Leveraging Multi-Model Land-Use Emissions Reveals a Rising Airborne Fraction of Atmospheric CO2 Over the Past Six Decades

OUTLET

arXiv

Abstract

The airborne fraction is the share of anthropogenic carbon dioxide emissions that remains in the atmosphere and is a key indicator of carbon-cycle response and remaining carbon budgets. Whether this share is rising remains debated because inference is sensitive to uncertainty in land-use and land-cover change (LULC) emissions. Here we use an expanded LULC-definition ensemble from Global Carbon Budget 2025 and estimate airborne-fraction trends with a mixed-effects model with random intercepts and slopes by LULC series. We find that airborne fraction increased over 1959-2024, from about 0.41 to about 0.48, and that this conclusion is robust to excluding the final year and to alternative specifications that propagate denominator uncertainty. These results clarify why earlier studies reported weak or inconclusive trend evidence and strengthen evidence that a larger share of emitted carbon dioxide is accumulating in the atmosphere.

Download

The working paper is available on ArXiv here.

Reproduction materials are available in the GitHub repository here. The repository contains links to the code and data used in the paper.

Recommended citation

Text

Vera-Valdés, J.E. (2026). “Leveraging Multi-Model Land-Use Emissions Reveals a Rising Airborne Fraction of Atmospheric CO2 Over the Past Six Decades”. ArXiv (2605.30242).

BibTex

@article{VeraValdes2026c,
  author = {Vera-Valdés, J.E.},
  title={Leveraging Multi-Model Land-Use Emissions Reveals a Rising Airborne Fraction of Atmospheric CO2 Over the Past Six Decades}, 
  doi = {10.48550/arXiv.2605.30242},
  url = {https://arxiv.org/abs/2605.30242},
  journal = {arXiv},
  year = {2026}
}