DOI: 10.5281/zenodo.17579107
title: Global Carbon Budget 2025, surface ocean fugacity of CO2 (fCO2) and air-sea CO2 flux of individual global ocean biogeochemical models and surface ocean fCO2-based data-products

description: Surface ocean fugacity of CO2 (fCO2) and air-sea CO2 flux data from individual Global Ocean Biogeochemistry Models (GOBMs) and surface ocean fCO2-based data-products (fCO2-products).There are three types of files: (1) one file per fCO2-product with gridded fields and regionally-integrated CO2 flux time-series, (2) one file per GOBM and simulation with gridded fields, and (3) one file with the globally and regionally-integrated time-series for the GOBMs for all four simulations.  

Note: These provided gridded outputs from fCO2-based data-products and GOBMs are regridded datasets, without adjustments. The best estimates of the annual global ocean carbon sink, based on the native grids of fCO2-products and GOBMs and with the adjustments described in the Global Carbon Budget 2025 (https://doi.org/10.18160/GCP-2025), are available in the Global Carbon Budget 2025 spreadsheet.

The regionally-integrated time-series are as provided by the contributing groups, i.e. integrated from their native grids. In order to reproduce Figure 14 of the Global Carbon Budget 2024 paper (https://doi.org/10.18160/GCP-2025), the river flux adjustment needs to be added to the CO2 flux estimated from the fCO2-products (North: 0.14 GtC yr-1, Tropics: 0.42 GtC yr-1, South: 0.09 GtC yr-1, see GCB 2025 paper). The sum of the regional fluxes may differ from the global estimates as reported in the GCB spreadsheet, because some adjustments were applied only for global fluxes.

Two of the 9 fCO2-producst (i.e. JMA-MLR and UExP-FNN-U) include a temperature adjustment to correct the the original fCO2 measurements from measurement depth to the surface layer at the air-sea interface following Ford et al (2025, https://doi.org/10.5281/ZENODO.15656803).

Model simulations:

Simulation A ('contemporary simulation', including effects of rising CO2, climate change and variability)

Simulation B ('control simulation', constant CO2, no climate change and variability)

Simulation C ('CO2 effect', forced by observed atmospheric CO2, but excludes climate change and variability)

Simulation D ('climate effect on natural carbon cycle', constant CO2, but includes climate change and variability)

What is in the files?

(1) The files for the fCO2-based data-products contain the following variables (temporal resolution: monthly):fgco2_reg: Regionally integrated air-sea CO2 flux (positive downward), monthly, for regions: global, north, tropics, southfgco2: Flux density of the total air-sea CO2 flux (positive downward), dimensions: time, latitude, longitudesfco2: Surface ocean fCO2, dimensions: time, latitude, longitudearea: Area per pixel, dimensions: latitude, longitudearea_reg: Total surface ocean area covered by native grid, for global, north, tropics, south

(2) The files for the GOBMs contain the following fields. Temporal resolution: monthly. Simulation A ('contemporary simulation', including effects of rising CO2, climate change and variability) and simulation B ('control simulation', constant CO2, no climate change and variability) are saved in separate files.

fgco2: Flux density of the total air-sea CO2 flux (positive downward), dimensions: time, latitude, longitudesfco2: Surface ocean fCO2, dimensions: time, latitude, longitude

(3) One file 'GCB2025_GOBMs_fgco2_timeseries_1959_2024.nc' with the globally and regionally-integrated CO2 flux time-series for all individual GOBMs,for simulations A, B, C and D. We also report an adjusted global time-series of simulation A that accounts for model drift (Aadj). It does not account for the 10% upscaling that is further applied for the calculation of SOCEAN. Regions: North, tropics, south. Temporal resolution: annual.

Fair data use statement:The data and model output provided on this site are freely available and were furnished by individual scientists who encourage their use.Citation: Please cite the Global Carbon Budget 2025 (Friedlingstein et al., 2025, ESSD, https://doi.org/10.18160/GCP-2025) for all data. In addition, please also cite the corresponding original reference for each dataset that has been used - see Table 4 in Global Carbon Budget 2025 for references of all the individual Global Ocean Biogeochemical Models and fCO2-based data-products. Further, for an overview of the Global Ocean Biogeochemical Model output, you may find it useful to cite Hauck et al. (2020, Frontiers, doi:10.3389/fmars.2020.571720).

Acknowledgement: Please add the following text in the acknowledgement of your paper: "We acknowledge the Global Carbon Project, which is responsible for the Global Carbon Budget and we thank the ocean modeling and fCO2-mapping groups for producing and making available their model and fCO2-product output."Co-authorship: An invitation of co-authorship to the contributing groups is encouraged if these data are the central data set of the publication.

Besides the surface fCO2 and air-sea CO2 flux data that is made available open access, we make additional 3D output from the Global Ocean Biogeochemical models (GCB-ocean) available upon request and with its own data policy.