Changes in terrestrial tropical carbon stocks have an important role in the global carbon budget. However, current observational tools do not allow accurate and large-scale monitoring of the spatial distribution and dynamics of carbon stocks1. Here, we used low-frequency L-band passive microwave observations to compute a direct and spatially explicit quantification of annual aboveground carbon (AGC) fluxes and show that the tropical net AGC budget was approximately in balance during 2010 to 2017, the net budget being composed of gross losses of −2.86 PgC yr−1 offset by gross gains of −2.97 PgC yr−1 between continents. Large interannual and spatial fluctuations of tropical AGC were quantified during the wet 2011 La Niña year and throughout the extreme dry and warm 2015–2016 El Niño episode. These interannual fluctuations, controlled predominantly by semiarid biomes, were shown to be closely related to independent global atmospheric CO2 growth-rate anomalies (Pearson’s r = 0.86), highlighting the pivotal role of tropical AGC in the global carbon budget.
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The IGBP land-cover classification map, EVI, forest area loss map, GRACE data for terrestrial groundwater storage, precipitation data, skin temperature product, global CO2 growth-rate data, MEI and the Baccini and Avitabile biomass maps are publicly available. The SMOS-IC soil moisture dataset is available via Centre Aval de Traitement des Données SMOS at http://www.catds.fr/Products/Available-products-from-CEC-SM/SMOS-IC. SMOS-IC L-VOD and AGC products, the Saatchi, Bouvet and Mermoz biomass maps are available from J.-P.W., S.S.S. (email@example.com), A. Bouvet (firstname.lastname@example.org) and S. Mermoz (email@example.com) both at CESBIO, Toulouse, France), respectively, on request.
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This work was jointly supported by the TOSCA (Terre Océan Surfaces Continentales et Atmosphère) CNES (Centre National d’Etudes Spatiales) programme, the European Space Agency Support to Science Element programme and SMOS Expert Support Laboratory contract, and the European Research Council Synergy grant ERC-2013-SyG-610028 IMBALANCE-P. P.C. acknowledges additional support from the ANR ICONV CLAND grant. J.C. has benefited from ‘Investissement d’Avenir’ grants managed by Agence Nationale de la Recherche (CEBA: ANR-10-LABX- 25-01; TULIP: ANR-10-LABX-0041; ANAEE-France: ANR-11-INBS-0001). M.B. was funded by an AXA postdoctoral fellowship. F.T. is supported by a Marie Skłodowska-Curie grant (project number 746347). R.F. acknowledges funding from the Danish Council for Independent Research (DFF) grant no. DFF–6111-00258. K.H. acknowledges support by the Belgian Science Policy Office-sponsored COBECORE project (contract BR/175/A3/COBECORE). L.F. acknowledges additional support from the National Natural Science Foundation of China (grant no. 41801247) and Natural Science Foundation of Jiangsu Province (grant no. BK20180806). Y.Q. and X.X. are supported in part by NASA Land Use and Land Cover Change programme (NNX14AD78G) and NASA Geostationary Carbon Cycle Observatory (GeoCarb) Mission (GeoCarb contract no. 80LARC17C0001).
Peer review information: Nature Plants thanks Edward Mitchard, Kolby Smith and the other, anonymous, reviewers for their contribution to the peer review of this work.
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