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

A globally integrated carbon observation and analysis
system is needed to improve the fundamental understanding
of the global carbon cycle, to improve our ability to
project future changes, and to verify the effectiveness of policies
aiming to reduce greenhouse gas emissions and increase
carbon sequestration. Building an integrated carbon observation
system requires transformational advances from the
existing sparse, exploratory framework towards a dense, robust,
and sustained system in all components: anthropogenic
emissions, the atmosphere, the ocean, and the terrestrial biosphere.
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 observation
system that can be built in the next decade. A key conclusion
is the substantial expansion of the ground-based observation
networks required to reach the high spatial resolution
for CO2 and CH4 fluxes, and for carbon stocks for addressing
policy-relevant objectives, and attributing flux changes
to underlying processes in each region. In order to establish
flux 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 measurements.
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 consistency
and accuracy so that they can be efficiently combined
in models to reduce uncertainties, in synergy with groundbased
data. Bringing tight observational constraints on fossil
fuel and land use change emissions will be the biggest challenge
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 fluxes, although over a small land
area (cities, industrial sites, power plants), as well as the inclusion
of fossil fuel CO2 proxy measurements such as radiocarbon
in CO2 and carbon-fuel combustion tracers. Additionally,
a policy-relevant carbon monitoring system should
also provide mechanisms for reconciling regional top-down
(atmosphere-based) and bottom-up (surface-based) flux estimates
across the range of spatial and temporal scales relevant
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 monitoring,
on improved international collaboration to fill gaps in the
current observations, on sustained efforts to improve access
to the different data streams and make databases interoperable,
and on the calibration of each component of the system
to agreed-upon international scales.