[LEAPSECS] negative leap second in 2029?

[Steve Allen]

On Sat 2024-03-30T16:03:30-0700 Paul Hirose hath writ:
> "Even a few years ago, the expectation was that leap seconds would always be
> positive, and happen more and more often," Duncan Agnew, a geophysicist at

The paper in Nature takes a very narrow view of history.
Agnew looks only at data in IERS C04.  That started in 1962 because

1) There were no available atomic time scales until the middle
of year 1961, so earlier earth rotation data were less precise
https://www.ucolick.org/~sla/leapsecs/taiepoch.html

2) The IAU had resolved that 1962-01-01 would be the date to
change from using the FK3 star catalog to using the FK4 star
catalog, and as noted in my TAI web page above that caused
a discontinuity in the value of time.

3) Although coordinated time existed before, it was 1962-01-01 when
BIH Paris was put in charge of what they would later name UTC.

4) The early atomic time scales from BIH were computed entirely
by hand.  The published values show arithmetic errors which
were never corrected.  With BIH perennially understaffed going
back farther in time would incorporate more such errors into C04.

With C04 there is only one point at which the core of the earth
made one of its huge shifts in angular momentum, and that was
coincidentally right around 1972.  Agnew further restricts his
analysis to only the earth rotation after 1972.

Agnew is certainly correct that melting ice caps are slowing the
rotation of the surface of the earth.  With the acceleration
being caused by whatever the core has been doing for the past
50 year Agnew is also correct that the meltwater is delaying
the need for a negative leap second.  But the analysis by
Agnew is blind to the long history of big changes in the core.

I think that is why Matsakis is quoted in one of the news articles
about not betting on predictions of earth rotation.  Also do not
forget McCarthy and Matsakis previously looking at the trend
https://insidegnss.com/will-we-have-a-negative-leap-second/

--
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