Forests dominate the land carbon sink, and forest-based carbon removal strategies have the potential to confer many benefits for the environment and the bio-economy. However, at scales ranging from individual sites to the entire globe, estimates of forest carbon uptake and storage (FCUS) vary by 50-100% (or more). Much of this uncertainty stems from a misalignment between our state-of-the-art understanding of FCUS and the decades-old tools used to estimate it in practice. Most operational protocols rely on ‘stock-change’ approaches that link FCUS to the change in woody biomass estimated from allometric equations and forest inventory data. While this approach is highly scalable, it has many critical limitations including the omission or imprecise calculation of carbon changes in branches, roots, and the soil. Over the past 20 years, an alternative, flux-based approach for quantifying FCUS has emerged, supported by rapidly growing networks of eddy covariance flux towers. While flux towers are viewed as the gold standard for measuring landatmosphere carbon exchanges, they have not yet been leveraged for policy-relevant forest carbon quantification, even though they record estimates of FCUS that are much higher than those produced by stock-change approaches. Our overall objective is to use the best-available science to confront these discrepancies through a robust intercomparison of stock- and flux-based measurement approaches. We will test an overarching hypothesis that the limitations of stock-based approaches have led to a systematic underestimation of how much carbon is removed from the atmosphere by undisturbed forests.