override co2 surface source to send to land/ocean by mvertens · Pull Request #294 · NorESMhub/CAM

mvertens · 2026-07-14T13:07:41Z

Summary: New ability to have co2 sent to land/ocean be different than used in radiation/chemistry

Purpose of changes: address ability to run the experiments outlined in NorESMhub/NorESM#825

Changes made to build system: None

Changes made to the namelist: New namelist group co2_surface_source_stream_nl
To activate this behavior edit user_nl_clm to have the following:

If you want to send latitude dependent 1850 CO2 forcing to land/ocean:

co2_surface_source = .true.
stream_co2_surface_source_mesh_filename = '$DIN_LOC_ROOT/atm/waccm/lb/cmip7_ghg_version20260607/esmf_mesh_20degLon.nc'
stream_co2_surface_source_data_filename = '$DIN_LOC_ROOT/atm/waccm/lb/cmip7_ghg_version20260607/ghg_cmip7_CMIP_CR-CMIP-1-0-0_1850_monthly_gnz_0p5degLat_version20260207_20degLon.nc'
stream_co2_surface_source_data_varname = 'CO2_LBC'
stream_co2_surface_source_taxmode = 'cycle'
stream_co2_surface_source_year_first = 1850
stream_co2_surface_source_year_last = 1850
stream_co2_surface_source_year_align = 1

If you want to send 1pct CO2 to land/ocean:

co2_surface_source = .true.
stream_co2_surface_source_mesh_filename = '$DIN_LOC_ROOT/atm/waccm/lb/cmip7_ghg_version20260607/esmf_mesh_20degLon.nc'
stream_co2_surface_source_data_filename = '$DIN_LOC_ROOT/atm/waccm/lb/cmip7_ghg_version20260607/ghg_cmip7_CMIP-1pctco2_CR-CMIP-1-0-0_0000-0166_monthly_gnz_0p5degLat_version20260207_20degLon.nc
stream_co2_surface_source_data_varname = 'CO2_LBC'
stream_co2_surface_source_taxmode = 'extend'
stream_co2_surface_source_year_first = 0
stream_co2_surface_source_year_last = 166
stream_co2_surface_source_year_align = 1

NOTE: a new namelist was also introduced for nitrogen deposition - stream_ndep_taxmode

Changes to the defaults for the boundary datasets: None

Substantial timing or memory changes: None

Detailed description of changes:
The above custom namelists must be set in user_nl_cam - there are no out of the box defaults.
The 1850 and 1pct CO2 files in $DIN_LOC_ROOT/atm/waccm/lb/cmip7_ghg_version20260607/ only had [lat,time] dimensions - and CDEPS cannot work with such files. As a result - 20deg longitude datasets were created for the above scenarios.
Verified that using the following compset 1

1850_CAM70%LT%NORESM%CAMoslo_CLM60%FATES-NCFB%NORESM_CICE_BLOM%HYB%ECO_MOSART_DGLC%NOEVOLVE_
SWAV_SESP

at ne16pg3_tn14 - the co2 diag field sent to the ocean had the expected behavior that was different than the co2 being used internally for the radiation in CAM.

mvertens · 2026-07-14T13:13:45Z

@tjiputra - I think I've implemented the behavior you wanted in NorESMhub/NorESM#825.
Could you please give this a test. I have tested that using the latitude dependent 1850 data (see namelist summary above) gives the latitude dependent data sent to blom - whereas cam is using a global surface mean for the radiation.

tjiputra · 2026-07-15T08:27:44Z

@mvertens - thank you. Should i test this on beta22 or other specific branch?

Using pr-noresm3_0_beta22 branch, I got this error during case.build:
ERROR: in _validate_pair (package Build::NamelistDefinition): Variable name stream_co2_surface_source_year_align not found in /cluster/work/projects/nn9560k/tjiputra/NorESM/NorESM_beta22/components/cam/bld/namelist_files/namelist_definition.xml

mvertens · 2026-07-15T08:42:25Z

@tjiputra - yes - please test this on beta22. However, this code is still in a PR status #294. For you to test this - you need to do the following

> git clone https://github.com/NorESMhub/NorESM
> cd NorESM
> git checkout pr-noresm3_0_beta22

edit .gitmodules to have the following

[submodule "cam"]
path = components/cam
#url = https://github.com/NorESMhub/CAM.git
#fxtag = noresm3_0_039_cam6_4_121
url = https://github.com/mvertens/CAM.git
fxtag = c07bbfc9
fxrequired = ToplevelRequired
fxDONOTUSEurl = https://github.com/NorESMhub/CAM.git

Then you can run the following

> ./bin/git-fleximod update

That should give you the CAM code you need. Please let me know if this is working for you.

tjiputra · 2026-07-15T09:24:23Z

@mvertens -
in user_nl_cam:
stream_co2_surface_source_mesh_filename = '$DIN_LOC_ROOT/atm/waccm/lb/cmip7_ghg_version20260607/esmf_mesh_20degLon.nc'
should be:
stream_co2_surface_source_mesh_filename = '$DIN_LOC_ROOT/atm/waccm/lb/cmip7_ghg_version20260607/esmf_mesh_20deglon.nc'

But the run crashes:
/cluster/work/projects/nn9560k/tjiputra/noresm/n1pctCO2-BGC.ne16pg3_tn14.beta22.2026-07-15/run/atm.log.1585890.260715-111118

(shr_stream_verifyTCoord) ERROR: calendar dates must be increasing
(shr_stream_verifyTCoord) date(n), date(n+1) = 11216 10116
(shr_stream_verifyTCoord) ERROR: calendar dates must be increasing

Case directory (Olivia):
/cluster/projects/nn9560k/tjiputra/NorESM/cases-noresm3dev/n1pctCO2-BGC.ne16pg3_tn14.beta22.2026-07-15

mvertens · 2026-07-15T09:37:28Z

@tjiputra - I had not tested the 1pctCO2 and I have you the wrong namelist:
can your try the following:

stream_co2_surface_source_year_first = 1
stream_co2_surface_source_year_last = 166
stream_co2_surface_source_year_align = 1

If this does not work - I'll try to duplicate the problem and resolve it.

tjiputra · 2026-07-15T12:04:14Z

@mvertens - the same error occurs again. It seems that it tries to read and cycle the first year even if I set

stream_co2_surface_source_year_first = 0
stream_co2_surface_source_year_last = 166
stream_co2_surface_source_year_align = 0

mvertens · 2026-07-15T12:22:37Z

@tjiputra - that's very odd. I'll track this down. Sorry you ran into this.

mvertens · 2026-07-15T15:06:37Z

@tjiputra - the problem is not in the code - it's in the dataset. I generated a time coordinate for this dataset and it seems to have duplicated the first year:
time = "0001-01-16", // time(1)
"0001-02-15", // time(2)
"0001-03-16", // time(3)
......
"0001-12-16", // time(12)
"0001-01-16", // time(13)
"0001-02-15", // time(14)
"0001-03-16", // time(15)
....
"0001-12-16", // time(24)
The problem was that the dataset started from year 0 - and I wanted to start from year 1. I'll go back to the year0 data and see if that works.

mvertens · 2026-07-15T15:21:38Z

@tjiputra - I have fixed this file on olivia and tested that the following user_nl_cam works:

co2_surface_source = .true.
stream_co2_surface_source_mesh_filename = '$DIN_LOC_ROOT/atm/waccm/lb/cmip7_ghg_version20260607/esmf_mesh_20deglon.nc'
stream_co2_surface_source_data_filename = '$DIN_LOC_ROOT/atm/waccm/lb/cmip7_ghg_version20260607/ghg_cmip7_CMIP-1pctco2_CR-CMIP-1-0-0_0000-0166_monthly_gnz_0p5degLat_version20260207_20degLon.nc'
stream_co2_surface_source_data_varname = 'CO2_LBC'
stream_co2_surface_source_taxmode = 'extend'
stream_co2_surface_source_year_first = 0
stream_co2_surface_source_year_last = 166
stream_co2_surface_source_year_align = 1

gold2718

I have several clean-up and documentation requests as well as some bug fixes and safety features.

gold2718 · 2026-07-15T13:27:04Z

 </entry>
+<entry id="stream_ndep_taxmode" type="char*256" category="Nitrogen Deposition"
+       group="ndep_stream_nl" valid_values="cycle,extend,limit" >
+time extrapolation mode.


Please add documentation similar to other xxx_taxmode namelist variables:

Suggested change

time extrapolation mode.

Time extrapolation algorithm to use for stream_ndep_data_filename.

- cycle: Simply cycle through the available model data (i.e., start over when the end is reached)

- extend: Use the final value when end of data is reached.

- limit: Halt the model run if the model time exceeds the available data.

Default: extend for transient, otherwise cycle

gold2718 · 2026-07-15T13:31:26Z

+</entry>
+<entry id="stream_co2_surface_source_mesh_filename" type="char*256" input_pathname="abs" category="CO2 surface source"
+       group="co2_surface_source_stream_nl" valid_values="" >
+Grid mesh file corresponding to sream_co2_surface_source_data_filename.


typo

Suggested change

Grid mesh file corresponding to sream_co2_surface_source_data_filename.

Grid mesh file corresponding to stream_co2_surface_source_data_filename.

gold2718 · 2026-07-15T13:33:10Z

+</entry>
+<entry id="stream_co2_surface_source_data_filename" type="char*256" input_pathname="abs" category="CO2 surface source"
+       group="co2_surface_source_stream_nl" valid_values="" >
+co2  stream data filename.


Suggested change

co2 stream data filename.

Data source file for reading CO2 concentrations to be passed to the surface if co2_surface_source=.true.

gold2718 · 2026-07-15T13:34:57Z

+</entry>
+<entry id="stream_co2_surface_source_data_varname" type="char*256" category="CO2 surface source"
+       group="co2_surface_source_stream_nl" valid_values="" >
+co2 varname on stream data file(s).


Suggested change

co2 varname on stream data file(s).

Variable name for reading CO2 concentrations in stream_co2_surface_source_data_filename.

gold2718 · 2026-07-15T16:30:13Z

+       ! error check
+       if ( trim(stream_co2_surface_source_taxmode) /= 'cycle'  .and. &
+            trim(stream_co2_surface_source_taxmode) /= 'extend' .and. &
+            trim(stream_co2_surface_source_taxmode) /= 'limit') then
+          call endrun(subName//': ERROR stream_co2_surface_source_taxmode '&
+               //trim(stream_co2_surface_source_taxmode)&
+               //' must be either cycle, extend or limit')
+       end if


Since stream_co2_surface_source_taxmode is broadcast, can this error check be moved into the logic below or inside the if (masterproc) logic where the namelist is read?

gold2718 · 2026-07-15T16:32:57Z

+    integer, intent(out) :: rc
+
+    ! local variables
+    character(*), parameter :: subName = "('stream_co2_surface_source_init')"


Please use correct syntax:

Suggested change

character(*), parameter :: subName = "('stream_co2_surface_source_init')"

character(len=*), parameter :: subName = "('stream_co2_surface_source_init')"

gold2718 · 2026-07-15T16:33:27Z

+    integer :: nml_error ! namelist i/o error flag
+    integer :: ierr      ! error status
+    integer :: nf        ! field counter
+    character(*), parameter :: subName = "('stream_co2_surface_source_readnl')"


Please use correct syntax:

Suggested change

character(*), parameter :: subName = "('stream_co2_surface_source_readnl')"

character(len=*), parameter :: subName = "('stream_co2_surface_source_readnl')"

gold2718 · 2026-07-15T16:34:05Z

+    integer  :: sec     ! seconds into current date for nstep+1
+    integer  :: mcdate  ! Current model date (yyyymmdd)
+    real(r8), pointer :: dataptr1d(:)
+    character(*), parameter :: subName = "('stream_co2_surface_source_interp')"


Please use correct syntax:

Suggested change

character(*), parameter :: subName = "('stream_co2_surface_source_interp')"

character(len=*), parameter :: subName = "('stream_co2_surface_source_interp')"

gold2718 · 2026-07-15T16:43:36Z

-    if (ierr /= 0) call endrun(trim(subname)//": FATAL: mpi_bcast: stream_ndep_year_align")

    ! Determine if ndep stream is active, and if not return
+    call mpi_bcast(stream_ndep_data_filename, len(stream_ndep_data_filename), mpi_character, 0, mpicom, ierr)


See comment in atm_stream_co2.F90 but make sure that all broadcasts are happening from the correct MPI task:

Suggested change

call mpi_bcast(stream_ndep_data_filename, len(stream_ndep_data_filename), mpi_character, 0, mpicom, ierr)

call mpi_bcast(stream_ndep_data_filename, len(stream_ndep_data_filename), mpi_character, mstrid, mpicom, ierr)

mvertens added 5 commits July 13, 2026 10:18

added new co2 surface source to overwrite co2_diag

5bb1dc9

fixed compiler problems

e09687d

updates to get 1850 test case working

0b96e55

added taxmode as namelists to both ndep and co2 streams

cba4505

changes to get tests for co2_surface_source working

c07bbfc

mvertens requested review from gold2718 and tjiputra July 14, 2026 13:10

mvertens changed the title ~~Feature/co2 surface source~~ override co2 surface source to send to land/ocean Jul 14, 2026

gold2718 requested changes Jul 15, 2026

View reviewed changes

-time extrapolation mode.
+Time extrapolation algorithm to use for stream_ndep_data_filename.
+- cycle: Simply cycle through the available model data (i.e., start over when the end is reached)
+- extend: Use the final value when end of data is reached.
+- limit: Halt the model run if the model time exceeds the available data.
+Default: extend for transient, otherwise cycle

	Grid mesh file corresponding to sream_co2_surface_source_data_filename.
	Grid mesh file corresponding to stream_co2_surface_source_data_filename.

	co2 stream data filename.
	Data source file for reading CO2 concentrations to be passed to the surface if co2_surface_source=.true.

	co2 varname on stream data file(s).
	Variable name for reading CO2 concentrations in stream_co2_surface_source_data_filename.

	character(*), parameter :: subName = "('stream_co2_surface_source_init')"
	character(len=*), parameter :: subName = "('stream_co2_surface_source_init')"

	call mpi_bcast(stream_ndep_data_filename, len(stream_ndep_data_filename), mpi_character, 0, mpicom, ierr)
	call mpi_bcast(stream_ndep_data_filename, len(stream_ndep_data_filename), mpi_character, mstrid, mpicom, ierr)

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