The Bizarre Reason Earth's Rotation Will Slow Down This Century

By Maddie Stone on at

If you’ve had your fill of depressing predictions for the future, here’s one that is both fascinating and as innocuous as they come: as ice caps melt, Earth’s rotation is slowing down, and that’s making our days ever so slightly longer.

That’s the conclusion of a Harvard-led study published today in Science Advances. According to the authors, shrinking glaciers are affecting both the rotation rate and axial tilt of the Earth, by redistributing all that once-frozen water around the world. As water shifts from poles toward the equator, our planet’s midsection is becoming a wee bit wider. And that extra girth is causing the Earth to brake—in the same way that a spinning skater can slow herself down by sticking her arms out.

The authors calculate that a day on Earth has already become (drumroll!) a millisecond longer over the past century—and that we could be in for another five milliseconds of day length by 2100. That’s in addition to the milliseconds of extra day length we’re slowly accruing through other natural processes, including the gravitational tug-of-war between the Earth and the Moon, and changes in the rotation rate of Earth’s core. Thankfully, we have leap seconds to straighten it all out and maybe wreak havoc on the Internet while we’re at it.

So, if you’re the kind of person who lives by the motto that every moment counts, try to make the most of those extra fractions of fractions. Do so for the 99.99% of humanity that won’t notice a damn thing.

[Read the full study at Science Advances]

Top: Blue Marble image, via Wikimedia


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