The role of the tropical carbon balance in determining the large atmospheric CO <sub>2</sub>  growth rate in 2023

Abstract. The global annual mean atmospheric CO2 growth rate in 2023 was one of the highest since records began in 1958, comparable to values recorded during previous major El Niño events. We do not fully understand this anomalous growth rate, although a recent study highlighted the role of boreal North American forest fires. We use a Bayesian inverse method to interpret global-scale atmospheric CO2 data from NASA's Orbiting Carbon Observatory (OCO-2). The resulting a posteriori CO2 flux estimates reveal that from 2022 to 2023, the biggest changes in CO2 fluxes of net biosphere exchange (NBE) – for which positive values denote a flux to the atmosphere – were over the land tropics. We find that the largest NBE increase is over eastern Brazil, with small increases over southern Africa and Southeast Asia. We also find significant increases over southeastern Australia, Alaska, and western Russia. A large NBE increase over boreal North America, due to fires, is driven by our a priori inventory, informed by independent data. The largest NBE reductions are over western Europe, the USA, and central Canada. Our NBE estimates are consistent with gross primary production estimates inferred from satellite observations of solar-induced fluorescence and from satellite observations of vegetation greenness. We find that warmer temperatures in 2023 explain most of the NBE change over eastern Brazil, with hydrological changes more important elsewhere across the tropics. Our results suggest that the ongoing environmental degradation of the Amazon is now playing a substantial role in increasing the global atmospheric CO2 growth rate.

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Publication Details

Journal
Atmospheric chemistry and physics
Published
2025-10-21
DOI
https://doi.org/10.5194/acp-25-13053-2025
Primary Topic
Atmospheric and Environmental Gas Dynamics
Type
article
Field-Weighted Citation Impact
0.00

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article

The role of the tropical carbon balance in determining the large atmospheric CO 2  growth rate in 2023

Xinrong Ren, Simonetta Montaguti, John A. Lee, Stephen M. Platt et al.
Atmospheric chemistry and physics
Atmospheric and Environmental Gas Dynamics
article

The role of the tropical carbon balance in determining the large atmospheric CO 2  growth rate in 2023

Xinrong Ren, Simonetta Montaguti, John A. Lee, Stephen M. Platt, Paolo Cristofanelli, Paul I. Palmer, Jingfeng Xiao, Casper Labuschagne, Steffen M. Noe, Irène Xueref-Rémy, Ove Hermansen, Martin Steinbacher, T. Luke Smallman, Liang Feng
article en

Abstract

Abstract. The global annual mean atmospheric CO2 growth rate in 2023 was one of the highest since records began in 1958, comparable to values recorded during previous major El Niño events. We do not fully understand this anomalous growth rate, although a recent study highlighted the role of boreal North American forest fires. We use a Bayesian inverse method to interpret global-scale atmospheric CO2 data from NASA's Orbiting Carbon Observatory (OCO-2). The resulting a posteriori CO2 flux estimates reveal that from 2022 to 2023, the biggest changes in CO2 fluxes of net biosphere exchange (NBE) – for which positive values denote a flux to the atmosphere – were over the land tropics. We find that the largest NBE increase is over eastern Brazil, with small increases over southern Africa and Southeast Asia. We also find significant increases over southeastern Australia, Alaska, and western Russia. A large NBE increase over boreal North America, due to fires, is driven by our a priori inventory, informed by independent data. The largest NBE reductions are over western Europe, the USA, and central Canada. Our NBE estimates are consistent with gross primary production estimates inferred from satellite observations of solar-induced fluorescence and from satellite observations of vegetation greenness. We find that warmer temperatures in 2023 explain most of the NBE change over eastern Brazil, with hydrological changes more important elsewhere across the tropics. Our results suggest that the ongoing environmental degradation of the Amazon is now playing a substantial role in increasing the global atmospheric CO2 growth rate.

Atmospheric chemistry and physicsVol. 25(20)
Centre National de la Recherche Scientifique (FR), University of New Hampshire (US), Estonian University of Life Sciences (EE), South African Weather Service (ZA), Institute of Atmospheric Sciences and Climate (IT), National Centre for Earth Observation (GB), Institut Méditerranéen de Biodiversité et d'Ecologie Marine et Continentale (FR), Institut de Recherche pour le Développement (FR), NILU (NO), Swiss Federal Laboratories for Materials Science and Technology (CH), NOAA Air Resources Laboratory (US), University of Maine (US), University of Edinburgh (GB)
National Science Foundation, National Aeronautics and Space Administration, Harvard University, Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung, National Institute of Standards and Technology, National Centre for Earth Observation
Openalex Percentile: Top 72%
Atmospheric and Environmental Gas Dynamics
DOIOpen Access PDFOpenAlex
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