and hn is more like reddit than it used to be
And every move you make
Every bond you break
Every step you take
I'll be changing you
Groundwater is mostly under ground... And the center of mass of all the surface crust is hundreds of kilometres from the center of mass of all the world's oceans.
I'm curious as to which side of the bridge you stand on, and your science/mathematics background
- pumped water gets used and flows to the oceans, far away
- we have pumped a lot of water (look up how much some places have subsided due to groundwater depletion).
- the earth's rotation is something we've worked out how to measure very, very precisely
It sounds completely plausible to me.
~8 trillion tons to raise the level an inch based on the simple math of surface area of a 24,000 mile diameter sphere, times 2/3rds water, as seen here:
https://www.answers.com/earth-science/What_Amount_of_water_r...
The water from aquifers is not just lifted a short distance up to the surface. It is used, ends up in rivers, and spreads around the world's oceans. And the places where we are pumping groundwater are not uniformly distributed around the Earth. We are essentially moving mass to the Pacific.
Genius HNer looks as the title, spouts some factually incorrect data to "debunk" it and gets upvoted to the top.
Sadly I'm not just describing this instance but internet discource in general. Critical thinking and analysis is dead in the age of "gotcha" hot takes.
They’re taking as read that the top level comment is wrong (as explained by a number of other comments), and making an observation about the circumstances surrounding the incorrect comment, as well as the theme it represents in the broader discourse.
In cases like this it's more than fair to call bullshit.
- Based on a cursory search, a large iceberg may weigh in at ~1 trillion tons. The calving process moves mass hundreds of kilometers away from Antarctica. This should be an effect of similar magnitude!
- The water cycle moves ~500 trillion tons of water each year. This water is moved hundreds of kilometers and isn’t evenly distributed over the course of a year. We should expect the impact of seasonal fluctuations in water distribution to thus have a comparatively much larger impact on the earth’s rotation.
I don’t think these numbers add up. I think we’re reading this story because it feeds into a certain kind of “we are hurting Mother Earth” mindset.
A-68 was part of Larsen C, a section of the Larsen Ice Shelf. Scientists found the crack beginning to form in November 2016. Scientists assess that A-68 "didn't just break through in one clean shot, [but] it formed a lace-network of cracks first."[5] The resulting iceberg was around 175 km long and 50 km wide, 5,800 km² in area, 200 m thick and weighed an estimated one trillion tonnes.[8][5]
I’m not sure if Wikipedia is right here however because the linked sources have changed to remove mentions of mass.
That said we should be able to do a pretty dumb calculation. 1 km3 of water weighs ~1 gt.
5800 km2 x 0.2 km = 1160 km3
1160 km3 of ice x 0.9 (density of ice compared to water) x 1 gt / 1 km3 leaves us with a mass of about 1044 gt or around 1 trillion tons.
Edit: also, I am not able to find an original source for the mass of B-15 being in the few billions range
More importantly, the article mentions removing annual effects on Polar Motion. They are averaging - somehow - to look at permanent changes. The annual effects may be an order of magnitude greater, it is not relevant.
Assume earth is a perfect sphere, let m be the mass of earth and r be the radius of earth. Let rdm be the relative mass of the water moved = 3e-8, let rdr be the relative distance of the water moved = 5e-6.
The change in momentum is rdm.m.(1+rdr)².r² - rdm.m.1².r² which is 2.rdm.rdr.m.r²= 3e-14mr². Looks about right for the change of axis you wanted.
There's other counter arguments but at least the oom analysis fits.
So you're talking about a change in angular momentum that is on the order of 10^(-20) times the angular momentum of earth (mr^2 \omega).
A change in the pole of earths rotation by 31 inches (10^(-7) times the radius of earch) corresponds to a change in angular momentum on the order of 10^(-14). So we seem to be off by 7 orders of magnitude.
I call bullshit.