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. ^[1] 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/year. It would, however, increase the environmental problem of acid rain.^[2][3][4]

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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]
• Creating a Saturn-like ring of small particles. ^[8]
• Putting a very large diffraction grating (thin wire mesh) in space, perhaps at the L1 point between the Earth and the Sun. This plan was proposed in 1989 by J. T. Early,^[9], and in 1997 by Edward Teller, Lowell Wood, and Roderick Hyde,^[10] In 2004, physicist and science fiction author Gregory Benford calculated that a rotating Fresnel lens 1000 kilometres across, 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 $10 billion. ^[11] In 2006, Benford outlined some possible side-effects of such a plan. ^[12]

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. ^[13]

References

See also

• Microwave power