Solar shade

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Use of solar shades is a proposed approach to the mitigation of global warming through planetary engineering. 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.[1]

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[edit] History

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.[2][3][4]

[edit] Methods

Methods which have been proposed include:

  • Releasing dust, sulfate particles, or reflecting micro-balloons into the stratosphere.[5] This proposal, not unlike the others, carries with it considerable risks, including increased drought.[6]
  • Enhancing low-level clouds.[7][8][9]
  • Creating a Saturn-like ring of small particles.[10]
  • Putting a very large diffraction grating (thin wire mesh) or lens in space, perhaps at the L1 point between the Earth and the Sun.[11][12][13][14]

The cooling effect that volcanic eruptions often have on the climate due to ash particles in the upper atmosphere can be seen as an analogy of how these methods might work.

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.[15]

[edit] 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 simplified in image. In addition, as a Fresnel lens it would only be a few millimeters thick.
The basic function of a space lens to mitigate global warming. In reality, a 1000 kilometre diameter lens is enough, much smaller than simplified in 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,[11], and in 1997 by Edward Teller, Lowell Wood, and Roderick Hyde.[12] 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.[13] 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.[14]

[edit] References

  1. ^ Committee on Science, Engineering, and Public Policy. Policy Implications of Greenhouse Warming: Mitigation, Adaptation, and the Science Base. National Academy Press, p. 447. ISBN 0-309-04386-7. 
  2. ^ Spencer Weart (July 2006). Aerosols: Effects of Haze and Cloud.
  3. ^ Crutzen, P. (August 2006). "Albedo enhancement by stratospheric sulfur injections: a contribution to resolve a policy dilemma?". Climatic Change 77 (3-4): pp. 211–220. doi:10.1007/s10584-006-9101-y. 
  4. ^ Harshvardhan (06/1978). "Albedo enhancement and perturbation of radiation balance due to stratospheric aerosols". 1978aepr.rept.....H. 
  5. ^ Crutzen, Paul J. (2006). "Albedo enhancement by stratospheric sulfur injections: A contribution to resolve a policy dilemma?". Climatic Change 77: 211–219. doi:10.1007/s10584-006-9101-y. 
  6. ^ Brahic, Catherine (2007-08-02), "'Sunshade' for global warming could cause drought" New Scientist.
  7. ^ Latham, J. (1990). "Control of global warming". Nature 347: 339–340. doi:10.1038/347339b0. 
  8. ^ Latham, J. (2002). "Amelioration of global warming by controlled enhancement of the albedo and longevity of low-level maritime clouds". Atmos. Sci. Lett. 3: 52–58. doi:10.1006/asle.2002.0099. 
  9. ^ Latham, J.; Salter, S.. "Preventing global warming by increasing cloud albedo". Retrieved on 2008-04-20. (A brief handout, with artist's renderings.)
  10. ^ LiveScience, Space Ring Could Shade Earth and Stop Global Warming
  11. ^ 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".
  12. ^ a b E. Teller, L. Wood, and R. Hyde (1997) "Global Warming and Ice Ages: Prospects for Physics-Based Modulation of Global Change".
  13. ^ a b See Russell Dovey, "Supervillainy: Astroengineering Global Warming and Bill Christensen, "Reduce Global Warming by Blocking Sunlight".
  14. ^ a b Gregory Benford (Comments at the 64th World Science Fiction Convention, August 2006.)
  15. ^ Teller, E.; Hyde, T.; Wood, L. (2002). "Active Climate Stabilization: Practical Physics-Based Approaches to Prevention of Climate Change" (PDF). . Lawrence Livermore National Laboratory Retrieved on 2008-04-21.

[edit] See also

[edit] External links