sulfur cycle, or by using artificial techniques such as reflective balloons.

Stratospheric sulfur aerosols

Stratospheric sulfur aerosols: proposed by Paul Crutzen,[8] with the purpose to modify the Earth's albedo with reflective or absorptive materials spread over portions of its surface. This would typically be achieved using hydrogen sulfide or sulfur dioxide, delivered using artillery, aircraft (such as the high-flying F15-C) or balloons.[15][16][8][17] Ozone depletion is a risk of such techniques[18], but only if high enough quantities of aerosols drift to, or are deposited in, polar stratospheric clouds before the levels of CFCs and other ozone destroying gases fall naturally to safe levels.[citation needed]This proposal, not unlike the others, carries with it considerable risks, including increased drought[19] or acid rain.[20]Broadly speaking, this technique is seen as a credible geoengineering scheme, although not one without major risks, and challenges for its implementation. This technique can give >3.7W/m2 of globally-averaged negative forcing,[3] which is sufficient to entirely offset the warming caused by a doubling of CO2.

Reflective aerosols or dust

Methods based on increasing the aerosol content in the lower stratosphere for climate modification were proposed by a Russian scientist, Budyko.[21]

United States Patent 5003186 suggested that tiny metal flakes could be "added to the fuel of jet airliners, so that the particles would be emitted from the jet engine exhaust while the airliner was at its cruising altitude." Alternative proposals, not known to have been published in peer-reviewed journals, include the addition of silicon compounds to jet fuel to make silicon dioxide particles in the exhaust.[22]

Alleged secret experiments with aircraft exhaust modification are referred to as the 'Chemtrail Mystery'.[23] or Chemtrail conspiracy theory.

In 1992, a report by the US National Academy of Sciences (NAS)[24] on geoengineering noted that dust is a better choice compared to sulphur, because dust is from natural soil and so should have no noticeable effect on the ground as it gradually falls into the troposphere and rains out. It estimated that about 1010 kg dust would be required to mitigate the warming from a doubling of atmospheric CO2 or about 1 kg dust per 100 t of carbon emissions.
[25]


An example of the effects of the imposition of aerosol particles in the atmosphere can be found in history. Comets have been blamed for the dramatic but brief cooling period which commenced in 1159 BCE, and resulted in widespread disruption to civilisations at the time.[26] However, this mechanism, and even the involvement of a comet, is not universally accepted. If a comet was indeed to blame, the action of its aerosols could also have been by the mechanism of cloud condensation nuclei. Other examples of climate change events linked to comets include the famines around 536 CE.[27]

Cloud whitening / marine cloud brightening / cloud reflectivity enhancement

Rotor ship Buckau - modern versions of such ships could spray seawater into the air to create clouds, shielding the earth from the sun.

Various schemes have been suggested,[28][29][30] such as that proposed by John Latham and Stephen Salter,[31][32] which works by spraying seawater in the atmosphere to increase the reflectiveness of clouds.[15] The extra condensation nuclei created by the spray will change the size distribution of the drops in existing clouds to make them whiter.[33] The sprayers would use fleets of unmanned Rotor ships known as Flettner vessels to spray mist created from seawater into the air to thicken clouds and thus reflect more radiation from the Earth.[34][35] The whitening effect is created by using very small cloud condensation nuclei, which whiten the clouds due to the Twomey effect.

This technique can give >3.7W/m2 of globally-averaged negative forcing,[3][35]which is sufficient to reverse the warming effect of a doubling of CO2.

Cloud seeding

Cloud seeding of cirrus clouds, has been proposed by David L Mitchell and William Finnegan. Their paper proposed the used of airliners to distribute the cloud-seeding materials.[36] They suggest that the technique "... does not have many of the drawbacks that stratospheric injection of sulfur species has."

Ocean sulfur cycle enhancement

Enhancing the natural sulfur cycle in the Southern Ocean[37] ocean by fertilizing a small portion with iron in order to enhance dimethyl sulfide production and cloud reflectivity. The goal is to slow Antarctic ice from melting and raising sea level.[38][39] Such techniques also tend to sequester carbon, but in this specific project the enhancement of cloud albedo was both the desired outcome and measured result.[17] An alternative technique proposes the vertical mixing of ocean water, to bring deep-water nutrients to surface plankton.[40][41] This technique can give only 0.016W/m2 of globally-averaged negative forcing, which is essentially insignificant for geoengineering purposes.[3]

Reflective balloons

Place billions of aluminized, hydrogen-filled balloons in the stratosphere has been suggested to provide a reflective screen.[33][42][43]

These reflectors would be placed at a high enough altitude so that they do not interfere with air traffic. The cost estimate is about 20 times as much as the distribution of dust in the stratosphere,[24] making these schemes economically nonviable. The large number of reflectors and the trash problem posed by their fall make the system unattractive.

Low stratospheric soot

Decreasing the efficiency of burning in engines of aircraft flying in the low stratosphere would maintain a thin cloud of soot to intercept sunlight.[44] However, the relationship between soot or other combustion products and climate change is complex,[45] with some types causing a warming effect.[46] Almost all aircraft cannot reach the stratosphere in most parts of the world.[citation needed]

Cloud seeding

Cloud stimulation can be carried out using a variety of methods, such as burning sulfur in ships or power plants to form sulfate aerosol in order to stimulate additional low marine clouds to reflect sunlight.[47] Liquid nitrogen can also be used,[48] as can silver iodide "Earlier, Reck (1978) studied the effect of increases in cloud cover and, using a radiative-convective atmospheric model, found that a 4 to 5 percent increase in low-level cloud cover would be sufficient to offset the warming predicted from a doubling of preindustrial CO2. This value is in reasonable agreement with Randall et al. (1984), who estimated that a 4 percent increase was required in the amount of marine stratocumulus, which comprises the bulk of the low clouds on a global basis."[33]

Terrestrial albedo modification

Cool roof

File:Roof-albedo.gif
The albedo of several types of roofs

Painting pavements and roof materials in white or pale colours to reflect solar radiation, known as 'cool roof' technology, and encouraged by legislation in some areas (notably California).[49] This is a benign technique,[50] although limited in its ultimate effectiveness by the costrained surface area available for treatment. This technique can give between 0.01-0.19W/m2 of globally-averaged negative forcing, depending on whether cities or all settlements are so treated.[3] This is generally insignificant when compared to the 3.7W/m2 of positive forcing from a doubling of CO2. However, in many cases it can be achieved at little or no cost by simply selecting different materials. Further, it can reduce the need for air conditioning, which causes CO2 emissions which worsen global warming. For this reason alone it is still demonstrably worth pursuing.

Reflective sheeting

Reflective plastic sheets covering 67,000 square miles of desert, to reflect the Sun’s energy.[51][52] This technique can give globally-averaged 1.74W/m2 of negative forcing,[3] which is insufficient to offset the 3.7W/m2 of positive forcing from a doubling of CO2, but is still a very significant contribution and is sufficient to offset the current level of warming (approx. 1.7W/m2). However, the effect would be strongly regional, and would not be ideal for controlling Arctic shrinkage, which is one of the most significant problems resulting from global warming.

Ocean litter

An early geoengineering idea was to use pale coloured floating litter within certain stable oceanic gyres. This litter would tend to group into large and stable areas, such as the Great Pacific Garbage Patch.[citation needed]

Farming, forestry, and land management

Forestry

Reforestation in tropical areas has a cooling effect. Deforestation of high-latitude and high-altitude forests exposes snow and this increases albedo.[53]

Grassland management

Changes to grassland have been proposed to increase albedo.[54] This technique can give 0.64W/m2 of globally-averaged negative forcing,[3] which is insufficient to offset the 3.7W/m2 of positive forcing from a doubling of CO2, but could make a minor contribution towards it.

High-albedo crop varieties

Selecting or genetically-modifying commercial crops with high albedo has been suggested.[55] This has the advantage of being relatively simple to implement, with farmers simply switching from one variety to another. Temperate areas may experience a 1°C cooling as a result of this technique.[56] This technique is an example of bio-geoengineering. This technique can give 0.44W/m2 of globally-averaged negative forcing,[3] which is insufficient to offset the 3.7W/m2 of positive forcing from a doubling of CO2, but could make a minor contribution towards it.

Space projects

Space-based geoengineering projects are seen by many commentators and scientists as being far-fetched at present.[citation needed]

Space mirrors

Mirrors in space: proposed by Roger Angel with the purpose to deflect a percentage of solar sunlight into space, using mirrors orbiting around the Earth.[15][57]

Moon dust

Mining moon dust to create a shielding cloud was proposed by Curtis Struck at Iowa State University in Ames [58][59][60]

Dispersive solutions

The basic function of a space lens to mitigate global warming. In reality, a 1000 kilometre diameter lens is enough, much smaller than what is shown in the simplified image. In addition, as a Fresnel lens it would only be a few millimeters thick.

Several authors have proposed dispersing light before it reaches the Earth by putting a very large diffraction grating or lens in space, perhaps at the L1 point between the Earth and the Sun. This plan was proposed in 1989 by J. T. Early,[61] and in 1997 by Edward Teller, Lowell Wood, and Roderick Hyde.[62] In 2004, physicist and science fiction author Gregory Benford calculated that a concave rotating Fresnel lens 1000 kilometres across, yet only a few millimeters thick, floating in space at the L1 point, would reduce the solar energy reaching the Earth by approximately 0.5% to 1%. He estimated that this would cost around US$10 billion up front, and another $10 billion in supportive cost during its lifespan.[63] Side-effects include that, if this lens were built and global warming were avoided, there would be less incentive to reduce greenhouse gases, and humans might continue to produce too much carbon dioxide until it caused some other environmental catastrophe, such as a chemical change in ocean water that could be disastrous to ocean life.[64]

Putting a very large diffraction grating (thin wire mesh) or lens in space, perhaps at the L1 point between the Earth and the Sun.[61][62][63][64]

See also

References

  1. ^ http://thehardlook.typepad.com/thehardlook/files/schnare_supplemental_testimony_a_framework_for_geoengineering.pdf
  2. ^ http://journals.royalsociety.org/content/84j11614488142u8/
  3. ^ a b c d e f g h Lenton, T. M., Vaughan, N. E. (2009). "The radiative forcing potential of different climate geoengineering options". Atmos. Chem. Phys. Discuss. 9: 2559–2608. http://www.atmos-chem-phys-discuss.net/9/2559/2009/acpd-9-2559-2009.pdf. 
  4. ^ Committee on Science, Engineering, and Public Policy (1992). Policy Implications of Greenhouse Warming: Mitigation, Adaptation, and the Science Base. National Academy Press. p. 447. ISBN 0-309-04386-7. http://fermat.nap.edu/openbook/0309043867/html/447.html. 
  5. ^ Hoyle, F., 1957: The Black Cloud, Harper and Brothers, New York.
  6. ^ Kahle, A. B., and D. Deirmendjian, 1973: The black cloud experiment, Rand Corporation report R-1263-ARPA, Santa Monica CA.
  7. ^ Spencer Weart (July 2006). "Aerosols: Effects of Haze and Cloud". http://www.aip.org/history/climate/aerosol.htm. 
  8. ^ a b c Crutzen, P. J. (2006). "Albedo Enhancement by Stratospheric Sulfur Injections: A Contribution to Resolve a Policy Dilemma?". Climatic Change 77: 211–220. doi:10.1007/s10584-006-9101-y. http://www.springerlink.com/content/t1vn75m458373h63/fulltext.pdf.  edit
  9. ^ Harshvardhan (June 1978). Albedo enhancement and perturbation of radiation balance due to stratospheric aerosols. 1978aepr.rept.....H. http://adsabs.harvard.edu/abs/1978aepr.rept.....H. 
  10. ^ http://climate.envsci.rutgers.edu/pdf/aciddeposition7.pdf
  11. ^ Teller, E.; Hyde, T.; Wood, L. (2002) (PDF). Active Climate Stabilization: Practical Physics-Based Approaches to Prevention of Climate Change. Lawrence Livermore National Laboratory. https://e-reports-ext.llnl.gov/pdf/244671.pdf. Retrieved 2008-04-21. 
  12. ^ http://www.sciencedaily.com/releases/2008/05/080527155519.htm
  13. ^ Ross, A.; Damon Matthews, H. (2009). [Expression error: Missing operand for > "Climate engineering and the risk of rapid climate change"]. Environmental Research Letters 4: 045103. doi:10.1088/1748-9326/4/4/045103.  edit
  14. ^ Ross, A.; Damon Matthews, H. (2009). [Expression error: Missing operand for > "Climate engineering and the risk of rapid climate change"]. Environmental Research Letters 4: 045103. doi:10.1088/1748-9326/4/4/045103.  edit
  15. ^ a b c Five ways to save the world-overview
  16. ^ http://www.wired.com/science/planetearth/magazine/16-07/ff_geoengineering
  17. ^ a b http://www.pmel.noaa.gov/pubs/outstand/bate1229/estimate.shtml
  18. ^ http://www.cosis.net/abstracts/EGU2008/10823/EGU2008-A-10823.pdf
  19. ^ Catherine Brahic (2007-08-02). "'Sunshade' for global warming could cause drought". http://www.newscientist.com/article/dn12397. Retrieved 2009-04-29. 
  20. ^ David Over. "Sulphur screens - 21st Century Challenges". Royal Geographic Society with IBG. http://www.21stcenturychallenges.org/60-seconds/sulphur-screens/. Retrieved 2009-04-29. 
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  22. ^ http://groups.google.com/group/geoengineering/web/jet-fuel-additive
  23. ^ http://earthislandinstitute.net/journal/index.php/eij/article/stolen_skies_the_chemtrail_mystery/
  24. ^ a b National Academy of Sciences, Policy implications of greenhouse warming: Mitigation, adaptation and the science base. National Academy Press, Washington DC, 1992, pp. 433–464.
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  26. ^ http://abob.libs.uga.edu/bobk/ccc/cc070799.html
  27. ^ http://www.topnews.in/comet-smashes-triggered-dry-fog-caused-famine-1500-years-ago-2106421
  28. ^ Latham, J. (1990). "Control of global warming" (PDF). Nature 347: 339–340. doi:10.1038/347339b0. http://www.mmm.ucar.edu/people/latham/files/Latham_Nature_1990.pdf. 
  29. ^ Latham, J.; Salter, S. (PDF). Preventing global warming by increasing cloud albedo. http://www.mmm.ucar.edu/people/latham/files/cloud_albedo_onepage_handout.pdf. Retrieved 2008-04-20.  (A brief handout, with artist's renderings.)
  30. ^ Keith Bower, et al. (2006). [Expression error: Missing operand for > "Assessment of a Proposed Technique for Global Warming Mitigation via Albedo-Enhancement of Marine Stratocumulus Clouds"]. Atmospheric Research 82 (1-2): 328–336. doi:10.1016/j.atmosres.2005.11.013. 
  31. ^ Latham, J. (2002). "Amelioration of global warming by controlled enhancement of the albedo and longevity of low-level maritime clouds" (PDF). Atmos. Sci. Lett. 3: 52–58. doi:10.1006/asle.2002.0099. http://www.mmm.ucar.edu/people/latham/files/cloud_albedo_atmos_sci_lett_2002.pdf. 
  32. ^ Salter, S, G. Sortino & J. Latham (2008). "Sea-going hardware for the cloud albedo method of reversing global warming". Phil. Trans. R. Soc. A 366 (1882): 3989–4006. doi:10.1098/rsta.2008.0136. PMID 18757273. http://rsta.royalsocietypublishing.org/content/366/1882/3989.full. 
  33. ^ a b c Panel on Policy Implications of Greenhouse Warming, National Academy of Sciences, National Academy of Engineering, Institute of Medicine (1992). Policy Implications of Greenhouse Warming: Mitigation, Adaptation, and the Science Base. The National Academies Press. ISBN 0585030952. http://books.nap.edu/openbook.php?record_id=1605&page=828. 
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  37. ^ Wingenter, Oliver W. (November 2007). [Expression error: Missing operand for > "New Directions: Enhancing the natural sulfur cycle to slow global warming"]. Atmospheric Environment 41 (34): 7373–5. doi:10.1016/j.atmosenv.2007.07.021. 
  38. ^ http://www.climos.com/news/articles/slowingglobal.htm Oliver W. Wingenter
  39. ^ Coale, K. H.; Johnson, K. S.; Buesseler, K.; Sofex Group. "SOFeX: Southern Ocean Iron Experiments. Overview and Experimental Design". American Geophysical Union Fall Meeting 2002. 2002AGUFMOS22D..01C. http://adsabs.harvard.edu/abs/2002AGUFMOS22D..01C. 
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  42. ^ Teller et al., 1997
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  45. ^ http://www.nasa.gov/missions/earth/smoke_clouds.html
  46. ^ http://www.gather.com/viewArticle.jsp?articleId=281474977306586
  47. ^ http://www.reason.com/news/show/30433.html
  48. ^ http://www.usatoday.com/weather/research/2008-02-29-china-weather_N.htm
  49. ^ Hashem Akbari, et al. (2008). "Global Cooling: Increasing World-wide Urban Albedos to Offset CO2". http://www.energy.ca.gov/2008publications/CEC-999-2008-020/CEC-999-2008-020.PDF. 
  50. ^ http://climatesafety.org/downloads/climatesafety.pdf
  51. ^ Alvia Gaskill. "Desert Area Coverage". Global Albedo Enhancement Project. http://www.global-warming-geo-engineering.org/Albedo-Enhancement/Surface-Albedo-Enhancement/Calculation-of-Coverage-Areas-to-Achieve-Desired-Level-of-ForcingOffsets/Desert-Area-Coverage/ag28.html. 
  52. ^ http://www.global-warming-geo-engineering.org/Albedo-Enhancement/Surface-Albedo-Enhancement/ag21.html
  53. ^ http://www.carbonplanet.com/downloads/Climate_Effects_of_Forests_Full.pdf
  54. ^ Hamwey, Robert M. (2005). "Active Amplification of the Terrestrial Albedo to Mitigate Climate Change: An Exploratory Study". arΧiv:physics/0512170 [physics.ao-ph]. 
  55. ^ http://www.newscientist.com/article/dn16428-a-highalbedo-diet-will-chill-the-planet.html
  56. ^ Ridgwell, A (2009). [Expression error: Missing operand for > "Tackling Regional Climate Change By Leaf Albedo Bio-geoengineering"]. Current Biology 19: 146. doi:10.1016/j.cub.2008.12.025. 
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  58. ^ Journal of the British Interplanetary Society, vol 60, p 1
  59. ^ Roger Angel, S. Pete Worden (Summer 2006). "Making Sun-Shades from Moon Dust". National Space Society, Ad Astra 18 (1). http://www.nss.org/adastra/volume18/angel.html. 
  60. ^ LiveScience, Space Ring Could Shade Earth and Stop Global Warming
  61. ^ a b See footnote 23 in E. Teller, L. Wood, and R. Hyde (1997) "Global Warming and Ice Ages: Prospects for Physics-Based Modulation of Global Change".
  62. ^ a b E. Teller, L. Wood, and R. Hyde (1997) "Global Warming and Ice Ages: Prospects for Physics-Based Modulation of Global Change".
  63. ^ a b See Russell Dovey, "Supervillainy: Astroengineering Global Warming and Bill Christensen, "Reduce Global Warming by Blocking Sunlight".
  64. ^ a b Gregory Benford (Comments at the 64th World Science Fiction Convention, August 2006.)

 

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