Naked Science Forum
Life Sciences => The Environment => Topic started by: Steve Boston on 20/05/2008 23:52:42
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Steve Boston asked the Naked Scientists:
If 97% volume of the earth's water is in the oceans how could (god forbid) even the complete melting of the polar ice raise sea levels by enough to measure? - especially if we include instrument accuracy and experimental error.
What do you think?
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It is all about volume. The volume of water tied up in ice is huge! If all of it melted, sea level would rise by 300 feet, minimum.
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The north and south poles are quite different. The melting of the north pole will not affect sea level because the water has already been displaced by the ice. Whereas, the melting of the ice at the south pole will cause sea levels to rise because the ice is on top of the land.
Try this
http://www.thenakedscientists.com/forum/index.php?topic=6730.msg175097#msg175097
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I do understand that to melt floating ice would reduce oceanic volume and to melt 'land ice' would increase it - but I still come back to the point that seas make up 97% of the water. Atmospheric moisture + 'land based water' = some part of 1 percent, so we are left with 2 point whatever percent (at very most) that could be added. I live next to the Forth Bridge in Scotland, and I can't imagine how anyone would even notice if the estuary were ever to get about 2 percent more full.
So I really can't see (pardon the pun) how we are supposed to end up stuck in big wooden boats full of two of every kind of beast, staring at the occasional mountain peak as we float by.
I am really looking for an explanation with facts and (simple) math and so forth.
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Hi Steve
good point, but don't forget the effect of thermal expansion on water too - when it heats up water expands. The amount is small for a tiny volume of water, but on the scale of the world's oceans the resulting sea level rise is more significant.
Chris
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Steve Boston asked the Naked Scientists:
If 97% volume of the earth's water is in the oceans how could (god forbid) even the complete melting of the polar ice raise sea levels by enough to measure? - especially if we include instrument accuracy and experimental error.
What do you think?
The oceans are quite deep though.
Get a long tall glass, filled with gin and tonic, then drop in an ice cube and see how much the level rises. Then drink the contents. Its worth repeating this a few times just to make sure you can see what is going on.
The ice cube is small in comparison to the amount of G&T, but because of the depth, the level increase is significant.
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I see that you inebriation is due solely to your dedication to the scientific investigations you conduct. Good lad.
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isostatic rebound will also contribute to sea level rise. As you melt the massive glaiciers on antarctica and greenland, the wieght of the ice is removed and those land masses rise.
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Greenlands ice sheet has been estimated, on average, to be about 2000m thick, with some areas possibly reaching 3000m in thickness. The Antarctic ice sheet has been estimated, on average, to be about 3000m thick, with some areas possibly reaching 5000m in thickness. Antarctica is about 14.2 million km2, so that equals (back of the napkin math here) about 42.6 million km3 of ice, but Im sure that is at least somewhat inflated, as not ALL of Antarctica is covered in ice (there ARE mountain ranges and such). Thats still a hell of a lot of ice. The Atlantic Ocean alone is about 354.7 million km3 of water, which, if turned to ice, would increase by about 9% to 386.6 million km3. Ill see if I can find estimates of the oceans in their entirety.
Given Greenlands surface area, there would still be an appreciable rise in sea level if the ice sheet melted completely, but unless that were to happen very slowly, the Gulf Stream would slow down enough to bring a rapid cooling of climate before that much cool, fresh water could reach the N Atlantic current. That in itself is more disastrous that sea level rise anyway. Interestingly, at least one new ice river in the ice sheet has had its source discovered...a magmatic intrusion is beneath its source waters. What this says for the rest of Greenland, I dont really know.
*IF* Antarctica were to melt completely, there is enough water locked up in ice on the continent to flood completely all of the world coastal areas. We have had over 130m (>400ft) of sea level rise since the end of the last ice age. Antarctica does not hold as much ice as that which melted at the beginning of the Holocene, so sea level rise would still be massive, but certainly less that 130m. 300ft is probably about correct. Fortunately, the main portion of Antarctica showing any signs of appreciable melting is the peninsula, which is not completely encapsulated by the circumpolar currents, and juts out into the Southern Ocean.
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The estimates that Im finding for the volume of the worlds oceans (not including adjacent seas) is about 1.37 billion km3. Melting 42.6 million km3 of ice would create about 39.9 million km3 of water. That is an increase in ocean volume of about 3%, and, at an average depth of 3790m, would bring a sea level increase of approximately (VERY approximately) 113.7m. This is about 373ft from Antarctica alone.
Someone please check my math, this seems a little high to me.
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frethack ... thank you for the math backing up my claim from my memory of reading some esoteric article. I am getting lazy in my old age.
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No prob :P ...gives me practice for next semester!
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Sorry about repeating myself - left a similar post on another topic that resembles this one; My query is as follows - The Earth spins through space like a giant gyroscope; how would such a gyroscope react to a significant mass displacement - mass now concentrated at the poles being evenly distributed around the earth? could this possibly trigger an inversion of the poles? any input would be appreciated.