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Erosion drives the export of particulate organic carbon from the terrestrial biosphere (POC biosphere ) and its delivery to rivers. The carbon transfer is globally significant and can result in drawdown of atmospheric carbon dioxide (CO 2 ) if the eroded POC biosphere escapes degradation during river transfer and sedimentary deposition. Despite this recognition, we lack a global perspective on how the tectonic and climatic factors which govern physical erosion regulate POC biosphere discharge, obscuring linkages between mountain building, climate, and CO 2 drawdown. To fill this deficit, geochemical (δ 13 C, 14 C and C/N), hydrometric (water discharge, suspended sediment concentration) and geomorphic (slope) measurements are combined from 33 globally-distributed forested mountain catchments. Radiocarbon activity is used to account for rock-derived organic carbon and reveals that POC biosphere eroded from mountain forests is mostly < 1300 14 C years old. Annual POC biosphere yields are positively correlated with suspended sediment yields, confirming results from Taiwan and a recent global analysis, and are high in catchments with the steepest slopes. Based on these relationships and the global distribution of slope angles (3-arc-second), it is suggested that topography steeper than 10° (16% of the continental area) may contribute ~ 40% of global POC biosphere erosional flux. Climate is shown to regulate POC biosphere discharge by mountain rivers, by controlling hydrologically-driven erosion processes. In catchments where discharge measurements are available (8 of the 33) a significant relationship exists between daily runoff (mm day − 1 ) and POC biosphere concentration (mg L − 1 ) ( r = 0.53, P < 0.0001). The relationship can be described by a single power law and suggests a high connectivity between forested hillslopes and mountain river channels. As a result, annual POC biosphere yields are significantly correlated with mean annual runoff ( r = 0.64, P < 0.0001). A shear-stress POC biosphere erosion model is proposed which can explain the patterns in the data. The model allows the climate sensitivity of this carbon flux to be assessed for the first time. For a 1% increase in annual runoff, POC biosphere discharge is predicted to increase by ~ 4%. In steeper catchments, POC biosphere discharge increases more rapidly with an increase in annual runoff. For comparison, a 1% increase in annual runoff is predicted to increase carbon transfers by silicate weathering solute fluxes in mountains by 0.4–0.7%. Depending on the fate of the eroded POC biosphere , river export of POC biosphere from mountains may act as an important negative feedback on rising atmospheric CO 2 and increased global temperature. Erosion of carbon from the terrestrial biosphere links mountain building and climate to the geological evolution of atmospheric CO 2 , while the carbon fluxes are sensitive to predicted changes in runoff over the coming century. [ABSTRACT FROM AUTHOR]