Thea level Thkeptithithm

[Morris Cod]

I am sure that everybody here has heard the claims by Al Gore regarding the possible rising of sea levels by 25m, due to Global Warming.

Can any of you learned types explain if that is possible?,ie;does that much water actually exist?

I am no genius, but it would seem to me that an extra 25m of H2O on the surface of the Earth would represent quite an enormous volume.

This is'nt a trick question,I am just curious as my daughter is doing a project on Al's flick and asked me that exact question.Had to say "I Dunno".

Any insights?

Cheers

[casebro]

Morris, your TH key is sticking.

I think I read that in the last warm period, the sea level was 1 1/2 meters higher than now. So if you think global warming is a natural recurrece, no big deal. If you think there is something unique and extreme about this warming period, than you better move to Colorado.

[Rassilon]

It's not just melted water that raises the sea level, existing water will take up more space as it gets warmer. As for exact numbers, I can't do much (if any) better than you did: "I dunno".

I tried to get these details from my geology instructor a few weeks back when we covered the topic, but, while he believes in global warming, he couldn't tell me how the estimates were calculated. He directed me here for more information:

http://www.exploratorium.edu/climate/index.html

I admit that the topic didn't really interest me enough to dig through the site for more than 15 minutes so I didn't find my answer.

[Morris Cod]

Actually, one of the bigger problems I have is finding the "happy medium" or the truth of the matter.It seems that you are either a complete non-believer, or an over the top extremist on the matter, the media seems to have lapped up every word Al utters.

[Rassilon]

I dug up my professor's lecture. Below are some slides from the lecture that may be useful to you.

http://forums.randi.org/imagehosting/9485454ac99649ed4.jpg

http://forums.randi.org/imagehosting/9485454ac983efd20.jpg

http://forums.randi.org/imagehosting/9485454ac9844bfb6.jpg

http://forums.randi.org/imagehosting/9485454ac98423f3e.jpg

...and to give credit where credit is due: these slides are from a geology 201 lecture by Kenneth E. Windom (http://www.ge-at.iastate.edu/windom.shtml).

[Morris Cod]

80.32m.....eeek!

[Soapy Sam]

Keep in mind that sea level is a dynamic relative measurement.
Rocks can go up as well as down.
Eustatic sea level rise in areas closest to melting ice sheets may be compensated for by isostatic rises in land level relative to sea level, due to the lithosphere rebounding after being pressed down into the mantle by the weight of ice.
There's a line across the UK from about Liverpool to Middlesbrough, north of which the land is actually rising relative to sea level, south of which it is sinking- because until recently (10000 years or so) Scotland was under ice.
Guess which side I live?

[geoman]

Guess which side I live?

You live in the middle of the bloody Caspian Sea, SoapySam, where the sea level variation over the past 50 years has been all over the shop. So don't try to fool us!

[Banbury]

Al Gore probably knows the Media well enough, to know that the only way to get their attention is to cry Universal Armageddon. And most people won't get of their butts unless they are personally threatened. Even if he might exaggerate somewhat, he's at least doing a good job in making people think about Global Warming.

[casebro]

80 meters, if every ice cube in the world melts. Just how warm does the world have to get to do that?

Notice the Holocene chart, that shows all the colored lines making 'noise', not just the black line of 'average'. Check out that light blue line, and remember that too is an 'average', and had spikes even higher. Our current temp spike is well within the 'noise' range.

[drkitten]

80 meters, if every ice cube in the world melts. Just how warm does the world have to get to do that?

Quite warm, possibly unrealistically so (although the ice caps were mostly absent during the Cretatious (sp?) period), so it's happened before.

Now -- how much would happen if the sea level "only" rose 20m? And how warm would the earth have to get?

[Dragonrock]

According to the Intuitor physics site in their review of the movie The Day After Tomorrow if all of the energy the strikes the earth were focused on Antarctica it would still take 2.6 years for all of the ice to melt. And this assumes that the ice was prewarmed to just below freezing. As it stands, it would take decades or, more likely, centuries for the sea to rise the 80 meters expressed in the slides.

Link to Intuitor's movie review.
http://www.intuitor.com/moviephysics/dayAft.htm

[RSLancastr]

But it's reassuring to think that no matter how high the water gets, it will never get above sea level.

[CBVan]

If we all had houseboats, this wouldn't worry anyone.

[Ladewig]

The ice at the North Pole is not on top of any land, so melting it would not produce any notable change in sea levels. However, there are ice sheets over a mile thick on top of land at the South Pole

[drkitten]

The ice at the North Pole is not on top of any land, so melting it would not produce any notable change in sea levels. However, there are ice sheets over a mile thick on top of land at the South Pole

Er. Not quite. Contrary to popular belief, the density of water is temperature-dependent. If the water currently trapped in the north polar ice caps were to warm to greater than 4 degrees, the overall effect would be to raise the current sea level.

[Ladewig]

Er. Not quite. Contrary to popular belief, the density of water is temperature-dependent. If the water currently trapped in the north polar ice caps were to warm to greater than 4 degrees, the overall effect would be to raise the current sea level.


How much?

[Rassilon]

If we all had houseboats, this wouldn't worry anyone.

Are you growing your food on that there houseboat, matey?

The ice at the North Pole is not on top of any land, so melting it would not produce any notable change in sea levels. However, there are ice sheets over a mile thick on top of land at the South Pole

That explains how "all others" on the slide can have 180,000 cubic km of ice, but it would only raise sea level 0.45 m (less than the Antartic Peninsula which has only 27,100 cubic km).

Er. Not quite. Contrary to popular belief, the density of water is temperature-dependent. If the water currently trapped in the north polar ice caps were to warm to greater than 4 degrees, the overall effect would be to raise the current sea level.

It's a popular belief that the density of water is not temperature dependent? Wow. Yes, 3.98 degrees C is when water is at it's maximum density (according to this source (http://www.newton.dep.anl.gov/askasci/chem03/chem03335.htm).)

How much?

See this link (http://www.simetric.co.uk/si_water.htm) for a table detailing the increase of volume due to temperature (the easiest table to use is at the bottom -- big surprise).

So to determine how much rise in water level is due to X degrees of increasing temperature, we need to determine how much ice melts (which will lower sea level if it's below the water and only increases to ~4° C or will increase sea level if it's on land). We also have to model the oceans, determine the rise in temperatures across the surface and depth to determine the change in existing water volume.

Hmm, well, it is Friday night. Maybe I'll make a first approximation of this... (If ever there was a cry for a female companionship, that was probably it. :rolleyes: )

[casebro]

Er. Not quite. Contrary to popular belief, the density of water is temperature-dependent. If the water currently trapped in the north polar ice caps were to warm to greater than 4 degrees, the overall effect would be to raise the current sea level.


Not so fast there DrKitten. Ice floats, no matter the temp of the liquid water. Liquid water has has a density that varies with temp. but it will never 'swell up' larger than ice. Therefore, the melted ice cap will have less volume. But it will NOT have any effect on the sea leavel, any more than sinking a ship will raise the level- the floating ship already displaces water exaclty equal to it's weight. Over all, I think melting the arctic will drop the sea level?

Also, the Greenland ice field is mostly actually below sea level. It is so heavy it has sunken the middle of the island. So it won't all flow into the sea. Antarctica could be similar?

ETA, note that the above slide re: icemelt does not show anything for arctic change. Probably not an ovesight.

ETA yet again to add I sure type slow.

[casebro]

Speaking of Greenland: It was discovered during the Medievel warming period, hence the name. Perhaps this GW will return it to it's former glory?

[Old man]

According to the Intuitor physics site in their review of the movie The Day After Tomorrow if all of the energy the strikes the earth were focused on Antarctica it would still take 2.6 years for all of the ice to melt. And this assumes that the ice was prewarmed to just below freezing. As it stands, it would take decades or, more likely, centuries for the sea to rise the 80 meters expressed in the slides.
Thanks for this info, Dragonrock. I’ve been wondering how to go about calculating this for a while now. It kinda makes you wonder just when the ‘warming’ that’s melting the ice now really did occur, doesn’t it?

Also, the Greenland ice field is mostly actually below sea level. It is so heavy it has sunken the middle of the island. So it won't all flow into the sea. Antarctica could be similar?
Case, Bro, while I agree with you on the subject of below sea level ice (and on GW, also), there's still quite a bite of ice above sea level there, too. I did a quick Google search last night, and came up with estimates of average Greenland ice sheet thickness that varied from 1.5 to 2.8 km. A couple of quick Google Earth traverses of Greenland makes me think that the average elevation is in the 2 to 2.5 km range, so it looks kinda like ‘Greenland’ is almost all snow/ice.

A long time ago, I ‘learned’ that sea levels were about 300’ feet (or around 90 meters) lower than they currently are at the height of the last glaciation. If all this is true, and there really is another 80 meters locked up in existing ice, the implication is that only just a little more than half of the ice that existed during the glaciation has melted.

This doesn’t seem to dovetail very well with the idea of an ice sheet ‘miles’ thick that stretched from Maine to past Minnesota, does it?

[blutoski]

Er. Not quite. Contrary to popular belief, the density of water is temperature-dependent. If the water currently trapped in the north polar ice caps were to warm to greater than 4 degrees, the overall effect would be to raise the current sea level.

Also: there is plenty of land near the north pole with ice on it. ie: Alaska, Canada, and Russia. Not to mention the south pole. These are above sea level for the most part, and runoff will flow into the ocean.

[casebro]

A long time ago, I ‘learned’ that sea levels were about 300’ feet (or around 90 meters) lower than they currently are at the height of the last glaciation.

Even Mann admits that there were past warm periods. How high were the sea levels during those?

[blutoski]

Also, the Greenland ice field is mostly actually below sea level. It is so heavy it has sunken the middle of the island. So it won't all flow into the sea. Antarctica could be similar?

It isn't. Antarctica has the highest average land elevation, and ice on top of it. "Miles high" is accurate.

Earth Observatory: Antarctica's Land and Ice Elevation (http://eobglossary.gsfc.nasa.gov/Newsroom/NewImages/images.php3?img_id=16758)

NASA's ICESat Satellite Sees Changing World Affecting Many (http://www.nasa.gov/vision/earth/lookingatearth/icesat_light.html)