Abstract

North America is both a source and sink of atmospheric carbon dioxide (CO₂). Continental sources – such as fossil-fuel combustion in the US and deforestation in Mexico – and sinks – including most ecosystems, and particularly secondary forests – add and remove CO₂ from the atmosphere, respectively. Photosynthesis converts CO₂ into carbon as biomass, which is stored in vegetation, soils, and wood products. However, ecosystem sinks compensate for only ~35% of the continent's fossil-fuel-based CO₂ emissions; North America therefore represents a net CO₂ source. Estimating the magnitude of ecosystem sinks, even though the calculation is confounded by uncertainty as a result of individual inventory- and model-based alternatives, has improved through the use of a combined approach.