Please register to participate in our discussions with 2 million other members - it's free and quick! Some forums can only be seen by registered members. After you create your account, you'll be able to customize options and access all our 15,000 new posts/day with fewer ads.
You also have to figure in the fact that freshwater from glacier melt will cause more rising seawater due to difference in density. It floats! It causes MUCH more rise in levels that frozen sea ice melting.
Wave action caused mixing with the top layer increasing salinity. Additionallly, despite being fresher, it is also very cold, which increases its density, causing it to further mix with the other water mass in a process called cabaling.
The amount of increased sea level rise due to melting sea ice is understated frequently. Once that melt water joins the rest of the ocean water mass a significant proportion of it will raise in temperature enough that it will under go thermal expansion. How much is currently being studied, but to say unequivocally that sea ice melting will not effect sea level is incorrect.
------->>> Lots of impressive mathmatics but your pseudo-science is just hooey and would be refuted by 99% of real climate scientists. I'm not one but I'm a geologist and already see major mistakes. For one, the ice cube in a glass in not an analog. In the north polar ice cap the analog works because the ice is over water like icewater in a glass. However, a major fraction is over the bedrock of Greenland. The ice really does melt and add ocean water volume. The same to a many-fold degree with all the south polar ice over the massive continent of Antarctica. This melt will cause a HUGE increase of sea level. Combined as much as 300 ' or more in 2 or 3 centuries albeit.
Also, your point about the ice pushing down the land they are on is true. However this actually means an INCREASE in the sea level raising effect! Isostatic rebound means the portion of Greenland and Antarctica below sea level will "bounce up" tectonically and replace water volume.
Additionally as the melt water mixes into ocean wate it warms and a some proportion of it will join the surface layer whee it will increase its volume through thermal expansion. By how much is currently unknown, but even sea ice melting can cause sea level rise.
I agree with the issues in the post you quoted about isostatic rebound, if nothing else there is overwhelming evidence that during the last glacial minima sea level was over 100m higher than now, just look at the coastal plains.
Post glacial rebound is cancelling out the effects of sea level rise.
Only in some localized areas. It is not globally equal, if for no other reason than only land covered with glaciers will rebound. Non- polar areas are absolutely seeing the effects of sea level rise.
I love it when fear-mongers try to call basic math skills "pseudo-science." If nothing else, it proves my point that those claiming such gloom and doom are clueless and invested in following the crowd instead of using independent thought.
As blind cleric points out, post glacial rebound is real, and has a mitigating effect. The seeming immovability of bedrock has been shown time and time again to be a false assumption. Little things like the Grand Canyon and the Himalayan uplift happened to "bedrock." You might want to invest in a refresher course on plate tectonics and plasticity.
In the meantime... if you can show and detail where the math is wrong, please do so. Calling it by pejoratives is not going to win any debate.
It is called isostatic rebound, and in areas where glaciers exist, it can account for approx 1 cm of upward movement a year. Which is great, if you are a region covered in ice, like Greenland or Antarctica. If you are not one of those areas there is no rebound.
Additionally, those non glacial land masses that are part of the same continental plate, will frequently see the opposite change. To use your, (what was it 3rd grade physics?) the land masses are like a raft "floating" on the plastic asthenosphere. Now take a really large land mass like North America (which is mostly one plate) and put something very heavy on one end, like a glacier. What effect will that have on the other end of the "raft"? It will cause it to rise up higher than the end being pushed on. Now remove that heavy object what happens? The end that had the glacier does rise, but the other end also sinks an equal amount. This is why the effects of isostatic change (the pushing of glaciers) is always localized rebound not global.
Only in some localized areas. It is not globally equal, if for no other reason than only land covered with glaciers will rebound. Non- polar areas are absolutely seeing the effects of sea level rise.
Right. I was responding to someone who asked why sea levels weren't rising as much in Alaska, and included that context in a quote.
Some parts of coastal Alaska weren't "recently" covered in ice, and they are experiencing sea level rise that is threatening communities.
It is called isostatic rebound, and in areas where glaciers exist, it can account for approx 1 cm of upward movement a year. Which is great, if you are a region covered in ice, like Greenland or Antarctica. If you are not one of those areas there is no rebound.
Additionally, those non glacial land masses that are part of the same continental plate, will frequently see the opposite change. To use your, (what was it 3rd grade physics?) the land masses are like a raft "floating" on the plastic asthenosphere. Now take a really large land mass like North America (which is mostly one plate) and put something very heavy on one end, like a glacier. What effect will that have on the other end of the "raft"? It will cause it to rise up higher than the end being pushed on. Now remove that heavy object what happens? The end that had the glacier does rise, but the other end also sinks an equal amount. This is why the effects of isostatic change (the pushing of glaciers) is always localized rebound not global.
Nice try. Really nice try. Your raft analogy is only 2nd grade physics though, and (to use a pun) a deflection.
The crust of the earth is divided into plates with subduction zones, etc., as you state, but the entire surface is covered with the "rafts" of the crust. The plates don't have wide open gaps where the other layers come to the surface. Because of that, the oceans can be more accurately thought of as another liquid "raft" on top of those rafts that comprise the crust.
When the overburden weight of a glacier is removed from one plate or raft, (as would happen if the ice overburdening Antarctica was to melt) that entire plate would rise because the pressure from under the plate is no longer counterbalanced by the overburden. (As an aside, the plates are not completely rigid, as in your tilting raft example.) Since the mantle is plastic but not compressible, the volume of mass migrating under that plate to lift it has to come from somewhere, and that somewhere can only be from under the other plates.
It might seem that I am arguing against myself with what I just stated, as I infer that all the plates other than Antarctica would then be lower and more likely to be covered with water. However... the overburden of the ice is now liquid water spread as a layer ONLY over the surface of the oceans - NOT the land. The effect then is to push the FLOOR of the ocean a little deeper more than to cause the surface level of the ocean to rise, except perhaps temporarily.
Nice try. Really nice try. Your raft analogy is only 2nd grade physics though, and (to use a pun) a deflection.
The crust of the earth is divided into plates with subduction zones, etc., as you state, but the entire surface is covered with the "rafts" of the crust. The plates don't have wide open gaps where the other layers come to the surface. Because of that, the oceans can be more accurately thought of as another liquid "raft" on top of those rafts that comprise the crust.
This is 100% not true. There absolutely are "gaps" they are called faults or mid ocean ridges. They are absolutely capable of and do move independently of one another. For example the pacific plate is moving NNW and the North American plate is moving WSW. Meanwhile they absolutely do move vertically in different directions as well.
Additionally, you are ignoring the fact that continental crust, and oceanic crust are different densities. If you must persist in the raft analogy, the continents are also granite rafts siting on top of basaltic ones. So the more correct image would be raft of continental crust and ocean sitting on top of oceanic/baslatic crust. The continental crust is what undergoes isostatic rebound, unless you are actually claiming oceanic crust is subject to isostatic rebound, are you claiming that? Therefore the rebounding of continental crust is absolutely as I described and is known to be LOCALIZED. Are you trying to claim that isostatic rebound is a global phenomenon?
Quote:
When the overburden weight of a glacier is removed from one plate or raft, (as would happen if the ice overburdening Antarctica was to melt) that entire plate would rise because the pressure from under the plate is no longer counterbalanced by the overburden. (As an aside, the plates are not completely rigid, as in your tilting raft example.) Since the mantle is plastic but not compressible, the volume of mass migrating under that plate to lift it has to come from somewhere, and that somewhere can only be from under the other plates.
This is where you raft analogy falls apart. The antarctic plate is unique among tectonic plates as having a centrally located glacier, this means it is the only raft being pushed down from roughly the center, so yes, the entire continent will rebound, assuming you removed all the glacier. But so would the rest of plate, which would change the basin of the southern ocean resulting in eustatic sea level rise.
Second, this is not the case for the other plates with significant glaciers.
Lets look at the last sentence. Yes as the one localized area rebounds, other plates MUST (as you mentioned due to compressibility) see a decrease in isostasy in order to maintain equilibrium.
Quote:
It might seem that I am arguing against myself with what I just stated, as I infer that all the plates other than Antarctica would then be lower and more likely to be covered with water. However... the overburden of the ice is now liquid water spread as a layer ONLY over the surface of the oceans - NOT the land. The effect then is to push the FLOOR of the ocean a little deeper more than to cause the surface level of the ocean to rise, except perhaps temporarily.
Wait, you do realize that plates are both continental an oceanic crust right? If the antarctic plate is seeing rebound across its entire plate that would raise the basin of the southern ocean as well.
So not only are you changing all of the known physics of isostasy but eustasy as well? You are accepting of isostatic rebound but refuse to acknowledge eustatic changes? Why?
Anyway what you are claiming would mean there was no relationship between changes in sea level and glaciation. But this is plain old not true, we know from many lines of evidence that periods of glacial minima correspond to increases in sea level. Are you also claiming there have been no changes in sea level in previous climate shifts?
"Anyway what you are claiming would mean there was no relationship between changes in sea level and glaciation. But this is plain old not true, we know from many lines of evidence that periods of glacial minima correspond to increases in sea level. Are you also claiming there have been no changes in sea level in previous climate shifts?"
First, I am not claiming that there is a unitary factor that affects the seacoasts and where the ocean and land meet. My point initially was, and still is, that the claims of hundreds of feet differences in sea level at the coasts due to ice melt is hogwash. If you noted the data on interglacial rise as cited earlier, it was less than a hundred feet. I wasn't there. I didn't influence it. Al Gore wasn't there. He most certainly didn't influence it.
If you want to claim I am saying stuff that I am not, go right ahead. If you want to try to find any excuse to dismiss what I have said, no matter how much you have to stretch, go right ahead. However, if that is your stance, it is a religious one and I don't argue against religious positions as it is a waste of my time and probably irritating to you.
Please register to post and access all features of our very popular forum. It is free and quick. Over $68,000 in prizes has already been given out to active posters on our forum. Additional giveaways are planned.
Detailed information about all U.S. cities, counties, and zip codes on our site: City-data.com.
Please register to participate in our discussions with 2 million other members - it's free and quick! Some forums can only be seen by registered members. After you create your account, you'll be able to customize options and access all our 15,000 new posts/day with fewer ads.
