[tz] [PROPOSED] Improve leapseconds support

Arthur David Olson arthurdavidolson at gmail.com
Sat Oct 6 23:44:20 UTC 2018

Perhaps accept leap seconds at the ends of months other than June or
December, but issue a warning? (And similarly for negative leap seconds?)


On Sat, Oct 6, 2018 at 7:42 PM Paul Eggert <eggert at cs.ucla.edu> wrote:

> Hal Murray writes:
> > A leap second other than June or December is probably an error in the
> input
> > data.
> Only if the input is intended to be the current official list of leap
> seconds.
> The recent code change was intended to make the code match the official
> rules
> better, which lets us better test software on outlandish-but-valid input.
> It's
> like the long-existing tzdb code that supports negative leap seconds,
> something
> that would also be an input error in data intended to be the official list.
> Steve Allen wrote:
> > This is definitely true in this era.  Assuming (bad thing to do) that
> > rotation of the crust does not undergo another strong deceleration the
> > two dates per year should be enough for the next 40 years.
> My eyeballing of the "extrapolated long-term trend" of Figure 18 of
> Stephenson
> et al. 2016 says that 2 leap seconds per year should be enough until 2300
> or so.
> This prediction is based entirely on historical data, though, and global
> warming
> is throwing another monkey wrench into such predictions. Although there's
> not a
> consensus on how global warming should affect length of day, you might be
> amused
> to read Mazzarella & Scafetta 2018, which reports that since 1850 the
> length of
> day has been negatively correlated with the global sea surface
> temperature,
> which suggests that global warming should mean that leap seconds will be
> rarer.
> If they're right, we may have to wait even longer than Stephenson et al.
> suggest
> before worrying about leap seconds other than June or December.
> Stephenson FR, Morrison LV, Hohenkerk CY. Measurement of the Earth's
> rotation:
> 720 BC to AD 2015. Proc Royal Soc A. 2016 Dec 7;472:20160404.
> https://dx.doi.org/10.1098/rspa.2016.0404
> Mazzarella A, Scafetta N. The Little Ice Age was 1.0–1.5 °C cooler than
> current
> warm period according to LOD and NAO. Clim Dyn. 2018.
> https://doi.org/10.1007/s00382-018-4122-6
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