Differences and uncertainties in land-use CO2 flux estimates

Abstract

Accurately estimating carbon dioxide (CO2) fluxes from land use and land-use change (FLUC) is critical to assessing nationally determined contributions and progress towards climate targets. In this Perspective, we compare five FLUC estimation approaches, discuss the origins of large uncertainties and discrepancies in estimates and consider how to improve estimate accuracy and better align individual estimates. Global FLUC estimates between 2000 and 2023 range from net emissions of 1.9 ± 0.6 PgC yr−1 (based on dynamic global vegetation models) to net removals of −1.0 PgC yr−1 (based on Earth observations), with other estimates from bookkeeping models, country reports and atmospheric inversions falling within this range. Discrepancies arise from each approach using different definitions for FLUC, the spatial extent of managed land and including degradation and environmental effects to varying degrees. As a result, each approach accounts for different fluxes and land areas. Uncertainties within individual estimates are attributed to quality of land-use data, observational constraints and incomplete process consideration. These uncertainties can be reduced through better separation of anthropogenic and natural CO2 fluxes, including the effects of anthropogenically driven ecosystem degradation and improving model parameterizations. Thus, future research should prioritise unambiguous and consistent definitions and conducting systematic evaluations against each other to improve the translation and harmonization of FLUC estimates, which is essential to support effective climate policies and optimize land-based climate change mitigation. Robust quantification of carbon dioxide fluxes from land use is critical for guiding climate change mitigation efforts and for improved understanding of the global carbon cycle. This Perspective explores the origins of uncertainties and discrepancies in established estimation approaches and considers strategies to improve, translate and harmonize flux estimates.