Sulfur Injection

We've almost listed them all, but one of our final geoengineering schemes to discuss is... Sulfur Particle Injection into the stratosphere.

Let's start with:

What?

Sulfur Particle Injection is the injection of sulfur particles into the stratosphere as a means of inducing global cooling, and increasing global albedo, and potentially diminishing the impacts of increasing carbon dioxide emissions (Rasch et al. 2008). It was first suggested by Budko (1977) (cited in Rasch et al. 2008) by burning sulfur from aeroplanes to create solar reflecting aerosols and the idea has generated large audiences of researchers and has since been developed further in detail. Sulfur aerosols can reside in both the troposphere and stratosphere, however within the application of geoengineering, the stratosphere has been selected as the residing site of Sulfur because it has a longer residence time. Aerosols will remain within the stratosphere for 1 to 2 years, as opposed to the troposphere where they will only remain for a week long period (Crutzen, 2006). This means that a smaller proportion of Sulfur would be required for the project, significantly reducing the risk of the application.

Why?

Climate Change of course! The ever-increasing carbon emission concentrations within the atmosphere are still a cause for frightful concern. Mitigation strategies thus far are being too slow at resolving a solution to reducing or putting a plug in carbon dioxide emission. Sulfur aerosol emissions into the stratosphere are an "emergency brake" (Crutzen, 2006), a rapid solution to the climate change problem.

How?

The idea of sulfate aerosol injection was to replicate that of a volcanic eruption. The 1991 eruption of Mount Pinatubo exerted 10TgS of sulfur dioxide into the stratosphere over a period of three days (Rasch et al. 2008) inducing a 0.5°C drop in global temperature over the following year (Lacis & Mishchenko, 1995; Crutzen, 2006). This colossal eruption successfully cooled the Earth system without any noticeable disruptions to the climate systems, and therefore was opportunist for geoengineering development of the mechanism. Research has sparked disagreement between scientists; Crutzen (2006) and Wigley (2006) both suggest that 5TgS per year is required to balance global warming associated with a doubling of atmospheric carbon dioxide. However Rasch et al. (2008) and Robock et al. (2008) suggest a smaller value of 1.5TgS per year. The consensus suggests at least 15 times the amount of stratospheric sulfur of today!

In order to replicate a volcanic eruption, research was undertaken to find a way to inject the sulfur into the stratosphere. Ideas including artillery shells, airplane jets and balloons (e.g. the SPICE project) all of which would release concentrated sulfur into small, local regions of air (Rasch et al. 2008). There has been success with this approach, namely the SPICE project. Sulfur can also be injected via an antecedent gas of the troposphere, which according to Rasch et al. (2008) will oxidise within the stratosphere to naturally transport Sulfur into the stratosphere. Anthropogenic carbonyl sulfide has been suggested as the antecedent gas however, carbonyl sulfide is only prevalent as 1-2TGs per year of which only 15% is anthropogenic (Montzka et al. 2007). A least a factor of 10 increase is needed for the global requirement of sulfur aerosols (Rasch et al. 2008).

Source: Gifbay

(Currently Who? and When? are not applicable... Perhaps answerable in due course!)

And why not?

As always, there are a multitude of reasons against a geoengineering project of this enormity. The highlighted risk of uncertainty of large scale planetary applications is still a major concern. In this case the sulfur particle emissions from volcanoes are single eruption events of which the effects last for a few years, whereas the geoengineering scheme proposes continual emissions of sulfur. Can the Earth's system cope with this? Similarly, no information exists on volcanic eruptions in a warmer climate than experienced today (Crutzen, 2006), would it have a significant impact on sulfur aerosol concentrations?

Concern also arises from its effect on regional climate. Research combining the Mount Pinatubo eruption and hydrology illustrates that the eruption caused a decrease in precipitation of 0.07 mm a day over land surfaces- even drought in South East Asia (Trenbirth & Dai, 2007), and further modelling simulations have supported this consequence. This could have major implications to ecological systems.

A final overruling concern is how long will it have to go on for? By resorting to technological approaches such as sulfur aerosol injection on a continual basis, can we ever stop? A huge risk of geoengineering is the consequence of having to terminate a process. All of the associated effects of increasing atmospheric carbon dioxide emissions would rapidly return at a rate that the Earth system is unable to adapt to. The consequences would be catastrophic. This means that sulfur aerosol injection may have to continue for centuries, even millennia into the future (Bengtsson, 2006)! Is it worth the risk or the cost of maintenance?

Result?

This proposal remains too high risk for the immediate future. However, this isn't to say experiments haven't continued to go ahead...


S xx