Climate Change Is Making Earth Wobble More As It Spins
The Earth, as many of us are (hopefully) already aware, rotates on its own axis, and that rotation serves as the basis for our 24-hour day. However, the Earth doesn't exactly experience what can be described as a smooth rotation, as it wobbles as it spins. Scientists with NASA have discovered new causes of this spin-axis drift, dubbed "polar motion," and it seems that climate change is behind one of the three.
Originally, scientists thought that there was only one reason for polar motion: glacial rebound, which is what happens when Earth's surface begins to reclaim its original shape after being depressed by glacial coverage during the last ice age. That's still considered to be a factor in polar motion, but scientists have identified two new processes that affect it as well.
In a new write-up over on NASA's website, scientists with the agency's Jet Propulsion Laboratory explain that the second process that could effect polar motion is mantle convection. Simply put, this is the circulation of material in Earth's mantle, fueled by heat from the planet's core. So far, we have two causes of polar motion that humans have little influence over.
The third cause of polar movement might be our own doing, though. Scientists have found that the redistribution of mass as the planet's cryosphere melts has had an affect on polar movement as well. Ice melt is obviously a concern all around the planet, but Greenland specifically is in a location that means its melting ice sheets have a pretty dramatic effect on polar motion.
In the image above, the effect all three processes have on polar motion is depicted by the solid pink line, with the influence of mantle convection, postglacial rebound, and Greenland ice loss depicted by the red, yellow, and blue dotted lines, respectively.
"There is a geometrical effect that if you have a mass that is 45 degrees from the North Pole — which Greenland is — or from the South Pole (like Patagonian glaciers), it will have a bigger impact on shifting Earth's spin axis than a mass that is right near the Pole," said NASA JPL's Eric Ivins, who is co-author of the paper "What drives 20th century polar motion?" published in Earth and Planetary Science Letters.
By discovering these three distinct causes of polar motion, scientists will now be able to gauge how much of an effect climate change, and therefore humanity, has on Earth's wobble. The idea, of course, is that as Greenland's ice continues to melt, polar motion will grow in intensity, so we can add that to the endless list of reasons to address the problem of climate change.