Abstract
Atmospheric inversions use measurements of atmospheric CO2 gradients to constrain regional surface fluxes. Current inversions indicate a net terrestrial CO2 sink in China between 0.16 and 0.35 PgC/yr. The uncertainty of these estimates is as large as the mean because the atmospheric network historically contained only one high altitude station in China. Here, we revisit the calculation of the terrestrial CO2 flux in China, excluding emissions from fossil fuel burning and cement production, by using two inversions with three new CO2 monitoring stations in China as well as aircraft observations over Asia. We estimate a net terrestrial CO2 uptake of 0.39–0.51 PgC/yr with a mean of 0.45 PgC/yr in 2006–2009. After considering the lateral transport of carbon in air and water and international trade, the annual mean carbon sink is adjusted to 0.35 PgC/yr. To evaluate this top-down estimate, we constructed an independent bottom-up estimate based on ecosystem data, and giving a net land sink of 0.33 PgC/yr. This demonstrates closure between the top-down and bottom-up estimates. Both top-down and bottom-up estimates give a higher carbon sink than previous estimates made for the 1980s and 1990s, suggesting a trend towards increased uptake by land ecosystems in China.
Highlights
The top-down and bottom-up estimates are consistent within their respective uncertainties
Considerable sources of systematic uncertainties still exist in these estimates, and the real uncertainties of both top-down and bottom-up estimates are likely higher than those calculated above
The top-down results for south and southwest China are very uncertain (Supplementary Fig. S3, Fig. S4), the results for eastern and northern China from different inversion systems are consistent within their uncertainties
Summary
Values have been adjusted with the national CO2 emissions from fossil fuel burning, cement manufacture, and gas flaring of 1.90 PgC yr−1 during 2006–2009 reported by the Carbon Dioxide Information Analysis Center[15]. Blue: constrained only with global CO2 datasets; orange: constrained with additional China Meteorological Administration (CMA)’s measurements (3 sites); and green: constrained with additional CMA and CONTRAIL aircraft CO2 measurements
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