Enhanced Weathering... Weather away!

Now this post will no doubt sound familiar.. Enhanced weathering? Wasn't that essentially the process behind ocean liming?

Yes, yes it was. However, this process is not confined to the oceans, but also to the biosphere.

Over millions of years rocks are worn away by rain, forming carbonates due to the slightly acidic nature of rain, as a result of its uptake of carbon dioxide. The alkaline carbonate formation, (usually calcium carbonate) is therefore induced by this chemical weathering process, and eventually washes down into the sea (Hamilton, 2013).

Source: Rgbstock

This background theory of the process of chemical weathering has been applied as a potential geoengineering scheme to reduce atmospheric carbon dioxide concentrations. Chemical weathering locks up carbon dioxide through chemical reactions between the rock minerals and air. The optimum material for enhanced weathering is Forsterite (magnesium olivine), due to it's high abundance and reactivity (Hartmann et al. 2013). An example of olivine (magnesium iron silicate) weathering with water and carbon dioxide is represented by the equation below, which results in magnesium carbonate and silicic acid, storing carbon in the process:

Schuiling et al. (2011) reviewed the above equation investigated by Kohler et al. (2010) which suggests that dissolution of 1 mole of Olivine can sequester 4 moles of carbon dioxide. This is through the consumption of carbon dioxide and the release of cations, in this case, Mg2+ into the solution. Enhanced weathering would use the natural process occurring above, but increase the surface area of rock for weathering, or increase temperature and pressure to influence ocean pH.

The process is rather advantageous. Ultimately it would help remove atmospheric carbon dioxide by accelerating natural geological processes transferring carbon and trace elements between the atmosphere, biosphere, and eventually the oceans, which is the aim of any geoengineering scheme. However, it also reduces ocean acidification- a variable caused by climate change, and induces the transferral of trace elements including phosphorous, silicon and potassium (Hartmann et al. 2013), which in turn, enhances biological productivity within the oceans, increasing photosynthesis and carbon dioxide uptake.

However, to uptake maximum carbon, theoretically the rock would have to be crushed, yet in practice, natural rock weathering is an extremely lengthy process, and ideas of quantity and volume of rock are unknown to be able to mitigate the high anthropogenic and atmospheric carbon concentrations. Similarly, should Olivine be prevalently used, it contains toxic metals including nickel that could accumulate within the biosphere, and in attempting to also reduce ocean acidification via this method, could result in higher alkalinity levels to which some marine organisms are not acclimatised (Cressey, 2014).

Enhanced weathering is therefore subject to the same flaws or uncertainties as the proposals discussed previously within this blog. Nothing has ever been induced in the large-scale, so some effects will always be unknown. Similarly, attempts at accelerating natural processes cannot guarantee emergency response to increasing carbon dioxide emissions, and combined with lack of human understanding, projects are no where near ready for installation.

Will we find an appropriate geoengineering method to solve our climate problems? Luckily proposed schemes are not limited to those discussed in this blog so far, stay tuned for more geoengineering projects! Next time- air purification!

S xx