Biosequestration

As previously mentioned the vast proportion of CO₂ in the atmosphere is naturally released and is in turn naturally absorbed.  Some is dissolved in rain and ultimately acidifies the oceans but a great deal is absorbed by plants in the process of photosynthesis; consuming water and usually releasing oxygen. 

This is a natural solar collector.  Plant absorption is increased if CO₂ levels rise and plants have access to sufficient water and sunlight.  Trials have been undertaken at higher CO₂ levels with a number of existing economic plants to determine such things as the ‘fertiliser effect’ higher water uptake and increased solar absorption. 

Obviously producing biofuel or food does not permanently sequester carbon and any credit should only apply the solar energy collected by the process; as this, in turn, reduces dependence on other energy sources. To get a full credit, similar technology might produce cellulose that could be charred and buried to improve soils or other carbon rich materials that could be safely buried in depleted mines or other suitable sites. Charing and burying of bagasse, straw and wood-waste is already a recognised sequestration technology.

It is clear that accelerated CO₂ absorption by conventional agriculture and plants, for example by reticulating CO₂ to greenhouses or forests, would be costly and would not fully deal with the vast quantities of CO₂ involved.  But some plants and bacteria evolved when CO₂ levels were very much higher and it appears to be possible to exploit their genome to modify them or other plants and organisms, to produce economically useful materials; at the same time absorbing large volumes of CO₂.

Several projects are already in underway internationally.  The most interesting involve algae that could be used to produce diesel fuel, directly or as chemical feedstock.  Other, possibly complimentary, options include modifying food crops like rice (to a C4 plant) so that additional CO₂ and sunlight are absorbed (and carbohydrate yields improved).

Again the problem is the scale required to make a difference. A very large solar collection area is required together with plentiful water.  Areas comparable to present broad acre agriculture will be required, probably as shallow lakes.  It would be particularly useful if algae that are comfortable in salt water could be adapted.

Again there are safety issues to be considered. These vast lakes or fields will be filled with genetically modified organisms and the regulatory environment relating to GM organisms and foods will need to be changed accordingly.