Global Carbon Budget 2020

Abstract. Accurate assessment of anthropogenic carbon dioxide (CO2) 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 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) and terrestrial

CO2 sink (SLAND) are estimated with global process models

constrained by observations. 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 last

decade available (2010–2019), EFOS was 9.6 ± 0.5 GtC yr−1 excluding the cement carbonation sink (9.4 ± 0.5 GtC yr−1 when the cement carbonation sink is included), and

ELUC was 1.6 ± 0.7 GtC yr−1. For the same decade, GATM was 5.1 ± 0.02 GtC yr−1 (2.4 ± 0.01 ppm yr−1), SOCEAN 2.5 ±  0.6 GtC yr−1, and SLAND 3.4 ± 0.9 GtC yr−1, with a budget

imbalance BIM of −0.1 GtC yr−1 indicating a near balance between

estimated sources and sinks over the last decade. For the year 2019 alone, the

growth in EFOS was only about 0.1 % with fossil emissions increasing

to 9.9 ± 0.5 GtC yr−1 excluding the cement carbonation sink (9.7 ± 0.5 GtC yr−1 when cement carbonation sink is included), and ELUC was 1.8 ± 0.7 GtC yr−1, for total anthropogenic CO2 emissions of 11.5 ± 0.9 GtC yr−1 (42.2 ± 3.3 GtCO2). Also for 2019, GATM was

5.4 ± 0.2 GtC yr−1 (2.5 ± 0.1 ppm yr−1), SOCEAN

was 2.6 ± 0.6 GtC yr−1, and SLAND was 3.1 ± 1.2 GtC yr−1, with a BIM of 0.3 GtC. The global atmospheric CO2

concentration reached 409.85 ± 0.1 ppm averaged over 2019. Preliminary

data for 2020, accounting for the COVID-19-induced changes in emissions,

suggest a decrease in EFOS relative to 2019 of about −7 % (median

estimate) based on individual estimates from four studies of −6 %, −7 %,

−7 % (−3 % to −11 %), and −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−1 persist for the

representation of semi-decadal variability in CO2 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 CO2 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 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 https://doi.org/10.18160/gcp-2020 (Friedlingstein et al., 2020).