Stratospheric Sulfur Injections

Today’s post focuses on an article by Crutzen (2006) with the title ‘Albedo enhancement by stratospheric sulfur injections: a contribution to solve a policy dilema?’. Crutzen describes the very controversial technique of actificially adding sulfur particles to the stratosphere to increase albedo.

Human emissions do not only consist of CO₂. Our industries also emit SO₂. Once emitted in the atmosphere SO₂ is processed into sulfate particles, which act as cloud condensation nuclei. More clouds can be formed, which causes a backscattering of incoming solar radiation and thereby enhances albedo. This can in consequence cool the earth’s surface and slow down global warming. The effect of great amounts of sulfur could be wittnessed after great volcanic eruptions e.g. Mount Pinatubo in 1991. The following diagram shows the reduced solar radiation that is transmitted after great volcanic eruptions:

(source: http://en.wikipedia.org/wiki/Stratospheric_sulfur_aerosols)

The idea of this geoengineering technique is now to artificially inject SO₂, S₂ or H₂S ‘near the tropical upward branch of the stratospheric circulation system’ (Crutzen 2006). This way the particles are transported into the stratosphere where they remain for 1-2 years. In lower heights in the troposphere their residence time is shorter and therefore more sulfur would be needed to achieve the same effect. So far this technique sounds like a solid plan, but it is not as easy as it seems to be: Sulfur can cause serious damage to the environment and to human’s health. It can e.g. cause premature death, “more than 500,000 […] per year worldwide (Crutzen 2006).

The dilemma is now that what is good for our health has negative effects in terms of climate change. A cleaner air can indeed lead to an additional warming of the earth’s surface. Crutzen estimates that a complete clean air leads to 0.8K warming of surface air temperature. However one suggestion is to clean the lower atmosphere level, which directly influence human’s health, and to inject sulfur above in the statosphere. Crutzen calculates the cost of stratospheric sulfur injections that are required to compensate for the additional warming and estimates a total price of US $25–50 billion/yr.

But is this really an option? As good as the intended effect is, we have to consider the negative side effects. In my opinion it is no solution to put at risk human health in this way. Sulfur particles may be injected in to the stratosphere but they will eventually loose height and affect us. I think the general idea to reflect sunlight is good, but there have to be other ways. Another method proposed is e.g. using mirrors in space or in the atmosphere. I want to discuss if this method might be an alternative in a later post.

What do you think about stratospheric sulfur injections? A way to save our climate or a way to destroy health and environment?

Literature:

Crutzen (2006) ‘Albedo enhancement by stratospheric sulfur injections: A contribution to resolve a policy dilemma?’ Climatic Change, 77 (3-4), 211-219.

Available online: http://www.springerlink.com/content/t1vn75m458373h63/