Sulphate Injection

Injection of sulphate aerosols into the stratosphere draws its inspiration on the natural (but imperfect) analogy of climate cooling from large volcanic eruptions such as Mt. Pinatubo in 1991 (Crutzen, 1991).

When large volcanoes erupt they emit sulphur dioxide into the atmosphere which reacts to form sulphate aerosols, which scatter shortwave and emit longwave radiation (Stenchikov et al., 1998).

Simple models studying the effects of sulphate aerosols have documented the temperature effects but do not take into account the change in stratospheric chemistry (Wigley 2006).

The effectiveness of geoengineered sulphate aerosol effectiveness and possible side effects have been judged by observational data (from volcanoes) (Stenchikov et al. 1998) (Crutzen 2006) atmosphere-ocean general circulation models (Robock et al. 2008), atmospheric chemistry modelling (Rasch et al. 2008) (Tilmes et al. 2008) and analysis of the radioisotope of Tungsten (185W) relating to atmospheric nuclear testing (Tuck et al. 2008).

A doubling of CO2 and its associated radiative forcing would require an increase in global albedo of 0.012 (assuming there is no absorbtion above the stratosphere) (Lenton and Vaughan 2009). The amount of sulphate aerosol needed is proportional to the size of particles and location of injection, these numbers range from 1.5 Tg S year−1 (Rasch et al. 2008) to 5 Tg S year−1 (Wigley 2006). Smaller particles (with a radius ∼ 0.1 μm) are more effective because they have no impact in the longwave, while the larger, volcanic-like particles absorb and emit in the longwave (Stenchikov et al. 1998).

The location of injection causes the residence time and special spread of particles in the stratosphere to vary greatly (Crutzen, 2006) (Wigley, 2006) (Rasch et al., 2008). According to Oman et al. (2005), Robock et al. (2008) and Rasch et al. (2008) residence time and global coverage is maximized when injections occur into the lower stratosphere over the tropics.

As for the mechanism of injection, artillery guns or balloons have been suggested as a delivery method for SO2 (Crutzen 2006); however due to microphysical and dynamic processes such a focused injection point could lead to coagulation of particles and subsequent fallout (Tuck et al. 2008) (Rasch et al. 2008). Consequently, others advocate a dispersed delivery method, such as high level aircraft to deliver the aerosol or precursor payload (Tuck et al. 2008; Rasch et al. 2008).

Promising yet again however the potential side effects here are huge which I will put in a later post (as per)!