Sulphur aerosol injection (SAI) is considered the most technologically feasible geoengineering option, and thus the most actively investigated currently.55 SAI seeks to enhance planetary albedo (surface reflectivity of the sun’s radiation) 56 through the injection of a gas such as sulphur dioxide or another gas that will ultimately react chemically in the stratosphere to form sulfate aerosols. Alternatively, this approach may be effectuated through direct injection of sulphuric acid.57 The high reflectivity of aerosols causes a negative forcing that could ultimately cool the planet.58 Potential delivery vehicles for stratospheric sulphur dioxide injection include aircraft, artillery shells, stratospheric balloons and hoses suspended from towers.59
The genesis of this approach was a suggestion made in 1974 by Russian climatologist Mikhail Budyko that potentially dangerous climate change could be countered by deploying airplanes to burn sulphur in the atmosphere, producing aerosols to reflect sunlight away.60 A number of recent studies have indicated that SAI could be an effective mechanism to ameliorate projected rises in temperature. A. V. Eliseev and others concluded that the amount of sulphur emissions required to compensate for projected warming by 2050 would be between five and 16 TgS/yr, increasing to between 10 and 30 TgS/yr by the end of the century.61 (page 7)
