Turn back the clock: Earth may soon have a negative leap second

Carly Torbett-Guiles

Contributing Writer

Earth, courtesy of NASA.

The Earth may be heading toward a negative leap second as scientists say timekeepers may have to subtract a second from clocks around the year 2029 due to the Earth rotating slightly faster, according to Geophysicist Duncan Agnew. 

Geophysicist at the Scripps Institution of Oceanography at the University of California, San Diego and author of the study Duncan Agnew said without the poles melting and slightly slowing the spin we would be looking at subtracting a second from the clocks as soon as 2026 or at the latest 2029.

The hot and liquid core at the center of the Earth is what is causing the Rotation to get slightly faster. But due to the ice melting at both of Earth’s poles it has been counteracting the slightly faster rotation. 

“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” said Agnew.

However, this discrepancy between astronomical time, which is tied to the Earth’s rotation, and atomic time, based on atomic clocks, became significant when atomic clocks were established as the official time standard over 55 years ago. Unlike 

When atomic clocks became the official time standard, they didn’t slow down like Earth’s rotation did. This created two types of time: “astronomical time,” based on Earth’s rotation, and “atomic time,” based on atomic clocks. They didn’t match up. 

Atomic time moved ahead by 2.5 milliseconds every day compared to Earth’s time. So, if an atomic clock said it’s midnight, Earth’s clocks would tick a bit slower, lagging behind by a fraction of a second, according to Agnew.

To fix this, international timekeepers added 27  extra leap seconds to our time between 1972 and 2016, to catch up Earth’s time with atomic time. This made sure they were in sync. But as the Earth’s slowdown rate lessened over time, the need for these 

leap seconds decreased. Around 2016 and 2018, the Earth started to speed up a bit, said Judah Levine, a physicist from the National Institute of Standards and Technology.

“It takes about 24 hours for the Earth to rotate. But the key word is rotate” said Agnew “ We are headed for a negative leap second.”

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