This has been discussed in CF before but without conclusion. It would certainly be useful to adopt a convention for it, because there are use-cases, as @peterkuma demonstrates. It's not a problem with the reference year itself, but with the definition of the calendar. Given the lengthy debates about what "calendar" means when we were discussing leap-seconds, I use that word with some nervousness! I mean by "calendar" the set of valid dates (DD-MM-YYYY), which is implied by the choice of the `calendar` attribute in CF.
In the standard calendar, as we all know, there is no year between 1 AD (CE) and 1 BC (BCE). I suppose it's because year 0 doesn't exist that COARDS chose year 0 to indicate climatological time. (CF supports that convention for compatibility with COARDS, which only deals with the real-world standard calendar.) I'm interested to see what @martinjuckes reports about NetCDF-4. If you accept 0 as a valid year number, it means you have to write 2 BC as year -1, 3 BC as year -2, etc. That seems rather confusing to me, and likely to lead to mistakes. However, it seems that this is what is done for the proleptic Julian calendar, which is used in astronomy. Wikipedia says, "year 1 of the Julian Period was 4713 BC (−4712)." It seems that there is a year 0 in that calendar. Is that correct? For model calendars, I guess that year zero probably does exist, because it's an inconvenience to arithmetic if you leave it out! If we decide there isn't a well-defined best answer, and there are divergent use-cases, we could define different CF calendars with and without year zero. -- You are receiving this because you are subscribed to this thread. Reply to this email directly or view it on GitHub: https://github.com/cf-convention/cf-conventions/issues/298#issuecomment-697722585 This list forwards relevant notifications from Github. It is distinct from cf-metad...@cgd.ucar.edu, although if you do nothing, a subscription to the UCAR list will result in a subscription to this list. To unsubscribe from this list only, send a message to cf-metadata-unsubscribe-requ...@listserv.llnl.gov.
