Global Carbon Budget 2019

Background

“Global Carbon Budget 2019” extends the budget series through 2018 with a 2019 projection, during a period of record-high emissions and intensifying policy focus on net-zero targets. Atmospheric CO2 continues to rise, crossing ~407 ppm in 2018, driven primarily by fossil fuel combustion with significant but smaller contributions from land-use change. This paper situates these trajectories within the industrial-era cumulative emissions that underpin IPCC remaining carbon budget assessments.

Goals and Methods

This study aims to provide updated, observation-constrained estimates of fossil emissions, land-use change emissions, atmospheric CO2 growth, and the land and ocean sinks for 1959-2018, plus a 2019 projection, while documenting methodological refinements. Fossil emissions are constructed from multiple datasets (CDIAC, UNFCCC inventories, BP statistics, cement process data) harmonized to produce country-level and global totals, including sectoral and bunker fuels. Land-use change emissions rely on bookkeeping models forced by updated land-use histories; atmospheric growth uses global CO2 measurements; and ocean and land sinks are estimated from global process models evaluated with targeted observational metrics, with the carbon budget imbalance used as a diagnostic.

Conclusions and Takeaways

For 2009-2018, mean fossil emissions were about 9.5 GtC yr⁻¹ and land-use change emissions around 1.5 GtC yr⁻¹, with sinks and atmospheric growth balancing within uncertainties but leaving residual semi-decadal discrepancies up to ~1 GtC yr⁻¹. Fossil emissions in 2018 reached a new high (around 10.0 GtC yr⁻¹), and cumulative emissions since 1750 totaled roughly 655 GtC. While 2019 projections suggest further growth, reinforcing the narrowing window for 1.5-2 °C-consistent pathways. For practitioners, the 2019 budget offers rigorously harmonized data for national inventories, modeling, and scenario assessment, but it also highlights that unresolved uncertainties in land-use emissions and sink variability still constrain high-precision estimates of remaining carbon budgets and verification of mitigation progress.