Geoengineering and ozone depletion

My last post suggests that there is large support for geoengineering schemes......but do the public really know the ins and outs of the matter? Much of the research that scientists have been carrying out is never seen by the average man on the street. Often only the benefits seem to be published outside of academic journals. My support for geoengineering schemes has diminished since I've started seriously looking into the matter. I recently found an article in science which strongly argues against Stratospheric Particle Injection as a valid geoengineering technique (Tilmes at al., 2008). It does however, at no point in this article discuss whether SRM would work but instead focuses on a significant negative impact - Polar ozone depletion. This post will offer a small summary however, this is a very short and punchy article which I would well recommend a read.

The depletion of the ozone results from two main factors:  

1. Anthropogenic halogen loading in the atmosphere
2. Activation of Chlorine

The most significant depletions of ozone have occurred over the Arctic regions. However, it’s not all bad news, we have already started a recovery!! Halogen loading has started to decline as the world is becoming more and more aware of the impacts. This has lead to the prediction that by 2070 levels will have returned to that of 1980. However, this article concludes by quantifying the delay in this recovery if stratospheric particle injection is put into action. Depending on the extent of the vertical expansion of the ozone hole, a recovery will be delayed by between 30 and 70 years.

The graph below results from a model based on two separate geoengineering scenarios. First, using ‘small’ aerosols and second,with ‘large’ aerosols.

Before looking at this graph it is vital to notice the presence of the background levels of particles. These have naturally (in this case without geoengineering) increased until 2000, resulting in the activation of stratospheric choline particles but then levels are shown to quickly recover over the next 70 years. However, with the introduction of geoengineering (especially using smaller particles) we very quickly backtrack and significant volumes of chlorine are ‘activated’ forming reactive radicles which significantly increases ozone depletion.

In conclusion, this article is the first to quantify the effects of this form of geoengineering on polar ozone depletion. It proposes that it could be hugely damaging and in fact, a step back in our fight against climate change. It highlights the uncertainties that arise on the ideal aerosol sizes and also suggests that the ozone loss from future volcanic eruptions will be exacerbated by the pre-existing levels of ‘artificial’ particles in the stratosphere. I for one am not so confident on geoengineering as I once was!!