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Methane is a short-lived greenhouse gas (GHG) modelled distinctly from long-lived GHGs such as carbon dioxide and nitrous oxide to establish global emission budgets for climate stabilisation. The Paris Agreement requires a 24-47% reduction in global biogenic methane emissions by 2050. Separate treatment of methane in national climate policies will necessitate consideration of how global emission budgets compatible with climate stabilisation can be downscaled to national targets, but implications of different downscaling rules for national food production and climate neutrality objectives are poorly understood. This study addresses that knowledge gap by examining four methods to determine national methane quotas, and two methods of GHG aggregation (GWP100 and GWP*) across four countries with contrasting agriculture, forestry and other land use (AFOLU) sectors and socio-economic contexts (Brazil, France, India and Ireland). Implications for production of methane-intensive food (milk, meat, eggs and rice) in 2050 and national AFOLU climate neutrality targets are explored. It is assumed that methane quotas are always filled by food production where sufficient land is available. Global methane budgets for 1.5 °C scenarios are downscaled to national quotas based on: grand-parenting (equal percentage reductions across countries); equity (equal per capita emissions); ability (emission reductions proportionate to GDP); animal protein security (emissions proportionate to animal protein production in 2010). The choice of allocation method changes national methane quotas by a factor of between 1.7 (India) and 6.7 (Ireland). Despite projected reductions in emission-intensities, livestock production would need to decrease across all countries except India to comply with quotas under all but the most optimistic sustainable intensification scenarios. The extent of potential afforestation on land spared from livestock production is decisive in achieving climate neutrality. Brazil and Ireland could maintain some degree of milk and beef export whilst achieving territorial climate neutrality, but scenarios that comply with climate neutrality in India produce only circa 30% of national calorie and protein requirements via rice and livestock. The downscaling of global methane budgets into national policy targets in an equitable and internationally acceptable manner will require simultaneous consideration of the interconnected priorities of food security and (land banks available for) carbon offsetting.

Abstract World agriculture needs to find the right balance to cope with the trilemma between feeding a growing population, reducing its impact on biodiversity and minimizing greenhouse gas (GHG) emissions. In this paper, we evaluate a broad range of scenarios that achieve 4.3 GtCO2,eq/year GHG mitigation in the Agriculture, Forestry and Other Land-Use (AFOLU) sector by 2100. Scenarios include varying mixes of three GHG mitigation policies: second-generation biofuel production, dietary change and reforestation of pasture. We find that focusing mitigation on a single policy can lead to positive results for a single indicator of food security or biodiversity conservation, but with significant negative side effects on others. A balanced portfolio of all three mitigation policies, while not optimal for any single criterion, minimizes trade-offs by avoiding large negative effects on food security and biodiversity conservation. At the regional scale, the trade-off seen globally between biodiversity and food security is nuanced by different regional contexts.