Science-Based Policy in the Development of Soil Carbon Offsets.

Long-term studies comparing soil management by conservation and full tillage on the Canadian prairies show that conservation tillage lowers greenhouse gas (GHG) emissions due to removals of atmospheric carbon by sequestration in soils as well as reductions of nitrous oxide and fossil fuel emissions.  The Specified Gas Emitters Regulation (2007) created a market between regulated companies and others who can voluntarily lower GHG emissions in Alberta, such as farm managers who adopt conservation tillage. Government of Alberta approved offset quantification protocols were developed to meet International Organization for Standardization (ISO) 14064-2 specifications and prescribe the basis for this carbon trade by linking measured emission reductions to management improvements that can be verified by independent third parties. The Tillage System Management protocol addressed the variability of soil carbon sequestration in conservation tillage using change coefficients developed for use in the National Inventory Report on GHG Sources and Sinks in Canada. Change coefficients were derived from outputs of the calibrated Century 4.0 model to account for soil spatial variability, weather patterns over 40 years, and typical mixes of cropping sequences. The change coefficients were then modified to account for offset policy requirements, including an additionality adjustment based on Census of Agriculture reports of adoption levels of conservation tillage, as well as a permanence discount based on the probability of tillage reversal. Net change coefficients for soil carbon sequestration were less than 30% of plot-scale measurements.  Since 2007, the Tillage System Management protocol has been used as the basis for registering over 11 million tonnes of carbon dioxide equivalents (Mt CO2e) on the Alberta Emissions Offset Registry.