A peer-reviewed study led by geoscientists from the University of Vienna and ETH Zurich has found that climate change is measurably slowing Earth’s rotation, making days longer at a rate unprecedented in the last 3.6 million years.
Key Findings
Earth's days are currently lengthening at a rate of 1.33 milliseconds per century. The scientists state this rate is largely unparalleled over the studied period, except during specific abrupt climate events in the distant past.
To reconstruct historical day lengths, the scientists used fossilized marine organisms called benthic foraminifera. By analyzing the chemical composition of these fossils, they inferred past sea-level fluctuations. A deep-learning algorithm was then applied to this data to calculate changes in Earth's day length over nearly 4 million years.
"The mathematical derivation of day length changes is based on these inferred sea-level fluctuations." — Dr. Mostafa Kiani Shahvandi, climate scientist and geophysicist at the University of Vienna
The researchers employed a physics-informed diffusion model designed to manage uncertainties in paleoclimate data.
Prof. Benedikt Soja of ETH Zurich stated that the current rapid increase in day length indicates that the rate of modern climate change is unprecedented since at least the late Pliocene, 3.6 million years ago. He attributes the current rise primarily to human influences. A similar rate of change was observed approximately 2 million years ago, attributed by the researchers to a natural spike in carbon dioxide (CO₂) and subsequent ice sheet melting.
Mechanism of Rotation Change
The mechanism identified by the researchers involves the melting of glaciers and polar ice sheets. This melting shifts Earth's mass from the poles toward the equator—a process comparable to a figure skater extending their arms to slow their rotation. The redistribution of mass alters the planet's oblateness, or its equatorial bulge.
Prof. Soja noted that such a shift requires the redistribution of approximately 1,000 gigatonnes of mass from the poles to the oceans. Dr. Kiani Shahvandi stated that the change in Earth's rotational energy is equivalent to that of a magnitude 9.0 earthquake.
Projections and Implications
The researchers project that under a high-emissions scenario, the rate of day lengthening could accelerate to approximately 2.62 milliseconds per century over the last few decades of the 21st century. This rate, they suggest, could surpass the historical influence of the Moon's gravity on Earth's rotation by the year 2100.
While millisecond changes are not noticeable in daily life, the study indicates they can affect ultraprecise timing systems essential for Global Positioning System (GPS) navigation and spacecraft guidance. The research also links this mass redistribution to broader environmental impacts, including sea-level rise.
Future research will examine the effects of groundwater depletion and changes in the water cycle on Earth's rotation.