New research shows that the impacts of human-caused climate change are so severe they are throwing time into disarray.
Melting polar ice due to global warming is changing the speed at which the Earth rotates and lengthening the length of the day. That trend will only accelerate over the course of this century as humans release more pollution that warms the planet, according to a study published Monday in the Proceedings of the National Academy of Sciences.
The changes are small - a matter of milliseconds per day - but in our high-tech, hyper-connected world, they have a significant impact on the computing systems we have come to rely on, including GPS.
It's another sign of the enormous impact humans are having on the planet. "This is a testament to the seriousness of ongoing climate change," said Surendra Adhikari, a geophysicist at NASA's Jet Propulsion Laboratory and one of the report's authors.
The number of hours, minutes, and seconds that each day lasts on Earth is determined by the speed of the Earth's rotation, which is influenced by a complex web of factors. These include processes in the planet's liquid core, the ongoing impact of melting vast glaciers after the last ice age, and the melting of polar ice due to climate change.
For millennia, however, the moon has dominated, increasing the length of a day by a few milliseconds each century. The moon exerts a pull on the Earth, causing the oceans to bulge toward it and gradually slowing the Earth's rotation.
Scientists have previously linked melting polar ice to longer days, but new research shows that global warming has a greater impact on time than recent studies have shown.
In the past, the impact of climate change on time was "not so dramatic," said Benedikt Soja, study author and assistant professor of space geodesy at Switzerland's ETH Zurich.
But that could change. If the world continues to spew planet-warming pollution, "climate change could become the new dominant force," overtaking the moon, he told CNN.
Here's how it works: As humans warm the world, glaciers and ice caps melt, and that meltwater flows from the poles toward the equator. This changes the shape of the planet - flattening it at the poles and bulging it in the middle - and slows its rotation.
The process is often compared to a spinning ice skater. When the skater pulls his arms toward his body, he spins faster. But when he moves his arms outward, away from his body, he spins slower.
The team of international scientists looked at a 200-year period, between 1900 and 2100, using observational data and climate models to understand how climate change has affected day length in the past and to predict its role in the future.
They found that the impact of climate change on day length has increased significantly.
Climate change-driven sea level rise caused the length of a day to vary between 0.3 and 1 millisecond during the 20th century. Over the past two decades, however, scientists calculated an increase in day length of 1.33 milliseconds per century, "significantly higher than at any time during the 20th century," the report said.
If planet-warming pollution continues to rise, warming the oceans and accelerating ice loss in Greenland and Antarctica, the rate of change will accelerate dramatically, the report found. If the world fails to curb emissions, climate change could lengthen the length of a day by 2.62 milliseconds by the end of the century - outstripping the natural impact of the moon.
"In just 200 years, we will have changed the Earth's climate system so much that we are now witnessing its impact on the way the Earth spins," Adhikari told CNN.
A few extra milliseconds of time per day may not be noticeable to humans, but it does have an impact on technology.
Accurate timekeeping is essential for GPS, which everyone with a smartphone will have, and also for other communication and navigation systems. These use very precise atomic time, based on the frequency of certain atoms.
Starting in the late 1960s, the world began using Coordinated Universal Time (UTC) to set time zones. UTC is based on atomic clocks, but it still keeps pace with the rotation of the planet. This means that at some point, "leap seconds" must be added or subtracted to keep in line with the Earth's rotation.
Some studies have also suggested a correlation between an increase in day length and an increase in earthquakes, said Mostafa Kiani Shahvandi, an author of the study and a geoscientist at ETH Zurich. But the connection remains speculative and much more research needs to be done to establish a clear link, he told CNN.
A paper on the same topic published in March concluded that climate change is increasingly slowing the Earth's rotation, but that processes in the Earth's core may be more important and may even speed up the rotation, making the day shorter.
"What we've done is go a little bit further and re-estimate these trends," Shahvandi said. They found that the influence of the molten core was dwarfed by that of climate change.
Duncan Agnew, a professor of geophysics at the University of California San Diego and an author of the March study, said the new study still aligns with his research, "and is valuable because it extends the results further into the future and looks at more than one climate scenario."
Jacqueline McCleary, an assistant professor of physics at Northeastern University who was not involved in the study, said the new research helps inform "a decades-long debate about exactly what role climate change will play in the changing length of the day."
While there is now general agreement that climate change will have a "net effect of lengthening the day," she told CNN, there is still uncertainty about which processes that affect time will dominate this century. This study finds that climate change is now the second most dominant factor, she said.
It's a sobering conclusion, said Soja of ETH Zurich. "We have to remember that we now have so much influence on the orientation of the Earth in space that we are dominating effects that have been going on for billions of years."
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