Interactions between Earth’s surface and the atmosphere influence climate, air quality and water cycles. Changes in one affect the others. Our actions — such as emission-control policies, urbanisation and forestry — also affect the atmosphere, land and seas. A global observatory has been discussed for more than a decade, but is only now becoming feasible. Instruments have matured; for example, today’s mass spectrometers can measure thousands of atmospheric chemicals at once. Regional initiatives to combine and broaden space- and ground-based monitoring are established well enough to roll out similar stations globally. Incomplete coverage from ground stations is the main limit to observations of Earth’s conditions. Satellites can continuously monitor some compounds, such as CO2, ozone and aerosols, almost planet-wide. But they cannot resolve processes or fluxes, or trace the hundreds of other compounds of interest. Satellite data must be ‘ground-truthed’ and models need data to validate them. Current networks of ground stations have been set up without considering the big picture, and the end result is that each discipline or team designs and builds stations to suit its purpose. Greenhouse gases, atmospheric chemicals and ecosystems are monitored at different sites. Furthermore, many funding agencies focus on national interests. A global observatory would allow cost-efficient tools to understand how the Earth system works. The session welcomes contributions on integration potential between disciplines and scales, the added value for collaboration and innovative solutions for promoting co-design of observations.