Fixing Co2 for CLM only in FHIST

[rambhari01]

Dear CESM users,

I am using the CESM2.2.2 (last pulled updates in april 2025). I am planning to run experiments with FHIST component set where atmosphere component see the CO2 concentration as historical and a fixed CO2 concentration (say 284.7ppm) for the land (CLM) component? I believe changing the following xmls params would do the needful?

1.) <entry id="CLM_CO2_TYPE" value="diagnostic">
-Change : "diagnostic " to "constant"

2.) <entry id="CCSM_CO2_PPMV" value="284.7">
- fixing the CO2 concentration.

I hope this is sufficient to run an experiment where CLM (vegetaion) see a fixed CO2 and atmosphere (CAM) run with historical co2 concentration.?

I am bit confused about the another namalist varibale as seq cplfld inparm as "flds_co2a=true" (by default it is true). For this as definition says "this adds prognostic CO2 and diagnostic CO2 at the lowest model level to be sent from the atmosphere to the land and ocean". Should I change this to "false"?

In the above case how should I change this namelist variable or keeping this as it is (true) wont affect the CO2 concentration fixed for the clm? Please help in understanding this.

Please point if I am missing something for above desired experiment setting.

Thank you

-Ram

 

[slevis]

I think (1) and (2) is all you need to do. If this doesn't work as you expect, let's revisit.

 

[slevis]

I do not know if it's necessary to change flds_co2a, though I also do not see harm in setting it to .false. just in case.