Melting Ice Slows Rotation

It is well known that climate change drives rising sea levels and intensifies weather patterns. However, recent geophysics research has revealed a startling new consequence of global warming: it is physically altering the rotation of our planet. The melting of polar ice sheets is redistributing enough mass to slow down Earth’s spin, a change significant enough to confuse the precise timekeeping systems that run our digital world.

The Science: How Water Weight Changes Planetary Spin

To understand how melting ice affects rotation, you have to look at the distribution of weight on the planet. For thousands of years, massive ice sheets have sat atop Greenland and Antarctica. As global temperatures rise, this ice melts into water and flows into the ocean. Because these landmasses are located at the poles, the water effectively moves from the top and bottom of the Earth toward the equator.

This creates a physical effect similar to a figure skater performing a spin. When a skater pulls their arms in tight, they spin faster. When they extend their arms outward, their rotation slows down. By moving mass (water) from the poles to the equator, Earth is essentially extending its arms. It becomes slightly wider around the middle, which increases its moment of inertia and slows its rotation speed.

A study published in the journal Nature by Duncan Agnew, a geophysicist at the Scripps Institution of Oceanography, quantified this effect. Agnew found that the rate of melt in Greenland and Antarctica has been significant enough to counteract other geophysical forces that typically speed up the planet’s spin.

The Conflict: Earth's Core vs. Surface Melt

The slowing caused by melting ice is happening against the backdrop of a complicated planetary tug-of-war. While the surface is slowing down due to ice melt, Earth’s liquid outer core has actually been causing the planet to spin faster for decades.

Since 1972, timekeepers at the International Earth Rotation and Reference Systems Service (IERS) have added “leap seconds” to Coordinated Universal Time (UTC). This was done because Earth’s rotation was historically slightly slower than the atomic clocks we use to measure precise time. However, starting around 2016, the acceleration caused by the liquid core became the dominant force. The Earth began spinning so fast that scientists predicted we would soon need a “negative leap second.”

A negative leap second involves skipping a second to align atomic time with the Earth’s position. This has never been done in history. Agnew’s research highlights that the braking effect of melting ice is so powerful that it has delayed this unprecedented event. Without the ice melt, we likely would have needed a negative leap second by 2026. Because of the mass redistribution from climate change, that deadline has likely been pushed back to 2029.

Why a Negative Leap Second is Dangerous

While a delay from 2026 to 2029 sounds minor, the implications for technology are massive. The global infrastructure of the internet, financial markets, and GPS relies on Unix time and Network Time Protocol (NTP). These systems are programmed to handle adding a second, but very few are tested for subtracting one.

Major tech companies like Google, Amazon, and Meta have expressed concern over the negative leap second. Their servers rely on time strictly increasing. If a second is deleted, computer systems might see the same timestamp twice or perceive time as moving backward. This can cause:

• Database crashes: Transaction logs that rely on sequential timestamps could corrupt.
• Financial errors: High-frequency trading algorithms that operate in microseconds could falter, causing potential market instability.
• Navigation failures: GPS requires precise time synchronization to calculate location; time errors lead to location errors.

The melting ice has inadvertently bought computer scientists three extra years to solve a problem that could otherwise crash critical digital infrastructure.

Quantifying the Melt

The scale of mass redistribution required to slow a planet is difficult to visualize. Data from NASA and the GRACE-FO (Gravity Recovery and Climate Experiment Follow-On) satellites provide concrete numbers. Greenland alone has been losing an average of 279 billion tons of ice per year since 1993. Antarctica is losing roughly 148 billion tons annually.

This is not just water filling a tub; it is a shift in the planet’s gravity field. This massive transfer of weight flattens the Earth slightly less at the poles and bulges it more at the equator. This shift is substantial enough that it has overtaken the influence of the Moon’s tidal friction in some calculations regarding day length.

Implications for Future Timekeeping

This phenomenon serves as a stark indicator that human activity has reached a geologic scale. We are not just altering the atmosphere; we are altering the physics of the planet’s motion.

The International Bureau of Weights and Measures (BIPM), which governs time standards, is already discussing eliminating leap seconds entirely by 2035 to avoid these technical hazards. They propose letting the difference between atomic time and Earth’s rotation grow larger than one second before making adjustments. The slowing effect of climate change validates this approach, as it proves that Earth’s rotation is too erratic and influenced by too many variables to serve as a strict anchor for digital timekeeping.

Frequently Asked Questions

Will days get noticeably longer for humans? No. The change in rotation is measured in milliseconds. You will not notice a longer day in your daily life. However, these milliseconds add up over years, which creates the discrepancy between atomic clocks and the Earth’s actual position.

Has the Earth’s rotation always been constant? No. Over millions of years, the Earth has generally been slowing down due to tidal friction caused by the Moon’s gravity. However, in the short term (decades), the speed fluctuates due to movements in the liquid core and atmospheric winds.

Who decides when to add or remove a second? The International Earth Rotation and Reference Systems Service (IERS) in Paris monitors the Earth’s rotation. They announce when a leap second is required, usually giving six months’ notice to technology companies and governments.

What is the difference between atomic time and solar time? Atomic time (TAI) is measured by the vibration of cesium atoms and is incredibly stable. Solar time (UT1) is based on the actual rotation of the Earth. Coordinated Universal Time (UTC), which serves as the world’s civil time, attempts to keep these two within 0.9 seconds of each other.