Geoengineering is a climate manipulating strategy that could potentially cool the planet and give researchers more time to find an efficient way to remove CO2 from the atmosphere. Injecting sulfate aerosol particles into the Earth’s atmosphere is one of the most popular strategies of geoengineering, as it would increase the albedo of the planet and reflect more light back into space. These sulfate aerosols, however, have to be a certain size to be effective in increasing the planet’s albedo, and particles with a radii of roughly 0.1 mm are the most efficient in cooling the planet (Heckendorn, et al, 2009). This paper shows which injection strategies will produce the smallest and most efficient aerosol particles, and how long these particles will stay in the atmosphere. This is of large concern since there is great speculation regarding aerosol injection, and if it ends up having negative impacts it would be even worse if the particles remained in the atmosphere for long periods of time. This paper also explains how risky injecting sulfate aerosols into the atmosphere can be, as increase aerosols reduce the amount of ozone in the atmosphere. Ellie Pickrell
Heckendorn, P., Weisenstein, D., Fueglistaler, S., Luo, B., Rozanov, E., Schraner, M., Thomason, L., Peter, T., 2009. The impact of geoengineering aerosols on stratospheric temperature and ozone. Environmental Resolution Letters 4.
Heckendorn et al ran a series of experiments on a global model. These calculations were carried out with two types of sulfur injection methods. The first was a continuous pumping of sulfur into the clouds with fluxes of 1,2,5 and 10 Mt/a, while the other simulations were pulsed injections with periods of one month and six months with fluxes of 5 Mt/a. The control group consisted of zero sulfur injections. All simulations were run for twenty-years with present day concentrations of ozone depleting substances, green house gas, carbon dioxide emissions, sea ice and sea surface temperatures.
The results of the simulations show that the surface area density of the aerosol particles increases as concentration increases. In simulation GEO5 (continuous injection with fluxes of 5 MT/a) the surface area density is larger than 40 mm2 cm-3. In the simulation where the injection takes place twice a year (GEO5p2), the surface area density is larger than 100 mm2 cm-3.
Next, Heckendorn et al looked at how the injection strategies affected the stratospheric residence time of the aerosols. They found that smaller particles have a longer residence time. For the GEO1 simulation (continuous injection with fluxes of 1 Mt/a), the residence time, referred to as aerosol burden, is 1.4 Mt S. For all the other simulations, the aerosol burden is less than one year with 3.7 Mt S for the GEO5 simulation and 6.0 Mt S for the GEO10 simulation (continuous injections with fluxes of 10 Mt/a). They also found that if the sulfur injection occurs at a higher altitude, the residence time increases.
Finally, Heckendorn et al looked at how the injection strategies would affect the mean O3 column. For the GEO5 simulation, the O3 column is predicted to decrease by 4.5%, and the GEO10 model predicted a decrease by 5.3%. These values are greater than the O3 loss due to the emission of greenhouse gases from 2002 to 2005, a decrease by 3.5%.
Although geoengineering by injection of sulfur aerosols into the Earth’s clouds has shown promise in cooling the planet and decrease levels of atmospheric CO2 concentrations, it also has the negative impact of reducing the Earth’s ozone layer.