Why the Earth Is Spinning Faster Than It Has in 50 Years
Why the Earth Is Spinning Faster Than It Has in 50 Years
In 2020, Earth recorded its shortest day since atomic clock measurements began in the 1960s. Scientists have been adding "leap seconds" to keep clocks aligned — but now they may need to subtract one for the first time ever.
The Record
- June 29, 2022: Shortest day ever recorded (Earth completed a rotation in 1.59 milliseconds less than 24 hours)
- July 26, 2022: Beat that record by 0.001 milliseconds
- Multiple shortest-day records broken in 2020-2025
- Earth spinning 1.3 milliseconds per day faster than it did in 2000
Why Earth's Rotation Changes
Normal slowdown:
- Earth's rotation has been gradually slowing for 4.5 billion years
- When Earth formed, a day was about 6 hours long
- Tidal friction from the Moon gradually slows rotation (1.7 milliseconds per century)
- This is why we've needed 27 leap seconds added since 1972
Recent speedup (why it's surprising):
1. Glacial isostatic adjustment:
- Since the last Ice Age ended (~11,700 years ago), land once covered by ice has been rebounding upward
- Greenland and Antarctica are still losing ice
- Less ice = less mass at poles = Earth becomes slightly more spherical
- More spherical = rotates faster (like a figure skater pulling in their arms)
2. Core dynamics:
- Earth's liquid outer core and solid inner core affect rotation
- The core's rotation rate changes over decades
- In the 1990s, the core slowed relative to the mantle (Earth's rotation slowed)
- Around 2000, the core started spinning faster again
- Current speedup may be related to core-mantle interaction changes
3. Climate change:
- Melting glaciers redistribute mass from poles to equator
- Counter-intuitively, some models show this can speed up rotation if the mass shifts in certain patterns
- Water storage changes (dams, groundwater depletion) also affect Earth's moment of inertia
4. Seismic activity:
- Large earthquakes can redistribute mass (2011 Japan earthquake shortened day by 1.8 microseconds)
- But effect is tiny and temporary
The Leap Second Problem
- 27 leap seconds added since 1972 (always positive — clocks were slower than Earth)
- If Earth continues speeding up, we may need a negative leap second — the first ever
- Scheduled for potential 2026-2029
- This is a headache for computing systems:
- Stock exchanges, airlines, and navigation systems rely on precise timing
- Many computer systems don't handle negative leap seconds
- GPS, telecommunications, and financial trading could glitch
The Impact on Technology
- GPS satellites require microsecond precision
- High-frequency trading: microsecond delays cost millions
- Telecommunications networks synchronized to atomic clocks
- Power grid synchronization
- Scientific instruments (radio telescopes, particle accelerators)
Why It Matters
Earth's rotation isn't constant — it's influenced by everything from the Moon to the core to the weather. The fact that we can measure changes of 1 millisecond is a testament to atomic clock precision. But it also means our timekeeping systems need constant adjustment.
The Future of Leap Seconds
- 2022 decision: International Bureau of Weights and Measures voted to eliminate leap seconds by 2035
- Replace with a "leap minute" applied less frequently
- This gives computing systems decades to adapt
- The change simplifies timekeeping but decouples civil time from astronomical reality
Fun Facts
- The Moon is moving away from Earth at 3.8 cm/year (laser ranging measurements)
- In ~600 million years, Earth days will be 25 hours long
- Eventually (billions of years): Earth will be tidally locked with the Moon (same side always facing)
- Mars days (sols) are 24 hours 37 minutes (almost identical to Earth!)
- Venus rotates backwards (retrograde) and takes 243 Earth days per rotation
The Takeaway
Earth's rotation speed is influenced by forces we're only beginning to understand — from deep within the core to melting ice sheets. The upcoming negative leap second will be the first in history, highlighting how our planet is changing faster than our timekeeping systems were designed to handle.