Pandey Sudhanshu, Chevallier Frédéric, Rödenbeck Christian, Byrne Brendan, Chatterjee Abhishek, Liu Junjie, Frankenberg Christian
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA.
Laboratoire des Sciences du Climat et de L'Environnement, LSCE/IPSL, CEA-CNRS-UVSQ, Université Paris-Saclay, Gif-sur-Yvette, France.
Nat Commun. 2025 Jul 24;16(1):6818. doi: 10.1038/s41467-025-61588-2.
The Global Carbon Project (GCP) compiles an updated global carbon budget each year, synthesizing state‑of‑the‑art estimates of anthropogenic CO emissions, land and ocean sinks, and the atmospheric CO 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) 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, 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.
全球碳项目（GCP）每年都会编制一份更新后的全球碳预算，综合人为碳排放、陆地和海洋碳汇以及大气中二氧化碳增长率的最新估计值。这些项之间的差值，即全球碳预算失衡，反映了各个组成部分估计值的总体误差。源自海洋边界层（MBL）表面采样瓶混合比观测值的增长率被认为是高度准确的。因此，过程模型对陆地和海洋碳汇的估计被视为失衡的主要来源。在此我们表明，当用海洋边界层增长率估计值来代表整个大气层时，会出现显著差异。使用大气通量反演估计值来校正这种差异，可将每年0.76拍克碳（PgC/yr）的均方根（RMS）失衡（来自2023年GCP报告）降低多达25%。对2017年和2023年GCP报告之间的失衡指标进行的进一步研究表明，由于每个碳预算组成部分的更新，失衡有所减少，总体减少了16%。这些减少提供了过程模型和清单排放估计值改进的定量证据，这是由增强的强迫数据和纳入新的碳循环过程推动的。总体而言，通过将过程模型和清单改进与大气增长率校正相结合，我们报告2017年至2023年GCP报告之间的均方根失衡降低了37%，从0.91降至0.57 PgC/yr。我们的研究结果表明，陆地和海洋过程模型比以前认为的更准确，并且对地球碳循环的科学理解正在改善。
