Global climate change is causing Earth's rotation to slow down, leading to a measurable lengthening of our days. Since the year 2000, days have become longer by approximately 1.33 milliseconds per century, a rate scientists say is unprecedented over the last 3.6 million years. This significant shift results primarily from the melting of polar ice sheets and mountain glaciers, which redistributes mass across the planet. Researchers from institutions including the University of Vienna, ETH Zurich, and the Scripps Institution of Oceanography have highlighted how human-driven climate change is now a major force altering Earth's fundamental dynamics.[baug+14]
How Melting Ice Changes Earth's Spin
The mechanism behind this slowdown is a fundamental principle of physics, similar to a figure skater extending their arms during a spin. As massive ice sheets in Greenland and Antarctica melt, the water flows from the poles towards the Earth's equator. This movement of mass away from the planet's axis of rotation causes Earth to spin more slowly. Mostafa Kiani Shahvandi, a postdoctoral researcher with the University of Vienna's Department of Meteorology and Geophysics, explained this phenomenon. "In our earlier work, we showed that the accelerated melting of polar ice sheets and mountain glaciers in the 21st century is raising sea levels, which slows Earth's rotation and therefore lengthens the day — similar to a figure skater who spins more slowly once they stretch their arms, and more rapidly once they keep their hands close to their body," Kiani Shahvandi said. This redistribution of water across the globe effectively makes the Earth's "waistline" thicker, thus slowing its rotational speed.[smithsonianmag+22]
This climate-driven deceleration is occurring even as another powerful force within Earth's interior works to speed up its rotation. The churning of Earth's liquid outer core has, in recent years, caused the solid part of the planet to spin slightly faster. This internal acceleration would typically shorten the length of a day. However, the slowing effect from melting ice is currently strong enough to counteract this, leading to an overall lengthening of days. Scientists are now observing a complex interplay between these different geological and climatic factors influencing Earth's precise rotational speed.[smithsonianmag+10]
Impact on Global Timekeeping
These subtle changes in Earth's rotation have tangible consequences for global timekeeping, particularly for Coordinated Universal Time (UTC), the international standard used to set all time zones. To keep atomic clocks, which define UTC, synchronized with Earth's slightly irregular astronomical time, "leap seconds" are occasionally added. Since 1972, 27 leap seconds have been added to account for the Earth's long-term slowing trend. However, the recent acceleration from the Earth's core had prompted discussions about the unprecedented need for a "negative leap second," where a second would be removed from the clock.[climateadaptationplatform+9]
The slowing effect from climate change is now delaying this potential need for a negative leap second. Without the accelerated ice melt, experts predicted that a negative leap second might have been required as early as 2026. Thanks to the ice melt, this adjustment may now be postponed until around 2029. Duncan Agnew, a geophysicist at the Scripps Institution of Oceanography, highlighted this unexpected consequence. "If polar ice melting had not recently accelerated, this problem would occur 3 years earlier," Agnew noted in a study. Removing a second from global timekeeping systems could create significant disruptions for computer networks, financial markets, and satellite navigation systems that rely on precise synchronization. International timekeepers are already planning to phase out leap second adjustments by 2035 to mitigate these challenges.[climateadaptationplatform+12]
Unprecedented Pace in Earth's History
The current rate of day lengthening is particularly striking when viewed through Earth's geological history. Researchers from the University of Vienna and ETH Zurich meticulously reconstructed ancient day-length fluctuations over the past 3.6 million years. They achieved this by studying the fossil remains of tiny, single-celled marine organisms known as benthic foraminifera. By analyzing the chemical composition of these fossils, scientists could infer past sea-level changes, which are directly linked to Earth's rotational speed.[baug+9]
Their findings revealed that while Earth's rotation has naturally varied throughout history due to factors like the growth and melting of continental ice sheets during ice ages, the present rate of slowdown is exceptional. "Only one time—around 2 million years ago—the rate of change in length of day was nearly comparable, but never before or after that has the planetary 'figure skater' raised her arms and sea levels so quickly as in 2000 to 2020," Kiani Shahvandi stated. Thisstrong correlation confirms that the current rapid increase in day length is primarily a consequence of human-induced climate change, making it a truly modern phenomenon in geological terms.[eurekalert+3]
The Bigger Picture
While the Moon's gravitational pull has been the primary driver of Earth's long-term rotational slowdown over billions of years, climate change is now adding a significant and accelerating factor. The melting of ice and the subsequent redistribution of water represent a substantial shift in mass that is measurably altering how our planet spins. Thisresearch underscores the pervasive and often unexpected ways in which human activities are impacting fundamental Earth systems. The ongoing studies continue to refine models that connect climate processes to Earth's rotational behavior, providing crucial insights into both planetary dynamics and long-term climate trends.[jpl+9]
