Global Carbon Budget 2021

Abstract

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 datasets and methodology 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 first time, an approach is shown to reconcile the difference in our ELUC estimate with the one from national greenhouse gas inventories, supporting the assessment of collective countries' climate progress. For the year 2020, EFOS declined by 5.4 % relative to 2019, with fossil emissions at 9.5 ± 0.5 GtC yr−1 (9.3 ± 0.5 GtC yr−1 when the cement carbonation sink is included), and ELUC was 0.9 ± 0.7 GtC yr−1, for a total anthropogenic CO2 emission of 10.2 ± 0.8 GtC yr−1 (37.4 ± 2.9 GtCO2). Also, for 2020, GATM was 5.0 ± 0.2 GtC yr−1 (2.4 ± 0.1 ppm yr−1), SOCEAN was 3.0 ± 0.4 GtC yr−1, and SLAND was 2.9 ± 1 GtC yr−1, with a BIM of −0.8 GtC yr−1. The global atmospheric CO2 concentration averaged over 2020 reached 412.45 ± 0.1 ppm. Preliminary data for 2021 suggest a rebound in EFOS relative to 2020 of +4.8 % (4.2 % to 5.4 %) globally. Overall, the mean and trend in the components of the global carbon budget are consistently estimated over the period 1959–2020, 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 changes 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 strength of the ocean sink over the last decade. This living data update documents changes in the methods and datasets used in this new global carbon budget and the progress in understanding of the global carbon cycle compared with previous publications of this dataset (Friedlingstein et al., 2020, 2019; Le Quéré et al., 2018b, a, 2016, 2015b, a, 2014, 2013). The data presented in this work are available at https://doi.org/10.18160/gcp-2021 (Friedlingstein et al., 2021).

Keywords

Affiliated Institutions

• Institut Pierre-Simon Laplace FR
• National Institute for Environmental Studies JP
• Jet Propulsion Laboratory US
• NSF NCAR Climate and Global Dynamics Laboratory US
• Sorbonne Université FR
• University of Exeter GB
• Wageningen University & Research NL
• Meteorological Research Institute
• University of Groningen NL
• Karlsruhe Institute of Technology DE
• Cooperative Institute for Research in Environmental Sciences US
• University of Reading GB
• NOAA Earth System Research Laboratory US
• Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung DE
• Oeschger Centre for Climate Change Research CH
• Ludwig-Maximilians-Universität München DE
• Japan Fisheries Research and Education Agency JP
• CEA Paris-Saclay FR
• University of Edinburgh GB
• NORCE Research AS
• Centre National de la Recherche Scientifique FR
• Appalachian State University US
• Met Office GB
• University of Illinois Urbana-Champaign US
• GEOMAR Helmholtz Centre for Ocean Research Kiel DE
• Utrecht University NL
• Météo-France FR
• University of East Anglia GB
• CSIRO Oceans and Atmosphere AU
• Forest Institute US
• Food and Agriculture Organization of the United Nations IT
• Institut de Recherche pour le Développement FR
• University of Cape Town ZA
• Leibniz Institute for Baltic Sea Research Warnemünde DE
• Nanjing University of Information Science and Technology CN
• Joint Research Centre IT
• Tsinghua University CN
• Western Sydney University AU
• Tyndall Centre GB
• Université Paris-Saclay FR
• Max Planck Institute for Biogeochemistry DE
• Woodwell Climate Research Center US
• Flanders Marine Institute BE
• National Centre for Atmospheric Science GB
• Commissariat à l'Énergie Atomique et aux Énergies Alternatives FR
• NOAA Pacific Marine Environmental Laboratory US
• National Oceanic and Atmospheric Administration US
• North Carolina School of Science and Mathematics US
• Hakai Institute
• NSF National Center for Atmospheric Research US
• Norwich Research Park GB
• Australian Antarctic Division AU
• Sun Yat-sen University CN
• University of Colorado Boulder US
• Université de Versailles Saint-Quentin-en-Yvelines FR
• Laboratoire des Sciences du Climat et de l'Environnement FR
• Environment and Climate Change Canada CA
• Bjerknes Centre for Climate Research
• International Institute for Applied Systems Analysis AT
• Marine Institute IE
• Tula Foundation CA
• Auburn University US
• University of Maryland, College Park US
• Laboratoire de Météorologie Dynamique FR
• NOAA Atlantic Oceanographic and Meteorological Laboratories US
• Stanford University US
• Japan Meteorological Agency JP
• Council for Scientific and Industrial Research ZA
• ETH Zurich CH
• Institute of Applied Energy JP
• Princeton University US
• University of Bern CH
• Max Planck Institute for Meteorology DE
• National Centre for Earth Observation GB
• Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques FR
• Bermuda Institute of Ocean Sciences BM
• University of Bergen
• National Institute of Water and Atmospheric Research NZ
• Goddard Space Flight Center US
• Université Fédérale de Toulouse Midi-Pyrénées FR
• University of Tasmania AU
• CICERO Center for International Climate Research

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