Thermal expansion: most of the rise so far has been because water expands when it warms.
Land ice: The threat of vastly greater sea level rise comes from the thawing of the ice caps on land in Greenland and Antarctica. Greenland is thawing a little, Antarctica perhaps not at all yet above land (it seems that ice on water is thawing underneath then refreezing at the surface, reducing volume but expanding extent -- which as you note would not affect sea level).
You are correct that ice in water does not cause sea level rise.
Wow, there are still people who think this is a valid test for the melting of glacial ice, that's sad.
Sadly for those who flunked science it doesn't work that way with glacial ice or thermal expansion, glacial ice is on land.
In the context of the sad example you offer that would be taking a glass that is already full and then adding the ice cube, but you will need a cloth to clean up the mess you make.
Expansion needs a larger body of water but is a scientific fact you warm water and it expands the effect is relatively small, but when the average depth of the worlds oceans is 4km a change of even a tiny percentage is going to be seen and in fact about half of current sea level rise is thermal expansion.
Deniers like kano have repeatedly stated that glacial ice is not melting and he has several times posted links to sea ice? to show that, Which at a level a denier might understand is like saying Ford is financially fine because here are Toyota's financial reports.
This is what actual glacial data shows - http://climate.nasa.gov/key_indicators#l...
Sea level is rising
http://climate.nasa.gov/key_indicators#s...
That's because the ice you put is free-floating and mostly water with only a small amount of air, which means most of it's mass actually floats inside of the water, and thus contributes to the over all mass, and ultimately the water level in your cup.
However, the ice caps and such, large portions protrude above the water over very large areas of water, and even on some land in places like the antarctic and Greenland. A single iceberg, even thousands of icebergs are not going to cause a significant change in over-all water level, however, over and across all those areas, having any ice melts contributes millions, billions of gallons of water added to the over-all global water level. Well, if it keeps happening, estimates show how much the water will rise.
However, that issue is one we can't control. If the globe decides to warm up, it really doesn't matter what we do, all of that stuff is going to happen, and the best we can do is prepare for it, study it, and try and start figuring out a way to steadily move people away from areas that will probably be submerged.
I'll stand with ya Jim Z!
The problem with calculating sea level rise is that science has a hard time detecting movement from plate tectonics which will cause the sea bottom to rise or fall.
The amazing thing about this Planet is that we do have a lot of water here and it does constitute over 95% of the greenhouse warming effect.
Most of the added water would come from the land run-off.
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As far as temperatures are concerned, the current warming period is well within natural climate variability. Looking back at the Little Ice Age (ended in the mid-1800s) and comparing it to The Medieval Warm Period (ended around 1250ad) we know that temperatures have varied by as much as 5C from the well established normal average temperature of the Planet.
We don't have accurate records showing Arctic Ice Melt anomalies, but science does try to reconstruct history when it comes to the Arctic.
If the ice cube is in the glass but frozen to the sides of the glass above the level of the water it will raise the water level when it melts.
I gave JimZ a thumbs-down here not because I give a hoot about his political preferences but for misstating for the X-hundredth time his qualification as "geologist" when it should be "abiotic oil 'geologist.' "
http://answers.yahoo.com/question/index?...
Large amounts of ice aren't submerged, but are tied up in glaciers.
It's more like having a block of ice in a shallow pan. It's not he part of the ice under the water level you need to worry about, but the ice above the water level.
not all melting ice is sea ice. You are forgetting melting ice on top of land, like Greenland. There is also some thermal expansion as ocean temps rise.
Footprint, if you came up with this thought entirely on your own, then great! It's thoughtful and I have to respect that. If this came from someone professing knowledge on this topic or from a similarly placed web site, then shame on them.
The recognition that melting ice, ice that is already displacing water, won't significantly change sea levels is important to know. It's physical knowledge and it bears on questions like sea level change. In general, melting floating ice will have little to no impact on sea levels. (The technicalities are nuanced -- the impact of the melting of floating ice on the global mean sea level is complicated. But as a rule the impact is less significant than other effects and can be largely ignored right now.)
But ice that is not already floating, but is instead sitting on land somewhere, will if melted and released into the oceans cause the global mean sea level to rise. A great deal of ice is located on land. Antarctica carries enough ice located on land to raise the global mean sea level perhaps 60 meters or more. Greenland's ice is on land and will, if melted, also cause sea levels to rise by about 7 meters. Probably less than a meter of ice is located in mountain glacier systems around the world (other than the ice sheets on Greenland and Antarctica, of course.) But these glaciers are important because they supply fresh water to many people, animals, and plants, even if they don't account for as much total sea level rise magnitude.
A term to learn is "eustatic sea level." This is the global mean sea level. Today, the more accurate measurements for this value come from altimetry data from satellites, which use microwave bounce and round-trip travel time to provide the height of the satellite above an instantaneous point on the sea surface. Corrections are then made for atmospheric delays and changes in those delays, electromagnetic scattering effets, geophysical effects, etc. Starting in 1992, the accumulated errors in the measurements dropped below 10cm, permitting for the first time our ability to actually make a firm statement of detection regarding the rising oceans. Before then, such accuracy required very long periods of averaging which delays detection. The level of accuracy now is on the order of 1-2cm with Topex/Poseidon and since then Jason-1 and Jason-2 have been placed in orbit, so accuracies are even better and faster at hand, now.
Ice loss accounts almost all of the eustatic sea level rise (removing thermal expansion from ocean warming due to global warming.) Perhaps 60% of this ice loss is from glaciers and ice caps rather than from the two ice sheets on Greenland and Antarctica. And the contribution of these smaller glaciers has accelerated. My own local area, whose fresh water supplies are essentially served by 11 glaciers on Mt. Hood, have seen the glacier volume decline by about 50% in the last 30 years, for example. So it is really fresh water supplies, in those areas where glaciers serve as fresh water storage, that will be impacted a great deal in the short run.
Thing is, we don't need to guess about any of this or hypothesize about it. Eustatic sea level rise is a fact, as is glacier retreat and the melting of the two ice sheets.
The issue of a melting north polar ice cap not affecting eustatic sea level is a distraction from these facts. So anyone who is claiming to be expressing an informed opinion then making an analogy to a cube of ice in a cup of water as evidence that there should be no sea level rise on Earth is being disingenuous. It's impressive if you come up with this analogy as thoughtfulness of your own. It's disingenuous, though, if someone professing to be informed brings it up.
Your experiment is a model for sea ice. For a model for land ice, put an ice cube on an inverted bowl.
Alot of ice is above land
If I leave an ice cube to melt in a drink, the water level of the drink shouldn't change because the ice should be the same mass as the water it produces.
Surface ice melts runs into ocean, ocean rises. Think for two seconds occasionally and you won't embarrass yourself so much
Bacheous was correct about thermal expansion. I don't think that we know that a warming climate wouldn't increase precipitation which conceivably might increase glaciation.
Edit, you will notice that I got a thumbs down. This is because AGW is all about politics and because it is, you have political zealots who think they know about science. As a geologist I understand that a warming climate doesn't necessarily mean shrinking glaciers. Glaciers recede and advance based on a number a factors, temperature being only one of them.
