[tz] Terminology: “Central European Summer Time” vs “Europe/Berlin”

Paul Eggert eggert at cs.ucla.edu
Thu Apr 15 00:03:33 UTC 2021

On 4/13/21 2:01 PM, Tim Parenti wrote:
> Additionally, we've seen many reports of individual jurisdictions recently
> considering changes to their clocks with varying degrees of coordination
> with their neighbors.

Yes, and there's large source of potential confusion here in real-world 

For example, the Sunshine Protection Act of 2021 proposed by Senators 
Rubio et al. would redefine "Pacific Standard Time" to mean 7 hours 
behind UTC, "Mountain Standard Time" to mean 6 hours behind UTC, etc. If 
it passes, most of Arizona will stop observing the old MST (-07) and I 
expect it will start observing the new PST (-07). The proposed law also 
seems to require the Navajo Nation, which currently observes the old 
MST/MDT (-07/-06), to switch to the new MST (-06).

If this happens, nomenclature issues will abound. For example, we could 
see this behavior in the GNU/Linux shell:

$ TZ=America/Los_Angeles date -d 2021-01-01 +"%Y-%m-%d %H:%M %z (%Z)"
2021-01-01 00:00 -0800 (PST)
$ TZ=America/Los_Angeles date -d 2022-01-01 +"%Y-%m-%d %H:%M %z (%Z)"
2022-01-01 00:00 -0700 (PST)
$ TZ=America/Phoenix     date -d 2021-01-01 +"%Y-%m-%d %H:%M %z (%Z)"
2021-01-01 00:00 -0700 (MST)
$ TZ=America/Phoenix     date -d 2022-01-01 +"%Y-%m-%d %H:%M %z (%Z)"
2022-01-01 00:00 -0700 (PST)

Any software that thinks that "PST" means "8 hours behind UTC" will be 
broken. As will any software that thinks that "PST" means "7 hours 
behind UTC", for older timestamps.

Admittedly such software is dicey anyway, but it's out there and it's in 
widespread use. This very email is being sent using the format of 
Internet RFC 5322, which defines "PST" to be equivalent to "-0800". 
(Luckily it says "PST" is obsolescent, but still....)

The situations for time zone abbreviations in Europe, the UK, Ireland, 
etc. will be even more complicated if they go through with plans to 
institute permanent DST or permanent standard time or whatever it is 
they might do. It surely will be an even bigger mess to name and 
abbreviate the resulting time zones.

To avoid the resulting fallout, perhaps we should remove all alphabetic 
time zone abbreviations from tzdb, other than "UTC" and the "xMT" 
abbreviations which are pretty much immune to this sort of thing and 
which we need for other reasons. Or at least we should perhaps remove 
alphabetic abbreviations for zones going through upheaval, as any such 
abbreviations are likely to confuse people.

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