Clearly, there is no definition of Permanence for Biosequestration that is dictated by Scientific Fact. The periods quoted range from 4 years to ‘forever’, with points of 20, 50, 55, 100, 200 and 500 years in between. The choice of 100 Years appears to have been a function of the need to find a scale on which to compare the Global Warming Potential of various Greenhouse Gases. Its choice as a time horizon took place as part of the negotiations around the Kyoto Protocols and was based on functional considerations. One function – the engagement of farmers in soil carbon sequestration activities – was overlooked. Several other functions are considered in the following “Time Horizon by Function” table.
Time Horizon 5 Years
1. Time required for excess CO2 to be taken up by plant or ocean. 2. Most acceptable compliance period for farmers. 3. A minimum reporting period. 4. A renewable contract period.
Time Horizon 25 Years
Function 1. Approximate period at which soil reaches theoretical saturation point, ie. “Steady State”. 2. Period covered by 5 renewable 5 year contracts.
Time Horizon 50 Years
1. Period in which removing 1tCO2 from the atmosphere and storing it counteracts the radiative forcing effect, integrated over a 100-year time horizon, of a 1 t CO2 pulse emission. (See "100 Years A Fiction" below)
2. Period in which soils and vegetation in the world’s agricultural lands can draw down the equivalent of 50ppm, stalling Global Warming for long enough for the shift to a low carbon economy can be made. (See "Bridge To The Future" below.)
3. Period in which the culture of Australian Agriculture is changed by two generations of farmers being incentivised by tradable offsets and stewardship payments for maintenance of carbon sequestered in the landscape.