Millot-Weil et al. (2026) Asian summer monsoon orbital variability directly paced by CO2 and precession, not eccentricity

Identification

• Journal: Nature Communications
• Year: 2026
• Date: 2026-08-22
• Authors: Jeanne Millot-Weil, Paul J. Valdes, Alex Farnsworth
• DOI: 10.1038/s41467-026-76856-y

Research Groups

• School of Geographical Sciences, University of Bristol, UK
• State Key Laboratory of Tibetan Plateau Earth System, Environment and Resources, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, China

Short Summary

This study demonstrates that the 100-kyr variability of the Asian summer monsoon is primarily driven by greenhouse gas concentrations rather than eccentricity, while the 20-kyr variability is directly paced by precession.

Objective

• To investigate the temporal pacing and intensity changes of the Asian summer monsoon to determine whether precession, eccentricity, or other forcings (CO2, ice sheets) exert the dominant control.

Study Configuration

• Spatial Scale: Asian summer monsoon region
• Temporal Scale: Last 800 kyr at a 4-kyr resolution

Methodology and Data

• Models used: Full-complexity climate model equilibrium simulations (four distinct series).
• Data sources: Simulations utilizing varying inputs for insolation, greenhouse gases, and ice sheet forcing.

Main Results

• 100-kyr Cycle: Greenhouse gases exert the dominant control via thermal forcing of the monsoon circulation.
• 20-kyr Cycle: Precession is the direct driver of variability.
• Secondary Factors: Direct contributions from eccentricity forcing and ice sheet variability are significantly smaller than those of CO2 and precession.
• Spatial Dynamics: Identified spatial heterogeneity in monsoon dynamics, which explains conflicting results found in various geological proxy records.

Contributions

• The research resolves a long-standing debate in paleoclimate literature regarding the pacing of the Asian summer monsoon by distinguishing between the roles of CO2 and orbital parameters.
• It provides a mechanism (spatial heterogeneity) to reconcile disparate proxy data.

Funding

• NERC GW4+ Doctoral Training Partnership studentship (Project NE/S007504/1)
• NERC grant NSFGEO-NERC "Solving the enigma of the Miocene South Asian monsoon conundrum. An analogue to our future" (Project NE/X015505/1)

Citation

@article{MillotWeil2026Asian,
  author = {Millot-Weil, Jeanne and Valdes, Paul J. and Farnsworth, Alex},
  title = {Asian summer monsoon orbital variability directly paced by CO2 and precession, not eccentricity},
  journal = {Nature Communications},
  year = {2026},
  doi = {10.1038/s41467-026-76856-y},
  url = {https://doi.org/10.1038/s41467-026-76856-y}
}