The importance of a life cycle approach for valuing carbon sequestration

Carbon sequestration (C-seq) in grassland has been proposed as a strategy to reduce the net contribution of livestock to climate change. Carbon stored in soils, however, can easily be re-emitted to the atmosphere if soil conditions change. The aim of this study was to evaluate the importance of C-seq for reducing the impact of dairy production on climate change over time, based on life cycle assessment. Annual emissions of carbon dioxide, methane and nitrous oxide (cradle-to-farm gate) were analysed for two types of dairy systems in the Netherlands: a grass-based system (high C-seq potential) and a maize-based system (low C-seq potential). Soil carbon fluxes were modelled to quantify the uptake and release of carbon dioxide in agricultural soils. The climate impact per ton of fat-and-protein corrected milk (FCPM) for each system was modelled over time, based on the radiative forcing and atmospheric lifetime of annual emissions and soil carbon fluxes. Systems were compared for a situation in which soil carbon was re-emitted after 20 years, or stored for an indefinite period of time. Results show that C-seq favours the grass-based system in the short-term, until the point at which soil carbon is reemitted (i.e., 20 years), or reaches equilibrium (after 70 years). Results demonstrate the importance of including both annual emissions and soil carbon fluxes by means of a life cycle approach, and to consider the climate impact over time, when
valuing the potential benefit of C-seq.