Preprints
https://doi.org/10.5194/egusphere-2025-1793
https://doi.org/10.5194/egusphere-2025-1793
06 May 2025
 | 06 May 2025

The role of the tropical carbon balance in determining the large atmospheric CO2 growth rate in 2023

Liang Feng, Paul Palmer, Luke Smallman, Jingfeng Xiao, Paulo Cristofanelli, Ove Hermansen, John Lee, Casper Labuschagne, Simonetta Montaguti, Steffen Noe, Stephen Platt, Xinrong Ren, Martin Steinbacher, and Irene Xueref-Remy

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 a role for boreal North American forest fires. We use a Bayesian inverse method to interpret global-scale atmospheric CO2 data from the NASA Orbiting Carbon Observatory. 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 southeast 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, USA, and central Canada. Our NBE estimates are consistent with gross primary production estimates inferred from satellite observations of solar induced fluorescence and with 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 ongoing environmental degradation of the Amazon is now playing a substantial role in increasing the global atmospheric CO2 growth rate.

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Liang Feng, Paul Palmer, Luke Smallman, Jingfeng Xiao, Paulo Cristofanelli, Ove Hermansen, John Lee, Casper Labuschagne, Simonetta Montaguti, Steffen Noe, Stephen Platt, Xinrong Ren, Martin Steinbacher, and Irene Xueref-Remy

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on egusphere-2025-1793', Hartmut Boesch, 02 Jun 2025
  • RC1: 'review comment on egusphere-2025-1793', Anonymous Referee #1, 16 Jun 2025
  • RC2: 'Comment on egusphere-2025-1793', Anonymous Referee #2, 16 Jun 2025
  • AC1: 'Comment on egusphere-2025-1793', Paul Palmer, 25 Jul 2025

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on egusphere-2025-1793', Hartmut Boesch, 02 Jun 2025
  • RC1: 'review comment on egusphere-2025-1793', Anonymous Referee #1, 16 Jun 2025
  • RC2: 'Comment on egusphere-2025-1793', Anonymous Referee #2, 16 Jun 2025
  • AC1: 'Comment on egusphere-2025-1793', Paul Palmer, 25 Jul 2025
Liang Feng, Paul Palmer, Luke Smallman, Jingfeng Xiao, Paulo Cristofanelli, Ove Hermansen, John Lee, Casper Labuschagne, Simonetta Montaguti, Steffen Noe, Stephen Platt, Xinrong Ren, Martin Steinbacher, and Irene Xueref-Remy
Liang Feng, Paul Palmer, Luke Smallman, Jingfeng Xiao, Paulo Cristofanelli, Ove Hermansen, John Lee, Casper Labuschagne, Simonetta Montaguti, Steffen Noe, Stephen Platt, Xinrong Ren, Martin Steinbacher, and Irene Xueref-Remy

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Short summary
2023 saw an unexpectedly high global atmospheric CO2 growth. Satellite data reveal a role for increased emissions over the tropics. Larger emissions over eastern Brazil can be explained by warmer temperatures, while changes in rainfall and soil moisture play more of a role in emission increases elsewhere in the tropics.
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