Song et al. (2026) Observationally constrained global warming hysteresis under CO2 removal

Identification

• Journal: Communications Earth & Environment
• Year: 2026
• Date: 2026-04-09
• Authors: Se-Yong Song, Duo Chan, Sang-Wook Yeh
• DOI: 10.1038/s43247-026-03484-1

Research Groups

• Earth Research Institute, University of California, Santa Barbara, Santa Barbara, CA, USA
• School of Ocean and Earth Science, University of Southampton, Southampton, UK
• Department of Climate and Energy Systems Engineering, Ewha Womans University, Seoul, South Korea

Short Summary

This study develops an observationally constrained data-driven emulator to quantify global warming hysteresis under carbon dioxide (CO2) removal. It projects that global warming during the CO2 removal phase will be 0.7 °C warmer than during the CO2 increasing phase at the same CO2 concentration, leading to a temporary overshoot of the 1.5 °C target even under stringent mitigation.

Objective

• To quantify the extent to which atmospheric carbon dioxide removal can reverse past global warming, specifically addressing the uncertainty in global warming hysteresis across existing models.

Study Configuration

• Spatial Scale: Global
• Temporal Scale: Historical (since 1850) to future projections, covering phases of CO2 increase and removal, and mitigation scenarios.

Methodology and Data

• Models used: Data-driven emulator based on a three-layer energy balance model.
• Data sources: State-of-the-art instrumental temperature datasets (DCENT, HadCRUT5.0.2.0, Berkeley Earth temperature for surface, IAP for ocean temperature), and model data from CMIP6 archives.

Main Results

• At the same carbon dioxide concentration, global warming during the CO2 removal phase is projected to be, on average, 0.7 °C (95% confidence interval: [0.5, 1.0]) warmer than during the CO2 increasing phase.
• This observationally constrained estimate narrows the inter-model range of 0.2–1.9 °C by more than 70%.
• Applied to mitigation scenarios, global warming is projected to temporarily overshoot the 1.5 °C target, even under stringent pathways reaching net-zero carbon dioxide emissions.

Contributions

• Developed a novel, observationally constrained data-driven emulator to assess global warming hysteresis under CO2 removal.
• Significantly reduced the uncertainty in quantifying the temperature difference between CO2 increase and removal phases compared to previous model ensembles.
• Provided robust projections indicating that a temporary overshoot of the 1.5 °C global warming target is likely, even with aggressive CO2 removal strategies.

Funding

• Future Leaders Fellowship UKRI2360 (D.C.)
• Korea Environment Industry and Technology Institute (KEITI) through Climate Change R&D Project for New Climate Regime funded by the Korea Ministry of Environment (MOE) (2022003560001) (S.-W.Y.)

Citation

@article{Song2026Observationally,
  author = {Song, Se-Yong and Chan, Duo and Yeh, Sang-Wook},
  title = {Observationally constrained global warming hysteresis under CO2 removal},
  journal = {Communications Earth & Environment},
  year = {2026},
  doi = {10.1038/s43247-026-03484-1},
  url = {https://doi.org/10.1038/s43247-026-03484-1}
}