Reduction in Earth’s carbon budget imbalance

Sudhanshu Pandey (), Frédéric Chevallier, Christian Rödenbeck, Brendan Byrne, Abhishek Chatterjee, Junjie Liu and Christian Frankenberg
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Sudhanshu Pandey: California Institute of Technology
Frédéric Chevallier: Université Paris-Saclay
Christian Rödenbeck: Max Planck Institute for Biogeochemistry
Brendan Byrne: California Institute of Technology
Abhishek Chatterjee: California Institute of Technology
Junjie Liu: California Institute of Technology
Christian Frankenberg: California Institute of Technology

Nature Communications, 2025, vol. 16, issue 1, 1-8

Abstract: Abstract The Global Carbon Project (GCP) compiles an updated global carbon budget each year, synthesizing state‑of‑the‑art estimates of anthropogenic CO2 emissions, land and ocean sinks, and the atmospheric CO2 growth rate. The residual between these terms, referred to as the global carbon budget imbalance, reflects the aggregate inaccuracies of the individual component estimates. Growth rates derived from marine boundary layer (MBL) surface flask mixing ratio observations are assumed to be highly accurate. Hence, land and ocean sink estimates from process models are viewed as the primary source of the imbalance. Here we show that substantial discrepancies arise when marine boundary layer growth rate estimates are used to represent the whole atmosphere. Correcting for this discrepancy using atmospheric flux inversion estimates reduces the 0.76 petagrams of carbon per year (PgC yr−1) root-mean-square (RMS) imbalance (from the 2023 GCP report) by up to 25%. Further investigation into the imbalance metric between the 2017 and 2023 GCP reports shows a reduction in imbalance resulting from updates to each carbon budget component, leading to a 16% overall reduction. These reductions provide quantitative evidence of improvements in process models and inventory emission estimates, driven by enhanced forcing data and the inclusion of new carbon cycle processes. Overall, we report a 37% reduction in the root-mean-square imbalance, from 0.91 to 0.57 PgC yr−1, between the 2017 and 2023 GCP reports by combining process model and inventory improvements with atmospheric growth rate corrections. Our findings indicate that land and ocean process models are more accurate than previously believed and that the scientific understanding of Earth’s carbon cycle is improving.

Date: 2025
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DOI: 10.1038/s41467-025-61588-2

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