Accurate assessment of anthropogenic carbon dioxide (CO2) 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. CO2 emissions from fossil fuels and industry (EFF) are based on energy statistics and cement production data, respectively, while emissions from land-use change (ELUC), mainly deforestation, are based on land-cover change data and bookkeeping models.
The global atmospheric CO2 concentration is measured directly and its rate of growth (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 (2007–2016), EFF was 9.4±0.5GtCyr−1, ELUC 1.3±0.7GtCyr−1, GATM 4.7±0.1GtCyr−1, SOCEAN 2.4±0.5GtCyr−1, and SLAND 3.0±0.8GtCyr−1, with a budget imbalance BIM of 0.6GtCyr−1 indicating overestimated emissions and/or underestimated sinks. For year 2016 alone, the growth in EFF was approximately zero and emissions remained at 9.9±0.5GtCyr−1. Also for 2016, ELUC was 1.3±0.7GtCyr−1, GATM was 6.1±0.2GtCyr−1, SOCEAN was 2.6±0.5GtCyr−1, and SLAND was 2.7±1.0GtCyr−1, with a small BIM of −0.3GtC. GATM continued to be higher in 2016 compared to the past decade (2007–2016), reflecting in part the high fossil emissions and the small SLAND consistent with El Niño conditions.
The global atmospheric CO2 concentration reached 402.8±0.1ppm averaged over 2016. For 2017, preliminary data for the first 6–9 months indicate a renewed growth in EFF of +2.0% (range of 0.8 to 3.0%) based on national emissions projections for China, USA, and India, and projections of gross domestic product (GDP) corrected for recent changes in the carbon intensity of the economy for the rest of the world.
This living data update documents changes in the methods and data sets used in this new global carbon budget compared with previous publications of this data set.