Understanding carbon dioxide (CO₂) fluxes from the terrestrial biosphere on a national scale is important for evaluating land use strategies to mitigate climate change. We estimate emissions of CO₂ from the UK biosphere using atmospheric data in a top-down approach. Our findings show that bottom-up estimates from models of biospheric fluxes overestimate the amount of CO₂ uptake in summer. This suggests these models wrongly estimate or omit key processes, e.g. land disturbance due to harvest.