The distribution of sources and sinks of carbon among the world's ecosystems is uncertain. Some analyses show northern mid-latitude lands to be a large sink, whereas the tropics are a net source1; other analyses show the tropics to be nearly neutral, whereas northern mid-latitudes are a small sink2,3. Here we show that the annual flux of carbon from deforestation and abandonment of agricultural lands in the Brazilian Amazon was a source of about 0.2 Pg C yr-1 over the period 1989–1998 (1 Pg is 1015 g). This estimate is based on annual rates of deforestation and spatially detailed estimates of deforestation, regrowing forests and biomass. Logging may add another 5–10% to this estimate4, and fires may double the magnitude of the source in years following a drought4. The annual source of carbon from land-use change and fire approximately offsets the sink calculated for natural ecosystems in the region5,6. Thus this large area of tropical forest is nearly balanced with respect to carbon, but has an interannual variability of ± 0.2 PgC yr-1.
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We thank A. Janetos, D. Nepstad, C. Prentice and R. Birdsey for comments on earlier drafts of the paper. This work was supported by the Terrestrial Ecology Program, the Land Cover and Land Use Change Program, and the Landsat Program in the NASA Office of Earth Science.
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Nature Sustainability (2018)