Diagnosing Carbon-Climate Feedbacks Using Space-Based Greenhouse Gas Observations

What controls the rate of increase of CO₂ and CH₄ in the atmosphere? It may seem self-evident but actually remains mysterious.  The increases of CO₂ and CH₄ result from a combination of forcing from anthropogenic emissions and Earth System feedbacks that dampen or amplify the effects of those emissions on atmospheric concentrations.  Today, emissions from land use and fossil fuel combustion are partitioned between the atmosphere, where they affect the climate, and a series of poorly understood sinks (see figure).  If these sinks change, the climate effect of the human enterprise will change.  Mush about the carbon-climate system, despite decades of research, remains without satisfactory answers; in the wake of recent climate negotiations, these uncertainties are unacceptable.  Emissions, long concentrated in the developed world, are now increasingly distributed globally with large uncertainties, leading to uncertainty about forcing to the carbon system. The fraction of anthropogenic CO₂ remaining in the atmosphere has remained remarkably constant over the last 59 years: why is this, and will it change in the future? CH₄, the other main greenhouse gas, concentrations are increasing after a decade of near-stabilization, and we have no compelling explanation for why this is occurring.  While greenhouse gases affect the global atmosphere, their sources and sinks are remarkably heterogeneous in time and space, and traditional in situ observing systems do not provide the coverage and resolution to resolve the above issues.  In the past few years, space-based technologies have proved increasingly capable of monitoring carbon stocks and fluxes, and could provide the measurements needed to close the carbon budget and quantify climate forcing and feedbacks and an observing system designed to quantify fluxes globally can and must be designed.