This talk by Corinne Le Quéré (University of East Anglia) at the 1st CHE General Assembly presented an overview of the activities in Work Package 1. WP1 (Coordinating Efforts on Reconciling top-down and bottom-up estimates) will address the current inconsistencies between satellite-based and in-situ based inversions, also in comparison with bottom-up estimates. The work package will gather and create multiple relevant satellite remote-sensing datasets and use them in developing data assimilation systems to specifically address four challenges: (i) optimally integrate satellite retrieval bias-correction into the data assimilation processing chain; (ii) minimize the impact of transport model errors on surface flux estimates; (iii) improve the model-data fusion techniques for joint natural and anthropogenic CO₂ emission estimates; (iv) deploy more advanced surface flux descriptions of natural and anthropogenic CO₂ emissions in the data assimilation chain. Easy and fast benchmarking of the outcomes of these systems will enable rapid innovation and the outcomes will be used at the end of the project to identify and outline developments towards a future data assimilation system that uses space-based remote sensing products.