CO2 emissions from cropland in Norway estimated by IPCC default and Tier 2 methods

Monitoring changes in soil organic carbon is linked not only to atmospheric CO2 dynamics, but also to the sustainability of agricultural systems, maintaining food security, reducing water pollution and soil erosion. In accordance with the Intergovernmental Panel on Climate Change (IPCC) methodology, a Tier 2 method for estimating CO2 emissions from cropland on mineral soils in Norway was developed and the results were compared with those of the default Tier 1 method. A soil C balance model, the introductory carbon balance model (ICBM) was used to calculate country-specific soil organic carbon (SOC) stock change factors for cropland management systems for the Tier 2 method. Annual CO2 emissions from cropland management were substantially higher when estimated by the default Tier 1 method (313 Gg CO2 per year) compared with Tier 2 (149 Gg CO2 per year). The differences between the results were mainly due to the default Tier 1 stock change factors for crop rotations without manure application, which led to greater CO2 emissions compared with the ICBM-based factors. Reduction in livestock numbers and reduced manure application to arable land were the main causes of net emissions from soil for both the methods. Policies to stabilize or increase livestock numbers could reduce soil CO2 emissions, although the impacts on other agricultural emissions sources, particularly methane from livestock, would need to be considered.