[tz] [PROPOSED] Mention the planned obsolescence of leap seconds

Paul Eggert eggert at cs.ucla.edu
Wed Dec 21 00:25:38 UTC 2022

 NEWS         |  4 ++++
 theory.html  | 15 ++++++++++++++-
 tz-link.html |  8 ++++++--
 3 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/NEWS b/NEWS
index 9b2d202..9ac3367 100644
--- a/NEWS
+++ b/NEWS
@@ -42,6 +42,10 @@ Unreleased, experimental changes
     'restrict' keyword consistently with their documentation.
     This may allow future optimizations.
+  Changes to commentary
+    Note that leap seconds are planned to be discontinued by 2035.
 Release 2022g - 2022-11-29 08:58:31 -0800
diff --git a/theory.html b/theory.html
index fbbb9e4..88bf720 100644
--- a/theory.html
+++ b/theory.html
@@ -818,7 +818,8 @@ href="https://www.dissentmagazine.org/blog/booked-a-global-history-of-time-vanes
     The relationship between POSIX time (that is, <abbr>UTC</abbr> but
     ignoring <a href="https://en.wikipedia.org/wiki/Leap_second">leap
-    seconds</a>) and <abbr>UTC</abbr> is not agreed upon after 1972.
+    seconds</a>) and <abbr>UTC</abbr> is not agreed upon.
+    This affects time stamps during the leap second era (1972–2035).
     Although the POSIX
     clock officially stops during an inserted leap second, at least one
     proposed standard has it jumping back a second instead; and in
@@ -1268,6 +1269,18 @@ between now and the future time.
   <h2 id="leapsec">Leap seconds</h2>
+Leap seconds were introduced in 1972 to accommodate the
+difference between atomic time and the less-regular rotation of the earth.
+Unfortunately they caused so many problems with civil
+timekeeping that they
+are <a href="https://www.bipm.org/en/cgpm-2022/resolution-4">planned
+to be discontinued by 2035</a>, with some as-yet-undetermined
+mechanism replacing them, perhaps after the year 2135.
+Despite their impending obsolescence, a record of leap seconds is still
+needed to resolve timestamps from 1972 through 2035.
 The <code><abbr>tz</abbr></code> code and data can account for leap seconds,
 thanks to code contributed by Bradley White.
diff --git a/tz-link.html b/tz-link.html
index d3b3766..608393f 100644
--- a/tz-link.html
+++ b/tz-link.html
@@ -1078,8 +1078,12 @@ leap second: its history and possible future</a>.
 <a href="https://www.ucolick.org/~sla/leapsecs/"><abbr>UTC</abbr>
 might be redefined
 without Leap Seconds</a> gives pointers on this
-contentious issue, which was active until 2015 and could become active
+contentious issue.
+The General Conference on Weights and Measures
+<a href="https://www.bipm.org/en/cgpm-2022/resolution-4">voted in 2022</a>
+to discontinue the use of leap seconds by 2035, replacing them with an
+as-yet-undetermined scheme some time after the year 2135.

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