Inference of GHG Emissions at Regional Scales: A Critical Review of Progress to Date
Abstract:Atmospheric data have proven invaluable in understanding the carbon cycle at global scales using trends in atmospheric mole fractions, and very local scales using eddy covariance measurements. Intermediate spatial domains remain challenging. Significant progress has been made in estimating regional sources and sinks of GHG, particularly when high data densities are available to constrain integrative modeling systems. These regional estimates, however, have not yet found much utility outside of the academic community working to develop these methods.
We will review the current state of regional inferences of GHG sources and sinks including flux tower upscaling and regional atmospheric inversions, focusing especially on uncertainty assessment. Numerous flux tower upscaling products and a smaller number of regional atmospheric inversions have been produced in recent years. These vary greatly in terms of their data density, uncertainty, and method of uncertainty assessment. Arguably, none to date have reached the level of a data product that can be used to evaluate models or rigorously identify changes in fluxes over time and space. We will assess the prospects for obtaining rigorous uncertainty estimates that can move these products out of the realm of methodological experimentation and towards operational assessment of regional GHG sources and sinks. Our review will include examples drawn from recent experiments including the NACP interim syntheses, the Chequamegon Ecosystem-Atmosphere Study, the NACP Midcontinental Intensive, and the Indianapolis Flux Experiment.