Global Carbon Budget 2021

Global Carbon Budget 2021

Abstract https://essd.copernicus.org/preprints/essd-2021-386/
Full preprint:  https://essd.copernicus.org/preprints/essd-2021-386/essd-2021-386.pdf

2020, Fossil CO2 emissions (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), emissions from land-use change (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, Atmospheric CO2 concentration is measured directly, and its growth rate (GATM) was 5.0 ± 0.2 GtC yr−1 (2.4 ± 0.1 ppm yr−1), ocean CO2 sink (SOCEAN) was 3.0 ± 0.4 GtC yr−1 and terrestrial CO2 sink (SLAND) was 2.9 ± 1 GtC yr−1, with a carbon budget imbalance (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 Fossil CO2 emissions (EFOS) relative to 2020 of +4.9 % (4.1 % to 5.7 %) globally.

Fossil CO2 emissions significantly decreased in 23 countries from 2010-2019 about 2.5 GtC yr fossil fuel CO2 emissions or around one quarter of world CO2 fossil emissions.

The remaining carbon budget for a 50% likelihood to limit global warming to 1.5°C, 1.7°C and 2°C has shrunk to 120 GtC (420 GtCO2), 210 GtC (770 GtCO2) and 350 GtC (1270 GtCO2) respectively, equivalent to 11, 20 and 32 years from the beginning of 2022, assuming 2021  emissions levels. Total anthropogenic emissions were 10.4 GtC yr-1 (38.0 GtCO2 yr-1) in  2020, with a preliminary estimate of 10.7 GtC yr-1 (39.4 GtCO2 yr-1) for 2021. The remaining carbon budget to keep global temperatures below the climate targets of the Paris Agreement has shrunk by 21 GtC (77 GtCO2) relative to the remaining carbon budget  estimate assessed in the IPCC AR6 Working Group 1 assessment. Reaching net zero CO2 emissions by 2050 entails cutting total anthropogenic CO2 emissions by about 0.4 GtC (1.4  GtCO2) each year on average, comparable to the decrease during 2020, highlighting the scale of the action needed.

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Received: 28 Oct 2021 – Accepted for review: 29 Oct 2021 – Discussion started: 04 Nov 2021
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 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 gases 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), 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 +4.9 % (4.1 % to 5.7 %) 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 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 (Friedlingstein et al., 2020; Friedlingstein et al., 2019; Le Quéré et al., 2018b, 2018a, 2016, 2015b, 2015a, 2014, 2013). The data presented in this work are available at https://doi.org/10.18160/gcp-2021 (Friedlingstein et al., 2021).

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