It’s well known that time is of the essence when it comes to the climate crisis. Melting polar ice caps is causing our planet to spin slower, increasing the length of days at an “unprecedented” rate, according to a study published on Monday.

The paper, published in the journal Proceedings of the National Academy of Sciences, shows that water flowing from Greenland and Antarctica is causing mass to increase around the equator, co-author Surendra Adhikari of NASA’s Jet Propulsion Laboratory told AFP.

“This is similar to a skater doing a pirouette by first keeping their arms close to their body and then extending them,” added co-author Benedikt Soja from ETH Zurich. “The initially fast rotation slows down as the masses move away from the axis of rotation, and physical inertia increases.”

The Earth is often thought of as a sphere, but it would be more accurate to call it a “flattened spheroid” that bulges slightly around the equator, a bit like a satsuma.

Most importantly, its shape is constantly changing, from the daily effects of tides affecting the oceans and the Earth’s crust, to the long-term effects of the drift of tectonic plates and the sudden, violent landslides caused by earthquakes and volcanoes.

The paper relied on observational techniques such as very-long-baseline interferometry, which allows scientists to measure the difference in how long it takes for radio signals from space to reach different points on Earth and use that to infer changes in the planet’s orientation and the length of the day.

He also used the Global Positioning System, which measures the Earth’s rotation to within hundredths of a millisecond, and even looked at old eclipse records spanning millennia.

Implications for space travel

If Earth rotated more slowly, the length of a day would be a few milliseconds longer than the standard 86,400 seconds. For now, the more important cause of the slowdown is the moon’s gravitational pull on the oceans in a process called “tidal friction,” which causes a gradual slowdown of 2.40 milliseconds per century over millions of years.

But Adhikari said the new study reached a surprising conclusion: if humans continue to emit high rates of greenhouse gases, the climate-warming impact will be greater than the moon’s influence by the end of the 21st century.

Between 1900 and today, climate caused days to lengthen by about 0.8 milliseconds; in the worst-case scenario, under a high-emissions scenario, climate alone will be responsible for days lengthening by 2.2 milliseconds by 2100, compared to the same baseline. This may not seem like a big deal, and it’s certainly not something humans can grasp.

But “there are certainly many implications for space and terrestrial navigation,” Adhikari said.

Knowing the exact orientation of Earth at any given time is critical when trying to communicate with spacecraft like the Voyager probes, which are currently far outside our solar system and where even a slight deviation of a centimeter or so could cause the spacecraft to be lost 1 kilometer away by the time it reaches its destination.