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

Abstract

Abstract. In support of the Global Stocktake of the Paris Agreement on Climate change, this study presents a comprehensive framework to process the results of atmospheric inversions in order to make them suitable for evaluating UNFCCC national inventories of land-use carbon dioxide (CO2) emissions and removals, corresponding to the Land Use, Land Use Change and Forestry and waste sectors. We also deduced anthropogenic methane (CH4) emissions regrouped into fossil and agriculture and waste emissions, and anthropogenic nitrous oxide (N2O) emissions from inversions. To compare inversions with national reports, we compiled a new global harmonized database of national emissions and removals from periodical UNFCCC inventories by Annex I countries, and from sporadic and less detailed emissions reports by Non-Annex I countries, given by National Communications and Biennial Update Reports. The method to reconcile inversions with inventories is applied to selected large countries covering 78 % of the global land carbon uptake for CO2, as well as emissions and removals in the land use, land use change and forestry sector, and top-emitters of CH4 and N2O. Our method uses results from an ensemble of global inversions produced by the Global Carbon Project for the three greenhouse gases, with ancillary data. We examine the role of CO2 fluxes caused by lateral transfer processes from rivers and from trade in crop and wood products, and the role of carbon uptake in unmanaged lands, both not accounted for by the rules of inventories. Here we show that, despite a large spread across the inversions, the median of available inversion models points to a larger terrestrial carbon sink than inventories over temperate countries or groups of countries of the Northern Hemisphere like Russia, Canada and the European Union. For CH4, we find good consistency between the inversions assimilating only data from the global in-situ network and those using satellite CH4 retrievals, and a tendency for inversions to diagnose higher CH4 emissions estimates than reported by inventories. In particular, oil and gas extracting countries in Central Asia and the Persian Gulf region tend to systematically report lower emissions compared to those estimated by inversions. For N2O, inversions tend to produce higher anthropogenic emissions than inventories for tropical countries, even when attempting to consider only managed land emissions. In the inventories of many non-Annex I countries, this can be tentatively attributed to either a lack of reporting indirect N2O emissions from atmospheric deposition and from leaching to rivers, or to the existence of natural sources intertwined with managed lands, or to an under-estimation of N2O emission factors for direct agricultural soil emissions. The advantage of inversions is that they provide insights on seasonal and interannual greenhouse gas fluxes anomalies, e.g. during extreme events such as drought or abnormal fire episodes, whereas inventory methods are established to estimate trends and multi-annual changes. As a much denser sampling of atmospheric CO2 and CH4 concentrations by different satellites coordinated into a global constellation is expected in the coming years, the methodology proposed here to compare inversion results with inventory reports could be applied regularly for monitoring the effectiveness of mitigation policy and progress by countries to meet the objective of their pledges.

Quantification of methane emissions from hotspots and during COVID-19 using a global atmospheric inversion

“…Except for Russia and Indonesia, these bring emission estimates in closer agreement with other top-down studies (e.g. Deng et al, 2021).…”

“…Using prior emission maps, we distributed total posterior emissions into 6 sector specific categories; energy, agriculture, waste, other anthropogenic, wetlands and fires. In agreement with multiple inverse studies (Deng et al, 2021) most of the overestimated emissions from China are found to originate from the energy sector (1.9 Tg yr -1 ) and specifically from the coal mining regions of Outer Mongolia, Shaanxi and Shanxi. Relative to the prior, posterior emissions are reduced from India (-3.0%) and Pakistan (-1.1%), increased from Brazil (+1.3%) and less than 1% different for the USA (0.5%), Indonesia (0.3%), EU27+UK (+0.1%) and Russia (-0.7%).…”

A comprehensive and synthetic dataset for global, regional, and national greenhouse gas emissions by sector 1970–2018 with an extension to 2019

“…Figure 9 further highlights the lack of recent official national emissions inventories for many non-Annex I countries. The BURs are also associated with less stringent reporting requirements in terms of sector, gas, and time coverage (Deng et al, 2021;Gütschow et al, 2016). This highlights the important role of global inventories such as EDGAR, CEDS, PRIMAP-hist, FAOSTAT, or those from IEA or BP among others that are equally as comprehensive in scope as those from Annex I countries.…”

“…GHG emissions reporting under the United Nations Framework Convention on Climate Change (UNFCCC) provides reliable, comprehensive, and up-to-date statistics for Annex I countries across all major GHGs. Non-Annex I countries -except the least devel-oped countries and small island states for which this is not mandatory -provide GHG emissions inventory information through biennial update reports (BURs) but with much less stringent reporting requirements in terms of sector, gas, and time coverage (Deng et al, 2021;Gütschow et al, 2016). As a result, many still lack a well-developed statistical infrastructure to provide detailed reports (Janssens-Maenhout et al, 2019).…”

Toward a long-term atmospheric CO2 inversion for elucidating natural carbon fluxes: technical notes of NISMON-CO2 v2021.1

“…However, in recent years, societal momentum to reduce CO2 emissions has strengthened globally in response to the 1.5°C /2.0°C target of the Paris agreement, and CO2 flux data from inverse analyses are becoming an important source of information used to independently evaluate national inventories. The latest studies by Chevalllier (2021) and Deng et al (2021) compared inversion fluxes with national inventories based on agriculture, forestry, and other land use changes (LUCs). However, they used data from global-scale inversions with horizontal resolutions generally around hundreds of kilometers.…”