OA http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate1528.html
Stratospheric aerosol particles and solar-radiation management : Nature Climate Change : Nature Publishing Group The deliberate injection of particles into the stratosphere has been suggested as a possible geoengineering scheme to mitigate the global warming aspect of climate change. Injected particles scatter solar radiation back to space and thus reduce the radiative balance of Earth. Previous studies investigating this scheme have focused primarily on sulphuric acid particles to mimic volcanic injections of stratospheric aerosol. However, the composition and size of volcanic sulphuric acid particles are far from optimal for scattering solar radiation. We show that aerosols with other compositions, such as minerals, could be used to dramatically increase the amount of light scatter achieved on a per mass basis, thereby reducing the particle mass required for injection. The chemical consequences of injecting such particles into the stratosphere are discussed with regard to the fate of the ozone layer. Research questions are identified with which to assess the feasibility of such geoengineering schemes.Many strategies and techniques for geoengineering Earth's climate have been suggested1, 2. The deliberate injection of aerosols into the stratosphere is a solar-radiation management (SRM) scheme, and has been suggested to be affordable and have a high effectiveness compared with other geoengineering schemes that have been suggested for mitigation of global warming1. However, it has also been suggested that SRM has a low associated safety compared with other geoengineering schemes, because of its possible effects on regional climate, stratospheric ozone, high-altitude tropospheric clouds and biological productivity1. The lower stratosphere already contains a sulphuric acid (H2SO4) aerosol layer produced from the oxidation of both biogenic and volcanic sulphur gases (OCS and SO2)3, 4. In addition to H2SO4 aerosol, there are other particulate matters of diverse origin present in the stratosphere, for example, volcanic mineral dusts, meteoric metals/oxides, carbonaceous material injected from aircraft operations and material transported from the underlying tropospheric regions5. The amounts from these sources are generally minor except in the event of major perturbations from explosive volcanic eruptions. The mean exchange time between the lower stratosphere and the troposphere is around 1–2 years, and submicrometre aerosols with a low settling velocity introduced into the stratosphere reside there for several years. Significant global surface cooling through the generation of stratospheric H2SO4 aerosol is observed after major volcanic eruptions near the Equator. The most significant eruption in recent times was Mount Pinatubo in the Philippines (1991), which reduced the average global temperature by ~0.5 K for ~2 years6, 7, 8, 9. As a result, research on the deliberate injection of stratospheric aerosol has consequently focused on the introduction of sulphate aerosol or precursor gases (SO2, H2S and OCS) so as to mimic the volcanic effect10, 11, 12. Aerosol compositions other than sulphate have been suggested, because they can offer more-effective radiation scattering by virtue of having greater refractive indices13, 14, 15, or possibly increase the particle lifetime in the stratosphere by the use of photophoretic levitation16. Furthermore, if a material with lower solar-radiation absorption is used, modelling suggests significant reduction in stratospheric heating leading to a lower perturbation of stratospheric circulation17.The most efficient use of injected particles is achieved when particles are injected into the tropical stratosphere (~20 km; Fig. 1). This injection strategy would maximize their meridional distribution within the atmosphere and atmospheric lifetime, owing to slow overturning (Brewer–Dobson) circulation in the stratosphere as indicated in Fig. 1 (Refs 18,19). Optimized particle properties could also minimize the amount of injected geoengineered material required, and hence reduce the deposition flux of aerosol at Earth's surface. Various methods for the introduction of geoengineered particles into the stratosphere have been proposed20, 21, 22 and the choice of delivery mechanism is beyond the scope of this Perspective. -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en.
