Add new CLM_CMIP_ERA XML variable in order to support CMIP6 SSP scenarios

[ekluzek]

In order to support future scenarios for cesm3.0 we will be supporting the ctsm5.3 SSP surface datasets. In order to do this, we will add a new XML variable to control it. By default it will be set to cmip6 for the SSP's and cmip7 for everything else. The user will be able to change it to cmip6 for a cmip7 default compset, but there may not be resolutions supported for what they are trying to do -- and it'll come back with saying we don't have a dataset for this resolution/compset. We will limit the support to only 1850 and/or SSP and for fewer resolutions.

There's a few other datasets where we have a single dataset to define it, and we can easily keep both the cmip6 version and the cmip7 version. So we might as well do this. And with the variable being explicit and required for the landuse.timeseries files -- we might as well have other datasets be pointing to the cmip6 version at the same time for consistency.

When we have future scenarios for CMIP7 -- we plan to remove the CMIP6 support. This is expected to be a ctsm6.1 activity for cesm3.1.

We started discussing this in CTSM SE meeting today and notes are in this document:

https://docs.google.com/document/d/1Np69hB9Rx0L19OqOlhtI6bH48D4oYxPwgmrGofrdgVM

Definition of done:

• Add XML variable to config_component.xml in cime_config: CLM_CMIP_ERA
• In config_component.xml have valid_options be cmip6/cmip7 and same in namelist_definition_ctsm.xml
• Read it in the perl build-namelist so it can be used, similar to other XML variables read in
• Add a function to handle it being set in build-namelist in $nl_flags
• In namelist_defaults_ctsm.xml add an attribute: cmip_era="cmip6" or cmip_era="cmip7" to the places it's needed (1850 fsurdat and SSP's)
• Error check: What happens when you ask for an SSP with cmip7? Fail in a graceful manner that tells you what to do
• Add a test for above to the namelist tester
• Run namelist tester to make sure it still works
• Run aux_clm and ctsm_sci (which runs some of these SSP's)
• Address in aux_clm needs ISSP Clm60 tests with ssp126, 370, and 585 #3255: Run all the SSPs in ctsm5.4 branch and make sure they all work and use the CMIP6 datasets (f09 for all, SSP2-4.5 for a bunch) (for ones not in aux_clm or ctsm_sci)

[ekluzek]

Adding next so we can figure out who will do this and when.

Also make sure we agree on the following:

• Name of CLM_CMIP_ERA
• Don't change supported resolutions (leave the current CMIP6 files in place)