Detection and attribution of regional CO₂ concentration anomalies using surface observations

In this study, observed episodes of CO₂ concentrations at eight Northern Hemisphere (NH) sites from 1993 to 2012 were analyzed. Five-day back trajectories were calculated for a potential source contribution function (PSCF) analysis. A normalized weight factor related to the occurrence of the episodes was applied to derive more reasonable CO₂ elevations and sequestrations. Weighted elevated (δCO₂(W_E)) and sequestered (δCO₂(W_S)) CO₂ episodes had large spatial discrepancies due to the differentiation of strength and patterns of CO₂ emissions/sinks in different regions. The most significant enhancement in CO₂ episodes was observed at Asian sites: δCO₂(W_E) increased by approximately 56% at an annual rate of ~4% yr^-1 from 1995 to 2010 at Waliguan (WLG) and by approximately 39% (~3% yr^-1) from 1997 to 2012 at Yonagunijima (YON). According to the PSCF analysis, these increases are largely attributed to the rapid increase in emissions in China. However, δCO₂(W_S) was also enhanced by 34.4% with a growth rate of 2.3% yr^-1 at WLG from 1995 to 2010 and ~26.2% (1.7% yr^-1) at YON from 1997 to 2012. Both δCO₂(W_E) and δCO₂(W_S) showed decreasing or relatively flat trends at Monte Cimone and Schauinsland, indicating reductions in emissions and sinks in central Europe. The different intensities/trends in emissions and sinks observed at different sites in the NH show that estimating future CO₂ levels is a complex problem. Atmospheric inverse and process-based ecosystem models should use more regional input data at high temporal and spatial resolutions for future carbon flux estimations.