Balancing the global carbon budget is a daunting task complicated by the fact that even the most essential values elude direct observation. Gross primary production, the amount of carbon used by terrestrial vegetation to fuel its annual growth, is often estimated by extrapolation from observations using climate models, including the Community Land Model (CLM). Terrestrial ecosystems are an extremely important sink for atmospheric carbon, so any misrepresentations of gross primary production can have strong effects on the understanding of the global carbon budget and may also potentially affect lawmakers' ability to plan around it. The widely used model, which is now in its fourth major version and seeks to represent the interplay between vegetation and climate, is known to overestimate global gross primary production by around 35 petagrams per year when compared to estimates derived from observations and other models, a surplus equivalent to about 6 times the annual carbon emissions of the United States. (Journal of Geophysical Research‐Biogeosciences, doi:10.1029/2010JG001593, 2011)