Climate change is making days longer – here’s how

Days have lengthened by the equivalent of 1.33 milliseconds per century in the past 20 years. The change may affect precise systems that rely on accurate data on the earth’s spin.

Accelerated melting of polar ice sheets is raising sea levels, slowing the earth's rotation.

Climate change is lengthening days at a rate scientists have called “unprecedented in 3.6 million years”.

Day length changes due to gravitational effects of the moon, as well as various geophysical processes acting within the earth's interior, at its surface, and in the atmosphere.

But climate change is also affecting day length. Previous research found that from 2000 to 2020, days lengthened by the equivalent of 1.33 milliseconds per century.

This rapid increase in day length implies that the rate of modern climate change has been unprecedented at least since the late Pliocene, 3.6 million years ago.

The change is due to accelerated melting of polar ice sheets and mountain glaciers. These are raising sea levels, which slows earth's rotation and therefore lengthens the day.

This is similar to a figure skater who spins more slowly once they stretch their arms, and more rapidly once they keep their hands close to their body, according to Mostafa Kiani Shahvandi of the University of Vienna’s Department of Meteorology and Geophysics.

Looking back into history

Researchers wanted to find out if there were other periods in history when climate increased day lengths at a similar pace.

To answer this question, the researchers used the fossilised remains of single-celled marine organisms known as benthic foraminifera.

They used the chemical composition of these organisms to calculate sea-level fluctuations and calculate the corresponding changes in day length, according to Kiani Shahvandi, a climate scientist and geophysicist from the University of Vienna.

By combining these results with a probabilistic deep learning algorithm, they found that during the past 2.6 million years, the growth and melting of large continental ice sheets repeatedly caused significant day-length variations via sea-level changes.

However, today’s increase in day length stands out in the past 3.6 million years, the researchers found.

There was only one time, around two million years ago, that experienced a similar rate of change in length of day, according to Shahvandi.

Though the change is only milliseconds, it can cause problems in many areas that use precise measurements of the Earth's rotation.

Rate of climate change is 'unprecedented'

But sea levels had never risen as quickly as between 200 and 2020, he added.

“This rapid increase in day length implies that the rate of modern climate change has been unprecedented at least since the late Pliocene, 3.6 million years ago.

"The current rapid rise in day length can be attributed primarily to human influences,” said Benedikt Soja, professor of Space Geodesy at ETH Zurich.

By the end of the 21st century, climate change is expected to affect day length even more strongly than the Moon, he said.

Even though the changes are only milliseconds, they can cause problems in many areas such as precise space navigation, which requires accurate information on Earth's rotation, he added.

News references:

Kiani Shahvandi and Benedikt Soja. Climate-induced length of day variations since the Late Pliocene. Journal of Geophysical Research: Solid Earth, 10 March 2026.

Kiani Shahvandi et al (2024). The increasingly dominant role of climate change on length of day variations. Proceedings of the National Academy of Sciences, 5 June 2024.