Cost of carbon capture as timber

Cost of carbon capture as timber

     More and more people are promoting the idea of saving the world from overheating by capturing atmospheric CO2 (as insoluble carbonates, c.f. limestone, or suphates, c.f. gypsum). But need that be an industrial process? Carbon capture happens naturally – in photosynthesis. The world has been through many cycles of high and low levels of atmospheric CO2. In the Durham coalfield one can count 7 successive coal seams as the climate cycled through carbon-depositing and coal-free layers. I want to know if we can logically advocate the growth of plants (trees and algae), as a cheaper, easier, and more attractive alternative to the yet-to-be-developed industrial process of carbon capture.

 

    I have long looked for a way of comparing the cost of industrial CCS ('Carbon Capture and Storage') with that of simply growing trees. I think I have an answer.

     Timothy Taylor's blog essay on Carbon Capture and Storage gives us a start. Carbon capture is cheapest when done at the sources of CO2 for the concentration can be far higher than ambient; let us say $80 (ranging from $15 to $120) per metric tonne captured. Capture at ambient concentration of 0.04% is about $200 (ranging from $120 - $350) per tonne.

     I have seen a figure of 48 pounds (weight) of CO2 fixed per tree-year. Likewise a figure of 2014 trees/km^2. Based on those figures, I find the capture of carbon dioxide (per Km^2-year) to be: 

    48 x 2014 = 96,672 lb, 

    or 43,850 kg, 

    or 43.85 metric tonnes per Km^2-year. 

So to fix a metric tonne each year you need land of:

    1/43.85 km^2, = 0.0228 Km^2 = 5.634 acres. 

     With this biological method of carbon capture the fixing is free; the cost is the cost of the land. In the United States the average cost of land is $14,326 per acre. If annual rent was at 1% of the capital cost (which is admittedly low),  to fix a metric tonne as wood, in the USA, would cost:  

    $14,326 x 5.634/100 = $807 per tonne-year.

     That is a pity! For I hoped that forestry would turn out to be cheaper than fooling around with chemical engineering. Unless, of course, the land is loaned free of charge, when the cost comes down to zero.