When the Earth rotates, it doesn’t just spin. The Earth also wobbles on its axis like a top, and now a NASA study has clarified just what causes that wobble. The study identifies three separate causes, and one of those is our fault.
Scientifically, the Earth’s wobble is known as “polar motion.” It’s a very small effect and barely noticeable with even sensitive equipment. Over the past century, the Earth’s axis has only moved about 30 feet, and it drifts about 4 inches per year.
According to the recent NASA study, there are three factors that cause this polar motion: mantle convection, glacier rebound, and polar ice loss. Previously, scientists believed that only one of these factors—glacial rebound—was responsible for nearly all polar motion. This new approach from NASA, however, identifies two additional sources, giving scientists a better look at how our planet spins and how humans are affecting that spin.
Mantle convection, one of the newly-identified causes of polar motion, is simply the circulation of Earth’s underground magma currents and the movement of its tectonic plates. Shifting parts of the mantle create unbalanced weight which can throw off the planet’s spin.
Glacial rebound is a little more complex. Essentially, heavy weight on the Earth’s poles, such as from massive glaciers during the last ice age, can actually cause the ground underneath them to be compressed. As those glaciers gradually melted, the Earth springs back to its original position, messing up its rotation slightly in the process.
A somewhat related phenomenon is polar ice loss, which certainly played a factor at the end of the ice age but is also very relevant today. When polar ice melts, the water flows into the oceans and spreads around the globe, destabilizing the planet’s rotation. In modern times, this is a very human-caused effect, as climate change is triggering unprecedented melting at the poles.
This new research shows that not only are humans altering the environment and every habitat on Earth, we’re even affecting the spin of the planet itself. Fortunately, this is one consequence of climate change that doesn’t have a negative impact. Scientists don’t anticipate there is anything to fear from slightly more axis wobble, but this is useful information to better understand the planet we live on.
Originally posted on Popular Mechanics