Earth’s days are getting longer. Climate change is to blame

Earth’s spin is slowing at an unprecedented rate, thanks to climate change

By Claire Cameron edited by Jeanna Bryner

Rising sea levels slow the Earth’s rotation, extending the length of an average day. And the current increase to a single average day — 1.33 extra milliseconds per century — is unprecedented in at least the past 3.6 million years, a new study finds.

Most people take for granted that a single day will last 24 hours, not a second more or less. But in reality, the length of a given day varies for a variety of reasons, including the Moon’s gravitational pull on the planet and geophysical processes in the Earth’s interior and surface, as well as atmospheric conditions.

Incredibly, climate change is expected to have a greater influence on day length than the moon by the end of this century, according to Benedikt Soja, the study’s senior author and a geophysicist at the Swiss Federal Institute of Technology Zurich.

On supporting science journalism

If you like this article, please consider supporting our award-winning journalism by subscribes. By purchasing a subscription, you help secure the future of impactful stories about the discoveries and ideas that shape our world today.

“Even if the changes are only milliseconds, they can cause problems in many areas, such as in precise space navigation, which requires accurate information about the Earth’s rotation,” he said in a statement.

The researchers behind the new study had previously found that climate change affects the length of the day, as rising sea levels – caused by melting glaciers and shrinking polar ice caps – affect the Earth’s spin.

The decline is linked to the distribution of the mass once held at the poles towards the planet’s midsection. In the statement, lead study author and geoscientist at the University of Vienna, Mostafa Kiani Shahvandi, compared the effect to “a figure skater who spins more slowly when they extend their arms, and faster when they hold their hands close to their body.”

In the new paper, published in Journal of Geophysical Research: Solid Earth, the researchers show that the increase in day length is higher now than it has been in millions of years. The researchers analyzed the chemical composition of fossils to infer changes in sea level over the past 3.6 million years. They then calculated the corresponding changes in the length of a day. Using a probabilistic deep learning algorithm to better model the physics of sea-level change, they found that as the planet’s ice has formed and melted, day length has fluctuated in lockstep. But today’s increase in day length is an outlier, according to the study.

“Only once – about 2 million years ago – was the rate of change in day length almost comparable, but never before or since has the planetary ‘figure skater’ raised its arms and sea level as rapidly as in 2000 to 2020,” said Kiani Shahvandi.

It’s time to stand up for science

If you liked this article, I would like to ask for your support. Scientific American has served as an advocate for science and industry for 180 years, and right now may be the most critical moment in its two-century history.

I have been one Scientific American subscriber since I was 12 years old, and it helped shape the way I see the world. SciAm always educates and delights me, and inspires a sense of awe for our vast, beautiful universe. I hope it does for you too.

If you subscribe to Scientific Americanyou help ensure our coverage is centered on meaningful research and discovery; that we have the resources to report on the decisions that threaten laboratories across the United States; and that we support both budding and working scientists at a time when the value of science itself is too often not recognised.

In return, you receive important news, captivating podcasts, brilliant infographics, can’t-miss newsletters, must-see videos, challenging games, and the world of science’s best writing and reporting. You can even give someone a subscription.

There has never been a more important time for us to stand up and show why science is important. I hope you will support us in that mission.