The length of a day on Earth is gradually increasing, and scientists say human-driven climate change is playing a significant role in this unexpected phenomenon. According to new research conducted by scientists from the University of Vienna and ETH Zurich, the planet’s rotation is slowing at a pace rarely observed in geological history.
The findings, published on 13 March, indicate that Earth’s days are currently becoming longer by about 1.33 milliseconds per century. While the change may appear extremely small, researchers emphasise that it represents the fastest shift detected over the past 3.6 million years.
Scientists attribute this trend primarily to the rapid melting of polar ice caused by global warming. As glaciers and ice sheets in the Arctic and Antarctic regions melt, vast quantities of water flow towards the oceans and gradually redistribute around the equatorial regions. This process alters the distribution of the planet’s mass and slightly changes the way Earth spins.
Researchers explain the effect through an analogy with a figure skater. When a skater spins with arms close to the body, the rotation is faster. However, when the arms extend outward, the spin slows down because the mass moves further away from the axis of rotation. Earth behaves in a similar way: as water from melting ice spreads away from the planet’s rotational axis, the rotation gradually slows.
Professor Benedikt Soja of the University of Vienna noted that natural variations in Earth’s rotation have occurred many times in the past. However, the rate of change observed in recent decades stands out. He explained that between 2000 and 2020 the shift in rotational speed was unusually rapid compared with historical records.
Although a millisecond may seem insignificant to most people, even such tiny variations can have meaningful consequences for modern technology. Many advanced systems rely on extremely precise time measurements. For example, spacecraft navigation requires highly accurate timing calculations in order to determine trajectories across vast distances in space. Satellite navigation networks, which guide aircraft, ships and smartphones, also depend on exact time signals.
Another area potentially affected is the global network of atomic clocks used to maintain international time standards. These clocks are calibrated against Earth’s rotation, and any variation in rotational speed can complicate the coordination of global timekeeping systems.
To understand how Earth’s rotation has evolved over millions of years, scientists examined fossils of an ancient single-celled marine organism known as benthic foraminifera. The chemical composition of the shells of these tiny organisms preserves clues about past ocean conditions and sea-level changes. By analysing these fossils, researchers reconstructed ancient environmental conditions and incorporated the data into a physics-informed machine learning model to estimate day length across several million years.
Their analysis revealed that around two million years ago, when Greenland was largely ice-free and covered with forests, the Earth’s rotation also slowed slightly. However, the pace of change observed during the last twenty-five years appears far more rapid than earlier natural variations, largely due to the acceleration of greenhouse gas emissions and global warming.
The research also suggests that climate change could soon become a dominant factor affecting the length of Earth’s day, potentially surpassing natural influences such as the gravitational interaction with the Moon.
The table below summarises key findings from the study.
| Period or Scenario | Estimated Change in Day Length | Primary Cause |
|---|---|---|
| Past natural variations (millions of years) | Small, gradual fluctuations | Natural climate cycles and ocean changes |
| Current trend | About 1.33 milliseconds per century | Polar ice melt and redistribution of mass |
| Projected late 21st century | Up to 2.62 milliseconds per century | Intensifying climate change |
| Historical comparison (around two million years ago) | Noticeable but slower changes | Reduced polar ice and natural climate shifts |
Scientists warn that by the 2080s climate-driven effects on Earth’s rotation could become stronger than the long-standing influence of lunar gravitational forces. If greenhouse gas emissions continue to increase and polar ice continues to melt rapidly, the length of Earth’s day may continue to grow at an accelerating rate.
Although the difference may remain imperceptible in daily life, the implications for scientific measurement, global positioning systems and space exploration could become increasingly significant in the decades ahead.