Pure and simple?

The main problem surrounding climate change is our anthropogenic influence on atmospheric carbon concentrations. Human activity has enhanced carbon dioxide emissions from pre-industrial times (~1750) of 260-270 ppm (Wigley, 1983) to 395.93ppm today (Co2now, 2014. The geoengineering schemes that we have discussed so far have focused on carbon dioxide removal from the atmosphere via a plethora of methods and avenues, from enhancing weathering processes, foresting land and adding nutrients to the oceans, but why not find a direct method to remove carbon from the atmosphere? Why not undergo air purification?

Since 2009, the idea proposed by Lackner was to manufacture 'artificial trees' to capture carbon from the atmosphere. The design can be seen below.

Source: geoengineering2012

The trees are able to mimic the planet's natural uptake of carbon dioxide, as the prongs contain sodium hydroxide, which acts to chemically consume carbon dioxide and transform sodium hydroxide (lye) into sodium carbonate (Biello, 2009). The carbon dioxide is then heated at 900 degrees celsius, releasing the carbon dioxide to enable sodium hydroxide to re-react with atmospheric carbon dioxide once more. The artificial tree is able to remove carbon dioxide from the atmosphere at a  much faster rate than natural photosynthesis (Schiffman, 2013), and scientists have envisaged the existence of forests of these artificial trees to optimise carbon removal.

The idea has been supported by both the UK Royal Society and the Institution of Mechanical Engineers as the safest and most effective geoengineering technology suggested. However many statistics from 2009, when the advent of this proposed solution occurred, implied that these artificial trees would be demonstrated in society by at least 2014, which of course is today. Has anybody witnessed any demonstration of artificial trees yet?

The Institution of Mechanical Engineers actually believed that post-demonstration in 2014, a full scale 'forest' of artificial trees could be implemented by 2018, and global deployment by 2040 (Biello, 2009). The questions have to be asked: Why has this not happened? What has hindered the project's progress?

The hindrance could be a result of a multitude of reasons. Firstly, the concept sounds appealing: carbon dioxide is removed from the atmosphere using successful and efficient devices, yet where does this captured carbon go? The carbon inventory proposed was underground, and some geological formations have been tried and tested, for example Basalt, as it has the ability to absorb carbon dioxide over decadal timescales to produce minerals (Biello, 2009). However there have been many caveats concerned with underground sequestration. For example, how will it impact groundwater supplies? Is there potential for carbon leakage back into the atmosphere?

Other problems with air purification are dominantly economical. The project requires large land area, production of electricity and manufacture and installation, which will all come at a huge economical expense. It has been proposed that 10 million artificial trees would be required to reduce ~12% of anthropogenic carbon emissions per year (Schiffman, 2013), ergo making a colossal change in carbon reduction to pre-industrial levels would require a huge volume of air purification devices across the globe. Similarly each artificial tree is estimated to cost $24,000, therefore even 100,000 trees is already $2.4 trillion in expenses. Can we afford this?

In response to these caveats, and the Institution of Mechanical Engineers' proposals in 2009 for air purification to be ready for deployment and installation during 2014, I found it extremely difficult to find any recent academic papers evaluating artificial trees (mitigating those of course that were in reference to artificial Christmas trees, the latter end of November was probably not the best time to look!) or air purification. In fact, the academic scene is quite muted on the subject- does this mean that this proposed 'safest and most effective geoengineering scheme' is not as hopeful as first thought?

Source: Cartoon Movement

Similarly I think that the theory does have huge potential, however, finding suitable land areas to deploy the trees globally will undoubtedly be a struggle. People are already adverse to the sight of windfarms, despite their benefits of clean, renewable energy, due to aesthetics and impact on house prices, so it is highly unlikely that they would take to having artificial trees implanted in their back garden.

How do you think this project compares to the schemes proposed so far?

S xx