Annual growth rates of column-averaged CO₂ inferred from Total Carbon Column Observing Network (TCCON)
Creators
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Karlsruhe Institute of Technology
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University of Bremen
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University of Wollongong
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Ames Research Center
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Cooperative Institute for Research in Environmental Sciences
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National Oceanic and Atmospheric Administration
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University of Toronto
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National Institute for Environmental Studies
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National Institute of Water and Atmospheric Research
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California Institute of Technology
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Finnish Meteorological Institute
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 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 yr−1. 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 yr−1. The impact of COVID-19-related emission reductions in 2020 was also examined: a decline of 0.4 ppm yr−1 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.
Copyright and License
© Author(s) 2026. This work is distributed under the Creative Commons Attribution 4.0 License. Published by Copernicus Publications on behalf of the European Geosciences Union.
Acknowledgement
This research was supported by the German Federal Ministry of Research, Technology and Space (BMFTR) through its project ACTRIS-D (Aerosols, Clouds and Trace gases Research Infrastructure), which provided personal funding for SM and essential support and resources for the data collection and analysis presented in this manuscript, and to the Helmholtz Research Program “Changing Earth”, Topic 1 “The Atmosphere in Global Change” at KIT. The authors acknowledge Dr. Ralf Sussmann (KIT/IMK-IFU) for providing the Garmisch TCCON data and Dr. Kei Shiomi (JAXA) for providing the Saga TCCON data used in this study.
The Eureka TCCON (Strong et al., 2022) measurements were made at the Polar Environment Atmospheric Research Laboratory (PEARL) by the Canadian Network for the Detection of Atmospheric Change (CANDAC), primarily supported by the Natural Sciences and Engineering Research Council of Canada, Environment and Climate Change Canada, and the Canadian Space Agency. The author gratefully acknowledges NASA, the California Institute of Technology (Caltech), and the Jet Propulsion Laboratory (JPL) for the OCO-2 and OCO-3 missions, which made this work possible. The TCCON station located at NASA's Armstrong Flight Research Center (formerly Dryden) is supported by NASA's Earth Science Division. The TCCON site at Rikubetsu is supported in part by the GOSAT series project. Darwin and Wollongong TCCON stations are supported by Australian Research Council grants DP160100598, DP140101552, DP110103118, DP0879468, and LE0668470, and NASA grants NAG512247 and NNG05GD07G. TCCON activities at the Lauder site are supported by the New Zealand Ministry of Business, Innovation and Employment Strategic Science Investment Fund. The author thanks Debra Wunch and Josh Laughner for their help in understanding the a priori CO2 calculations used in TCCON retrievals. The author thanks ChatGPT (GPT-5, OpenAI) for valuable assistance in code debugging and improving the clarity of the manuscript. The authors extend their sincere appreciation to the two anonymous reviewers and to the editor, Andrew Feldman, for their insightful and constructive comments that helped improve the quality of this manuscript.
Funding
This work was funded by the German Federal Ministry of Research, Technology, and Space (BMFTR) within the ACTRIS-D project (grant no. 01LK2001B) and by the Helmholtz Research Program Changing Earth – Sustaining our Future within the Helmholtz research field Earth and Environment.
The article processing charges for this open-access publication were covered by the Karlsruhe Institute of Technology (KIT).
Code Availability
The TCCON retrievals are available from the Caltech library at https://doi.org/10.14291/TCCON.GGG2020 (TCCON Team, 2022). In-situ observation data from the Mauna Loa Observatory (MLO) are available from https://gml.noaa.gov/data/ (last access: 11 July 2025). CAMS global inversion-optimised CO2 mean column values are available from https://ads.atmosphere.copernicus.eu/ (last access: 2 October 2025). CO2 annual and gridded emissions are available from the EDGAR database: https://edgar.jrc.ec.europa.eu/dataset_ghg2024 (last access: 4 August 2025). The DLM code used to fit the CO2 time series and calculate annual growth rates is available at https://doi.org/10.5281/zenodo.14772372 (Hachmeister, 2025).
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- Discussion Paper: 10.5194/egusphere-2025-4080 (DOI)
Funding
- Federal Ministry of Education and Research
- 01LK2001B
- Helmholtz Centre for Environmental Research
- Karlsruhe Institute of Technology
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- Caltech groups
- Division of Geological and Planetary Sciences (GPS)
- Publication Status
- Published