Recent findings indicate that our days are growing longer, as human-induced climate change spurs the melting of glaciers and ice sheets. This redistribution of planetary mass is causing the Earth’s rotation to slow down.
Consequently, our days are currently stretching out by 1.33 milliseconds per century—a rate scarcely seen over millions of years.
Should this pattern persist, the climatic impact on daylight duration could overshadow the influence of the Moon by the century’s close, marking a significant, albeit unwelcome, human footprint.
These observations are detailed in a recent paper authored by geologists from the University of Vienna and ETH Zurich, published in the Journal of Geophysical Research: Solid Earth.
In this pioneering study, the scientists examined fossilized marine organisms known as foraminifera and developed a deep learning algorithm to gauge sea-level fluctuations, thereby calculating shifts in Earth’s day length over nearly 4 million years.
“By examining the chemical makeup of fossil foraminifera, we can infer past sea levels and subsequently compute the corresponding changes in the length of a day through mathematical modeling,” explains Mostafa Kiani Shahvandhi from the University of Vienna.
Foraminifera are particularly valuable due to their potent forensic potential. These single-celled organisms construct shells (often quite elaborate) around themselves using minerals dissolved in seawater.
As they existed for over 500 million years and thrived wherever oceans were present, their remains serve as a kind of ancient climate proxy.
The researchers validated their findings by applying a newly developed, physics-based diffusion model—a probabilistic deep learning technique designed to account for inherent uncertainties in paleoclimatic data.
“This model accurately mirrors the physical mechanisms driving sea-level change while remaining robust against the considerable uncertainties embedded within paleoclimatic records,” states Kiani Shahvandhi.
Overall, this research synthesizes and builds upon the team’s prior work describing how the melting of global glaciers and polar ice caps shifts Earth’s mass from the poles toward the equator.
This movement alters our planet’s oblateness, or how bulging it is at its center—a characteristic shared by many of its inhabitants. The result is a mass redistribution, akin to a figure skater slowing rotation by extending their arms outwards.
Specifically, the new study aimed to quantify how the current lengthening of the day compares to past eras. The analysis reveals that such an effect has been absent for millennia, except during a few abrupt climatic shifts when ice sheets either grew or melted during rapid planetary cooling or warming events.
“This rapid lengthening of the day suggests that the current pace of climatic change is unparalleled, at least since the Late Pliocene, which was 3.6 million years ago,” notes study co-author Professor Dr. Bendoct Soja from ETH Zurich. “Therefore, the present swift increase in day length can be attributed primarily to human influence.”
While 1.33 milliseconds seems minuscule compared to the remaining 86,400 seconds in any given day, this shift is more than enough to disrupt communication technologies and space navigation systems.
Furthermore, more pessimistic projections suggest this trend could accelerate, causing a change of approximately 2.62 milliseconds per century during the final decades of the 21st century, which would surpass the Moon’s influence on Earth’s day length.
“Only once—about 2 million years ago—were the rates of day-length change nearly comparable, but never before, and never since, has the planetary ‘figure skater’ extended its arms and raised sea levels as quickly as it has between 2000 and 2020,” says Kiani Shahvandhi.
From a purely scientific, detached perspective, the capacity to alter the rotational mechanics of an entire planet stands as a testament to human capability.
Unfortunately, this overall exerts a detrimental effect on our planet and, moreover, results in a (minor) extension of the workday.
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