Global Carbon Budget 2020

Accurate assessment of anthropogenic carbon dioxide (CO 2 ) 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 CO 2 emissions ( E FOS ) are based on energy statistics and cement production data, while emissions from 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 (2010–2019), E FOS 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 E LUC was 1.6 ± 0.7 GtC yr −1 . For the same decade, G ATM was 5.1 ± 0.02 GtC yr −1 (2.4 ± 0.01 ppm yr −1 ), S OCEAN 2.5 ± 0.6 GtC yr −1 , and S LAND 3.4 ± 0.9 GtC yr −1 , with a budget imbalance B IM 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 E FOS 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…