Is Climate Change Slowing Earth’s Rotation Affecting Timekeeping?

A paper published in Nature in March 2024 argues that melting polar ice due to global warming affects the Earth’s rotation, which could impact precision timekeeping.

Timekeeping is an exact science in a highly technological society, so the slight changes in Earth’s rotation pushed global authorities to invent the concept of the “leap second” more than 50 years ago.

For much of history, time was measured by the Earth’s rotation, known as astronomical time. In 1967, a new version of timekeeping was adopted, which is the atomic clock. However, the two versions of time – astronomical and atomic- did not match. Astronomical time fell behind atomic time by 2.5 milliseconds every day. Those incremental fractions of seconds accumulated into a whole second every few years, and to match the two, the international timekeepers in 1972 decided to add a “leap second” in June or December for astronomical time to catch up to the atomic time known as the Coordinated Universal Time or UTC.

A leap second adds a second to the time. For example, instead of 11:59 and 59 seconds turning to midnight, there would be another second at 11:59 and 60 seconds. On the other hand, negative leap seconds would go from 11:59 and 58 seconds directly to midnight, skipping a second.

Between 1972 and 2016, 27 leap seconds were added as the Earth slowed. But in recent years, the Earth’s rotation has sped up a bit, overtaking atomic time. This speeding up, according to the study, is caused by the Earth’s hot liquid core or molten fluid that is acting in unpredictable ways with its eddies and flows. Still, starting from 1990, the melting of the ice caps in Antarctica and Greenland has masked the speeding effect. Melting ice shifts the Earth’s mass toward the equator, redistributing it and slowing the planet’s spin on its axis.

So, Agnew’s paper states that although the Earth’s core is speeding up its rotation, the shift in mass caused by the planet’s warming is slowing it down.  

Without climate change’s effect, the Earth’s acceleration might require timekeepers to add a “negative leap second” at the end of 2026, but because of climate change‘s slowing effect, this could be unnecessary until 2029.

The study shows that timekeepers may face the opposite problem of subtracting a second. However, even positive leap seconds in the past have caused problems for systems that require precise time. In 2012, Time reported that some computer systems mishandled the leap second, causing problems for Reddit, Linux, Qantas Airlines, and others. Although time adjustments like inserting leap seconds cause problems, they are needed as some satellite systems, like Russia’s system, rely on astronomical time, so eliminating leap seconds will cause problems for them.

While adding a second is complicated enough, the article notes that subtracting a second is more challenging for software programs because they are designed to add and not subtract time.

That is why the world’s timekeepers agreed in 2022 to scrap the leap second by 2035.

Some experts believe that a negative leap second will not be needed because of the overall slowing trend from tides, which has been around for centuries and continues, but the shorter trends in Earth’s core come and go.

Agnew also believes that inserting a negative leap minute is very unlikely and hopes that his research will prompt the world’s timekeepers to consider dropping the leap second sooner than 2035.

Read the study: A global timekeeping problem postponed by global warming