Days are getting slightly longer — and it's due to climate change

Climate change is causing widespread global impacts, but now scientists are finding that it's altering the very planet itself. Earth's rotation is slowing down, extending the length of a day ever so slightly.

As temperatures rise, massive amounts of ice are melting from Greenland and Antarctica. That meltwater flows into the oceans, redistributing the mass closer to the equator. When the planet is thicker around the middle, its daily rotation takes a bit longer.

"It's a testament to the gravity of climate change, in a sense," says Surendra Adhikari of NASA's Jet Propulsion Laboratory, who's an author of the study, just released in the Proceedings of the National Academy of Sciences.

The change is tiny, measured in milliseconds, which is one-thousandth of a second. While that may not be noticeable at the human scale, it can affect computer systems that control financial transactions, GPS navigation and the power grid.

"Everyday life is not sensitive at the one-second level," says Judah Levine, a physicist at the National Institute of Standards and Technology. "Technology may be, and people use technology and they don't quite realize the sensitivity."

Why days aren't exactly 24 hours

A clock measures a day as 24 hours on the nose, but on a highly dynamic planet like the Earth, exactly 24 hours isn't entirely true.

"If you want to be more precise, the length of day changes every day basically," Adhikari says. "Today is maybe slightly longer or shorter than yesterday."

A broad range of forces is continually acting on the planet's rotation. The pull of the moon is steadily slowing the Earth's turn by a few milliseconds per century. The rotation of the solid iron core at the planet's center can also fluctuate slightly, causing the outer layer of the Earth to speed up or slow down. Even the movement of the Earth's crust, now slowly rebounding after being covered in ice during the last ice age, affects the rotation.

Now, rapidly melting ice at the poles is shifting the planet's mass, raising the level of the ocean at the equator. Since 1993, global sea levels have risen by 4 inches on average and will likely rise by 2 feet or more by the end of the century, depending on how much humans curb the climate pollution generated from burning fossil fuels.

As a result, the Earth is now slightly wider at its center, which slows its rotation much like a spinning figure skater. Skaters with their arms extended spin slower than those with their arms pulled close to their bodies. Adhikari and his colleagues found that melting ice has slowed the planet's rotation by 1.33 milliseconds per century since 2000. If emissions remain high, that will increase to 2.62 milliseconds by the end of the century.

Adding leap seconds

While that amount of time doesn't mean much to everyday life, it can pose problems for highly connected computer networks that society relies on. GPS and space navigation, as well as financial institutions and cellphone networks, all rely on being synchronized by time. Adjusting their clocks can be a major technological headache.

Since 1972, 27 leap seconds have been added to world time to account for the Earth's slowing rotation. The problem arises because timekeeping is controlled by atomic clocks now, not the spin of the Earth. But to keep that time matched up with the planet's rotation, seconds have had to be added. Tech companies have since rallied against the adjustments, saying they can cause networks to collapse.

Now, experts say climate change will need to be factored into those decisions. But melting ice has far more serious consequences for the planet than time. Millions of people face losing their homes as polar ice melts and sea levels keep rising.

"If you live in a low-lying coastal area, then you're not concerned about leap seconds," Levine says. "That's the least of your worries. You have much more serious problems to deal with."