Naked Science Forum

General Science => General Science => Topic started by: Herman Melville on 04/06/2009 12:37:15

Title: If sea levels are rising, how do we measure 'height above sea level'?
Post by: Herman Melville on 04/06/2009 12:37:15

Heights are given as 'above sea level'. But sea levels are rising. So how do we measure how high something is? Does this mean Mount Everest is slightly less high than it used to be?

Should we start measuring objects' height by their distance from the centre of the Earth? Is this even possible?

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Title: If sea levels are rising, how do we measure 'height above sea level'?
Post by: Don_1 on 04/06/2009 13:33:34

I see your point, but the tectonic plates are constantly on the move, so heights above sea level, or indeed from the Earths center are constantly changing. This may be no more than a millimeter in a quiet year to a drastic change in a year when there is a significant shift of the plates resulting in an earthquake. At which time a difference of several meters could be recorded in less than a minute.

In 1999 Everest was measured at 29,035 ft. that's 7ft higher than its height of 29,028 ft. which had previously been the accepted height above sea level determined in 1954. Was the different height recording due to error of one or the other measurements, or was it due to the Indian sub-continent pushing northward toward Nepal?

So cartographers need never fear unemployment, the face of the Earth is constantly changing.

Title: If sea levels are rising, how do we measure 'height above sea level'?
Post by: Herman Melville on 04/06/2009 14:03:11

Quote from: Don_1 on 04/06/2009 13:33:34

I see your point, but the tectonic plates are constantly on the move, so heights above sea level, or indeed from the Earths center are constantly changing.

So is the Earth's centre is a fixed point we can calculate heights from, even if the surfaces themselves undulate with the plates?

Title: If sea levels are rising, how do we measure 'height above sea level'?
Post by: Don_1 on 04/06/2009 14:48:11

It's a whole lot easier to work it out using GPS and the average sea level.

Title: If sea levels are rising, how do we measure 'height above sea level'?
Post by: DoctorBeaver on 04/06/2009 17:26:03

Localised sea-levels are constantly changing anyway with the effect of tides, high & low pressure weather systems, distance of the moon from Earth, etc. And if John Prescott goes bathing the average sea-level rises significantly (adds "allegedly" to avoid a being sued for slander).

Title: If sea levels are rising, how do we measure 'height above sea level'?
Post by: Don_1 on 04/06/2009 17:36:57

Quote from: DoctorBeaver on 04/06/2009 17:26:03

And if John Prescott goes bathing the average sea-level rises significantly (adds "allegedly" to avoid a being sued for slander).

Hehehe............       The truth always hurts, allegedly.