Climate change is causing days on Earth to lengthen at 'unprecedented rates': Study

The days are getting longer as global temperatures continue to rise, new research shows.

As ice sheets at the Earth's poles melt, the redistribution of mass from the resulting sea-level rise is increasing the length of day at "an unprecedented rate," according to a study published in the Proceedings of the National Academy of Sciences on Monday.

For millennia, Earth's length of day has been gradually increasing by a few milliseconds per century. The increase is largely due to the moon's gravitational pull, which has gradually slowed Earth's rotation, as well as the glacial isostatic adjustment process -- that is, the movement of molten rock in the planet's mantle towards the polar regions, specifically in Northern Hemisphere, Surendra Adhikari, a geophysicist at NASA's Jet Propulsion Laboratory and one of the study's authors, told ABC News.

But melting ice sheets and glaciers in the Arctic and Antarctica also have had an increasing effect on length of day due to the transportation of large amounts of mass from the poles to the equator, the researchers found after examining the impact of climate change-induced sea-level rise on length of day since 1900. As a result, the Earth's normal oblate shape, resembling a somewhat flattened sphere bulging at the equator, is flattening even more, Adhikari said.

A sustained increase of the length of day on Earth has always been evident, based on data that goes back 3,000 years, Adhikari said. But the same amount of increase in milliseconds per century that occurred in the thousands of years prior to the year 2000 is expected to occur in this century alone, and climate change is the likely culprit, Adhikari said.

"By the end of 21st century, if in the high-emission scenarios, it could be that the climate impact alone will overtake the impact of the Earth-moon dynamics," Adhikari said.

The findings reveal the planetary-scale impact of modern climate change on Earth, the study says.

"It gives context as to the gravity, if I may, of the ongoing climate [emergency]," Adhikari told ABC News.

The redistribution of mass driven by melting of the Greenland and Antarctic Ice Sheets occurred at unprecedented rates over the last two decades, according to the study.

Fluctuations in sea level have caused the length of Earth's day to vary between 0.3 and 1.0 milliseconds per century during the 20th century. But since 2000, the length of day has increased by a rate of about 1.33 milliseconds per century, the researchers found.

The length of day could even reach a rate of an additional 2.62 milliseconds per century by the end of the 21st century should greenhouse gas emissions continue unabated, the study says.

While additional milliseconds added to a day every century won't significantly change day-to-day life for humans on Earth, the impacts will still be profound, mainly on timekeeping, Adhikari said.

In March, Nature released research that shows how melting polar ice is changing Earth's rotation , which affects how time is measured.

Coordinated Universal Time, or UTC, was made the international standard for time measurement in 1960. But the UTC may ultimately need to incorporate a "negative leap second" due to the planet's inconsistent rotation, spurred by climate change.

The impact of losing a second could have severe consequences on universal computing systems, Patrizia Tavella, a member of the Time Department at the International Bureau of Weights and Measures in France, wrote in an article accompanying the study.

Satellite navigation, software, telecommunication, trade, and even space travel rely on precise UTC timekeeping.

In the future, modern society may need to rely on quantum or atomic clocks for accurate timekeeping and precision navigation, Adhikari said, adding, "That enables us to do more precise navigation from Earth and space."

ABC News' Leah Sarnoff contributed to this report.