How to load/save a CMIP netcdf file and not have Iris change the time coordinate calendar?

[mo-garethsjones]

After Iris 3.11.1 it appears that while loading a netcdf as a cube, Iris changes the time coordinate calendar settings of "Gregorian" to "Standard".
https://scitools-iris.readthedocs.io/en/v3.11.1/whatsnew/3.3.html#incompatible-changes

I understand the motivation, but I need to see/use the calendar designation that exists in the netcdf file and be able to write a new netcdf with the same calendar setting. How can I stop the calendar being ``silently changed to “standard”'' on load/save in Iris > 3.11.1?

[rcomer]

This is controlled by the CALENDAR_ALIASES dictionary in cf_units. I think it should be enough to just remove "gregorian" from that dictionary. E.g.

import cf_units

cf_units.CALENDAR_ALIASES.pop('gregorian')

[mo-garethsjones]

That is great. That works for me. Ta

[stephenworsley]

It looks like the code changes in #4847 largely affect non-netcdf loading. As such the behaviour of netcdf loading/saving ought to be controled, as @rcomer suggests, via cf_units. However I would imagine that this would not work for, say, pp loading since this is hard coded in Iris. I don't supose there is any cause for making Iris more sensitive to the state of cf_units in such cases, or otherwise adding avenues for user control?