The CO2 Human Emissions (CHE) project has been tasked by the European Commission to prepare the development of a European capacity to monitor anthropogenic CO2 emissions. The monitoring of fossil fuel CO2 emissions has to come with a reported and sufficiently low uncertainty in order to be useful for policymakers. In this context, the main approaches to estimate fossil fuel emissions, apart from bottom-up inventories, are based on inverse transport modelling either on its own or within a coupled carbon cycle fossil fuel data assimilation system. Both approaches make use of atmospheric CO2 and other, co-emitted tracers (e.g., CO and NOx). While inverse transport modelling relies on the availability of prior fossil fuel CO2 emission estimates and uncertainties as well as prior biogenic fluxes and uncertainties, the coupled carbon cycle fossil fuel data assimilation system can be employed completely independent from fossil fuel CO2 emission estimates because of the included process knowledge.

The key requirements within the CHE project stem from research done in the Science-layer Work-packages (WP1-4) and connecting the specific requirements of the CHE Monitoring and Verification System prototype that are detailed in the CHE Service-layer Work-package WP5. These are detailed in the deliverables D5.2, D5.4, D5.6, D.5.8, respectively covering the Earth observations, the modelling components, the data assimilation methodology and the uncertainty characterisation. The current report is focusing on the prototype implementation roadmap, requirements and priorities in consideration of the calendar of milestones described within the Paris Agreement and in the European Commission CO2 Task Force reports (CO2 blue, red, green reports, https://www.copernicus.eu/en/news/news/new-co2-green-report-2019-published).