Abstract. 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 synthesize data sets and methodologies to quantify the five major components of the global carbon budget and their uncertainties. Fossil CO2 emissions (EFOS) are based on energy statistics and cement production data, while emissions from land-use change (ELUC), mainly deforestation, are based on land use and land-use change data and bookkeeping models. Atmospheric CO2 concentration is measured directly, and its growth rate (GATM) is computed from the annual changes in concentration. The ocean CO2 sink (SOCEAN) is estimated with global ocean biogeochemistry models and observation-based data products. The terrestrial CO2 sink (SLAND) is estimated with dynamic global vegetation models. The resulting carbon budget imbalance (BIM), the difference between the estimated total emissions and the estimated changes in the atmosphere, ocean, and terrestrial biosphere, is a measure of imperfect data and understanding of the contemporary carbon cycle. All uncertainties are reported as ±1σ. For the year 2021, EFOS increased by 5.1 % relative to 2020, with fossil emissions at 10.1 ± 0.5 GtC yr−1 (9.9 ± 0.5 GtC yr−1 when the cement carbonation sink is included), and ELUC was 1.1 ± 0.7 GtC yr−1, for a total anthropogenic CO2 emission (including the cement carbonation sink) of 10.9 ± 0.8 GtC yr−1 (40.0 ± 2.9 GtCO2). Also, for 2021, GATM was 5.2 ± 0.2 GtC yr−1 (2.5 ± 0.1 ppm yr−1), SOCEAN was 2.9  ± 0.4 GtC yr−1, and SLAND was 3.5 ± 0.9 GtC yr−1, with a BIM of −0.6 GtC yr−1 (i.e. the total estimated sources were too low or sinks were too high). The global atmospheric CO2 concentration averaged over 2021 reached 414.71 ± 0.1 ppm. Preliminary data for 2022 suggest an increase in EFOS relative to 2021 of +1.0 % (0.1 % to 1.9 %) globally and atmospheric CO2 concentration reaching 417.2 ppm, more than 50 % above pre-industrial levels (around 278 ppm). Overall, the mean and trend in the components of the global carbon budget are consistently estimated over the period 1959–2021, but discrepancies of up to 1 GtC yr−1 persist for the representation of annual to semi-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 extratropics, and (3) a discrepancy between the different methods on the strength of the ocean sink over the last decade. This living data update documents changes in the methods and data sets used in this new global carbon budget and the progress in understanding of the global carbon cycle compared with previous publications of this data set. The data presented in this work are available at https://doi.org/10.18160/GCP-2022 (Friedlingstein et al., 2022b).

The ocean has absorbed the equivalent of 39% of industrial-age fossil carbon emissions, significantly modulating the growth rate of atmospheric CO 2 and its associated impacts on climate. Despite the importance of the ocean carbon sink to climate, our understanding of the causes of its interannual-to-decadal variability remains limited. This hinders our ability to attribute its past behavior and project its future. A key period of interest is the 1990s, when the ocean carbon sink did not grow as expected. Previous explanations of this behavior have focused on variability internal to the ocean or associated with coupled atmosphere/ocean modes. Here, we use an idealized upper ocean box model to illustrate that two external forcings are sufficient to explain the pattern and magnitude of sink variability since the mid-1980s. First, the global-scale reduction in the decadal-average ocean carbon sink in the 1990s is attributable to the slowed growth rate of atmospheric pCO 2. The acceleration of atmospheric pCO 2 growth after 2001 drove recovery of the sink. Second, the global sea surface temperature response to the 1991 eruption of Mt Pinatubo explains the timing of the global sink within the 1990s. These results are consistent with previous experiments using ocean hindcast models with variable atmospheric pCO 2 and with and without climate variability. The fact that variability in the growth rate of atmospheric pCO 2 directly imprints on the ocean sink implies that there will be an immediate reduction in ocean carbon uptake as atmospheric pCO 2 responds to cuts in anthropogenic emissions. Plain Language Summary Humans have added 440 Pg of fossil fuel carbon to the atmosphere since 1750, driving up the atmospheric CO 2 concentration. But not all of this carbon remains in the atmosphere. The ocean has absorbed 39%, substantially mitigating anthropogenic climate change. Though this "ocean carbon sink" is a critical climate process, our understanding of its mechanisms remains limited. Of great interest is the unexplained slowdown of the ocean carbon sink in the 1990s and a subsequent recovery. In this work, we use a simple globally-averaged model to show that two processes external to the ocean are sufficient to explain the slowing of the ocean carbon sink in the 1990s. First, a reduced rate of accumulation of carbon in the atmosphere after 1989 reduced the atmosphere-ocean gradient that drives the ocean sink. Second, the eruption of Mt Pinatubo led to changes in ocean temperature that modified the timing of the sink from 1991 to 2001. We illustrate that the most important control on the decade-averaged magnitude of the ocean sink is variability in the growth rate of atmospheric CO 2. This implies that as future fossil fuel emission cuts drive reduced growth of atmospheric CO 2 , the ocean sink will immediately slow down.

The ocean significantly modulates atmospheric CO 2 , having absorbed approximately 38% of industrial-age fossil carbon emissions (Friedlingstein et al., 2020). Under high emission scenarios, the ocean sink is projected to grow and become the primary sink for anthropogenic carbon emissions over the next several centuries (Randerson et al., 2015). Under low emission scenarios, such as those that would limit global warming to 2°C, the ocean carbon sink will decline rapidly as the near-surface waters that hold the bulk of anthropogenic carbon (Gruber et al., 2019) come into equilibrium with the atmosphere (Cox, 2019;Jones et al., 2016). As the long-term response to the changing atmospheric pCO 2 unfolds, the ocean sink will continue to be modified on seasonal to decadal timescales by climate variability and change. Ultimately, our ability to accurately monitor the fate of anthropogenic carbon in the Earth system requires a quantification of the spatially resolved variability of the ocean carbon sink on timescales from seasonal to multidecadal. To achieve this goal, global maps of surface ocean pCO 2 are required, from which air-sea CO 2 exchange can be derived.The direction of the air-sea CO 2 flux is set by the gradient in pCO 2 across the air-sea interface with additional controls from the gas transfer velocity and CO 2 solubility setting the magnitude. Satellites cannot directly measure surface ocean pCO 2 ; therefore, hindcast simulations with ocean models (Friedlingstein et al., 2020) and observation-based gap-filling techniques (Rödenbeck et al., 2015) are integral to providing a global