A new generation of soil models promises to more accurately predict the carbon cycle in soils under climate change. However, measurements of ¹⁴C (the radioactive carbon isotope) in soils reveal that the new soil models face similar problems to the traditional models: they underestimate the residence time of carbon in soils and may therefore overestimate the net uptake of CO₂ by the land ecosystem. Proposed solutions include restructuring the models and calibrating model parameters with ¹⁴C data.