Abstract
Over the past three decades, assessments of the contemporary global carbon budget consistently report a strong net land carbon sink. Here, we review evidence supporting this paradigm and quantify the differences in global and Northern Hemisphere estimates of the net land sink derived from atmospheric inversion and satellite-derived vegetation biomass time series. Our analysis, combined with additional synthesis, supports a hypothesis that the net land sink is substantially weaker than commonly reported. At a global scale, our estimate of the net land carbon sink is 0.8 ± 0.7 petagrams of carbon per year from 2000 through 2019, nearly a factor of two lower than the Global Carbon Project estimate. With concurrent adjustments to ocean (+8%) and fossil fuel (−6%) fluxes, we develop a budget that partially reconciles key constraints provided by vegetation carbon, the north-south CO2 gradient, and O2 trends. We further outline potential modifications to models to improve agreement with a weaker land sink and describe several approaches for testing the hypothesis.
| Original language | English |
|---|---|
| Article number | eadr5489 |
| Journal | Science Advances |
| Volume | 11 |
| Issue number | 37 |
| DOIs | |
| State | Published - Sep 12 2025 |
Funding
Acknowledgments: we acknowledge the world climate Research Programme, which, through its working Group on coupled Modelling, coordinated and promoted cMiP6. we thank the climate modeling groups for producing and making their model output available, the earth System Grid Federation (eSGF) for archiving the data and providing access, and the multiple funding agencies that support cMiP6 and eSGF. we also thank the Transcom 3 modeling teams for sharing their model simulations. Funding: This work was supported by the US department of energy Office of Science Reducing Uncertainties in Biogeochemical interactions through Synthesis and computation (RUBiScO) Science Focus Area (F.M.H. and J.T.R.), nASA’s Modeling, Analysis, and Prediction Program grant 80nSSc21K1362 (J.T.R.), nASA’s earth information System-Fire Research Program (J.T.R.), nASA’s FireSense grant 80nSSc24K1317 (J.T.R.), US national Science Foundation grant RiSe-2425932 (J.T.R.), US national Science Foundation grant Oce-2124014 (F.P.), US department of energy grant de-Sc0022177 (F.P.), a US national Science Foundation Graduate Research Fellowship Program grant dGe-1839285 (J.e.K.), nASA’s Arctic and Boreal vulnerability experiment grant 80nSSc23K0140 (J.A.w., J.T.R., and M.A.F.), US national Science Foundation grants 1802880, 2003017, 2044937, and iOS-2325700 (w.R.L.A.), the david and Lucille Packard Foundation (w.R.L.A.), the University of california Laboratory Fees Research Program grant LFR-20-652467 (A.T.T.), US national Science Foundation grants 2003205 and 2216855 (A.T.T.), and the Gordon and Betty Moore Foundation grant GBMF1197 (A.T.T.). Author contributions: conceptualization: J.T.R., Y.L., F.M.H., A.T.T., w.R.L.A., S.S.S., A.S.d., and M.L.G. Methodology: J.T.R., Y.L., w.F., F.P., L.Y., A.B., S.S.S., and A.S.d. Software: J.T.R., w.F., F.P., and A.S.d. validation: J.T.R., Y.L., F.P., L.Y., and S.S.S. Formal analysis: J.T.R., Y.L., M.M., w.F., L.Y., S.S.S., and A.S.d. investigation: J.T.R., w.F., S.S.S., L.Y., and A.S.d. Resources: J.T.R., A.B., F.M.H., S.S.S., and A.S.d. data curation: J.T.R., w.F., M.M., L.Y., A.B., and A.S.d. visualization: J.T.R., Y.L., M.M., L.Y., and S.S.S. writing—original draft: J.T.R., A.T.T., w.R.L.A., and S.S.S. writing—editing and review: J.T.R., Y.L., w.F., J.e.K., F.M.H., A.T.T., L.Y., c.w., J.A.w., w.R.L.A., A.B., M.A.F., S.S.S., A.S.d., and M.L.G. Supervision: J.T.R. and F.P. Project administration: J.T.R. Funding acquisition: J.T.R., F.P., J.e.K., F.M.H., J.A.w., A.T.T., w.R.L.A., and M.A.F. Competing interests: J.T.R. is on the council of external Science Advisors of the One conservancy Science program of The nature conservancy (Tnc). A.T.T. serves as a Science Advisor for watershed Technology inc. All other authors declare that they have no competing interests. Data and materials availability: All the data needed to evaluate the conclusions in this review are publicly available. The cO2 data used to compute the interhemispheric gradient in the two-box atmospheric inversion are from the Scripps institution of Oceanography cO2 Program (https://scrippsco2.ucsd. edu/). The fossil fuel emission time series and other annual budget information are from the Global carbon Project 2023 budget (https://www.globalcarbonproject.org/). The cMiP6 model simulations analyzed for CveG, nBP, GPP, and nPP are available on the earth System Grid Federation (https://wcrp-cmip.org/cmip-data-access/). The remote sensing–derived biomass products are available on Zenodo (https://doi.org/10.5281/zenodo.4161694) and Microsoft’s Planetary computer (https://planetarycomputer.microsoft.com). The atmospheric O2 and cO2 used to close the carbon cycle budget using dual tracers are from the Scripps institution of Oceanography Oxygen Program (https://scrippso2.ucsd.edu). The Python and ncL code used to generate the figures in this manuscript can be found on Zenodo: https://doi.org/10.5281/zenodo.15115994. We acknowledge the World Climate Research Programme, which, through its Working Group on Coupled Modelling, coordinated and promoted CMIP6. We thank the climate modeling groups for producing and making their model output available, the Earth System Grid Federation (ESGF) for archiving the data and providing access, and the multiple funding agencies that support CMIP6 and ESGF. We also thank the TransCom 3 modeling teams for sharing their model simulations. This work was supported by the US Department of Energy Office of Science Reducing Uncertainties in Biogeochemical Interactions through Synthesis and Computation (RUBISCO) Science Focus Area (F.M.H. and J.T.R.), NASA’s Modeling, Analysis, and Prediction Program grant 80NSSC21K1362 (J.T.R.), NASA’s Earth Information System-Fire Research Program (J.T.R.), NASA’s FireSense grant 80NSSC24K1317 (J.T.R.), US National Science Foundation grant RISE-2425932 (J.T.R.), US National Science Foundation grant OCE-2124014 (F.P.), US Department of Energy grant DE-SC0022177 (F.P.), a US National Science Foundation Graduate Research Fellowship Program grant DGE-1839285 (J.E.K.), NASA’s Arctic and Boreal Vulnerability Experiment grant 80NSSC23K0140 (J.A.W., J.T.R., and M.A.F.), US National Science Foundation grants 1802880, 2003017, 2044937, and IOS-2325700 (W.R.L.A.), the David and Lucille Packard Foundation (W.R.L.A.), the University of California Laboratory Fees Research Program grant LFR-20-652467 (A.T.T.), US National Science Foundation grants 2003205 and 2216855 (A.T.T.), and the Gordon and Betty Moore Foundation grant GBMF1197 (A.T.T.).