Boreal and arctic ecosystems have been responding to elevated temperatures and atmospheric CO₂ over the last decades. It is not clear if these ecosystems are sequestering more carbon or possibly becoming sources. This is an important feedback of the carbon cycle to global warming. We studied monthly biological land CO₂ fluxes inferred from atmospheric CO₂ concentrations using inverse models and found that net summer CO₂ uptake increased, resulting in a small increase in annual CO₂ uptake.