Sea Level as a Point of Measurement

Acitnoids said:
https://www.topchinatravel.com/mount-everest/the-height-of-mount-everest.htm

Once again, understand that but I am not sure if that is a "standard". This link suggests Mt. Everest is rising at 4mm per year. I assume that is based on some sort of "standardization" of sea level. Yet it does not give an average (i.e. 4mm per/yr +/- 2mm). A mention of an average sea level is completely absent from the literature would you disagree?

On average yes, I can understand but what I am suggesting is this is not a standard. Yet this measurement is used for real world applications!

Sea level as a "standard of measurement" is useless as an average if we wish to know weather patterns for example.

I guess the point is going over your head. Could you please share when, as you say, this measurement has "changed all the time" in the scientific use of this particular measurement ?

Aviation, Cartography, Meteorology are just a few that require this measurement, averaged or not. Accuracy/prediction depends on this point in space.
Click to expand...
I do not have a definite answer, but this article: https://en.wikipedia.org/wiki/Sea_level_rise explains that sea level is measured by satellites in Earth orbit. It is not explicitly stated, but I presume the deviations in this orbit from circular are known and thus such a measurement fixes the height of the sea relative to the centre of the Earth. This, after all, is the one fixed point in the system we can rely on.

According to my information the rate of rise of the Himalayas (relative to the centre of the Earth, I presume) is >1cm/yr and the mean rate of rise of the sea is ~3mm/yr.

But you are right. The articles I have seen on the web do not explicitly state what the rates of rise are measured relative to, so it is bit frustrating. Perhaps if a geologist reads this thread, he or she can confirm or explain further. Post 18 from Iceaura suggests it is not that simple.
 
Thank you exchemist,

I agree, it is not a simple question which is why I asked here.

The center of the Earth seems like an ideal start point but that insures sea level is still the dominant factor.

I appreciate your take, .... thx

Maybe that start point could add to predictions but .... *shrug* ... as of now not accurate enough.

Seriously, thx=> <=
 
Last edited:
exchemist said:
but I presume the deviations in this orbit from circular are known and thus such a measurement fixes the height of the sea relative to the centre of the Earth.
Click to expand...
At a given time and location.
That is a good start, but mind the earth is not spherical and it is spinning. So there is no single distance from the level surface of the sea to a center point of the planet - no "the" planetary sea level in that sense. Then enter currents, the moon, various interactions of geography and spin, and so forth. (no small factors)

Brief nod in pop sci: https://curiosity.com/topics/mount-...-the-tallest-mountain-in-the-world-curiosity/
Our measuring system also minimizes the height of Ecuador's Mount Chimborazo. It rises just over 20,500 feet (6,250 meters) above sea level. However, it has a superlative of its own: Of all the mountains in the world, it's the one whose summit is farthest from the center of the Earth.
Click to expand...
Note the size of the difference: Everest is more than 2500 meters taller measured from it's local virtual sea level, but it's peak is closer to the center of the planet.
 
Last edited:
Let me give an example of the O.P. and maybe you can tell me if my conclusion is accurate.

https://www.nationalgeographic.com/environment/global-warming/sea-level-rise/

This link from National Geographic states that the mean sea level has risen over the past 20 years at a rate of 3.2mm per year on average. We have already stated in this thread that the elevation of Mt Everest is rising by 3-4mm per year on average.

Given these facts would I be wrong to conclude that the elevation of Mt Everest has essentially stayed to same over the past 20 years because of the rising mean sea level?
 
iceaura said:
No. I'm saying there is more than one possible standard or reference, and to find out which one was used one should consult the published work.

? Not sure how I suggested that.
Click to expand...

Please, I beg you not consider this as a snarky comment. The title of this thread is called "Sea Level as a Point of Measurement". I was not asking about satellite data or the center of the Earth as a point of reference. I work with different points of reference everyday do to my occupation.

Elevation is based on "sea level" (I thought "mean" was implied). With all do respect I didn't care about Altitude and what not regarding this thread. I am only concerned with "Sea Level as a Point of Measurement" and what that means as a definition.

Thank you for trying to understand my POV.
 
Last edited:
Acitnoids said:
Elevation is based on "sea level" (I thought "mean" was implied)
Click to expand...
"Mean" is not exactly what would be involved. Sea level is a complicated calculation, and it varies by location.
Acitnoids said:
Given these facts would I be wrong to conclude that the elevation of Mt Everest has essentially stayed to same over the past 20 years because of the rising mean sea level?
Click to expand...
Probably, yes. Depending on how those facts were calculated. Everest's "elevation" (not the same as height, necessarily) is measured - usually, but not inevitably, as my link pointed out - from a virtual sea level calculated for its latitude. The amount that particular sea level has risen is not likely to be the "mean sea level" rise of the planet as a whole.
 
Acitnoids said:
I am only concerned with "Sea Level as a Point of Measurement" and what that means as a definition.
Click to expand...
It would seem a fairly stable standard and even on dry land, "sea-level" measurements do provide a relatively precise global "mean", IMO

It is used in Geographic mapping a lot
Definition of GIS
Click to expand...
A geographic information system (GIS) is a system designed to capture, store, manipulate, analyze, manage, and present all types of geographical data. The key word to this technology is Geography – this means that some portion of the data is spatial. In other words, data that is in some way referenced to locations on the earth.
Click to expand...
https://researchguides.library.wisc.edu/GIS

And specifically in topology and topography, if I recall .

https://viewer.nationalmap.gov/advanced-viewer/
 
Last edited:
Acitnoids said:
Elevation is not based on local sea levels such as tides. Elevation is based on a "mean sea level"; yes?
Click to expand...
No. Elevation above sea level (mean sea level) is above

a calculated virtual sea level for that location,
or the local sea and its level,
or relative to some other surveyed point whose elevation was determined by one of those two.

Quoting your link, first paragraph, key aspect highlighted by me:
Mean sea level (MSL) (often shortened to sea level) is an average level of the surface of one or more of Earth's oceans = =
- - -
A common and relatively straightforward mean sea-level standard is the midpoint between a mean low and mean high tide at a particular location.
Click to expand...
 
Write4U said:
I agree, it has nothing to do with ocean depth but with the physical tendency of water to seek gravitational leveling at the surface (sea-level).
Click to expand...
The shape of that surface is called a "geode". If one wishes to measure Everest's absolute height from its carefully defined "sea level" to within 4mm, that is what one would use.
https://en.wikipedia.org/wiki/Figure_of_the_Earth
The geoid, on the other hand, coincides with that surface to which the oceans would conform over the entire Earth if free to adjust to the combined effect of the Earth's mass attraction (gravitation) and the centrifugal force of the Earth's rotation. As a result of the uneven distribution of the Earth's mass, the geoidal surface is irregular and, since the ellipsoid is a regular surface, the separations between the two, referred to as geoid undulations, geoid heights, or geoid separations, will be irregular as well.

The geoid is a surface along which the gravity potential is everywhere equal and to which the direction of gravity is always perpendicular (see equipotential surface).
Click to expand...
Note that comment about mass distribution: since massive amounts of rock have significant gravitational pull, the sea will be attracted to ("sideways"), pile up against, and attain a higher level near, features such as Greenland with its ice cap.

Note that if one assumes the earth to be a sphere, and mean sea level to be some distance from the center of that sphere, Greenland would be entirely below sea level.
 
Last edited:
The last time I was in Panama City the tides raised and lowered the cruiser by nearly six feet. The dock was over our heads and then level with our main deck. The locals told me that "Sea level" there was at the point of highest tides. It's just a convention people agree on.
 
Acitnoids said:
This hypothetical point in space
Click to expand...

it is a subjective hyperthetical equilibrium of relative matter fields in varying correlative states.

it is not a point in space because it only exists because of "relative matter fields in varying correlative states".


i was about to give you a serious scientific answer(i was formulating a paragraph or 2 in my head) until i read your last 2 sentences.
at which point i realised your a climate science denier & likely a trumpsterdiver

Acitnoids said:
If it is not fixed then why do mountains stay at the same height? Should that difference have an impact on predicting the weather?
Click to expand...
 
Acitnoids said:
"Mean sea level" is just another way of saying "average sea level" yes?

https://en.m.wikipedia.org/wiki/Sea_level

This is an "Ideal sphere" that gives a constant water level which makes calculation easier. Or do we have a different definition for "mean sea level"?
Click to expand...

iceaura said:
The shape of that surface is called a "geode". If one wishes to measure Everest's absolute height from its carefully defined "sea level" to within 4mm, that is what one would use.
https://en.wikipedia.org/wiki/Figure_of_the_Earth
Note that comment about mass distribution: since massive amounts of rock have significant gravitational pull, the sea will be attracted to ("sideways"), pile up against, and attain a higher level near, features such as Greenland with its ice cap.

Note that if one assumes the earth to be a sphere, and mean sea level to be some distance from the center of that sphere, Greenland would be entirely below sea level.
Click to expand...

I didn't think I was publishing a thesis here heh. I guess I could have said:

"An ideal circular-ish average that depicts a hypothetical surface tension between the atmosphere and global bodies of water while taking into account geographic and astrophysic influences none of which reflects reality because this is just a mean average after all yet this allows for easier calculations".

I'm sorry but I thought saying "ideal sphere" placed in parentheses was much easier ☺
 
Last edited:
You must log in or register to reply here.
Back
Top