[tz] Did Greenland abolish daylight saving from 2024 on?

Paul Eggert eggert at cs.ucla.edu
Fri Nov 17 22:47:49 UTC 2023

On 2023-11-17 11:34, Guy Harris wrote:

> The former would mean that "Daylight Savings Time", in POSIX, is always a time when clocks are turned forward, i.e. is always "summer time", even if that means that "standard time" and "Daylight Savings Time" are in effect at the same time.

That doesn't sound right, as POSIX says that in a TZ setting like 
TZ='IST-1GMT0,M10.5.0,M3.5.0/1' IST (+01) is standard time and GMT (+00) 
is daylight saving time.

> Do they explicitly define "Daylight Savings Time" in this fashion in some place?

There's no entry "Daylight Saving Time" in the POSIX glossary. However, 
the above is clear from POSIX's spec for the TZ environment variable.

> I like the term "alternative"

The term "alternative time" was a POSIX invention, as I think ISO C has 
always called it "daylight saving time". However, this invention seems 
to have caused more confusion than it's cured, as Draft 3 of the next 
POSIX standard has gone back to saying "Daylight Saving Time" and does 
not mention "alternative time" there.

> The only way in which I could see it being read as assigning a meaning to "Daylight Savings Time" is indirectly, by speaking of "std" and "dst" as fields in the TZ environment variable setting (rather than speaking of "std" and "alt"), as "dst" suggests that it refers to "Daylight Savings Time", and thereby suggesting that "Daylight Savings Time" is an alternative to "standard time".

There's no confusion there. If you say TZ='UTC0' then UTC is the 
abbreviation for standard time and tm_isdst must be zero. Similarly for 
TZ='IST-1GMT0,M10.5.0,M3.5.0/1', where tm_isdst must be zero for IST and 
  and positive for GMT. There no plausible way to read POSIX otherwise, 
and this is independent of what non-POSIX sources say about "daylight 
saving time".

> Is there *any* place where non-computer-nerds and non-time-nerds speak of "daylight saving time" being in effect during the winter?

Most sources that go to that level of precision can plausibly be called 
the speech of time or computer nerds (and this includes the Wikipedia 
page you just edited :-).

That being said, I have seen winter time called "daylight saving" in the 
context of the rare places that observe winter time. See, for example, 
my 2017-04-09 comment about Namibia in the 'africa' file.

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