Cultured meat (also known as ‘clean’ or ‘lab-grown’ meat), has been suggested as a means of reducing the significant climate impacts associated with meat production. We explore this claim by testing a range of cultured meat and beef cattle ‘carbon footprints’ (the greenhouse gas emissions per unit of meat produced) in a climate model. Conventional beef production is associated with emissions of carbon dioxide (CO2), nitrous oxide, and particularly methane, while the emissions associated with currently proposed cultured systems are almost entirely CO2 from fossil fuel energy generation. In some of the speculated cultured production systems, meat production is sufficiently energy-efficient that it would have a much lesser impact on the climate than cattle systems, even without decarbonisation. In some proposed systems, however, cultured meat is highly energy-intensive, and would lead to more warming that cattle production in the long-term. It is not yet clear what the emissions footprints of real cultured production systems will look like. In addition, if emissions from either production system are stopped or reduced, the predominantly methane-driven warming from cattle is largely reversed, while the increased temperatures resulting from burning fossil fuels will persist unless this CO2 is actively removed from the atmosphere. The relative climate impacts of cultured meat and beef cattle therefore depend on the specific production systems that are realised, and the availability of decarbonised energy.