posted 02-27-2003 11:56 PM            

Climate Change 2001:
Working Group III: Mitigation http://www.grida.no/climate/ipcc_tar/wg3/176.htm

Excerpt:

Summaries by Early (1989), NAS (1992), and Flannery et al. (1997) consider a variety of ways by which the albedo of the earth might be increased to try to compensate for an increase in the concentration of infrared absorbing gases in the atmosphere (see also Dickinson, 1996). The possibilities include atmospheric aerosols, reflective balloons, and space mirrors.

Most recently, work by Teller et al. (1997) has re-examined the possibility of optical scattering, either in space or in the stratosphere, to alter the earth’s albedo and thus to modulate climate. The latter work captures the essence of the concept and is summarized briefly here to provide an example of what is envisioned. In agreement with the 1992 NAS study, Teller et al. (1997) found that ~107 t of dielectric aerosols of ~100 nm diameter would be sufficient to increase the albedo of the earth by ~1%. They showed that the required mass of a system based on alumina particles would be similar to that of a system based on sulphuric acid aerosol, but the alumina particles offer different environmental impact.

In addition, Teller et al. (1997) demonstrate that use of metallic or optically resonant scatterers can, in principle, greatly reduce the required total mass of scattering particles required. Two configurations of metal scatterers that were analyzed in detail are mesh microstructures and micro-balloons. Conductive metal mesh is the most mass-efficient configuration. The thickness of the mesh wires is determined by the skin-depth of optical radiation in the metal, about 20 nm, and the spacing of wires is determined by the wavelength of scattered light, about 300nm. In principle, only ~105t of such mesh structures are required to achieve the benchmark 1% increase in albedo.

The proposed metal balloons have diameters of ~4 mm and a skin thickness of ~20nm. They are hydrogen filled and are designed to float at altitudes of ~25km. The total mass of the balloon system would be ~106t. Because of the much longer stratospheric residence time of the balloon system, the required mass flux (e.g., tonnes replaced per year) to sustain the two systems would be comparable. Finally, Teller et al. (1997) show that either system, if fabricated in aluminium, can be designed to have long stratospheric lifetimes yet oxidize rapidly in the troposphere, ensuring that few particles are deposited on the surface..... [more]

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Re: Geo-engineering

*Posted by James Risbey on September 16, 1997 at 18:10:33:
*In Reply to: Geo-engineering posted by Neil Strachan on September 12,1997 at 17:08:02:
http://hdgc.epp.cmu.edu/eppclass/wwwboard/messages/35.html

Your question 2 was on how long geoengineering measures such as seeding the atmosphere with aerosols would give us?

Here there are multiple tradeoffs at stake and there is no definitive time answer to your question. It depends how much we want to trade off some things versus other things. For instance we can continue to seed the atmosphere with aerosols (or put sails in space) to increase the earth's albedo to keep pace with the increase in greenhouse forcing. We will just have to keep putting more and more aerosols up as the greenhouse forcing increases with time. This will get more and more expensive (unless the delivery cost of putting them into the stratosphere comes down with time) and the side effects of spreading aerosols through the stratosphere will also presumably increase the more we put up there (aerosols will fall out of the stratosphere into the troposphere and so will pollute the tropsosphere. On the plus side, we'll have great sunsets!). At some point we might decide that the cure (aerosols in the stratosphere and attendent costs and side effects) is worse than the disease (greenhouse warming). But that is a multi-valued trade-off and it is not easy to say just when the tradeoff point is reached.....

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Previously posted references:

"GEOENGINEERING: A CLIMATE CHANGE MANHATTAN PROJECT" -Deborah http://www.metatronics.net/lit/geo2.html#two

"Turning Down the Heat" -arkansas_skywatcher http://www.cosmiverse.com/space092101.html

"Edward Teller Advances Global Warming Cure" -bucky b http://www.ncpa.org/pi/enviro/envpd/pdenv125.html

"Climate Controls" -bucky b http://www.reason.com/9711/fe.benford.html