Global Carbon Budget 2017

Background

“Global Carbon Budget 2017” updates the evolving anthropogenic carbon dioxide (CO2) budget to 2016, capturing emissions growth, atmospheric accumulation, and sink responses in a period of strong climate policy debate. Atmospheric CO2 averaged about 402.8 ppm in 2016 and continues to rise as fossil fuel emissions remain the dominant anthropogenic CO2 source, with land-use change providing an additional contribution. The paper situates these changes within industrial-era cumulative emissions and increasing concerns about remaining carbon budgets.

Goals and Methods

This study aims to quantify fossil and industrial emissions (EFF), land-use change emissions (ELUC), atmospheric CO2 growth (GATM), and land (SLAND) and ocean (SOCEAN) sinks for 1959–2016, with a focus on decadal means and the 2016 budget. It introduces a revised methodology that estimates land and ocean sinks directly from process-based models constrained by observations, while tracking the carbon budget imbalance (BIM) explicitly instead of folding residuals into the land sink. Fossil emissions draw on the Carbon Dioxide Information and Analysis Center (CDIAC), UNFCCC reports, and BP energy statistics; ELUC uses multiple bookkeeping models; GATM comes from global CO2 observations; and sink estimates are evaluated against atmospheric inversions and additional observational data products.

Conclusions and Takeaways

For 2007–2016, mean fossil emissions were around 9.4 GtC yr⁻¹ and land-use change emissions were about 1.3 GtC yr⁻¹, while sinks and atmospheric growth closed the budget with a decadal imbalance of roughly 0.1 GtC yr⁻¹. In 2016, fossil emissions grew modestly to about 9.9 GtC yr⁻¹, atmospheric CO2 continued to rise, and cumulative 1870–2017 emissions reached about 610 ± 65 GtC, with approximately 70% from fossil sources and 30% from land-use change. The explicit BIM highlights remaining structural uncertainties (up to ±2 GtC yr⁻¹ in some years), signaling to practitioners that both emissions reporting and sink modelling still limit precise remaining carbon budget estimates and motivating multiple, observation-constrained approaches.