Global Warming Potential of farming systems across England: possible mitigation and co-benefits for water quality and biodiversity

Agriculture is a key contributor to gaseous emissions causing climate change, the degradation of water quality and biodiversity loss. The extant climate change crisis is driving a focus on mitigating agricultural gaseous emissions, but wider policy objectives, beyond net zero, mean that evidence on the potential co-benefits or trade-offs associated with on-farm intervention is warranted. For novelty, aggregated data on farm structure and spatial distribution for different farm types were integrated with high resolution data on the natural environment to generate representative model farms. Accounting for existing mitigation effects, the Catchment Systems Model was then used to quantify Global Warming Potential, emissions to water and other outcomes for water management catchments across England under both business-as-usual and a maximum technically feasible mitigation potential scenario. Mapped spatial patterns were overlain with the distributions of areas experiencing poor water quality and biodiversity loss to examine potential co-benefits. The median business-as-usual GWP20 and GWP100, excluding embedded emissions, were estimated to be 4606 kg CO2 eq. ha-1 (inter-quartile range 4240 kg CO2 eq. ha-1) and 2334 kg CO2 eq. ha-1 (inter-quartile range 1462 kg CO2 eq. ha-1), respectively. The ratios of business-as-usual GHG emissions to monetized farm production ranged between 0.58- 8.89 kg CO2 eq. £-1 for GWP20, compared with 0.53-3.99 kg CO2 eq. £-1 for GWP100. The maximum mitigation potentials ranged between 17-30% for GWP20 and 19-27% for GWP100 with both corresponding medians estimated to be ~24%. Here, we show for the first time, that the co-benefits for water quality associated with reductions in phosphorus and sediment loss were both equivalent to around a 34% reduction, relative to business-as-usual, in specific management catchment reporting units where excess water pollutant loads were identified. Several mitigation measures included in the mitigation scenario were also identified as having potential to deliver co-benefits for terrestrial biodiversity.