A set of high-top CESM simulations of the Last Glacial Maximum (LGM), conducted by Jiang Zhu, was designed to assess how stratospheric dynamics and chemistry influence simulated LGM temperatures. These experiments used CESM2(WACCM6ma) with the paleoclimate modifications described in Zhu et al. (2022). Compared with preindustrial conditions, the LGM simulations produce a weaker stratospheric circulation, 10–35% less tropospheric ozone, and 10–50% more ozone in the lower stratosphere. Despite these dynamical and chemical differences, the resulting additional cooling in surface and tropospheric temperatures is small, less than 5%, relative to parallel simulations using a low-top atmosphere without stratospheric chemistry. Overall, the results suggest that stratospheric dynamics and chemistry have only a limited direct influence on glacial–interglacial temperature change.

Simulated LGM cooling in CESM2(WACCM6ma)

Simulated LGM cooling in CESM2(WACCM6ma), shown relative to the corresponding low-top model. “HighTopA” denotes an additional sensitivity experiment with aerosol modifications that may be more appropriate for glacial climate conditions.

Further details are provided in the paper below (some science and technical considerations for setting up the simulation are available in the Supporting Information):

  • Zhu, J., Otto-Bliesner, B. L., Garcia, R., Brady, E. C., Mills, M., Kinnison, D., & Lamarque, J.-F. (2022). Small impact of stratospheric dynamics and chemistry on the surface temperature of the Last Glacial Maximum in CESM2(WACCM6ma). Geophysical Research Letters, 49, e2022GL099875. https://doi.org/10.1029/2022GL099875

We kindly ask that you reference the appropriate paper(s) and acknowledge the PaleoclimateWG and computing resources from NSF and NCAR CISL when presenting results based on these simulations in either oral or written form. 

Project Details

  • Simulation Names: 
    • LGM: b.e21.BWma1850.f19_g17.PaleoCalibr.21ka.04 and b.e21.BWma1850.f19_g17.PaleoCalibr.21ka.05 (with additional aerosol modifications)
    • PI: b.e21.BWma1850.f19_g17.PaleoCalibr.PI.04
  • Model Versions: CESM2.1
  • Resolution: 1.9x2.5_gx1v7 (nominal 2° atmosphere/land and 1° ocean/sea ice)
  • Years:  300 years for LGM and 300 years for PI
  • Ensemble Size: one
  • Time Frequencies Saved: Monthly
  • Machine: NWSC Cheyenne
  • Compsets: B1850 (1850_CAM60%WCCM_CLM50%SP_CICE_POP2_RTM_SGLC_SWAV)

Data Acquisition

  • The LGM and PI simulations are available on the NWSC computing storage at:

    /glade/campaign/cesm/community/palwg/PaleoCalibr

  • On ESGF, search with the following keywords:
    Source ID: CESM2-WACCM-FV2
    Variant Label: r1i2p2f1
    Version: 20220915

Diagnostics

Diagnostics for the LGM simulations may be added later.