Hacker News Reader

Comment by 0hijinks | Hacker News Reader

>> ...we can see that, in less than two decades, Earth has tilted 31.5 inches as a result of pumping groundwater. This equates to .24 inches of sea level rise.

For those confused how they managed that geometric analysis, the sea level rise mentioned in the paper [1] is caused by groundwater depletion. The tilt is caused by groundwater depletion. The sea level rise is not caused by the tilt.

[1] https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2023GL10...

View on HN

Figure 1 in the above paper packs a lot of interesting information: https://agupubs.onlinelibrary.wiley.com/cms/asset/d7c477fa-3...

One important factor shown there is that dams hold back water on land, so act to decrease sea levels. It is not as big an effect as groundwater depletion, but is significant (around half as much).

The net effect of these two is much less than the other factors causing sea level rise (melting land ice) - looks like around 10% of total sea level rise comes from groundwater depletion+dams combined.

here's the problem with dams filling up and offseting ocean rise, amost all of the potential large dams, have been built and are full now, and that offset has masked some ocean rise, which is now accelerating, but all of the "planning" ,climate mitigation policy, treatys, etcerlalala, has been working with the wrong numbers. the wild card is changes in salinity and temperature shutting down the main thermo transfer currents at each pole, setting off deap ocean warming and expansion. not good.

Not to mention that inches are not a measure of angle, they’re a measure of length. I would prefer a proper measure of angle such as arcseconds. With some dirty math (taking 31.5 inches as an arc segment of earth’s polar circumference) yields a tilt of roughly 4 milliarcseconds, an extremely small angle to say the least.

I, and I suspect many others, have no clue what an arcsecond is and thus it's significance in anything. Inches also doesn't really give accurate significance, but at least it's relatable and doesn't leave me 100% lost, and I can focus on the message that something significant has been discovered, which may require some action.

I think it's pretty apparent that ~1 yard, i.e. about one step at a typical walking stride, is tiny relative to the circumference of the earth. I agree that it's a more understandable measure for most people than "arcseconds"

What happened to degrees or radians?

A degree is too big for the effect, the division of the degree into 60 arcminutes and the arcminute into 60 arcseconds is the standard subdivision of degrees as an angle measurement going back to the Sumerians.

Still doesn't say much to many. Temperature will be what comes to mind first for the lay person when they hear "degree", blank stare for "radian". But pretty much everyone in the US knows what an "inch" is, and the rest of the world can do a quick lookup/conversion. And everyone knows immediately on seeing the headline that something moved from its usual spot to somewhere else.

Again... AI blows, but ...

"Calculate the fraction of the circumference represented by the arc segment:Divide the arc segment length by the Earth's polar circumference (in inches):31.5 inches / 1,574,896,558.4 inches = 0.0000000200012759 Radians.

Which is kinda interesting, as it calculates the earths' circumference in Inches. 1.57 Billion inches.

I would still have been lost as I use the metric system. Just use whatever is most accurate, and I will research it.

The site is US-based, and thus caters primarily to the US "lay person" first.

An arcsecond is 1/60 of an arcminute; an arcminute is 1/60 of a degree (°); a degree is 1/360 of a full turn. A "milliarcsecond" is probably an unfamiliar unit (an angle so slight will only be used in extremely specialized contexts), so if you like you could decimalize this to an angle of 0.000001°.

The measure of distance on earth is probably more easily comprehended by almost everyone though.

  > The measure of distance on earth is probably more easily comprehended by almost everyone though.

The measurement itself is useless without knowing the size of the Earth, which very few people know offhand. That said, 30 inches sounds like something tangible, and that's the important information here. That human activity had a measurable, tangible effect on the Earth.

Although I hate/detest using AI, I asked Google to calculate it...

0.0000072 degrees is 25.92 milliarcsecond.

Assuming that the Earth is a perfect sphere, which it is not, so now...

I have to burn up some Mathematica time, and have it calculated in elliptical coordinates.

Sigh. This is why I read the comments. Thank you.

On a very large and massive object unexpected changes of such magnitude may be a 'small angle' but they still require so much energy that an explanation is warranted.

So just to clarify, what you’re saying is that the volume of water we’ve pumped is directly responsible for the observed sea level rise? The article makes it sound as if the tilt is what was responsible, and I was curious about the mechanics of that.

Reply on news.ycombinator.com