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).
Anthropogenic climate change: the impact of the global carbon budget
