Intensifying animal production is generally advocated to mitigate greenhouse gases emissions associated with production of animal-source food. Sheep farming systems (SFSs) in Spain are generally considered to be pasture-based and extensive, but large differences in input utilization, land use and intensification level exist. Their environmental impacts, therefore, are expected to differ also. We used life cycle assessment (LCA) to evaluate greenhouse gases (GHGs) emissions of three contrasting meat-sheep farming systems in Spain, which differed in their degree of intensification (reproduction rate, land use and grazing management). The GHGs emissions of these systems varied from 19.5 to 25.9 kg CO2-eq per kg of lamb live weight, or 39.0–51.7 kg CO2-eq per kg of lamb meat, with highest values referring to the pasture-based livestock system. In addition to meat, however, these SFSs also provide other services to society (e.g. public goods such as biodiversity and landscape conservation). We valued these services for each SFSs based on agri-environmental subsidies of the EU and used farm economic values to allocate GHGs emissions of SFSs between meat and cultural ecosystem services. When accounting for multifunctionality, GHGs emission per kg of lamb live weight among the SFSs was reversed: with lowest values for the pasture-based system (13.9 kg CO2-eq per kg of lamb live weight) and highest for zero-grazing system (19.5 kg CO2-eq per kg of lamb live weight). A comparison of GHGs emissions among SFSs should account for the multifunctionality of pasture-based livestock systems.