Abstract Using micro-simulation modelling techniques this paper examines methane emissions across Irish farms. The effects of a carbon equivalent tax on average family farm income are analysed at both the farm and regional level. The spatial micro-simulation model developed uses a technique called simulated annealing to match the Irish Census of Agriculture data to a National Farm Survey. The main advantage of the spatial micro-simulation approach is the fact that it allows one to account for the heterogeneity in the farm population across space. The results of the modelling process are presented using GIS mapping techniques and highlight the fact that there would be significant regional variation in the burden of an agricultural tax that was based on a rate per unit of methane emissions. The results also demonstrate that if the methane tax revenue raised was redistributed in the form of an environmental subsidy to farmers participating in an agri-environmental scheme (the Rural Environment Protection Scheme (REPS)) it would encourage farmers to participate in the scheme and could also have the effect of moving low income farms up the earnings distribution ladder.