Global Carbon Budget 2020

Friedlingstein, Pierre ; O'Sullivan, Michael ; Jones, Matthew W. ; Andrew, Robbie M. ; Hauck, Judith ; Olsen, Are ; Peters, Glen P. ; Peters, Wouter ; Pongratz, Julia ; Sitch, Stephen ; Le Quéré, Corinne ; Canadell, Josep G. ; Ciais, Philippe ; Jackson, Robert B. ; Alin, Simone ; Aragão, Luiz E. O. C. ; Arneth, Almut ; Arora, Vivek ; Bates, Nicholas R. ; Becker, Meike ; Benoit-Cattin, Alice ; Bittig, Henry C. ; Bopp, Laurent ; Bultan, Selma ; Chandra, Naveen ; Chevallier, Frédéric ; Chini, Louise P. ; Evans, Wiley ; Florentie, Liesbeth ; Forster, Piers M. ; Gasser, Thomas ; Gehlen, Marion ; Gilfillan, Dennis ; Gkritzalis, Thanos ; Gregor, Luke ; Gruber, Nicolas ; Harris, Ian ; Hartung, Kerstin ; Haverd, Vanessa ; Houghton, Richard A. ; Ilyina, Tatiana ; Jain, Atul K. ; Joetzjer, Emilie ; Kadono, Koji ; Kato, Etsushi ; Kitidis, Vassilis ; Korsbakken, Jan Ivar ; Landschützer, Peter ; Lefèvre, Nathalie ; Lenton, Andrew ; Lienert, Sebastian ; Liu, Zhu ; Lombardozzi, Danica ; Marland, Gregg ; Metzl, Nicolas ; Munro, David R. ; Nabel, Julia E. M. S. ; Nakaoka, Shin-Ichiro ; Niwa, Yosuke ; O'Brien, Kevin ; Ono, Tsuneo ; Palmer, Paul I. ; Pierrot, Denis ; Poulter, Benjamin ; Resplandy, Laure ; Robertson, Eddy ; Rödenbeck, Christian ; Schwinger, Jörg ; Séférian, Roland ; Skjelvan, Ingunn ; Smith, Adam J. P. ; Sutton, Adrienne J. ; Tanhua, Toste ; Tans, Pieter P. ; Tian, Hanqin ; Tilbrook, Bronte ; van der Werf, Guido ; Vuichard, Nicolas ; Walker, Anthony P. ; Wanninkhof, Rik ; Watson, Andrew J. ; Willis, David ; Wiltshire, Andrew J. ; Yuan, Wenping ; Yue, Xu ; Zaehle, Sönke

Année de publication
2020
Résumé
<p align=justify><strong class="journal-contentHeaderColor">Abstract.</strong> Accurate assessment of anthropogenic carbon dioxide (CO<span class="inline-formula"><sub>2</sub></span>) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere in a changing climate - the "global carbon budget" - is important 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 methodology to quantify the five major components of the global carbon budget and their uncertainties. Fossil CO<span class="inline-formula"><sub>2</sub></span> emissions (<span class="inline-formula"><i>E</i><sub>FOS</sub></span>) are based on energy statistics and cement production data, while emissions from land-use change (<span class="inline-formula"><i>E</i><sub>LUC</sub></span>), mainly deforestation, are based on land use and land-use change data and bookkeeping models. Atmospheric CO<span class="inline-formula"><sub>2</sub></span> concentration is measured directly and its growth rate (<span class="inline-formula"><i>G</i><sub>ATM</sub></span>) is computed from the annual changes in concentration. The ocean CO<span class="inline-formula"><sub>2</sub></span> sink (<span class="inline-formula"><i>S</i><sub>OCEAN</sub></span>) and terrestrial CO<span class="inline-formula"><sub>2</sub></span> sink (<span class="inline-formula"><i>S</i><sub>LAND</sub></span>) are estimated with global process models constrained by observations. The resulting carbon budget imbalance (<span class="inline-formula"><i>B</i><sub>IM</sub></span>), 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 <span class="inline-formula">±1<i>σ</i></span>. For the last decade available (2010-2019), <span class="inline-formula"><i>E</i><sub>FOS</sub></span> was 9.6 <span class="inline-formula">±</span> 0.5 GtC yr<span class="inline-formula"><sup>-1</sup></span> excluding the cement carbonation sink (9.4 <span class="inline-formula">±</span> 0.5 GtC yr<span class="inline-formula"><sup>-1</sup></span> when the cement carbonation sink is included), and <span class="inline-formula"><i>E</i><sub>LUC</sub></span> was 1.6 <span class="inline-formula">±</span> 0.7 GtC yr<span class="inline-formula"><sup>-1</sup></span>. For the same decade, <span class="inline-formula"><i>G</i><sub>ATM</sub></span> was 5.1 <span class="inline-formula">±</span> 0.02 GtC yr<span class="inline-formula"><sup>-1</sup></span> (2.4 <span class="inline-formula">±</span> 0.01 ppm yr<span class="inline-formula"><sup>-1</sup></span>), <span class="inline-formula"><i>S</i><sub>OCEAN</sub></span> 2.5 <span class="inline-formula">±</span>  0.6 GtC yr<span class="inline-formula"><sup>-1</sup></span>, and <span class="inline-formula"><i>S</i><sub>LAND</sub></span> 3.4 <span class="inline-formula">±</span> 0.9 GtC yr<span class="inline-formula"><sup>-1</sup></span>, with a budget imbalance <span class="inline-formula"><i>B</i><sub>IM</sub></span> of <span class="inline-formula">-</span>0.1 GtC yr<span class="inline-formula"><sup>-1</sup></span> indicating a near balance between estimated sources and sinks over the last decade. For the year 2019 alone, the growth in <span class="inline-formula"><i>E</i><sub>FOS</sub></span> was only about 0.1 % with fossil emissions increasing to 9.9 <span class="inline-formula">±</span> 0.5 GtC yr<span class="inline-formula"><sup>-1</sup></span> excluding the cement carbonation sink (9.7 <span class="inline-formula">±</span> 0.5 GtC yr<span class="inline-formula"><sup>-1</sup></span> when cement carbonation sink is included), and <span class="inline-formula"><i>E</i><sub>LUC</sub></span> was 1.8 <span class="inline-formula">±</span> 0.7 GtC yr<span class="inline-formula"><sup>-1</sup></span>, for total anthropogenic CO<span class="inline-formula"><sub>2</sub></span> emissions of 11.5 <span class="inline-formula">±</span> 0.9 GtC yr<span class="inline-formula"><sup>-1</sup></span> (42.2 <span class="inline-formula">±</span> 3.3 GtCO<span class="inline-formula"><sub>2</sub></span>). Also for 2019, <span class="inline-formula"><i>G</i><sub>ATM</sub></span> was 5.4 <span class="inline-formula">±</span> 0.2 GtC yr<span class="inline-formula"><sup>-1</sup></span> (2.5 <span class="inline-formula">±</span> 0.1 ppm yr<span class="inline-formula"><sup>-1</sup></span>), <span class="inline-formula"><i>S</i><sub>OCEAN</sub></span> was 2.6 <span class="inline-formula">±</span> 0.6 GtC yr<span class="inline-formula"><sup>-1</sup></span>, and <span class="inline-formula"><i>S</i><sub>LAND</sub></span> was 3.1 <span class="inline-formula">±</span> 1.2 GtC yr<span class="inline-formula"><sup>-1</sup></span>, with a <span class="inline-formula"><i>B</i><sub>IM</sub></span> of 0.3 GtC. The global atmospheric CO<span class="inline-formula"><sub>2</sub></span> concentration reached 409.85 <span class="inline-formula">±</span> 0.1 ppm averaged over 2019. Preliminary data for 2020, accounting for the COVID-19-induced changes in emissions, suggest a decrease in <span class="inline-formula"><i>E</i><sub>FOS</sub></span> relative to 2019 of about <span class="inline-formula">-</span>7 % (median estimate) based on individual estimates from four studies of <span class="inline-formula">-</span>6 %, <span class="inline-formula">-</span>7 %, <span class="inline-formula">-</span>7 % (<span class="inline-formula">-</span>3 % to <span class="inline-formula">-</span>11 %), and <span class="inline-formula">-</span>13 %. Overall, the mean and trend in the components of the global carbon budget are consistently estimated over the period 1959-2019, but discrepancies of up to 1 GtC yr<span class="inline-formula"><sup>-1</sup></span> persist for the representation of semi-decadal variability in CO<span class="inline-formula"><sub>2</sub></span> fluxes. Comparison of estimates from diverse approaches and observations shows (1) no consensus in the mean and trend in land-use change emissions over the last decade, (2) a persistent low agreement between the different methods on the magnitude of the land CO<span class="inline-formula"><sub>2</sub></span> flux in the northern extra-tropics, and (3) an apparent discrepancy between the different methods for the ocean sink outside the tropics, particularly in the Southern Ocean. 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<span id="page3272"/> of this data set (Friedlingstein et al., 2019; Le Quéré et al., 2018b, a, 2016, 2015b, a, 2014, 2013). The data presented in this work are available at <a href="https://doi.org/10.18160/gcp-2020" target="_blank">https://doi.org/10.18160/gcp-2020</a> (Friedlingstein et al., 2020).</p>
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