Greenhouse gas emissions projections: phase 1 and phase 2 modelling results

11. Land Use, Land-Use Change and Forestry (LULUCF) sector

The work on this sector was completed by UK CEH.

The unique and biologically complex characteristics of this sector meant that a sector specific model was used to generate the projections. The methodological approach to the work was very different to that taken in the other sectors of the work. Details of the work are provided in Appendix 1. The complexity of the LULUCF sector also contributes to relatively high uncertainty in the net emissions from this sector, as all sources and sinks are based on computer models rather than direct measurement. It is a very active area of scientific development, with annual methodological improvements. As the sector is a combination of sources and sinks, a change in one activity can have a relatively large impact on the net sectoral emissions.

The main focus of emission projections in this sector were afforestation and peatland restoration. Net emissions from afforestation were estimated using the Woodland Carbon Code Calculator (see Appendix 1, section 8.1), calibrated to match results from the CARBINE model used for the national greenhouse gas inventory (this model is proprietary to Forest Research and was not available for this project).

Net emissions from peatland restoration were calculated using the same peatland condition base-map and emission factors used in the national GHG inventory (see Appendix 1, section 8.2). Three abatement scenarios were modelled:

• Low - restoration focused in the uplands (i.e. Modified Bog and Extensive Grassland), and an average (2018-2020) restoration rate to 2030;
• Central - restoration focussed in the uplands (i.e. Modified Bog and Extensive Grassland) to reach 591 kha of restoration by 2045;
• High - restoration targeted at higher-emitting land categories (40% reduction in Extraction, Cropland and Intensive Grassland), and the remaining split across the upland categories, to reach 591 kha of restoration overall by 2045.

The Low, Central and High peatland restoration scenarios results in estimated emissions reductions of 0.2 , 2.0, and 2.9 MT CO₂e, respectively, by 2045. In the High scenario, the reduction of operational peat extraction provides additional emissions saving of 0.1 Mt CO₂e from a reduction in carbon lost by oxidation of the harvested peat. The emissions reductions from the Central and High scenarios are substantial and demonstrate that targeted restoration in the lowlands can result in additional emissions reductions; however, the feasibility of this scenario is unclear due to the large uncertainty in the estimates of the land areas involved.

In the overall SG Projections model, an offset of -4073.866 kt CO₂e is applied to output of the LULUCF modelling work from 2021 onwards to remove a large time series inconsistency in emissions. This inconsistency arises from the use of different methods/models for the calculation of organic soil emissions under Forestry: a Tier 2 approach (using a time-independent emission factor) rather than the CARBINE process-based model used in the UK GHGI, which implies a variable emission factor over time (See Appendix 1, section 8.3). The offset provides a smooth emissions trajectory that allows a partial comparison with the Scottish Sector Emissions Envelope for LULUCF. This offset was applied by the Ricardo modelling team.