Discoveries

April 18, 2024

Earth Time

Listen to Today's Edition

Global warming is widely credited for causing ice to melt at both the Earth’s poles, leading to a rise in sea levels.

And that in turn is shifting water, causing our planet to spin more slowly, Scientific American reported.

Combined with other forces that alter Earth’s rotation speed, this may impact timekeeping. In a recent study, scientists suggested we may soon have to delete a “leap second,” for the first time.

As miles-thick ice sheets melt, their mass shifts away from the poles toward the equator, slowing down Earth’s rotation – it’s similar to how figure skaters spin rapidly on ice with their arms up around their heads, and then slow when they bring their arms down and extend them outward.

For a few decades already, timekeepers have observed that our planet’s rotation has been slowing down because of other factors, including tides. They have added leap seconds to Coordinated Universal Time (UTC), which most of the world uses. Those seconds are added at the end of a given day: Its last minute would be 23:59:60 instead of 23:59:59.

But the study established that the slow-down induced by ice melt had also overshadowed the fact that our Earth’s rotation has actually sped up.

In the last half-century, days have gotten about 0.0025 of a second shorter because of changes in the rotation of Earth’s liquid outer core, over 1,300 miles deep.

Without global warming, we might have retracted that extra second sooner, but the researchers predicted a deletion would be needed by 2028 or 2029.

Nonetheless, experts say leap seconds are not that relevant. The International Bureau of Weights and Measures even voted to abolish them by 2035.

“The Earth is not a perfect timekeeper,” one physicist told Scientific Alert.

This story originally appeared in the April 18, 2024 newsletter, Gangland Elections.