A globally integrated carbon observation and anal-ysis system is needed to improve the fundamental under-standing of the global carbon cycle, to improve our ability to project future changes, and to verify the effectiveness of poli-cies aiming to reduce greenhouse gas emissions and increase carbon sequestration. Building an integrated carbon obser-vation system requires transformational advances from the existing sparse, exploratory framework towards a dense, ro-bust, and sustained system in all components: anthropogenic emissions, the atmosphere, the ocean, and the terrestrial bio-sphere. The paper is addressed to scientists, policymakers, and funding agencies who need to have a global picture of the current state of the (diverse) carbon observations. We identify the current state of carbon observations, and the needs and notional requirements for a global integrated carbon observa-tion system that can be built in the next decade. A key conclu-sion is the substantial expansion of the ground-based obser-vation networks required to reach the high spatial resolution for CO2 and CH4 ?uxes, and for carbon stocks for address-ing policy-relevant objectives, and attributing ?ux changes to underlying processes in each region. In order to establish ?ux and stock diagnostics over areas such as the southern oceans, tropical forests, and the Arctic, in situ observations will have to be complemented with remote-sensing measure-ments. Remote sensing offers the advantage of dense spatial coverage and frequent revisit. A key challenge is to bring remote-sensing measurements to a level of long-term consis-tency and accuracy so that they can be ef?ciently combined in models to reduce uncertainties, in synergy with ground-based data. Bringing tight observational constraints on fossil fuel and land use change emissions will be the biggest chal-lenge for deployment of a policy-relevant integrated carbon observation system. This will require in situ and remotely sensed data at much higher resolution and density than currently achieved for natural ?uxes, although over a small land area (cities, industrial sites, power plants), as well as the in-clusion of fossil fuel CO2 proxy measurements such as ra-diocarbon in CO2 and carbon-fuel combustion tracers. Addi-tionally, a policy-relevant carbon monitoring system should also provide mechanisms for reconciling regional top-down (atmosphere-based) and bottom-up (surface-based) ?ux esti-mates across the range of spatial and temporal scales rele-vant to mitigation policies. In addition, uncertainties for each observation data-stream should be assessed. The success of the system will rely on long-term commitments to monitor-ing, on improved international collaboration to ?ll gaps in the current observations, on sustained efforts to improve access to the different data streams and make databases interopera-ble, and on the calibration of each component of the system to agreed-upon international scales
