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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.
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.