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Carbon Sequestration - Potential Carbon Sequestration into Crop / Grassland Root Systems


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Carbon Sequestration Calculator

The amount of carbon as CO2 currently in the atmosphere is approx Pg, and that in the soil is approx Pg.

If the global land area for crops is Mha and that for grassland is Mha, and an extra m depth of roots are grown, and they take up % (by mass at an equivalent carbon density of 1000 kg/m3 ) of the relevant soil volume, then the extra amount of carbon that could be sequestered by the above land areas is kg.m-2 = t.ha-1.

This equates to Pg ( M tons) , if the C in the roots and other sequestered carbon are re-respired over a period of years.

As 1 Pg is equivalent to 0.51 ppmv atmospheric CO2, this would decrease the CO2 in the atmosphere by

                ppmv, the current value of ppmv would decrease to ppmv. **      

    Notes: edit text and press tab to goto next field.

    The minimum atmospheric CO2 is capped at ~ 150 ppmv; the calculator will try to impose limits on the inputs to ensure this.

    ** Without taking into account the rate of increase of atmospheric CO2 caused by the burning of fossil fuel etc.

Time Needed to Complete Sequestration

The graph below is plotted assuming that the rate at which the long root crops can be seeded is % of the total area available per year. This equates to a seeding rate of Mha per year. Complete sequestration will therefore take years.

This graph takes into account the estimated rate of increase of atmospheric CO2 due to fossil fuel consumption. The current rate of increase of atmospheric CO2 is taken to be equivalent to an extra ppmv per annum.

This figure requires browser support for the HTML5 canvas element.

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Figure 1:

A simple linear model is assumed. The left-hand scale is the total carbon load PgC (soil + atmosphere), with colour indicating source: soil, atmoshere and new emissions. The right-hand scale is total atmosheric CO2 ppmv.

Pre-Industrial Atmospheric CO2 is taken to be 553 PgC (284 ppmv); pre-industrial carbon bound in soil is taken as 1560 PgC.

Useful background

  • 1 Pg = 1 Gt. 1 ha = 104 m2. 1 km2 = 102 ha.
  • As 750 Pg is equivalent to 385 ppmv atmospheric CO2, decreasing the atmospheric CO2 by 1.0 Pg decreases it by 0.5133 ppm
  • Atmospheric CO2 has been increasing by 3-4 Pg/y, ca 1.8 ppm/y.
  • We discuss only CO2 and not other GHGs.
  • Coal reserves represent 3510 Pg C  and oil reserves 230 Pg C
  • Forests occupy 48.5 Mkm2 (= 4850 Mha) and woodland and shrubland occupy 8.5 Mkm2 (= 850 Mha). We assume that these already have deep roots and are not an immediate target of agriculture.
  • We do not discuss trapping CO2 in the ocean or lakes (we wish to avoid their acidification), nor take into account the effect of the pseudo-equilibrium that exists between CO2 in the oceans / lakes and the CO2 in the atmosphere.
  • There are approx 41.4 . 106 km2 of just rainfed arable land, and 130.56 . 106 km2 of total land area excluding polar regions


Last update: 28th June 2011


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