CESM1 Single Forcing Large Ensemble Project

The CESM1 “Single Forcing” Large Ensemble Project is a publicly available set of climate model simulations useful for addressing the individual roles of anthropogenic aerosols, greenhouse gases and land-use/land-cover in historical and future climate change. These simulations use the same model, forcing configuration and initialization protocol as the CESM1 Large Ensemble Project, but keep either industrial aerosols (AER), biomass burning aerosols (BMB), greenhouse gases (GHG) or land-use/land-cover (LULC) conditions fixed at 1920 while all other external anthropogenic and natural forcing factors evolve following historical and future (RCP8.5) scenarios. There are 3 sets of ensembles: XGHG (20 members, 1920-2080), XAER (20 members, 1920-2080), and XBMB (15 members, 1920-2029). All members are branched from the first member of the “all forcing” CESM1 Large Ensemble on January 1, 1920 by applying a small (order of 10-14 K) random noise perturbation to their initial atmospheric temperature fields. The impact of the withheld forcing factor can be deduced by subtracting the ensemble-mean of each “X” ensemble from the ensemble-mean of the original “all forcing” CESM1 Large Ensemble. Details are provided in the reference paper below.

Note: A bug was discovered in the 5-member XLULC ensemble (previously described on this page) where land use and land cover were mistakenly evolving in time. These simulations have been pulled from distribution.

We kindly ask that you acknowledge the CESM Project and CISL supercomputing resources (doi:10.5065/D6RX99HX) and reference Deser et al. (2020) when presenting results based on the CESM1 “Single Forcing” Large Ensembles in either oral or written form.

Deser, C., A. S. Phillips, I. R. Simpson, N. Rosenbloom, D. Coleman, F. Lehner, A. Pendergrass, P. DiNezio and S. Stevenson, 2020: Isolating the Evolving Contributions of Anthropogenic Aerosols and Greenhouse Gases: A New CESM1 Large Ensemble Community Resource. J. Climate, 33, 7835-7858, doi:10.1175/JCLI-D-20-0123.1.[Article] [Supplemental Materials]

A 3 member ensemble that is complementary to the XAER has also been performed as discussed in Simpson et al (2023).  These simulations begin in 1850 and evolve under ONLY time varying industrial aerosols with the other forcings held fixed at 1850's values.  

Project Details

  • Simulation Names:
    • XGHG: b.e11.B20TRLENS_RCP85.f09_g16.xghg.0XX, XX = 01-20
    • XAER: b.e11.B20TRLENS_RCP85.f09_g16.xaer.0XX, XX = 01-20
    • XBMB: b.e11.B20TRLENS_RCP85.f09_g16.xbmb.0XX, XX = 01-15
    • AAER: b.e11.B1850LENS.f09_g16.aaer.00X / b.e11.B1850LENS.f09_g16.aaer.RCP85.00X, X = 1-3
  • Model Version: CESM1.1 Codebase | Documentation
  • Resolution: 0.9x1.25_gx1v6 (CESM nominal 1o grid)
  • Years: 1920-2080 (XGHG, XAER), 1920-2029 (XBMB), 1850-2050 (AAER)
  • Ensemble Size: 20 members (XGHG, XAER), 15 members (XBMB), 3 members (AAER)
  • Time Frequencies Saved: Monthly, Daily
  • Machine: NCAR:Cheyenne
  • Compsets: B20TRLENS / BRCP85LENS
  • Additional Notes: All ensembles use the identical configuration as the CESM1 Large Ensemble but with the following differences:
    • The XGHG ensemble does not have time-evolving greenhouse gases.
    • The XAER ensemble does not have time-evolving aerosols.
    • The XBMB ensemble does not have time-evolving biomass burning.
    • The AAER ensemble ONLY has time-evolving industrial aerosols; all other forcings are held fixed at 1850's values. 

Data Acquisition

This data is available on both the NCAR Climate Data Gateway (Web Access) and NCAR's casper system (NCAR Internal).

  • NCAR Internal

    Location on NCAR's campaign store or on the NCAR machine casper:


  • Web Access

    The following are step by step directions on how to download this data from the Climate Data Gateway.

    1. Proceed to the Climate Data Gateway CESM1 Large Ensemble page (XGHG, XAER and XBMB ensembles) or the Climate Data Gateway CESM1 Large Ensemble AAER Ensemble page (AAER ensemble).
    2. Scroll to the bottom of that page under Child Datasets, and click on the component and time frequency you are interested in.
    3. The files are organized by variable, listed at the end of each link. Click on the variable you are interested in.
    4. Click on the Download Options button. At this point, if you have not logged into the Climate Data Gateway you can do so now. If you have not registered before, registration is free and quick.
    5. Upon logging in you will see a file listing. Once you have identified a file that you would like to download, click on the check box to the left of the file name. Note that you can select multiple files on this page at once. (However, one cannot select/download multiple files across variables at once.) When you are finished selecting files, scroll to the top (or bottom) of the page and click on the Download Options for Selection box.
    6. Click the Request File Transfer from Archive, and choose whether to use a curl, wget or python script to download your selected data.