Rising sea levels are making each day slightly longer, and there's no sign it's going to stop, a new study funded in part by NASA and the Canadian government has found.
Published Monday, the paper from researchers in Canada, the United States and Switzerland studied the downstream effects of climate change on the very physics of the planet itself.
"Every single day has [a] slightly different length, because of so many factors, including … climate change," said study co-author Surendra Adhikari in an interview with CTVNews.ca.
"This is … a testament of the gravity of ongoing climate change."
The pale blue dot(-oid)
The relationship between carbon emissions and our choreography in the cosmic ballet comes down to something most Earthlings take for granted: The planet's shape.
Contrary to popular belief, Planet Earth isn't actually a perfect sphere. While the surface of land around the world is remarkably smooth on the planetary scale, what most forget to consider is water; in particular, how that water moves.
As the planet spins on its axis, the distribution of Earth's oceans is impacted by that force, and like in a centrifuge, the liquid is pushed out from the centre, especially near the equator.
As a result, Earth, its oceans and all, bulges out at the middle, creating not a sphere, but a shape scientists refer to an oblate spheroid. That oblateness, or the size of the bulge at the equator, is central to Adhikari and co.'s findings.
In short, as rising global temperatures melt the polar ice caps, more of the Earth's water supply is converted to liquid, allowing it to swell the oblate bulge along the equator, when it might previously have stayed locked away in the ice.
The swelling, in turn, changes the dynamics of how Earth spins in the first place, and invariably, the rotation decelerates.
"If you see how a figure skater controls their motion … if they have to slow down, they just extend their arms or legs, which is basically the same concept," Adhikari explained. "It has everything to do with the conservation of angular momentum."
A matter of milliseconds
Though days are measured at a standardized length of 86,400 seconds each, the actual time it takes for a point on the Earth's surface to make a full rotation is getting ever-so-slightly longer, at a rate scientists say could get more severe as the perils of climate change deepen.
Relative to the age of the Earth, the 24-hour day is fairly new, a height reached after billions of years of growth. Five-hundred million years ago, a day-night cycle might have clocked just 22 hours in total; another billion years back, and scientists estimate something closer to 19 hours.
Historically, the rate of increase attributable to climate change has been slow, hovering between 0.3 and one added daily millisecond each 100 years between 1900 and 2000. But as the industrial revolution's aftereffects have intensified, the rate has grown, clocking in at roughly 1.33 milliseconds per day, per century, since the turn of the millenium.
Adhikari and his colleagues' research found that in a high-emissions scenario, by 2100, it could surpass 2.5 milliseconds, marking the first time that humanity's influence on the Earth's spin would be greater than that of the Moon and the tides.
"Over the course of Earth’s geological evolution, tidal friction by the moon has been the dominant cause of the … increase in [length of day]," the study concludes.
"If, however, greenhouse gas emissions continue to rise, the increase in atmospheric and oceanic warming and associated ice melting will lead to a much higher rate … becoming the most important contribution to the long-term [length-of-day] variations."
Time to get a new watch?
In practical terms, a few extra milliseconds per day over the course of a human lifetime isn't the most pressing impact of climate change, though Adhikari notes that computer systems, which rely on the 86,400-second day, may require an adjustment as the intricacies of time start to pass out of sync.
It's a problem that physicists and computer scientists alike have monitored since the 1970s, long understood to require occasionally shoehorning an extra "leap second" into counts by atomic clocks to avoid widespread logistical headaches.
According to a recent study from the University of California San Diego, the impacts of climate change on the Earth's rotation might further complicate when and how those leap seconds need to be inserted; an additional piece of a vexing international puzzle.
"This will pose an unprecedented problem for computer network timing," the study reads. "Global warming is already affecting global timekeeping."
Whether the Earth's spin brings on its own mini-Y2K any time soon, Adhikari says the NASA study's findings stand as a symbol for humanity's influence on our planet, that in just a few hundred years of industrialization, the side effects may some day surpass those of the massive celestial body hanging in our night sky.
"It's really profound," he said. "In a way, we have messed up our climate system so much so that we are witnessing its impact on the very way our Earth spins … a tiny human being, who is doing some stupid things, and making this happen."
