Global Carbon Budget 2021

Background

“Global Carbon Budget 2021” updates the budget to 2020 and projects 2021, analyzing the rebound of carbon dioxide (CO2) emissions after the initial downturn during the COVID-19 pandemic. Atmospheric CO2 continues to increase, with decadal mean growth reaching ~5.1 GtC yr⁻¹ for 2011–2020 and concentrations surpassing 412 ppm.

Goals and Methods

This paper quantifies fossil and land-use emissions and their partitioning into atmospheric growth, land, and ocean sinks for 1959–2020, emphasizing the 2011–2020 decade and the dynamics of the 2019–2021 period. Fossil emissions are built from harmonized national inventories, the Carbon Dioxide Information Analysis Center (CDIAC), BP, and cement process data; land-use change emissions come from multiple bookkeeping models driven by Land-Use Harmonization (LUH2)/History Database of the Global Environment 3.3 (HYDE3.3); sinks are obtained from observation-constrained ocean and land models, with a budget imbalance term tracking inconsistencies.

Conclusions and Takeaways

For 2011–2020, average fossil emissions were 9.5 ± 0.5 GtC yr⁻¹ and land-use change emissions 1.1 ± 0.7 GtC yr⁻¹, with atmospheric CO2 growth of 5.1 ± 0.02 GtC yr⁻¹, an ocean sink of 2.8 ± 0.4 GtC yr⁻¹, and a land sink of 3.1 ± 0.6 GtC yr⁻¹, yielding a small negative budget imbalance. In 2020, fossil emissions fell to 9.3 ± 0.5 GtC yr⁻¹, but projections suggest a strong rebound in 2021 to about 9.9 ± 0.5 GtC yr⁻¹. However, newer land-use forcing reduced recent land-use change emissions estimates and indicated a tentative decreasing trend in land-use emissions, though with low confidence. For policy and modelling, the 2021 budget shows that the pandemic-induced dip only briefly interrupted the long-term upward trend in CO2 emissions and underscores major remaining uncertainties in land-use dynamics and their reflection in global inventories.