The STILT Footprint Tool viewer service, provided by ICOS, allows users to visualise the variation over time of predicted CO2 concentrations from anthropogenic and natural sources, as these would be observable at a specific location (like a measurement station). At the same time, a map shows the corresponding “footprint” - the spatial extent of the regions contributing to the predicted CO2 concentrations. The data that are available in the viewer have been previously calculated using the STILT Footprint Tool on-demand footprint calculator service https://stilt.icos-cp.eu/worker/. While the STILT footprints are primarily interesting for greenhouse gas researchers wishing to understand to what extent observation station networks can provide representative coverage of all important sources and sinks of CO2 in the European continent, the visualisations of how the regions of influence for the different contributions to the potentially observable CO2 concentration vary over time and space are also interesting for non-experts. The STILT Footprint Tool is based on model simulations that combine the Lagrangian transport model STILT (Stochastic Time Inverted Lagrangian Transport), data on anthropogenic emissions from the EDGAR inventory, and biospheric sources and sinks estimated by the biosphere model VPRM (Vegetation Photosynthesis and Respiration Mode). The model framework has been developed at the Max Planck Institute for Biogeochemistry and is implemented as a web-based service at the ICOS Carbon Portal. You can read more here https://www.icos-cp.eu/data-services/tools/stilt-footprint. Both the STILT Footprint Tool viewer and STILT Footprint Tool on demand calculator services are provided by ICOS Carbon Portal in the context of ATMO-ACCESS project. Therefore an ATMO-ACCESS login is required to use them.