The effects of human-caused climate change are so overwhelming that they’re playing out over time, according to a new study.
Melting polar ice caps caused by global warming are changing the speed of Earth’s rotation and increasing the length of each day, according to research published Monday in the Proceedings of the National Academy of Sciences. That trend will accelerate this century as humans continue to pump in planet-warming pollution.
While the changes are small—measured in milliseconds per day—they have a significant impact on the computing systems we rely on in our high-tech, hyperconnected world, including GPS.
It’s another sign of the enormous impact humans are having on the planet. “This is a testament to the severity 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 make up each day on Earth is determined by the Earth’s rotation rate, which is affected by a complex set of factors, including processes in the planet’s fluid core, the ongoing effects of melting massive glaciers after the last ice age, and melting polar ice caps due to climate change.
But for millennia the moon’s influence has been dominant, increasing the length of a day by a few milliseconds every century. The moon exerts a gravitational 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 caps to longer days, but new research suggests that global warming has a greater impact on time than recent studies have shown.
Benedikt Soja, an assistant professor of space geodesy at ETH University in Zurich, Switzerland, and an author of the study, said that in the past, the impact of climate change over time “was not this dramatic.”
But that could change. If Earth continues to pump out planet-warming pollution, “climate change could become the new dominant factor” and overtake the role of the moon, he told CNN.
Here’s how it works: As humans warm the Earth, glaciers and ice sheets melt, and that meltwater flows from the poles to the equator. This changes the shape of the planet — flattening it at the poles and bulging more in the middle — slowing its rotation.
The process is often likened to a spinning ice skater. When the skater pulls their arms in toward their body, they spin faster. However, if they move their arms outward, away from their body, their spin slows down.
An international team of scientists used observational data and climate models to examine a 200-year period from 1900 to 2100 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.
Sea level rise triggered by climate change caused the length of a day to change by between 0.3 and 1 millisecond in the 20th century. But over the past two decades, scientists have calculated a day length increase of 1.33 milliseconds per century, “significantly higher than at any time in the 20th century,” according to the report.
The report said the rate of change would accelerate rapidly if planet-warming pollution continued to rise, warming oceans and accelerating ice loss in Greenland and Antarctica. If the world fails to control emissions, climate change could increase the length of a day by 2.62 milliseconds by the end of the century, surpassing the natural effects of the moon.
“In 200 years, we will have changed the Earth’s climate system so much that we are witnessing the impact of that on the way the Earth spins,” Adhikari told CNN.
A few milliseconds of additional time per day may not be noticeable to humans, but it has an impact on technology.
Precise timekeeping is vital to GPS and other communications and navigation systems, which anyone with a smartphone will have. These use extremely precise atomic time, based on the frequency of specific atoms.
Starting in the late 1960s, the world began using Coordinated Universal Time (UTC) to determine time zones. UTC is based on atomic clocks but still moves at the same rate as the planet’s rotation. This means that at some point “leap seconds” must be added or subtracted to maintain alignment with the Earth’s rotation.
Some studies have also suggested a correlation between the increase in day length and the increase in earthquakes, said Mostafa Kiani Shahvandi, a geologist at ETH Zurich and study author. But the link is still speculative and much more research is needed to establish a clear link, he told CNN.
A paper on the same subject published in March concluded that as climate change gradually slows down the Earth’s rotation rate, processes in the Earth’s core may become more important and even speed it up, shortening the length of the day.
“What we did was go a little further and re-estimate these trends,” Shahvandi said. They found that any impact from the molten core outweighed the impact from 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 overlaps with his own research and is “valuable because it pushes the conclusion further and looks at multiple climate scenarios.”
The new research sheds light on “the decades-long debate about exactly how climate change will play a role in day length change,” said Jacqueline McCleary, an assistant professor of physics at Northeastern University who was not involved in the study.
He told CNN that there was now general agreement that climate change would have a “net day-lengthening effect,” but there was still uncertainty about which processes would dominate time in this century. He said the study concluded that climate change was now the second most dominant factor.
This is a sobering conclusion, said Soja of ETH Zurich. “We have to consider that we now influence the Earth’s orientation in space so much that we are dominating influences that have persisted for billions of years.”
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