Scientists from the University of Vienna and ETH Zurich reveal that Earth’s days are lengthening at an unprecedented rate of 1.33 milliseconds per century, the fastest change in 3.6 million years. Climate change drives this shift as melting polar ice and glaciers redistribute water toward the equator, slowing the planet’s rotation.
How Climate Change Slows Earth’s Spin
Melting ice sheets release water that flows equatorward, increasing Earth’s moment of inertia much like a figure skater extending arms to slow a spin. This follows the law of conservation of angular momentum: mass farther from the rotation axis reduces spin speed, extending day length.
Professor Benedikt Soja, co-author from the University of Vienna, states: “While natural cycles caused variations in the past, the current rate of change, due to human impact, is so rapid that it stands out in climate history. 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.”
Unprecedented in Geological History
Analysis of fossilized benthic foraminifera shells provides chemical traces of ancient sea levels over 3.6 million years. A physics-informed machine learning model converted these into day length changes, confirming no prior period matched today’s acceleration.
The most rapid natural shift occurred about 2 million years ago amid high CO2 levels and ice-free Greenland, yet it lagged behind the last 25 years’ human-induced changes.
Impacts on Modern Technology
These millisecond shifts evade human perception but threaten precise systems. Professor Soja notes: “Even though the changes are only milliseconds, they can disrupt systems that require extremely precise time keeping. This includes space navigation, GPS and satellite navigation systems, and synchronisation of atomic clocks.”
Projections indicate climate effects will surpass the moon’s gravitational influence by the 2080s, potentially adding 2.62 milliseconds per century to day length by century’s end.
