Current systematic carbon-cycle observations and the need for implementing a policy-relevant carbon observing system

[摘要] A globally integrated carbon observation and analysis system is needed toimprove the fundamental understanding of the global carbon cycle, to improveour ability to project future changes, and to verify the effectiveness ofpolicies aiming to reduce greenhouse gas emissions and increase carbonsequestration. Building an integrated carbon observation system requirestransformational advances from the existing sparse, exploratory frameworktowards a dense, robust, and sustained system in all components:anthropogenic emissions, the atmosphere, the ocean, and the terrestrialbiosphere. The paper is addressed to scientists, policymakers, and fundingagencies who need to have a global picture of the current state of the(diverse) carbon observations. We identify the current state of carbonobservations, and the needs and notional requirements for a global integratedcarbon observation system that can be built in the next decade. A keyconclusion is the substantial expansion of the ground-based observationnetworks required to reach the high spatial resolution for CO₂ andCH₄ fluxes, and for carbon stocks for addressing policy-relevantobjectives, and attributing flux changes to underlying processes in eachregion. In order to establish flux and stock diagnostics over areas such asthe southern oceans, tropical forests, and the Arctic, in situ observationswill have to be complemented with remote-sensing measurements. Remote sensingoffers the advantage of dense spatial coverage and frequent revisit. A keychallenge is to bring remote-sensing measurements to a level of long-termconsistency and accuracy so that they can be efficiently combined in modelsto reduce uncertainties, in synergy with ground-based data. Bringing tightobservational constraints on fossil fuel and land use change emissions willbe the biggest challenge for deployment of a policy-relevant integratedcarbon observation system. This will require in situ and remotely sensed dataat much higher resolution and density than currently achieved for naturalfluxes, although over a small land area (cities, industrial sites, powerplants), as well as the inclusion of fossil fuel CO₂ proxy measurementssuch as radiocarbon in CO₂ and carbon-fuel combustion tracers.Additionally, a policy-relevant carbon monitoring system should also providemechanisms for reconciling regional top-down (atmosphere-based) and bottom-up(surface-based) flux estimates across the range of spatial and temporalscales relevant to mitigation policies. In addition, uncertainties for eachobservation data-stream should be assessed. The success of the system willrely on long-term commitments to monitoring, on improved internationalcollaboration to fill gaps in the current observations, on sustained effortsto improve access to the different data streams and make databasesinteroperable, and on the calibration of each component of the system toagreed-upon international scales.

[学科分类] 地球化学与岩石