Terrestrial carbon storage is limited by nitrogen availability, which could become more of a problem with increased CO2 levels. Different models show variability in how they simulate nitrogen cycling, which affects how much carbon they predict can be stored in the future. Models tend to overestimate certain nitrogen-related factors in tropical regions and underestimate them in temperate regions. More data on nitrogen cycling is needed to improve the accuracy of these models and better predict future carbon storage in terrestrial ecosystems.