North American carbon dioxide sources and sinks: magnitude, attribution, and uncertainty

North America is both a source and sink of atmospheric carbon dioxide (CO 2 ). 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 CO 2 from the atmosphere, respectively. Photosynthesis converts CO 2 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 CO 2 emissions; North America therefore represents a net CO 2 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.