Regional trends in terrestrial carbon exchange and their seasonal signatures

The trends of terrestrial carbon exchange and their mechanistic drivers are key components in understanding how carbon reservoirs will respond to climate change. Here we show trends in seasonal non-fossil land-atmosphere carbon exchange from 1980 to 2008 using atmospheric CO₂ inversion results. Four indices were analysed: growing-season net flux (GSNF), dormant-season net flux (DSNF), amplitude and annual net carbon flux (NCF). We find that the global land carbon sink is intensifying at -0.057 ± 0.01 PgC yr^-2, resulting in -1.65 ± 0.29 PgC of additional uptake over the period examined. This increased total land uptake is driven by a decline in the DSNF (-0.04 ± 0.01 PgC yr^-2) and intensification of the GSNF (-0.02 ± 0.008 PgC yr^-2). Regional analysis shows the dominant role of the southern half of the African continent; intensification of the GSNF (-0.02 ± 0.005 PgC yr^-2) and a decline in the DSNF (-0.013 ± 0.004 PgC yr^-2) imply that Africa has shifted from a net carbon source in the 1980s to near-neutral emissions. By contrast, a weakening of the GSNF is found in temperate North America (0.015 ± 0.007 PgC yr^-2) and tropical America (0.01 ± 0.005 PgC yr^-2).