Scientists from the CoCO2 project have contributed to a new synthesis of emissions for methane (CH₄) and nitrous oxide (N₂O) for the European Union and the United Kingdom. The results, published in Earth System Science Data, compare estimates from bottom-up (BU) and top-down (TD) approaches for the European Union and UK (EU27 + UK), and updates earlier syntheses (Petrescu et al., 2020, 2021). While currently comparisons between CH₄ and N₂O atmospheric inversion estimates and National Greenhouse Gas Inventories (NGHGIs) is highly uncertain because of the large spread in the inversion results, the study concludes that atmospheric inversions inferred from observations represent the most independent data against which inventory totals can be compared. Expected improvements in the modelling of atmospheric transport and natural surface fluxes, together with more and better observations, are likely to bring the atmospheric inversions to a mature tool for verifying emission inventories for CH₄, N₂O and other GHGs in the coming years.