For the first time in history, global timekeepers may have to consider the unprecedented step of subtracting a second from clocks due to Earth's slightly faster rotation. This potential "negative leap second" could occur around 2029, according to a study published in the journal Nature.
"This is an unprecedented situation and a big deal," said Duncan Agnew, the study's lead author and a geophysicist at the Scripps Institution of Oceanography. "It's not a huge change in the Earth's rotation that's going to lead to some catastrophe or anything, but it is something notable. It's yet another indication that we're in a very unusual time."
The melting of ice at both poles has been counteracting Earth's burst of speed, likely delaying this global second of reckoning by about three years, Agnew noted.
Earth's rotation has been generally slowing down for thousands of years due to the effect of tides caused by the moon's gravitational pull. However, the planet's hot liquid core, a large ball of molten fluid, acts in unpredictable ways, with eddies and flows that can cause fluctuations in the rotation rate.
"In 2016 or 2017 or maybe 2018, the slowdown rate had slowed down to the point that the Earth was actually speeding up," said Judah Levine, a physicist at the National Institute of Standards and Technology.
The introduction of atomic clocks as the official time standard more than 55 years ago established two versions of time – astronomical and atomic – which didn't match. To reconcile this difference, international timekeepers have been adding a "leap second" every few years, adjusting astronomical time to catch up with atomic time.
However, the potential need for a negative leap second, where a second is skipped instead of added, presents new challenges. "It's likely to be tougher to skip a second because software programs are designed to add, not subtract time," said Dennis McCarthy, retired director of time for the US Naval Observatory.
While some experts believe the trend toward needing a negative leap second is clear, others argue that the shorter-term fluctuations in Earth's core rotation may be temporary. The debates surrounding leap seconds highlight the intricate interplay between physics, global power politics, climate change, and technology in our modern world's timekeeping systems.
