Run idealized emission driven noresm2 experiments without clm SourceMods

[TomasTorsvik]

Transfered from NorESM issue 551

Is your feature request related to a problem? Please describe.
In the past, when running idealized emission driven noresm2 experiments, it has been common practice to include a modified lnd_import_export.F90 file in SourceMods/src.clm/. The only modification is to replace

lnd_import_export.F90:L250-252

       if ( (co2_ppmv_val < 10.0_r8) .or. (co2_ppmv_val > 15000.0_r8) )then
          call endrun( sub//' ERROR: CO2 is outside of an expected range' )
       end if

with

       if ( (co2_ppmv_val < 10.0_r8) .or. (co2_ppmv_val > 15000.0_r8) )then
          write(iulog,*)'JT CO2 outside range= ', co2_ppmv_val, co2_type_idx
       end if

so that the simulation doesn't end if large CO2 values are encountered.

Describe the solution you would like to see
Would it be possible to make this test on the CO2 values optional, e.g. make a namelist switch to replace the ERROR with WARNING if the user wants to run an idealized emission setup?

It would be nice to have this option available for NorESM versions 2.0, 2.1, 2.3 and 2.5.

[kjetilaas]

To me, it makes sense to put in this option. But I think @mvdebolskiy or @mvertens can answer better how to do this, and how much work it is.

[mvdebolskiy]

@TomasTorsvik which tag for NorESM this applies to?

[TomasTorsvik]

@mvdebolskiy
NorESM2.0.8 use release-clm5.0.14-Nor_v1.0.4. This is the one I'm most interested in, as we do these experiments with comparison to CMIP6 simulations.

We probably want to do similar type of simulations in future versions of NorESM, so it would be good to have this functionality also in the development version.

[mvdebolskiy]

@TomasTorsvik then I suggest you making PRs to release-clm5.0.14-Nor and noresm branches with these modifications.

[TomasTorsvik]

@mvdebolskiy , @mvertens
The latest code release corresponds to release-clm5.0.14-Nor_v1.0.4, but the latest tag is release-clm5.0.14-Nor_v1.0.7 (NorESM2.1.1 is on release-clm5.0.14-Nor_v1.0.5). Are later tags backwards compatible (i.e. is the release-clm5.0.14-Norbranch still CMIP6 compatible with the latest changes on that branch)?