There have been many attempts, over the last few decades, to find ways to talk about global warming that convey the immense scale of what we’re doing to our planet, but one of the more effective ones, in my opinion, is being able to point to the fact that through ice melt, we’ve actually moved enough mass to shift the axis around which our planet spins. It’s not something that affects our lives, but it does convey the message that what’s happening really is planet-sized.
Unfortunately, it turns out that’s not the only way in which we’ve been messing with Earth’s axis. As you may be aware, humanity has something of a problem with unsustainable water usage. Even without global warming, we’re pulling it out of the ground far faster than it’s being replenished, and polluting a lot of it in the process. How much water have we been pumping? Enough to shift the planet:
By pumping water out of the ground and moving it elsewhere, humans have shifted such a large mass of water that the Earth tilted nearly 80 centimeters (31.5 inches) east between 1993 and 2010 alone, according to a new study published in Geophysical Research Letters, AGU’s journal for short-format, high-impact research with implications spanning the Earth and space sciences.
Based on climate models, scientists previously estimated humans pumped 2,150 gigatons of groundwater, equivalent to more than 6 millimeters (0.24 inches) of sea level rise, from 1993 to 2010. But validating that estimate is difficult.
One approach lies with the Earth’s rotational pole, which is the point around which the planet rotates. It moves during a process called polar motion, which is when the position of the Earth’s rotational pole varies relative to the crust. The distribution of water on the planet affects how mass is distributed. Like adding a tiny bit of weight to a spinning top, the Earth spins a little differently as water is moved around.
“Earth’s rotational pole actually changes a lot,” said Ki-Weon Seo, a geophysicist at Seoul National University who led the study. “Our study shows that among climate-related causes, the redistribution of groundwater actually has the largest impact on the drift of the rotational pole.”
Water’s ability to change the Earth’s rotation was discovered in 2016, and until now, the specific contribution of groundwater to these rotational changes was unexplored. In the new study, researchers modeled the observed changes in the drift of Earth’s rotational pole and the movement of water — first, with only ice sheets and glaciers considered, and then adding in different scenarios of groundwater redistribution.
The model only matched the observed polar drift once the researchers included 2150 gigatons of groundwater redistribution. Without it, the model was off by 78.5 centimeters (31 inches), or 4.3 centimeters (1.7 inches) of drift per year.
“I’m very glad to find the unexplained cause of the rotation pole drift,” Seo said. “On the other hand, as a resident of Earth and a father, I’m concerned and surprised to see that pumping groundwater is another source of sea-level rise.”
“This is a nice contribution and an important documentation for sure,” said Surendra Adhikari, a research scientist at the Jet Propulsion Laboratory who was not involved in this study. Adhikari published the 2016 paper on water redistribution impacting rotational drift. “They’ve quantified the role of groundwater pumping on polar motion, and it’s pretty significant.”
The location of the groundwater matters for how much it could change polar drift; redistributing water from the midlatitudes has a larger impact on the rotational pole. During the study period, the most water was redistributed in western North America and northwestern India, both at midlatitudes.
Countries’ attempts to slow groundwater depletion rates, especially in those sensitive regions, could theoretically alter the change in drift, but only if such conservation approaches are sustained for decades, Seo said.
I would not have guessed that pumped water would rate higher than melting land ice, but apparently it’s easy to under-estimate just how much water our species uses, particularly for agriculture. I’m saying nothing new here, but we’ve got to stop treating natural resources as though they are infinite, and require no maintenance. We are fully capable of using water more efficiently, it’s just that doing so would require changes in how things are run, and that might as well be the end of the world, for the folks profiting off the status quo.
I don’t believe overpopulation is really a problem we need to work on. That said, the size of our population, combined with the technology at our disposal, means that we can change the surface of this planet in massive ways. That’s not an inherently bad thing – if nothing else, it means we can repair some of the damage we’ve done – but it does mean that if we want our species to continue, and to have a future worth living in, we need to start changing how we use resources, and what we do with them afterwards. Not only is this level of over-exploitation not needed for everyone to have a decent standard of living, it’s actively detrimental to that goal. It is making this planet a worse place to live, all to satisfy the pathological greed of capitalist, and we’re reaching the point where either it ends, or we do.