Climate change is making days longer, study says

The impacts of man-made climate change are so devastating that they are actually disrupting the weather, according to new research.

Melting polar ice caused by global warming is changing the speed of Earth’s rotation and lengthening the length of each day, in a trend that is expected to accelerate over the course of this century as humans continue to release planet-warming pollution, according to the study published Monday (15) in the Proceedings of the National Academy of Sciences.

The changes are small – a matter of milliseconds a day – but in our hyper-connected, high-tech world they have a major impact on the computer systems we rely on, including GPS.

It’s yet 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 an author of the report.

The number of hours, minutes and seconds that make up each day on Earth is dictated by the speed of the Earth’s rotation, which is influenced by a complex set of factors. These include processes in the planet’s fluid core, the ongoing impact of the melting of huge glaciers after the last ice age, as well as the melting of polar ice due to climate change.

For millennia, however, the Moon’s impact has dominated, increasing the length of a day by a few milliseconds per century. The Moon exerts a force on Earth, causing the oceans to swell toward it, gradually slowing Earth’s rotation.

Scientists have previously made links between melting polar ice and longer days, but new research suggests global warming has a greater influence on the weather than recent studies have shown.

In the past, the impact of climate change on weather “has not been so dramatic,” said Benedikt Soja, study author and assistant professor of space geodesy at Switzerland’s ETH Zurich.

But that may be changing. If the world continues to produce planet-warming pollution, “climate change could become the new dominant factor,” overtaking the moon’s role, he told CNN .

Here’s how it works: As humans warm the world, glaciers and ice sheets melt, and meltwater flows from the poles toward the equator. This changes the shape of the planet—flattening it at the poles and bulging in the middle—and slowing its rotation.

The process is often compared to an ice skater. When the skater pulls their arms in toward their body, they spin faster. But if they move their arms outward, away from their body, the spin slows down.

The team of international scientists analyzed a 200-year period between 1900 and 2100, using observational data and climate models to understand how climate change affected day length in the past and to project its role in the future.

They found that the impact of climate change on day length has increased significantly.

Rising sea levels, fueled by climate change, have caused the length of a day to vary by between 0.3 and 1 millisecond in the 20th century. Over the past two decades, however, scientists have calculated an increase in day length of 1.33 milliseconds per century, “significantly greater than at any time in the 20th century,” the report said.

If planet-warming pollution continues to rise, warming oceans and accelerating ice loss in Greenland and Antarctica, the rate of change is set to accelerate, the report concluded. 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 impacts of the Moon.

“In just 200 years, we will have altered the Earth’s climate system so much that we are witnessing its impact on the very way the Earth rotates,” Adhikari told CNN .

A few milliseconds of additional time per day may be imperceptible to humans, but it has an impact on technology.

Accurate timekeeping is vital for GPS, which is found in all smartphones, as well as other communication and navigation systems. They use highly accurate atomic time, based on the frequency of certain atoms.

Starting in the late 1960s, the world began using Coordinated Universal Time (UTC) to define time zones. UTC relies on atomic clocks, but it still tracks the rotation of the planet. This means that at some point it will be necessary to add or subtract “leap seconds” to keep in line with the Earth’s rotation.

Some studies have also suggested a correlation between increasing day length and increased earthquakes, said Mostafa Kiani Shahvandi, the study’s author and a geoscientist at ETH Zurich. But the link is still speculative and much more research is needed to establish any clear link, he told CNN .

A paper on the same topic published in March concluded that while climate change was increasingly slowing Earth’s rotation, processes in the Earth’s core could be more important and actually speeding 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 influence from the molten core was offset by that 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 fits within his research, “and is valuable because it extends the result 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 changing day length.”

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 weather-affecting processes 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 consider that we are now influencing the Earth’s orientation in space so much that we are overpowering effects that have been at work for billions of years.”