Why is it in the News?

Glaciers are melting so fast that we may need to delay adding that 'negative leap second' to keep clocks aligned with Earth's rotation.

What Is a Leap Second?

• Leap seconds serve as a tool to synchronize global timekeeping with the Earth's gradually slowing rotation due to factors such as the melting and refreezing of ice caps.
• Introduced in the early 1970s, leap seconds are added periodically to Coordinated Universal Time (UTC) to align it with the Earth's actual rotation time.
• UTC is derived from the combined output of over 300 highly precise Atomic clocks worldwide, which offer accuracy within 1 second over millions of years.
• In contrast, Astronomical Time (UT1) corresponds to the Earth's rotation and determines day length.
• The primary reason for leap second additions is the irregularity of Earth's rotation, influenced by various factors like the moon's gravitational forces, causing ocean tides.
• This creates a gradual desynchronization between UTC and UT1. When the discrepancy between UTC and UT1 nears 0.9 seconds, a leap second is added to UTC, ensuring global timekeeping remains aligned with the Earth's rotation.
• Since its introduction, 27 leap seconds have been added to UTC, typically on June 30 or December 31.
• The leap second system continues to serve as an essential mechanism for maintaining synchronization between atomic timekeeping and the Earth's rotation.

What is Negative Leap Second?

• A negative leap second is a proposed time adjustment involving the subtraction of one second from our clocks to synchronize them with Earth's rotation.
  • Unlike positive leap seconds, which are added to account for slower rotation, a negative leap second would address the Earth spinning faster than usual.
• So far, no negative leap second has been implemented since Earth's rotation has generally been slow in recent decades.
• However, as Earth's rotation has recently accelerated, timekeepers are considering using negative leap seconds for the first time.
• The International Earth Rotation and Reference Systems Service (IERS) closely monitors the Earth's rotation and determines when to add or subtract leap seconds.
• A decision to implement a negative leap second would serve as a corrective measure, ensuring our timekeeping systems remain aligned with the planet's rotation.
• While negative leap seconds have yet to be utilized, they offer a potential solution to the challenge posed by variations in Earth's rotational speed, ensuring the ongoing synchronization of our timekeeping methods with the planet's natural rhythms.