Human-caused climate change is having profound impacts on the planet, including altering the length of a day, according to recent research. This effect is due to polar ice melt caused by global warming, which changes Earth’s rotation speed, increasing each day’s length. This trend is expected to accelerate throughout the century as humans continue to emit planet-heating pollution, according to a study published in the Proceedings of the National Academy of Sciences.
The changes in day length are minute, amounting to milliseconds each day, but they have significant implications for the high-tech, interconnected systems we depend on, such as GPS. “This is a testament to the gravity of ongoing climate change,” said Surendra Adhikari, a geophysicist at NASA’s Jet Propulsion Laboratory and one of the report’s authors.
The length of a day on Earth is determined by the speed of Earth’s rotation, influenced by numerous factors including processes in the planet’s fluid core, the melting of massive glaciers since the last ice age, and the current melting of polar ice due to climate change. Historically, the moon has been the primary factor, gradually lengthening the day by a few milliseconds per century by exerting a gravitational pull that causes ocean bulges, slowing Earth’s rotation.
Previous research has linked polar ice melt to longer days, but this new study indicates that global warming is a more significant factor than previously thought. “In the past, the impact of climate change on time has not been so dramatic,” said Benedikt Soja, a study author and assistant professor of space geodesy at ETH Zurich. However, he notes that this is changing, with climate change potentially becoming the dominant factor over the moon if current pollution levels persist.
As humans warm the planet, glaciers and ice sheets melt, and the resulting meltwater flows from the poles toward the equator. This redistribution of mass changes Earth’s shape, flattening it at the poles and causing it to bulge at the equator, which in turn slows its rotation. This process is akin to a spinning ice skater extending their arms to slow their spin.
The international team of scientists examined a 200-year period from 1900 to 2100, using observational data and climate models to assess how climate change has influenced day length in the past and to predict future impacts. They found that climate change’s impact on day length has significantly increased. In the 20th century, sea level rise caused by climate change altered the length of a day by 0.3 to 1 millisecond. In the past two decades, the increase has been 1.33 milliseconds per century, a rate significantly higher than any time in the previous century.
If emissions continue to rise, warming the oceans and accelerating ice loss in Greenland and Antarctica, the rate of change is expected to increase dramatically. The report predicts that if emissions are not curbed, climate change could lengthen the day by 2.62 milliseconds by the end of the century, surpassing the natural effects of the moon.
“In barely 200 years, we will have altered the Earth’s climate system so much that we are witnessing its impact on the very way Earth spins,” Adhikari told CNN. While a few extra milliseconds per day might go unnoticed by humans, it affects technology. Accurate timekeeping is crucial for GPS and other communication and navigation systems, which rely on highly precise atomic time.
Since the late 1960s, the world has used coordinated universal time (UTC) to set time zones, relying on atomic clocks but keeping pace with Earth’s rotation. This means “leap seconds” must occasionally be added or subtracted to maintain alignment with Earth’s rotation.
Some studies have suggested a link between increased day length and an uptick in earthquakes, according to Mostafa Kiani Shahvandi, a study author and geoscientist at ETH Zurich. However, this connection remains speculative, requiring much more research to establish any definitive link.
A paper on the same topic published in March found that while climate change was increasingly slowing Earth’s rotation, processes in Earth’s core could counteract this by speeding it up, thus shortening day length. “What we have done is to go a little bit further and re-estimate these trends,” said Shahvandi, noting that their study found the influence of the molten core was outweighed by that of climate change.
Duncan Agnew, a professor of geophysics at the University of California San Diego and author of the March study, stated that the new study aligns with his research, extending its results further into the future and considering more climate scenarios. Jacqueline McCleary, an assistant professor of physics at Northeastern University not involved in the study, said the research contributes to a longstanding debate about the role of climate change in altering day length.
While there is now general consensus that climate change will have a “net lengthening effect on the day,” McCleary told CNN, there has been uncertainty about which processes will dominate this century. This study concludes that climate change is now the second most dominant factor. “We have to consider that we are now influencing Earth’s orientation in space so much that we are dominating effects that have been in action for billions of years,” said Soja.
The profound impacts of human activity on the planet are increasingly evident, not only in the environment but in the fundamental mechanisms of Earth’s rotation. This research underscores the far-reaching consequences of climate change, emphasizing the urgent need to address the root causes of global warming.