Comparing national greenhouse gas budgets reported in UNFCCC inventories against atmospheric inversions

[摘要] In support of the global stocktake of the Paris Agreementon climate change, this study presents a comprehensive framework to processthe results of an ensemble of atmospheric inversions in order to make theirnet ecosystem exchange (NEE) carbon dioxide (CO 2 ) flux suitable forevaluating national greenhouse gas inventories (NGHGIs) submitted bycountries to the United Nations Framework Convention on Climate Change(UNFCCC). From inversions we also deduced anthropogenic methane (CH 4 )emissions regrouped into fossil and agriculture and waste emissions, as well asanthropogenic nitrous oxide (N 2 O) emissions. To compare inversionresults with national reports, we compiled a new global harmonized databaseof emissions and removals from periodical UNFCCC inventories by Annex Icountries, and from sporadic and less detailed emissions reports bynon-Annex I countries, given by national communications and biennial updatereports. No gap filling was applied. The method to reconcile inversions withinventories is applied to selected large countries covering ∼90  % of the global land carbon uptake for CO 2 and top emitters ofCH 4 and N 2 O. Our method uses results from an ensemble of globalinversions produced by the Global Carbon Project for the three greenhousegases, with ancillary data. We examine the role of CO 2 fluxes caused bylateral transfer processes from rivers and from trade in crop and woodproducts and the role of carbon uptake in unmanaged lands, both notaccounted for by NGHGIs. Here we show that, despite a large spread acrossthe inversions, the median of available inversion models points to a largerterrestrial carbon sink than inventories over temperate countries or groupsof countries of the Northern Hemisphere like Russia, Canada and the EuropeanUnion. For CH 4 , we find good consistency between the inversionsassimilating only data from the global in situ network and those usingsatellite CH 4 retrievals and a tendency for inversions to diagnosehigher CH 4 emission estimates than reported by NGHGIs. In particular,oil- and gas-extracting countries in central Asia and the Persian Gulf regiontend to systematically report lower emissions compared to those estimated byinversions. For N 2 O, inversions tend to produce higher anthropogenicemissions than inventories for tropical countries, even when attempting toconsider only managed land emissions. In the inventories of many non-Annex Icountries, this can be tentatively attributed to a lack of reportingindirect N 2 O emissions from atmospheric deposition and from leaching torivers, to the existence of natural sources intertwined with managedlands, or to an underestimation of N 2 O emission factors for directagricultural soil emissions. Inversions provide insights into seasonal andinterannual greenhouse gas fluxes anomalies, e.g., during extreme eventssuch as drought or abnormal fire episodes, whereas inventory methods areestablished to estimate trends and multi-annual changes. As a much densersampling of atmospheric CO 2 and CH 4 concentrations by differentsatellites coordinated into a global constellation is expected in the comingyears, the methodology proposed here to compare inversion results withinventory reports (e.g., NGHGIs) could be applied regularly for monitoringthe effectiveness of mitigation policy and progress by countries to meet theobjective of their pledges. The dataset constructed by this study ispublicly available at https://doi.org/10.5281/zenodo.5089799 (Deng et al., 2021).

[学科分类] 眼科学