Solar shade

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. [cite book |url=http://fermat.nap.edu/openbook/0309043867/html/447.html |title=Policy Implications of Greenhouse Warming: Mitigation, Adaptation, and the Science Base |author=Committee on Science, Engineering, and Public Policy |publisher=National Academy Press |page=p. 447 |isbn=0-309-04386-7]

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. [ cite web
url=http://www.aip.org/history/climate/aerosol.htm
title=Aerosols: Effects of Haze and Cloud
author=Spencer Weart
date=July 2006] [ cite journal
quotes =
author = Crutzen, P.
date =
year = 2006
month = August
title = Albedo enhancement by stratospheric sulfur injections: a contribution to resolve a policy dilemma?
journal = Climatic Change
volume = 77
issue = 3-4
pages = pp. 211–220
issn =
pmid =
doi = 10.1007/s10584-006-9101-y
id =
url = http://www.springerlink.com/content/t1vn75m458373h63/fulltext.pdf
language =
format =
accessdate =
laysummary =
laysource =
laydate =
quote = ] [ cite journal
quotes =
author = Harshvardhan
date = 06/1978
year = 1978
month = June
title = Albedo enhancement and perturbation of radiation balance due to stratospheric aerosols
journal =
volume =
issue =
pages =
issn =
pmid =
doi =
id = 1978aepr.rept.....H
url = http://adsabs.harvard.edu/abs/1978aepr.rept.....H
language =
format =
accessdate =
laysummary =
laysource =
laydate =
quote = ]

Methods

Methods which have been proposed include:
* Releasing dust, sulfate particles, or reflecting micro-balloons into the stratosphere. [cite journal |url=http://www.springerlink.com/content/t1vn75m458373h63/fulltext.pdf |title=Albedo enhancement by stratospheric sulfur injections: A contribution to resolve a policy dilemma? |journal=Climatic Change |year=2006 |volume=77 |pages=211–219| doi=10.1007/s10584-006-9101-y |author=Crutzen, Paul J.] This proposal, not unlike the others, carries with it considerable risks, including increased drought.Brahic, Catherine (2007-08-02), " [http://environment.newscientist.com/article/dn12397-sunshade-for-global-warming-could-cause-drought.html 'Sunshade' for global warming could cause drought] " "New Scientist".]
* Enhancing low-level clouds. [cite journal |last=Latham |first=J. |year=1990 |title=Control of global warming |journal=Nature |volume=347 |pages=339–340 |url=http://www.mmm.ucar.edu/people/latham/files/Latham_Nature_1990.pdf |doi=10.1038/347339b0] [cite journal |last=Latham |first=J. |year=2002 |title=Amelioration of global warming by controlled enhancement of the albedo and longevity of low-level maritime clouds |journal=Atmos. Sci. Lett. |pages=52–58 |doi=10.1006/asle.2002.0099 |url=http://www.mmm.ucar.edu/people/latham/files/cloud_albedo_atmos_sci_lett_2002.pdf |volume=3] [cite paper |url=http://www.mmm.ucar.edu/people/latham/files/cloud_albedo_onepage_handout.pdf |last=Latham |first=J. |title=Preventing global warming by increasing cloud albedo |coauthors=Salter, S. |accessdate=2008-04-20 (A brief handout, with artist's renderings.)]
* Creating a Saturn-like ring of small particles. [LiveScience, [http://www.livescience.com/technology/050627_warming_solution.html Space Ring Could Shade Earth and Stop Global Warming] ]
* Putting a very large diffraction grating (thin wire mesh) or lens in space, perhaps at the L1 point between the Earth and the Sun.See footnote 23 in E. Teller, L. Wood, and R. Hyde (1997) " [https://e-reports-ext.llnl.gov/pdf/231636.pdf Global Warming and Ice Ages: Prospects for Physics-Based Modulation of Global Change] ".] E. Teller, L. Wood, and R. Hyde (1997) " [https://e-reports-ext.llnl.gov/pdf/231636.pdf Global Warming and Ice Ages: Prospects for Physics-Based Modulation of Global Change] ".] See [http://www.kuro5hin.org/story/2005/4/7/41932/19363 Russell Dovey, "Supervillainy: Astroengineering Global Warming] and [http://www.technovelgy.com/ct/Science-Fiction-News.asp?NewsNum=370 Bill Christensen, "Reduce Global Warming by Blocking Sunlight"] .] Gregory Benford (Comments at the 64th World Science Fiction Convention, August 2006.)]
* Space sunshade, numerous reflective glass discs in space.

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. [cite paper
author=Teller, E.
coauthors=Hyde, T.; Wood, L.
title=Active Climate Stabilization: Practical Physics-Based Approaches to Prevention of Climate Change
date=2002
format=PDF
publisher=Lawrence Livermore National Laboratory
url=https://e-reports-ext.llnl.gov/pdf/244671.pdf
accessdate=2008-04-21]

Dispersive solutions

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,See footnote 23 in E. Teller, L. Wood, and R. Hyde (1997) " [https://e-reports-ext.llnl.gov/pdf/231636.pdf Global Warming and Ice Ages: Prospects for Physics-Based Modulation of Global Change] ".] , and in 1997 by Edward Teller, Lowell Wood, and Roderick Hyde.E. Teller, L. Wood, and R. Hyde (1997) " [https://e-reports-ext.llnl.gov/pdf/231636.pdf Global Warming and Ice Ages: Prospects for Physics-Based Modulation of Global Change] ".] 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.See [http://www.kuro5hin.org/story/2005/4/7/41932/19363 Russell Dovey, "Supervillainy: Astroengineering Global Warming] and [http://www.technovelgy.com/ct/Science-Fiction-News.asp?NewsNum=370 Bill Christensen, "Reduce Global Warming by Blocking Sunlight"] .] 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.Gregory Benford (Comments at the 64th World Science Fiction Convention, August 2006.)]

References

ee also

* Microwave power

External links

* " [http://environment.newscientist.com/article/dn11993 Solar shield could be quick fix for global warming] ", New Scientist