Sunday, 10 January 2016

Carbon Sequestration

To all my fellow readers,

I found this video that analyses another CDR geoengineering process known as carbon sequestration and I thought I would share it with you.

This process aims to pump CO2 deep underground in a carbon pool and store it there for 10,000 or more years (Lorenz and Lal 2014).  There are two types of carbon sequestration, biotic and abiotic (Figure 1).  Biotic Carbon sequestration involves an enhancement of the natural processes of absorbing carbon.  Carbon dioxide naturally dissolves in the soil through combustion and decomposition (Lal 2004).  Therefore, forming soil organic carbon (SOC) and soil inorganic carbon (SIC), which absorbs carbon down the soil profile.  The enhancement of this process can increase the absorption of CO2 at faster rates and can be undertaken through land use, biofuels and an increase in organic biomass known as biochar (Lorenz and Lal 2014).  Biochar is the burning of organic material to form a charcoal, which can sink underground (Lorenz and Lal 2014).  This blog aims to analyse biochar as an example of biotic carbon sequestration.  Furthermore, Abiotic Carbon sequestration is a human engineering process, where CO2 is artificially injected deep in the soil surface (usually in saline aquifers to form carbonates) or deep in ocean sinks (Lal 2008). 

Figure 1: Representation of Carbon Sequestration
Source: Carboncycle 

Biotic Implications

The biotic sequestration of carbon through biochar may be very beneficial for crops and trees as it improves the quality of the soil due to more nutrients (Lal 2004).  The soil pH increases, due to the biochar process, leading to a reduction of acidic soil, which may be induced by Aluminium toxicity (Lorenz and Lal 2014).  The biochar reduces Aluminium toxicity and the soil gains the ability to hold moisture, leading to plants growing faster and stronger (Lal 2008). Therefore, there may be a decrease in the need of fertilisers and water, leading to a reduction of agricultural costs (Lorenz and Lal 2014).  Additionally, in the case of crops, agricultural yield may increase, leading to more economic benefits for people, as studies through experiments, show that crop productivity increases by 11% (Lorenz and Lal 2014).  Nonetheless, various types of soil and biochar react differently and some may be more effective than others (Lorenz and Lal 2014).  Thus, it may be deduced, that this geoengineering process not only reduces global CO2 levels, it is also beneficial for plant growth.

However, although there may be some positive impacts with an increase in biochar activities, it may lead to a change in microorganisms found in plants (Lorenz and Lal 2014). In the long-run microorganisms may adapt to biochar implications.  Consequently, this may influence plant growth thus making this process less beneficial forcing some plant species to shift their populations elsewhere or forcing species to adapt to this environment (Lorenz and Lal 2014).  However, there is little research on long-term impacts of biochar as a geoengineering process and it is hard to assess to what degree plants and crop yield may be affected in the long-run, compared to short-term impacts (Lorenz and Lal 2014).  Therefore, it is questionable to what degree biotic carbon sequestration may be affective.

Another negative impact may be that an increase in biochar activities may reduce the surface albedo due to the charcoal produced (Lorenz and Lal 2014).  A decrease in surface albedo may increase temperatures and reduce SOC absorption due to higher decomposition rates.  Thus questioning to what degree this geoengineering process will be affective.

Furthermore, to form biochar, burning takes place, thus CO2 is expected to slightly increase during this burning process (Lorenz and Lal 2014).  Once the process is complete and biochar is formed, the soil begins to absorb carbon. This questions to what degree CO2 levels will be absorbed due to the initial CO2 release.  The undertaken studies regarding biotic carbon sequestration occupy a time frame of 1-4 years (Lorenz and Lal 2014).  Therefore, there is high uncertainty if this process will be as effective and efficient as desired in the long-run.  Additionally, methane (CH4) may increase due to by-products created by biochar, thus increasing atmospheric green house gases (Lorenz and Lal 2014).  With an increase in green house gases, climate change impacts may not be mitigated.  Therefore, it is questionable to what degree this process may be successful to reduce global temperatures.

Abiotic Implications

When undertaking abiotic carbon sequestration, it is very hard to predict any impacts induced on ecosystems and the hydrological cycle, as it is very hard to process computationally (Lal 2008).  Nonetheless, a main concern is to develop an efficient process of injecting carbon deep in the soil or ocean and avoiding any leakages back to the surface (Lal 2008).  These leakages may reduce the effectiveness of this geoengineering process and may even pollute freshwater aquifers or make oceans more acidic (Lal 2008).  Moreover, costs may be relatively high as it is hard to inject CO2 deep underground efficiently and technological advancements may be essential to undertake this process effectively (Lal 2008).

Overarching Disadvantage

Lastly, an overarching concern is to ensure that CO2 is injected deep in the soil and it stays there for a very long time (Lal 2008).  For this process to be successful, the CO2 must stay in the carbon sink for a minimum of 5,000-10,000 years (Lorenz and Lal 2014).  If it stays stored for just 100 years, this may not be enough to reduce climate change impacts efficiently (Lorenz and Lal 2014).


Overall, carbon sequestration is a risky process and of high uncertainty.  I believe for it to be a viable process a lot more research and technological advancements may be necessary to reduce negative implications.  I think although it sounds very plausible, induced, carbon sequestration may not be worth undertaking, as it may not be as effective as desired and may not work as efficiently as needed.  What is your opinion on this process?

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