The Moon is making your days longer, and most people have no idea

You probably haven’t noticed, but your days are getting longer. Not in the “I wish this workday would end” sense, but literally. The Earth is slowing down, and the Moon is applying the brakes. The numbers show it. Scientists have confirmed it. Here's the kicker: our own carbon footprint is now part of the equation.

The Moon is drifting away, and taking our time with it
Each year, the Moon moves about 1.5 inches (3.8 cm) farther away from Earth. That sounds like a little change, but that slow drift has had a huge impact on the length of our days over billions of years. In the early days of Earth, a full day was less than 13 hours in length. Now it’s 24, and still climbing.

The reason boils down to tidal friction. As the Earth rotates, the Moon’s gravity pulls on the oceans, creating the familiar high and low tides along the coasts of places like Miami or Cape Cod. But there’s a delicate tug of war going on. The Earth spins faster than the Moon orbits, so the tidal bulge in the ocean gets pulled a little ahead of the Moon. That misalignment acts as a brake on the spin of our planet, transferring energy to the Moon and nudging it into a slightly higher orbit year after year.

A peer-reviewed study posted on arXiv, which analyzed centuries of lunar laser ranging data and eclipse records, found that Earth’s day has been getting longer by approximately 1.09 milliseconds per century since the late 1600s. Some estimates, based on ancient eclipse observations, put it even higher, at 1.78 milliseconds per century. It may seem like nothing, but, compounded over the 4.5 billion years of Earth’s history, that is everything.

Why your phone clock might eventually need fixing
Here is where things start to look surprisingly modern. The same climate change that’s producing record-breaking summers across the American South and melting glaciers in Alaska is now measurably affecting how fast the Earth spins. All that water is moving towards the planet's equator, making Earth's waistline a little bigger as ice sheets in Greenland and Antarctica melt.

In a landmark study published in Nature, geophysicist Duncan Agnew of the Scripps Institution of Oceanography at UC San Diego found that melting polar ice is slowing Earth’s rotation just enough to affect global timekeeping. Atomic clocks, the same systems that synchronize your smartphone, GPS and financial transactions, are calibrated to Earth’s rotation. The planet has actually been spinning a little faster in recent decades due to changes in its liquid outer core, and for the first time in history, scientists were preparing to wipe a “negative leap second” from global clocks. Agnew's research indicated that ice melt from climate change has delayed that unprecedented step by about three years, putting it around 2028.

"Things are happening that are unprecedented," Agnew said. It's staggering to think that human activity could, by any measure, measurably change the rotation speed of an entire planet.

The Atlantic Ocean is secretly supercharging the tides
There’s another crazy twist to the story. The Moon's gravitational pull on Earth is not constant; it varies with the shape of the oceans. We're in a very high-drag period right now, and part of that is the North Atlantic.

The present shape and size of the North Atlantic basin create a natural resonance; the water sloshes back and forth with a frequency that almost matches the tides. The net effect is that tides today are significantly bigger than they would be otherwise. It’s like giving a kid a push on a swing at the right moment; the timing magnifies the motion. This resonance will die away and then recur in different forms as the continents drift, for millions of years to come.

What this means for the rest of us
None of this will impact your morning commute. Changes to Earth’s rotation are so slow that they are measured in milliseconds per century. But zoom out far enough, and the picture is humbling. The Moon shaped the very rhythm of life on this planet, the length of our days, the force of our tides, perhaps even the origin of life itself.

The Moon has been slowing the Earth down for 4.5 billion years. It took humanity a few decades to get in on it.