The carbon budget of South Asia Academic Article uri icon

abstract

  • <p><strong>Abstract.</strong> The source and sinks of carbon dioxide (CO<sub>2</sub>) and methane (CH<sub>4</sub>) 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<sub>2</sub> inversions, the net biospheric CO<sub>2</sub> flux in South Asia (equivalent to the Net Biome Productivity, NBP) was a sink, estimated at ?104 ± 150 Tg C yr<sup>&amp;minus;1</sup> during 2007–2008. Based on the bottom-up approach, the net biospheric CO<sub>2</sub> flux is estimated to be ?191 ± 193 Tg C yr<sup>&amp;minus;1</sup> 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<sup>&amp;minus;1</sup> (2) the annual net carbon flux from land-use change of ?14 ± 50 Tg C yr<sup>&amp;minus;1</sup>, which resulted from a sink of ?16 Tg C yr<sup>&amp;minus;1</sup> due to the establishment of tree plantations and wood harvest, and a source of 2 Tg C yr<sup>&amp;minus;1</sup> due to the expansion of croplands; (3) the riverine export flux from terrestrial ecosystems to the coastal oceans of +42.9 Tg C yr<sup>&amp;minus;1</sup>; and (4) the net CO<sub>2</sub> emission due to biomass burning of +44.1 ± 13.7 Tg C yr<sup>&amp;minus;1</sup>. Including the emissions from the combustion of fossil fuels of 444 Tg C yr<sup>&amp;minus;1</sup> for the 2000s, we estimate a net CO<sub>2</sub> land–atmosphere flux of 297 Tg C yr<sup>&amp;minus;1</sup>. In addition to CO<sub>2</sub>, a fraction of the sequestered carbon in terrestrial ecosystems is released to the atmosphere as CH<sub>4</sub>. Based on bottom-up and top-down estimates, and chemistry-transport modeling, we estimate that 37 ± 3.7 Tg C yr<sup>&amp;minus;1</sup> were released to atmosphere from South Asia during the 2000s. Taking all CO<sub>2</sub> and CH<sub>4</sub> fluxes together, our best estimate of the net land–atmosphere CO<sub>2</sub>-equivalent flux is a net source of 334 Tg C yr<sup>&amp;minus;1</sup> for the South Asian region during the 2000s. If CH<sub>4</sub> emissions are weighted by radiative forcing of molecular CH<sub>4</sub>, the total CO<sub>2</sub>-equivalent flux increases to 1148 Tg C yr<sup>&amp;minus;1</sup> suggesting there is great potential of reducing CH<sub>4</sub> emissions for stabilizing greenhouse gases concentrations.</p>