Climate change is slowing the Earth’s rotation and the way in which we measure time may need to change, a study has found.

Synchronised global timekeeping is crucial for maintaining the accuracy of various technologies, from smartphones to computer networks. 

Currently, leap seconds are added roughly every two to three years to help align atomic clocks with the Earth’s irregular rotation. In 1972, a day defined by the Earth’s rotation was 0.0025 seconds (2,500 microseconds) longer than the one defined by atomic clocks. Over the course of a year, the accumulated difference was almost a second, so a leap second was used to keep the difference from getting any larger. But in 2023, the two kinds of day differed by only 80 microseconds, so the difference in time over a year added up to only 0.03 seconds.

Researchers at Scripps Institution of Oceanography at UC San Diego warn that within the next decade, a negative leap second – or a minute lasting only 59 seconds – might become necessary due to changes in the Earth’s rotation.

While the concept of leap seconds has traditionally been associated with positive adjustments to account for the Earth’s slowing rotation, climate change is increasing the likelihood that a negative leap second may be needed. 

Scripps geophysicist Duncan Agnew believes that in today’s interconnected world, even a small deviation in timekeeping could result in significant disruptions.

“Even a few years ago, the expectation was that leap seconds would always be positive, and happen more and more often,” he said. “But if you look at changes in the Earth’s rotation, which is the reason for leap seconds, and break down what causes these changes, it looks like a negative one is quite likely.”

The study delves into the relationship between timekeeping and climate change, highlighting how the melting of land ice at high latitudes, a consequence of global warming, contributes to shifts in the Earth’s rotation rate. The water melting off icebergs amounts to a significant transfer of mass away from the poles towards the equator, which slows down the Earth’s rotation rate. The dynamics of Earth’s liquid core also play a role in altering the planet’s spin.

The research suggests that without the influence of global warming, the need for a negative leap second might have arisen earlier. Agnew believes that a negative leap second might be needed some time in 2028, but without the slowing of Earth’s rotation caused by melting ice, it would have been expected about three years earlier. 

However, while this postponement gives more time to prepare computer systems for the change, it is only a trivial benefit compared to the massive problems caused by global warming, Agnew added.