As governments elaborate strategies to counter climate change, there is a need to compare the different options available on an environmental basis. This study proposes a life cycle assessment (LCA) framework integrating the Lashof Mg-year accounting methodology that allows the assessment and comparison of different carbon mitigation projects (e.g. biofuel use, sequestering plant, afforestation project, etc.). The Lashof accounting methodology is chosen amid other methods of greenhouse gas (GHG) emission characterization for its relative simplicity and capability of characterizing all types of carbon mitigation projects. It calculates the cumulative radiative forcing caused by GHG emission within a predetermined time frame. Basically, the developed framework uses the Mg-year as a functional unit and isolates impacts related to the climate mitigation function with system expansion. The proposed framework is demonstrated with a case study of tree ethanol pathways (maize, sugarcane and willow). Study shows that carbon mitigation assessment through LCA is possible and that it could be a useful tool for decision makers as it can compare different projects regardless of their original context. Case study reveals that the system expansion scenario and the efficiency at reducing carbon emissions of the carbon mitigation project are critical factors having significant impact on results. Also, framework proves to be useful at treating land-use change emission as they are considered through the functional unit.