Abstract. The source and sinks of carbon dioxide (CO 2 ) and methane (CH 4 ) due to anthropogenic and natural biospheric activities were estimated for the South Asian region (Bangladesh, Bhutan, India, Nepal, Pakistan and Sri Lanka). Flux estimates were based on top-down methods that use inversions of atmospheric data, and bottom-up methods that use field observations, satellite data, and terrestrial ecosystem models. Based on atmospheric CO 2 inversions, the net biospheric CO 2 flux in South Asia (equivalent to the Net Biome Productivity, NBP) was a sink, estimated at −104 ± 150 Tg C yr −1 during [2007][2008]. Based on the bottom-up approach, the net biospheric CO 2 flux is estimated to be −191 ± 193 Tg C yr −1 during the period of 2000-2009. This last net flux results from the following flux components: (1) the Net Ecosystem Productivity, NEP (net primary production minus heterotrophic respiration) of −220 ± 186 Tg C yr −1 (2) the annual net carbon flux from land-use change of −14 ± 50 Tg C yr −1 , which resulted from a sink of −16 Tg C yr −1 due to the establishment of tree plantations and wood harvest, and a source of 2 Tg C yr −1 due to the expansion of croplands; (3) the riverine export flux from terrestrial ecosystems to the coastal oceans of +42.9 Tg C yr −1 ; and (4) the net CO 2 emission due to biomass burning of +44.1 ± 13.7 Tg C yr −1 . Including the emissions from the combustion of fossil fuels of 444 Tg C yr −1 for the 2000s, we estimate a net CO 2 landatmosphere flux of 297 Tg C yr −1 . In addition to CO 2 , a fraction of the sequestered carbon in terrestrial ecosystems is released to the atmosphere as CH 4 . Based on bottom-up and top-down estimates, and chemistry-transport modeling, we estimate that 37 ± 3.7 Tg C-CH 4 yr −1 were released to atmosphere from South Asia during the 2000s. Taking all CO 2 and CH 4 fluxes together, our best estimate of the net land-atmosphere CO 2 -equivalent flux is a net source of 334 Tg C yr −1 for the South Asian region during the 2000s. If CH 4 emissions are weighted by radiative forcing of molecular CH 4 , the total CO 2 -equivalent flux increases to 1148 Tg C yr −1 suggesting there is great potential of reducing CH 4 emissions for stabilizing greenhouse gases concentrations.

The source and sinks of carbon dioxide (CO₂) and methane (CH₄) due to anthropogenic and natural biospheric activities were estimated for the South Asia region (Bangladesh, Bhutan, India, Nepal, Pakistan and Sri Lanka). Flux estimates were based on top-down methods that use inversions of atmospheric data, and bottom-up methods that use field observations, satellite data, and terrestrial ecosystem models. Based on atmospheric CO₂ inversions, the net biospheric CO₂ flux in South Asia (equivalent to the Net Biome Productivity, NBP) was a sink, estimated at −104 ± 150 Tg C yr^−1 during 2007–2008. Based on the bottom-up approach, the net biospheric CO₂ flux is estimated to be −191 ± 193 Tg C yr^−1 during the period of 2000–2009. This last net flux results from the following flux components: (1) the Net Ecosystem Productivity, NEP (net primary production minus heterotrophic respiration) of −220 ± 186 Tg C yr^−1 (2) the annual net carbon flux from land-use change of −14 ± 50 Tg C yr^−1, which resulted from a sink of −16 Tg C yr^−1 due to the establishment of tree plantations and wood harvest, and a source of 2 Tg C yr^−1 due to the expansion of croplands; (3) the riverine export flux from terrestrial ecosystems to the coastal oceans of +42.9 Tg C yr^−1; and (4) the net CO₂ emission due to biomass burning of +44.1 ± 13.7 Tg C yr^−1. Including the emissions from the combustion of fossil fuels of 444 Tg C yr^−1 for the decades of 2000s, we estimate a net CO₂ land-to-atmosphere flux of 297 Tg C yr^−1. In addition to CO₂, a fraction of the sequestered carbon in terrestrial ecosystems is released to the atmosphere as CH₄. Based on bottom-up and top-down estimates, and chemistry-transport modeling, we estimate that 37 ± 3.7 Tg C-CH₄ yr^−1 were released to atmosphere from South Asia during the 2000s. Taking all CO₂ and CH₄ fluxes together, our best estimate of the net land-to-atmosphere CO₂-equivalent flux is a net source of 334 Tg C yr^−1 for the South Asia region during the 2000s. If CH₄ emissions are weighted by radiative forcing of molecular CH₄, the total CO₂-equivalent flux increases to 1148 Tg C yr^−1 suggesting there is great potential of reducing CH₄ emissions for stabilizing greenhouse g...

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