Sigmond et al. (2025) Jet stream response to future Arctic sea ice loss not underestimated by climate models

Identification

• Journal: npj Climate and Atmospheric Science
• Year: 2025
• Date: 2025-12-04
• Authors: Michael Sigmond, Lantao Sun
• DOI: 10.1038/s41612-025-01262-y

Research Groups

• Canadian Centre for Climate Modelling and Analysis, Environment and Climate Change Canada, Victoria, British Columbia, Canada
• Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado, USA

Short Summary

This study proposes a new, more robust emergent constraint based on lower stratospheric winds to assess climate models' ability to project the winter jet stream response to Arctic sea ice loss. The findings indicate that climate models do not systematically underestimate this response, reducing projection uncertainty by 62% and increasing confidence in future poleward jet stream shifts.

Objective

• To develop and apply a more robust emergent constraint, based on lower stratospheric winds, to determine if climate models underestimate the winter jet stream response to future Arctic sea ice loss, thereby addressing questions about the robustness of previous emergent constraints.

Study Configuration

• Spatial Scale: Global climate models, focusing on the Northern Hemisphere mid-latitudes, Arctic, North Atlantic, and Pacific regions.
• Temporal Scale: Winter season (December-February, DJF) response to future Arctic sea ice loss, using simulations representing present-day (year-2000 radiative forcing) and future sea ice conditions. Observed present-day climatology is based on 1981-2014 reanalysis data.

Methodology and Data

• Models used:
  • Bespoke versions of two state-of-the-art climate models: Canadian Earth System Model version 5 (CanESM5, CanESM5-G) and Community Earth System Model version 2 (CESM2, CESM2-G1, CESM2-G2).
  • Multi-model archive from the Polar Amplification Model Intercomparison Project (PAMIP), including 12 models (AWI-CM-1-1-MR, CanESM5, CESM1-WACCM-SC, CESM2, CNRM-CM6-1, E3SM-1-0, EC-Earth3, FGOALS-f3-L, HadGEM3-GC31-MM, IPSL-CM6A-LR, MIROC6, NorESM2-LM), supplemented by CanESM5-G, CESM2-G1, and CESM2-G2, for a total of 15 models.
  • CMIP6 historical simulations from 12 models (CanESM5, CESM2, CESM2-FV2, CESM2-WACCM, CESM2-WACCM-FV2, GFDL-ESM4, HadGEM3-GC31-LL, HadGEM3-GC31-MM, IPSL-CM6A-LR, MPI-ESM1-2-LR, MRI-ESM2-0, UKESM1-0-LL).
• Data sources:
  • Coordinated sea ice loss experiments following the PAMIP protocol (pdSST-pdSIC and pdSST-futArcSIC).
  • CMIP6 historical simulations for investigating orographic gravity wave drag.
  • Observed present-day (1981-2014) neck region winds from three reanalysis products: ERA5, MERRA-2, and JRA-55.
  • Statistical analysis: Bootstrapping for uncertainty quantification, Student's t-test for significance, linear regression for emergent constraints.

Main Results

• Controlled single-model experiments with CanESM5 and CESM2 demonstrate that perturbing present-day lower stratospheric (neck region) winds significantly alters the jet stream response to sea ice loss.
• A robust relationship was identified across 15 PAMIP models between the strength of present-day neck region winds and the atmospheric circulation response to sea ice loss, including the stratospheric polar vortex, tropospheric zonal wind, and near-surface jet latitude.
• A new emergent constraint based on present-day neck region winds reduces the uncertainty in the jet stream response to sea ice loss by 62% for the stratospheric polar vortex, tropospheric zonal wind, and near-surface jet latitude.
• This emergent constraint indicates that the real-world response closely matches the multi-model mean, suggesting no systematic underestimation of the jet stream response by climate models, contrary to previous studies.
• The accuracy of neck region wind simulation is crucial for accurately projecting the response to future sea ice loss, and the amplitude of orographic gravity wave drag (OGWD) schemes is a key determinant of neck region wind strength in models.

Contributions

• Proposes a novel and more robust emergent constraint for the winter jet stream response to Arctic sea ice loss, addressing limitations and uncertainties of previous constraints.
• Significantly reduces the uncertainty (by 62%) in climate model projections of the jet stream response to sea ice loss.
• Increases confidence in climate model projections of a future poleward shift of the zonal-mean jet stream in response to global warming, by demonstrating that models do not systematically underestimate the sea ice loss component.
• Highlights the critical importance of accurately simulating lower stratospheric (neck region) winds and properly tuning orographic gravity wave drag schemes in climate models for reliable future climate projections.

Funding

• NSF AGS-2300038 (L.S.)

Citation

@article{Sigmond2025Jet,
  author = {Sigmond, Michael and Sun, Lantao},
  title = {Jet stream response to future Arctic sea ice loss not underestimated by climate models},
  journal = {npj Climate and Atmospheric Science},
  year = {2025},
  doi = {10.1038/s41612-025-01262-y},
  url = {https://doi.org/10.1038/s41612-025-01262-y}
}