Carbon sequestration is the act of isolating and storing carbon from the atmosphere, and tree planting is commonly believed as the best way to sequester carbon dioxide, one of the harmful gases which cause global warming. However, this approach is imperfect because, once a tree dies, it decomposes, and all the carbon it has sequestered will eventually escape; in other words, trees are carbon sinks which last only as long as they live. Furthermore, they are susceptible to fire and need a considerable amount of land to grow, which can be impractical in an urban environment. Ocean fertilising (adding minerals into deserted sections of the sea to encourage phytoplankton growth) is another option, but one which risks all manner of side-effects, such as triggering algal blooms, and hindering deep sea life such as coral from carrying out the process of photosynthesis. This not only counteracts the sequestration effect, but also disrupts marine ecosystems putting vulnerable species at risk. 

However, there is a way to sequester carbon which does not require substantial space or disrupt ecosystems.  

It comes in the form of enhanced rock weathering. This simple yet highly effective method was developed by Carbfix, a project based in Iceland. The initial scope of this project was on land, but large areas of the sea also have potential for this process. 

It is a system of carbon capture in which carbon dioxide, dissolved in water, is applied to rock, especially basalt (and other ultramafic rock types). As carbon dioxide forms an acidic solution when dissolved in water (carbonic acid), the water corrodes the rock, releasing minerals to which the carbon bonds, thus forming stable compounds such as calcium carbonate. 

CO2+H2O→H2CO3

Ca(OH)2+CO2→ CaCO3+H2O

 The exact precipitates vary depending on the minerals in the rock, but the principle remains the same: one carbonate and some hydrogen ions are produced which can also be reacted away to form other products.  

The site is completely stable within around two years of being formed. 

This allows the sequestration of carbon dioxide from a place where it is in high supply, such as a power station or possibly a city, to a location suitable for storage, for example an area on the seabed. A limitation to take into consideration is the fact that some of the suitable sequestration sites, such as those on the Mid-Atlantic Ridge, would be difficult to transport carbon dioxide to as they are too geographically isolated. However, the fact that the process does not require prior set-up, such as the crushing of the rock, makes it considerably easier to undertake and, being largely automated, long-term staffing costs would be low.  

Of course, this alone, is not the only solution to the global warming issue and it will only work with international cooperation to fund the scheme, which will likely have high initial costs and no profit. However, the selling of “Carbon Credits” to corporations as a form of carbon offsetting could help reduce costs as much as possible. Nevertheless, Artificial Carbon Capture through enhanced rock weathering looks set to be a major part in fighting ever-increasing emissions levels which show little sign of slowing down. 

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