Global Carbon Budget 2018
2018
Abstract. Accurate assessment of anthropogenic carbon dioxide
( CO 2 ) emissions and their redistribution among the atmosphere,
ocean, and terrestrial biosphere – 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 data sets and methodology to quantify the five major components of
the global carbon budget and their uncertainties. Fossil CO 2
emissions ( E FF ) are based on energy statistics and cement
production data, while emissions from land use and land-use change ( E LUC ),
mainly deforestation, are based on land use and land-use change data and
bookkeeping models. Atmospheric CO 2 concentration is measured
directly and its growth rate ( G ATM ) is computed from the annual
changes in concentration. The ocean CO 2 sink ( S OCEAN )
and terrestrial CO 2 sink ( S LAND ) are estimated with
global process models constrained by observations. The resulting carbon
budget imbalance ( B IM ), 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 ±1 σ . For the last decade available (2008–2017), E FF was
9.4±0.5 GtC yr −1 , E LUC 1.5±0.7 GtC yr −1 , G ATM 4.7±0.02 GtC yr −1 ,
S OCEAN 2.4±0.5 GtC yr −1 , and S LAND 3.2±0.8 GtC yr −1 , with a budget imbalance B IM of
0.5 GtC yr −1 indicating overestimated emissions and/or underestimated
sinks. For the year 2017 alone, the growth in E FF was about 1.6 %
and emissions increased to 9.9±0.5 GtC yr −1 . Also for 2017,
E LUC was 1.4±0.7 GtC yr −1 , G ATM was 4.6±0.2 GtC yr −1 , S OCEAN was 2.5±0.5 GtC yr −1 , and S LAND was 3.8±0.8 GtC yr −1 ,
with a B IM of 0.3 GtC. The global atmospheric
CO 2 concentration reached 405.0±0.1 ppm averaged over 2017.
For 2018, preliminary data for the first 6–9 months indicate a renewed
growth in E FF of + 2.7 % (range of 1.8 % to 3.7 %) based
on national emission projections for China, the US, the EU, and India and
projections of gross domestic product corrected for recent changes in the
carbon intensity of the economy for the rest of the world. The analysis
presented here shows that the mean and trend in the five components of the
global carbon budget are consistently estimated over the period of 1959–2017,
but discrepancies of up to 1 GtC yr −1 persist for the representation
of semi-decadal variability in CO 2 fluxes. A detailed comparison
among individual estimates and the introduction of a broad range of
observations show (1) no consensus in the mean and trend in land-use change
emissions, (2) a persistent low agreement among the different methods on
the magnitude of the land CO 2 flux in the northern extra-tropics,
and (3) an apparent underestimation of the CO 2 variability by ocean
models, originating outside the tropics. This living data update documents
changes in the methods and data sets used in this new global carbon budget
and the progress in understanding the global carbon cycle compared with
previous publications of this data set (Le Quere et al., 2018, 2016,
2015a, b, 2014, 2013). All results presented here can be downloaded from
https://doi.org/10.18160/GCP-2018 .
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