Estimating terrestrial GHG emissions and uptake in China: Progress and prospects

Background/Question/Methods

Terrestrial ecosystems may act as a source or a sink for the atmospheric greenhouse gases (GHG) of CO₂, CH₄ and N₂O, depending on land use and management. Over the last decade, scientists have made great efforts to estimate China's terrestrial GHG emissions and uptake. Field measurement-based data, inventory–satellite-based data and process-based models were used in these estimates. This presentation provides an overview of existing estimates from various studies.

Results/Conclusions

Over the period from 1980 to the late 1990s/early 2000s, a net terrestrial carbon sink was estimated to be 190±63Tg C/yr in China, of which ~56% comes from biomass carbon. The estimated higher carbon sink occurred in south and southeast China. Forest ecosystems dominated the carbon sinks, accounting for ~45% of the national total. Large–scale reforestation/afforestation contributes ~40% to the total forest carbon sink. Methane emissions from natural wetlands and irrigated rice cultivation were estimated to be 1.8±0.1Tg/yr and 7.7±1.9Tg/yr, respectively. Higher CH₄ emissions occurred in southern China, where double-rice cropping systems dominated, accounting for ~55% of the total rice paddy emissions in China. Methane uptake by aerobic soils was reported to be 2.56Tg/yr. Nitrous oxide emissions were estimated to be 1.32±0.27Tg/yr, of which ~45% comes from cropland. The synthetic fertilizer N-induced direct N₂O emission accounts for ~63% of the total cropland emissions, and increased from 1980 to 2000 with an average rate of 14.4Gg/yr. A substantial N₂O emission occurred in eastern and south central China, accounting for ~65% of the total cropland emissions. In light of global warming potential at a 100- year time horizon, the terrestrial carbon sink amounted to ~0.76Pg CO₂-eq/yr in China. Approximately 83% of the sink was offset by terrestrial CH₄ and N₂O emissions. The anthropogenic sources of CH₄ and N₂O offset approximately 40% of the sink.

Although scientists have made great efforts to estimate China’s terrestrial GHG emissions and uptake, large uncertainties existed in these estimates, especially for the soil carbon sequestration and emission. Special attention should be given to reduce the uncertainties. Moreover, the large–scale reforestation/afforestation has greatly contributed to terrestrial carbon sink in China, and the implementation of reforestation/afforestation will be continued. Understanding the future changes in the reforestation/afforestation-induced carbon sink is required.