That's why some nations - the United States perhaps most prominently - have been calling for the end of the leap second, which they say adds an extra moving part to a machine that's already whirring along smoothly. Tinkering with our clocks simply creates an opportunity for something to go wrong. Like the "Y2K" phenomenon of a decade ago, they argue that if some systems fumble the leap second addition, catastrophic failures could ensue.

Others like Britain, Canada, and China - perhaps recalling the Y2K disaster that never was - argue that in the four decades the leap second has been in use, no such catastrophe has occurred. And in the meantime, the world's atomic clocks remain synced to the astronomical day.

The problem here is that atomic clocks have defined the second since 1967, at which point the new definition of time was pegged to the length of an astronomical day in 1900. But the Earth's rotation has slowed since then. To most of us, that slowing in Earth's rotation is extremely negligible. But to something as precise as an atomic clock, the change is noticeable if only slightly. If things were allowed to run their natural courses, the Earth would keep slowing and the atomic clocks would not. Atomic clocks are already running a bit ahead of the astronomical day, which has grown longer between sunrise and sunset. Without the leap second, thousands and thousands of years from now our atomic clocks would strike midnight at mid-day.

"So what?" you might ask. And the vast majority of nations involved in this debate said the same thing when polled last year, when only 16 expressed any opinion whatsoever. Of those, thirteen wanted to abolish the leap second - and they very well may get their way today. But never you mind - any change wouldn't go into effect until 2018, so on June 30th you'll get your extra second whether you want it or not.

[NYT]