Agriculture in Ireland accounts for a higher proportion of greenhouse gas (GHG) emissions than in any other EU member state. Furthermore as part of the EU’s commitment to reduce emissions by 20 percent by 2020, Ireland is one of the few countries who will have to cuts its 2005 GHG emissions level by the full 20 percent. Given the magnitude of the cut in national emissions that is required and the size of agriculture’s contribution to Ireland’s total emissions, the agriculture sector has been identified by some parties as a sector that could make a significant contribution to achieving the national target. In order to evaluate the impact on Irish farmers of reducing GHG emissions it is necessary to first estimate the marginal cost of emissions abatement. This paper uses Irish farm-level data to construct a linear programming model which in turn is used to estimate the marginal abatement cost curve for GHG emissions on Irish farms and this is aggregated to estimate a marginal cost curve for the agriculture sector. The impact of an emissions tax in achieving targeted levels of GHG emissions will be measured under a baseline scenario of no policy change.