CMIP7 CO2 emissions

[JorgSchwinger]

@DirkOlivie @mvertens @tjiputra

I have produced a CO2 surface emissions file, similar to what has been used in CMIP6, but I have a couple of questions:

1. I added up emissions from all sectors and concatenated files into one. The horizontal resolution is unchanged from the input4MIPs data (0.5x0.5 degree). I understood the emissions will be interpolated online, is this correct @mvertens ?

2. There is data available from 1750-2023, and in CMIP6 we have all these data in one file. However due to the much higher resolution files are getting large and for now I produced only the period 1850-2023, which should be sufficient(?) Any insights/opinions on this?

3. In the CMIP6 file there is a variable date (in the format YYYYMMDD) in addition to time. In the new files there is only time (days since 1750-01-01-00000) so far. Is the date variable needed?

4. I will now look into aircraft emissions. Dirk mentioned that online interpolation will also be done in the vertical, is this correct @mvertens ?

[mvertens]

@JorgSchwinger - fossil fuel and aircraft emissions are not ingested by CAM using CDEPS inline functionality. In terms of your questions:

1. Yes the fossil fuel emissions are no interpolated online.
2. CDEPS inline functionality can ingest multiple files if that is needed. One file is fine for now - but if separate files are needed in the future - there is no problem with that.
3. In terms of time interpolation - the only variable that the CDEPS uses from the file is the time variable. The date variable is not used (but it's nice to have if the user wants a quick look at the date)
4. Yes - the online intepolation takes care of the vertical interpolation as well.

[JorgSchwinger]

Thanks for the clarifications @mvertens ! And sorry I'm having more questions...

1. Regarding aircraft CO2 emissions: In cmip6, there is "altitude" and "altitude_int" in the files (the latter being the altitude at level interfaces). Is "altitude_int" needed? It is not in the cmip7 input4MIPs data, but if it is needed I can add it during the pre-processing.

2. How is the time-dimensions handled in NorESM? Is there time-interpolation? In this case I guess I need to append one year (duplicate the last year of the historical as has been done for the cmip6 data) in order to facilitate time-interpolation. HOWEVER, I think it would be preferable if there was NO time-interpolation. This is because we want to exactly conserve the CO2-inputs prescribed in the input files (and the inputs have to be interpreted as monthly means). In light of the CO2 conservation discussion that we currently have, I think this would be preferable because with time interpolation we cannot precisely say how much emission the model saw (unless we would introduce a new output). Any thoughts on this @DirkOlivie @mvertens @tjiputra ?

[tjiputra]

@JorgSchwinger, thank you very much for preparing the CO2 emissions files. I also think that time-interpolation should be avoided. Perhaps this was initially introduced to (i) facilitate conversion from annual to monthly emissions fields and (ii) avoid abrupt change during transition from historical to future scenarios (?).

[mvertens]

@JorgSchwinger @tjiputra
In the latest cam tag that has the online regridding:

1. The vertical interpolation in CAM needed both altitude and altitude_int. The data is on the "altitude" levels - but the vertical interpolation needs the interface levels (altitude_int) in order toconserve the interpolated to conserve the total column. It looks like altitude_int starts at 0 and is just the midpoint between the altitude values (e.g. see /cluster/shared/noresm/inputdata/atm/cam/ggas/emissions-cmip6_CO2_anthro_ac_175001-201512_fv_0.9x1.25_c20181011.nc).

2. The time interpolation for both ffuel and aircraft is nearest in time - there is not time interpolation by default. And the mapping algorithm is first order conservative.

[mvertens]

@JorgSchwinger - could you please make sure that there are no string attributes (e.g. string drynhx:units = "kg m-2 s-1" ) in your files. This was also discussed here - #742.

[JorgSchwinger]

@mvertens

1. ok I will add altitude_int that is no problem.
2. There are no string attributes in the files (in the case of N-deposition, these attributes were already in the original input4MIP files, the input4MIPs CO2 files do not have them).
3. Regarding time-interpolation: The nearest-in-time method means, it will NOT be necessary to add an additional year before and after the historical time period, i.e. files covering 1850-01-01 to 2023-12-31 are fine?

[mvertens]

@JorgSchwinger - for 3. I think you are right - but I have not tested that. I'll give it a try once you point me to the files.

[JorgSchwinger]

Ok, I will produce new files (with altitude_int) on Monday and copy them to the input-data directory. I'll ping you when the are there.

[JorgSchwinger]

@mvertens I have now copied the surface and aircraft emissions to /cluster/shared/noresm/inputdata/atm/cam/ggas

surface: emissions-cmip7_CO2_anthro_surface_CMIP_CEDS-CMIP-2025-04-18_185001-202312_0.5x0.5_c20250119.nc
aircraft: emissions-cmip7_CO2_anthro_ac_CMIP_CEDS-CMIP-2025-04-18_185001-202312_0.5x0.5_c20250119.nc

Please let me know if I should change anything regarding the file format and/or structure.

Here is a comparison of total (surface+ac) emissions between CMIP6 and CMIP7:

[mvertens]

@JorgSchwinger @gold2718 - I will bring these two datasets into CAM and issue a PR once I've run the CAM regression tests with these.