Add piClim* experiments

[znichollscr]

• Add a number of other experiments #83

[znichollscr]

@bethdingley if you're able to help with tagging people to ask about the questions above, that would be great

[bethdingley]

These are AerChemMIP experiments, you'll need to chat with @fmoconnor and @duncanwp (not sure what Stephanie Fiedler's GitHub handle is, but she is also a co-chair if anyone can tag her)

[fmoconnor]

I'm not entirely sure what the question is! AerChemMIP has the following piClim-* experiments:
piClim-control
piClim-AQ
piClim-aer
piClim-BC
piClim-O3
piClim-CH4
piClim-N2O
piClim-ODS
piClim-NOx
piClim-SO2
piClim-OC
piClim-NH3 for forcing estimates. These are all in AFT. See Table 1 from https://egusphere.copernicus.org/preprints/2025/egusphere-2025-5669/

[fmoconnor]

There are also other piClim-X experiments for quantifying different biogeochemical feedbacks. These are:
piClim-2xdust*
piClim-2xss*
piClim-2xfire*
piClim-2xBVOC*
piClim-2xWet
piClim-2xPOApDMS
piClim-2xflash
piClim-p4K. These are also for the AFT. See Table 4 in https://egusphere.copernicus.org/preprints/2025/egusphere-2025-5669/

[fmoconnor]

And there's an additional one for time-evolving forcing over the historical period: piClim-histall. This isn't for AFT and matches an experiment in RFMIP. See Table 6 in https://egusphere.copernicus.org/preprints/2025/egusphere-2025-5669/

[fmoconnor]

@znichollscr If the above information isn't sufficient, please let us know!

[fmoconnor]

piClim-CH4 can be either concentration-driven or emissions-driven, depending on the capability of the model and what was used in piClim-control

[fmoconnor]

We also have transient atmos-only experiments in AerChemMIP but I haven't added these here, but could do if also required!

[znicholls]

Thanks @fmoconnor I'm trying to figure out how this fits with what is in the Dunne et el paper Table 1, Table 3 and Figure 3: https://gmd.copernicus.org/articles/18/6671/2025/gmd-18-6671-2025.pdf

(@eleanororourke @bethdingley you may also have insights on the questions below)

For example, do the papers you've linked supersede Dunne et al? Is there just content missing from Dunne et al? Does Dunne et al 'override' the papers you've linked and actually only the experiments listed in Dunne et al are AFT experiments? Something else?

Re piClim-histall, in Dunne et al Table 3 this is listed as requiring 251 years (I assume to go from 1850 to 2100). So is the hist in the name just a legacy thing, or is Dunne et al wrong and this only needs 172 years (to go from 1850 to end of 2021)?

[bethdingley]

actually only the experiments listed in Dunne et al are AFT experiments?
It's this - what is summarised in Dunne et al is just the Fast Track experiments, AerChemMIP2 have more experiments than that

[znichollscr]

Ok so Dunne et al Table 3 says piClim-X where X = CH4, N2O, NOX, ODS, SO2 i.e. 5 experiments. Then it says simulation years are "43 x 6" which suggests 6 experiments. Do you know which is correct and, if there should be 6 experiments, what the sixth is?

(It's not piClim-control or piClim-anthro or piClim-4xCO2, they're all covered in Table 1 of Dunne et al already)

[eleanororourke]

The piClim-histall experiment is described as:
An uncoupled (atmosphere and land) experiment with interactive vegetation in which sea surface temperatures (SST) and sea ice concentrations (SIC) are fixed at model-specific pre-industrial control climatology. Transient forcing to be consistent with historical forcing used in the DAMIP hist-all experiment and future forcing to be consistent with the ScenarioMIP medium scenario forcing.
And in the Pincus et al, 2026 RFMIP paper is from 1850-2100.

For piClim-X we also have the piClim-aer which sits under RFMIP rather than AerChemMIP making up the six with CH4, N2O, NOX, ODS, SO2.

[znichollscr]

The piClim-histall experiment is described as

Yes. My confusion is the name. Why is it called piClim-histall when it includes a future (i.e. non-historical) bit? Is this just a legacy thing (it didn't used to include history, now it does) or a mistake?

For piClim-X we also have the piClim-aer which sits under RFMIP rather than AerChemMIP making up the six with CH4, N2O, NOX, ODS, SO2.

Hmm but that has its own row where it says 30 simulation years. I guess the 30 years for piClim-aer are just double counted.

[eleanororourke]

I will ask Robert to clarify!

And yes I think the 30 simulation years is double counted - will add to list of corrections for when scenario names are updated in Dunne et al.

[eleanororourke]

@znicholls Tim Andrews (one of RFMIP chairs) has confirmed it is legacy from CMIP6 and they want to keep the same (covering 1850-2100).

[znichollscr]

Closing in favour of znichollscr#5