Smart Science

First thing is where do you want to measure it? The sea is not "level" There are highs and lows. A city like Venice may offer some insight for a local measurement.

A pressure measurement may in fact be a better way. Anchoring the sensor to the sea floor may offer more reliable measurements than gained from the local tide gauge.

Modeling what happened several millions of years ago to give a reasonable resolution, will be an interesting undertaking. In 250 million years would the earths rotation have slowed sufficiently to skew readings? Would one of the massive asteroid strikes, moved the earths orbit? either added or removed significant amounts of water?

Thanks for pointing out the site, seems interesting, I'll add it my list

As ice melts, as well erosion of land changes the weight of the earths surface "floating" on the liquid core, what reference point? That and space dust/meteors, are always adding more mass to the earth, as well. There will be uplifting where surface mass is removed, and sinking where this mass has settled.

I live where 270 million year old Devonian lime stone is now 1200 feet above see level. And it's unknown how thick this surface bedrock is to me. So if this was formed as a shallow inland sea, it had to initially keep sinking for the enormous depth of limestone to be formed.

I'm going to assume that as the polar ice melts, those areas of the earths surface will float higher, and displace more ocean water volume to effectively causing higher ocean levels to any of the inhabited coastal areas.

The big problem with the "Global Warming" and Ice Melt scenario is most of the commentators seem to focus on a small sector of the situation- The weight of the glaciers is so minimal in comparison to soil and rock that deformation from melting is minimal and not significant- The continents have been rising and sinking for millions of years due to platel movement and eruptions, so huge amounts of sedimentary deposition have occurred and also the igneous magmas have moved up in many case- non of this will or has had any critical factoring of of the ice melt.

Water/Ice expands approximately 4% when it freezes so when it melts the volume is reduced buy this amount- so this compensates for the above water portion of the ice and some on the land- and if temperatures in the Arctic and Antarctic are sufficiently high to cause melting then the evaporation of water in tropical and temperate regions also increases so on a general basis with some few local exceptions the earths water levels will remain the same- most coastal changes in levels are due to plates rising and sinking from continental driftl

Sir,

I'm not sure about the first paragraph, but I have strong doubts about the second.

Although the melting of floating ice shelves will not change the elevation of the ocean any, the melting of glacial ice deposits on land will result in their running off into the ocean. This run-off will add to the total volume of water in the ocean and therefore cause its level to rise. I would agree with anyone who points out that the land level under the Greenland ice cap is slightly below sea level in the middle portion, but the massive amount of ice above this cannot be ignored as your post suggests. I will also agree with anyone who points out that melting of the glacial cap is followed by a rebound of the rock strata underneath. However this rebound is a millennia-long event, so it will not help those species and land areas that have been inundated by the rise of the ocean level at the beginning of this rebound period. See the brief USGS article at: http://pubs.usgs.gov/fs/fs2-00/. In it, the calculated sea level rise is given for each major glacial deposit. The total of all is over 80 meters!

Evaporation of water is followed by precipitation (in one form or another). I hope you are not proposing that the entire volume of water in the ice caps is eliminated from the ocean's volume by its being suspended in the atmosphere as water vapor. Instead, I suggest that the net effect of evaporation is zero.

--JMM

Satellite photos may be the best way. I have read somewhere recently that satellite views show that the glaciers are smaller; that is, they cover less area. I think this would also show up as rising seas; that is, the shorelines have moved inland. However, some will surely point out that the land may be sinking.

I may have read this in the ebook Prescription for the Planet by Tom Blees.

Shrinking glaciers may actually result in the land rising.

I recently read reports that stated that the area around the Great Lakes in North America is still rising as it rebounds from all the ice that covered it in the last ice age.

Hooker

Now the question: What was the impact of ice caps melting , we assume that the closer to the poles, the ice is accumulated to high glaciers, their mass has in impact on the earth liquid mantle, and hence formation/deformation of the topography?

I wish the article defined what they mean by "stable" in terms of human life spans. It is probably useful to know what conditions were 3 million years ago to understand conditions today, but (nearly) completely useless in making human scale decisions affecting coastal communities today, or 50-100 years into the future. For instance, I would guess that the ground beneath Charlotte, NC has not moved up or down noticeably relative the the ocean bottom since it was founded, with the exception of a minor earth quake last year, but the water level has been more dynamic.

I think that the "stable reference point" is the center of the earth.

For a rough cut, there is the "great circle" which, ignoring that the earth is an oblate spheroid, has a circumference such that an angle of one minute of arc with the vertex at the center of the earth, is subtended at the perimeter of the great circle by a distance called a "nautical mile". Thus, the circumference of a great circle is 21,600 nautical miles or 40,024,800 meters.

For the more discerning there is the earth's center of mass as a "stable reference point". This point, which is known to a high degree of accuracy is the reference point of the World Geodetic System and is the reference point of the Global Positioning System. With reference to the oblate shape of the earth this reference has an equatorial axis of 6,378,137 meters and a polar axis of 6, 356,752.3142 meters. Both these numbers radii.

It is with reference to this that the height of Mt. Everest and the depth of the Challenger Deep may be determined.

You baffled me because you brought a very good point.

Meanwhile I had another brain smart which will push the question yet in another direction.

I was wondering what statistical system we are using for the ocean water level which as we all know is dynamic with the tides and atmosperic pressure and even with waves and swell. Are all parts of this world using the same algorithm? Or is there room for evolution?

Given we measure from the centre of the Earth (which makes entirly sense) the sealevel should be a statistical middle point. Would this be correct?

I suggest that you look up "geodesy". This is a complicated subject.

In the days before GPS when men were men and celestial navigation was necessary, the "great circle" was considered "sealevel". This was perfectly adequate for off-shore navigation. For in-shore navigation where tides are necessary to be considered, the tidal reference is with respect to a tidal station in the vicinity of the area covered by the chart.

The depth contours shown on the chart are usually referenced to "low mean springs."