Reply on RC2

<strong class="journal-contentHeaderColor">Abstract.</strong> Accurate assessment of anthropogenic carbon dioxide (CO₂) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere in a changing climate is critical to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe and synthesise datasets and methodologies to quantify the five major components of the global carbon budget and their uncertainties. Fossil CO₂ emissions (E_FOS) are based on energy statistics and cement production data. Emissions from land-use change (E_LUC) are estimated by bookkeeping models based on land-use and land-use change data. Atmospheric CO₂ concentration is measured at surface stations, and the global atmospheric CO₂ growth rate (G_ATM) is computed from the annual changes in concentration. The global net uptake of CO₂ by the ocean (S_OCEAN, called the ocean sink) is estimated with global ocean biogeochemistry models and observation-based <em>f</em>CO₂-products. The global net uptake of CO₂ by the land (S_LAND, called the land sink) is estimated with dynamic global vegetation models. Additional lines of evidence on land and ocean sinks are provided by atmospheric inversions, atmospheric oxygen measurements, ocean interior observation-based estimates, and Earth System Models. The sum of all sources and sinks results in the carbon budget imbalance (B_IM), a measure of imperfect data and incomplete understanding of the contemporary carbon cycle. All uncertainties are reported as &plusmn;1&sigma;. For the year 2024, E_FOS increased by 1.1 % relative to 2023, with fossil emissions at 10.3 &plusmn; 0.5 GtC yr^&minus;1 (including the cement carbonation sink, 0.2 GtC/yr), E_LUC was 1.3 &plusmn; 0.7 GtC yr^&minus;1, for total anthropogenic CO₂ emissions of 11.6 &plusmn; 0.9 GtC yr^&minus;1 (42.4 &plusmn; 3.2 GtCO₂ yr^&minus;1). Also, for 2024, G_ATM was 7.9 &plusmn; 0.2 GtC yr^&minus;1 (3.73 &plusmn; 0.1 ppm yr^&minus;1), 2.2 GtC above the 2023 growth rate. S_OCEAN was 3.4 &plusmn; 0.4 GtC yr^&minus;1 and S_LAND was 1.9 &plusmn; 1.1 GtC yr^&minus;1, leaving a large negative B_IM (&minus;1.7 GtC yr^&minus;1), suggesting that the total sink or G_ATM is strongly overestimated in 2024. The global atmospheric CO₂ concentration averaged over 2024 reached 422.8 &plusmn; 0.1 ppm. Preliminary data for 2025 suggest an increase in E_FOS relative to 2024 of +1.1 % (0.2 % to 2.2 %) globally, and atmospheric CO₂ concentration increasing by 2.3 ppm reaching 425.7 ppm, 52 % above the pre-industrial level (around 278 ppm in 1750). Overall, the mean and trend in the components of the global carbon budget are consistently estimated over the period 1959&ndash;2024, with a near-zero overall budget imbalance, although discrepancies of up to around 1 GtC yr^&minus;1 persist for the representation of annual to decadal variability in CO₂ fluxes. Comparison of estimates from multiple approaches and observations shows: (1) a persistent large uncertainty in the estimate of land-use change emissions, (2) a low agreement between the different methods on the magnitude of the land CO₂ flux in the northern extra-tropics, and (3) a discrepancy between the different methods on the mean ocean sink. This living data update documents changes in methods and datasets applied to this most-recent global carbon budget as well as evolving community understanding of the global carbon cycle. The data presented in this work are available at <a href="https://doi.org/10.18160/GCP-2025" target="_blank" rel="noopener">https://doi.org/10.18160/GCP-2025</a> (Friedlingstein et al., 2025c).