Significant Influence of Lateral Carbon Fluxes on Regional U.S. Carbon Budgets
| Authors: | B. Byrne, J. Liu, Grant M. Domke, S. M. Ogle, G. D. Ferreira, Y. M. Bar‐On, H. Nesser, E. Bilir, A. A. Bloom, D. J. Hayes, B. Poulter, K. W. Bowman, K. J. Davis |
| Year: | 2026 |
| Type: | Scientific Journal |
| Station: | Northern Research Station |
| DOI: | https://doi.org/10.1029/2025GB009020 |
| Source: | Global Biogeochemical Cycles |
Abstract
Observations of atmospheric carbon dioxide (CO 2) are expected to play a critical role in monitoring, reporting, and verification designed to track progress toward the reduction goals of greenhouse gas emissions. In this study, we construct a comprehensive regional carbon budget for seven National Climate Assessment regions of the contiguous United States (CONUS) over 2015–2020. We demonstrate that lateral carbon movement across regions, along with their resulting endpoint CO 2 emissions, represent a major contributor to the interpretation of regional net surface‐atmosphere fluxes of CO 2 . When accounting for lateral carbon fluxes, “top‐down” flux estimates from v10 Orbiting Carbon Observatory 2 (OCO‐2) Modeling Intercomparison Project (MIP) agree, within uncertainty, with inventory‐based carbon stock change estimates in six out of seven National Climate Assessment regions ‐ except for the Southwest. The total net carbon exchange from the top down is 925 ± 339 Tg carbon per year (Tg C/year), consistent with the 974 Tg C/year estimate from the inventory. Notably, lateral carbon flows in the form of harvested wood products and riverine carbon burial are responsible for an estimated 16% of the total carbon stock changes occurring across CONUS. Averaged over the seven regions, accounting for lateral transport and their endpoint carbon emissions improves the consistency between inventory and top‐down estimates by 31%. Our study presents a roadmap for reconciling the inventories and top‐down atmospheric inversions at sub‐national scale and highlights the importance of accurate representation of lateral carbon flows for using top‐down estimates with national inventories.
Plain Language Summary: As nations commit to reducing greenhouse gas emissions, reliable systems for monitoring and verifying carbon fluxes at national and sub‐national levels are essential. This study generates a detailed carbon budget for seven National Climate Assessment regions across CONUS over 2015–2020, revealing the critical role of lateral carbon fluxes—such as harvested wood products and riverine carbon burial—in shaping the changes in carbon stock and net exchange of carbon dioxide between the land and atmosphere across the contiguous United States. Our findings show that their omission can significantly affect the attribution of top‐down estimates for regional carbon budgets. Incorporating lateral carbon transfers will be key to improving the accuracy and consistency of regional carbon monitoring systems that are needed to guide and verify carbon emissions management.