Annual Growth Rates of Column-Averaged CO₂ Inferred from Total Carbon Column Observing Network (TCCON)

Abstract. Monitoring annual atmospheric CO₂ growth rates is a key constraint on assessing the long-term effectiveness of emission reduction strategies. We analyzed annual growth rates of column-averaged dry-air mole fractions of CO₂ (XCO₂) using long-term data from 12 sites within the Total Carbon Column Observing Network (TCCON), spanning four regions: the Arctic, two Northern Hemisphere midlatitude bands (40–50° N and 30–40° N), and the Southern Hemisphere. While in situ ground-based measurements provide detailed records of near-surface CO₂ concentrations, XCO₂ reflects the column-averaged abundance across the entire atmosphere, offering a complementary perspective.

We compared TCCON-derived growth rates with ground-based in situ observations from the Mauna Loa Observatory (MLO). Three calculation methods—Monthly Mean (MM), Fourier Fit residuals (FF), and Dynamic Linear Model (DLM)—were evaluated, with particular attention to the Eureka site, where polar night introduces substantial data gaps. In addition, the Copernicus Atmosphere Monitoring Service (CAMS) reanalysis product was used to assess consistency with TCCON-based growth rates and to evaluate each method’s robustness to missing data. Among the methods tested, the DLM approach proved most resilient to data gaps.

Regionally averaged CO₂ growth rates, calculated from 2010 or from the earliest available data through 2024, ranged from approximately 2.33 to 2.40 ppm per year. The most prominent signal was associated with the 2015–2016 El Niño–Southern Oscillation (ENSO) event, during which growth rates increased by up to 1.7 ppm per year. The impact of COVID-19-related emission reductions in 2020 was also examined: a decline of 0.4 ppm per year was observed in the 30–40° N region, whereas other regions showed no significant decline. Correlation analysis between growth rates and ENSO strength revealed significant relationships in the Southern Hemisphere and at Mauna Loa, but not in northern mid- or high-latitude regions.