Jump to content

If the polar ice caps melts it shouldn't cause the sea level to rise.


alchemy
 Share

Recommended Posts

Im no climatologists...but I read somewhere...that our climate system is also determined by the salinity ...in that ....if the salinity of the sea changes (as will be the case when all teh ice meltes)....the climate will unpredictably change as well.

Link to comment
Share on other sites

Ok we know that global warming is a fact and it can cause the polar ice caps to melt. But my question is this, isn't the polar ice caps just a giant block of ice that sits on top of the ocean? So even if it melts its shouldn’t cause the sea level to rise a lot.

 

Let me give you some better terms to work with here. There's a distinction that needs to be made.

 

Sea ice floats on top of water. Like ice cubes in a glass, sea ice displaces as much water as it weighs, and for that reason when it melts the water level remains unchanged. So you are correct in your suspicion that melting polar sea ice will not alter the water level.

 

Glaciers and ice sheets do not float on water. They sit on top of land. There are glaciers all over the world, and large ice sheets covering most of Greenland and Antarctica, like other people have mentioned. When glaciers and ice sheets melt, the water from them either flows into the ocean directly or evaporates and precipitates before flowing into the ocean. Either way, short of freezing again on top of land somewhere else, it's going to go into the ocean.

 

The polar ice caps are made up of both sea ice and ice sheets. So long story short: polar sea ice is not a concern in terms of water level, but polar ice sheets are.

 

That's not to say that sea ice isn't a concern in terms of global warming. One important property of sea ice is that it's highly reflective, having a reflectivity (known as an albedo) of about 90%. That's to say, 90% of the light hitting the ice bounces right back out into space. When sea ice melts and changes into ocean water, it becomes dark and thus highly absorbant. Rather than reflecting 90% of the light that hits it back into space, it absorbs 90% of the light. That light is retained by the water as heat. This increases the heat in the region, and helps cause nearby sea ice to melt and turn into light absorbing ocean water. This process is known as a feedback loop, because it feeds on itself.

Link to comment
Share on other sites

Here is another problem with the melting of the ice on Antarctica. The ices has a lot of weight, and this weight is pushing the continent of Antarctica downwards. When the Ice melts this will allow Antarctica to rise, along with the seabed around it (continental shelf). This riseing of the seabed will also displace water and contribute to a further rise in sea levels.
I'm a bit curious about this. As I understand it, if the Earth's crust rises in one place, it has to fall in other places. Also, the center of gravity and so forth has to remain more or less in place, or in balance. So as a mental exercice, if the antarctic icecap did all melt, lets look at this logical but not neccessarily chronological sequence:

 

1. Antarctic ice cap slides into sea and melts.

2. Sea levels rise, shifting center of gravity North.

3. Sea levels rise a little extra in North and a little less in South in response to shift in center of gravity.

4. Antarctic Crust rises some in response to loss of weight.

5. Equator tightens a bit under weight of extra water and in response to rising of antarctic, further increasing sea level rise closer to equator.

6. Changes in sesmic activity in response to shifts in pressure and contraction of crust at the equator and expansion of crust in Antarctic???

 

Not really sure. Just thinking out loud. I think you are right though in that there would be somewhat more sea level nearer the equator, and considerably less or even negative sea level rise nearer the Antarctic. As for the sesmic stuff I'm not sure as I think that stff gets really complicated. The other thing that gets weird is that if a mass of ice gets moving in a certain direction, like mostly towards Australia say, or mostly some other way, then wouldn't that change the Earths axis of rotation in some way, which might change our winters and summers in some way. Also if the distribution of heating and cooling of the Earths mantle changes that could change circulations within the mantle which might also change the Earths rotation and continental drifts and sesmic activity and so forth. Just as complicated as weather I should think, though a lot slower.

Link to comment
Share on other sites

I think you are right though in that there would be somewhat more sea level nearer the equator, and considerably less or even negative sea level rise nearer the Antarctic.

This is exactly what is going on in England at the moment. The southern parts of England are sinking and the Northern parts are rising. This is because of the last Ice age when ice covered the northern parts of England. The weight of all that ice pushed the northern parts of England down and this forced the southern parts up. Now that the weight has gone, the crust is rebounding and adjusting it's self.

 

2. Sea levels rise, shifting center of gravity North.

I don't think this effect would be all that big. Also remember there is ice in the Arctic that would also melt shifting the CM south. These would most likely cancel each other out (or nearly cancel out). The melting of the Arctic wouldn't cause a rise in the sea levels, but as far as changing the CM it would have the same effect as the Antarctic. This means point 3, 5 and 6 won't really happen.

 

The other thing that gets weird is that if a mass of ice gets moving in a certain direction, like mostly towards Australia say, or mostly some other way, then wouldn't that change the Earths axis of rotation in some way, which might change our winters and summers in some way.

Although there is a lot of mass locked up in the ice, it is an insignificant fraction of the mass of the Earth. So it wouldn't have any significant effect on the rotation of the Earth.

 

There might be some change in the rotation of the Earth by a fraction of a second, that is only picked up by atomic clocks, but nothing as significant as you suggested.

Link to comment
Share on other sites

  • 3 weeks later...
Im no climatologists...but I read somewhere...that our climate system is also determined by the salinity ...in that ....if the salinity of the sea changes (as will be the case when all teh ice meltes)....the climate will unpredictably change as well.
I can't remember where I read this, but it was actually a very serious reputable article, that said we should let higher salinity water from the pacific flow through the Panama Canal into the Atlantic because it would reduce global warming (or something to that effect. It might have been in a book... but then again it could be wrong)

 

So apparently salinity does have an effect on the climate if it's leading people to advocate moving water between oceans through the Panama Canal.

Link to comment
Share on other sites

..good point .. but ice caps are huge and deep into the water - its a 'eureka ' (look the guy up who said this) moment i.e. get in the bath and the bath water rises;

Yes, the Arctic ice cap is in water, but a lot of the Antarctic ice cap is over land. So, because the Antarctic ice cap is over land, it is not currently displacing water. If it them melts, it will add to the level in the oceans (just as poring water from melted ice cubes into a glass).

Link to comment
Share on other sites

Antarctica consists of huge glaciers atop bedrock.The Western Antarctic shelf is a floating ice sheet that is on the coast of antarctica. This shelf acts as a dam for any run off or movement of land based ice.If the western antarctic shelf melts or if there is a slight rise in sea level to dettach the antarctic shelf from the edge of the bedrock,the sheer weight of the land based glacier could slide into the water, dramatically raising sea levels.This is similar to stacking ice cubes in a glass of water so that the bottom ice cube touches the bottom of the glassand the top ice cubes are not floating on the water.When the ice above the water melts it displaces the water causing the water to overflow the glass.

Link to comment
Share on other sites

  • 4 weeks later...
This is exactly what is going on in England at the moment. The southern parts of England are sinking and the Northern parts are rising. This is because of the last Ice age when ice covered the northern parts of England. The weight of all that ice pushed the northern parts of England down and this forced the southern parts up. Now that the weight has gone, the crust is rebounding and adjusting it's self.

 

Then how do you explain Pevensey castle, the site of the Battle of Hastings in 1066 ? Just about as far South as you can get in England and originally built by the Romans AD 290 on a peninsula, where the sea once washed against its walls, it is now over a mile inland, and nearby Hailsham at that time also on the coast, is now over 6 miles inland. This would seem to be both inconsistent with the South sinking and sea levels rising over the past 2,000 years !

 

Perhaps it’s also worth mentioning the icecap did in fact extend to the South coast of England where the glaciers carved out the smooth chalk sedimentary rocks now known as the South Downs

Link to comment
Share on other sites

1. Antarctic ice cap slides into sea and melts.

2. Sea levels rise, shifting center of gravity North.

3. Sea levels rise a little extra in North and a little less in South in response to shift in center of gravity.

4. Antarctic Crust rises some in response to loss of weight.

5. Equator tightens a bit under weight of extra water and in response to rising of antarctic, further increasing sea level rise closer to equator.

6. Changes in sesmic activity in response to shifts in pressure and contraction of crust at the equator and expansion of crust in Antarctic???

 

Perhaps a bit more to consider here

 

Changes in sea levels are in the most part not due to ice melting at all. They are primarily caused by two main effects, local changes resulting in land masses rising or falling, and global changes which are due to the thermal expansion of the water in the oceans. The sea level has little to do with the melting of ice, since this process takes hundreds of thousands of years, during which time there are several glacial and interglacial periods reversing the process.

 

If all the ice in the World were to melt, the sea level would rise to the order of 80m above current levels. But this process, even if it were uninterrupted, would take the best part of a further 32,000 years at the current rate of melting. However during the next couple of thousand years or so, we will most probably have been plunged into our next glacial period, reversing the entire process and eventually reducing the sea level by as much as 50m or more. The melting of all our ice is not a scenario we need to consider.

 

The last major icemelt was 130,000 years ago, when temperatures were higher than at present. Most of the Northern hemisphere ice melted, contributing to a rise in sea level of 3.5m above current levels. However coral records indicate the sea level actually rose by 6m or more at this time, the balance of 2.5m being due to thermal expansion of water in the oceans, since the Antarctic ice sheet remained intact at this time. But coral records would most likely be generated in tropical zones where the water is warmer and the marginal effect of the centrifugal force produced by the Earth’s rotation would be greatest, resulting in slightly more of any icemelt migrating towards the equator. The effective acceleration of gravity at the poles is 980.665 cm/sec/sec while at the equator it is 3.39 cm/sec/sec less. The increased water depth in equatorial regions would create greater pressure on the ocean floor, and the reduction in weight of land based ice in the polar regions would also result in the elevation polar land masses. We also know that local gravitational effects of submerged mountains and canyons currently cause the formation of massive dents in the surface of the oceans, some measuring as much as 20m deep x 150km wide. It cannot therefore be assumed that any change in sea level would be uniform at all latitudes.

 

Although much is made of falling ice cliffs due to global warming, this is an annual event known as the Spring Breakup, and the ice reforms again during each Winter. We should also consider that although the edges of icecaps may temporarily melt, the overall amount of ice on the planet may actually increase, or more likely remain fairly stable. A warmer climate would allow the atmosphere to sustain more water vapour, itself the most potent of all greenhouse gases, and some of this will inevitably condense and fall as additional snow in the polar and mountainous regions, thus increasing the thickness of ice sheets. Both the thickening of the ice sheets and the increased water vapour in the atmosphere will contribute to a reduction in the sea level. The amount of water currently held in the atmosphere is equivalent to about 2.5cms of ocean depth, which represents the total rise in sea level over the past decade.

 

By 2100 some predict that temperatures may be similar to those 130,000 years ago, so perhaps we should base our predictions on past events. The increase in temperature shouldn’t be accompanied by storms and tidal increases causing devastation to coastal areas, since wild weather is primarily caused by the difference in temperature between the poles and the equator, and this temperature gap will be narrowing. We should therefore experience more stable weather patterns. Also back in 130,000 YBP most of Antarctica remained ice-covered, despite the sea level rising 6m or more. The icecap didn’t slide into the sea and the warming climate resulted in vast areas of frozen wilderness in the Northern hemisphere, particularly in Greenland, Canada and Russia, becoming inhabitable agricultural territory, far outweighing any relatively small erosions of current coastlines.

Link to comment
Share on other sites

  • 1 month later...
So apparently salinity does have an effect on the climate if it's leading people to advocate moving water between oceans through the Panama Canal.

There are some "small" problems with this, the Panama Canal is a fresh water system that is fed from the center via a large lake. The center of the canal is also at a significantly higher elevation than the two ends, hence the systems of locks at both ends of the Canal. In order to pump Pacific seawater to the Atlantic we would have to move it up hill against the flow of fresh water AND destroy a fresh water ecosystem in the process. It would be a heck of a lot easier to create a pipeline to do this.

 

Oh and has anyone thought of the ecological impact of moving vast quantities of Pacific sea water and the organisms it contains into the Atlantic? Dealing with the bilge water of ships is bad enough.

Link to comment
Share on other sites

I'm suprised that no-one has mentioned the latent heat or "heat sink" effect the 80 cal./gm needed to effect the state change will have. Once it is liquid, this will resume at 1 cal./gm. per degree Celsius. Obviously a much greater potential for rapid temperature fluctuations and weather perturbations, and not a constant dance with the freezing point and coherent flow, as it is now.

Link to comment
Share on other sites

  • 2 years later...

Ok think of it this way if you have a shallow dish thats halfway filled with water and rock it back and forth it creates waves that maintain the same consistency throughout. Now if you were to add a solid mass to this dish that is 10 x the density of water and rocked the dish back and forth it would create bigger more unstable waves while leaving the level of water pretty much the same. So in theory the biggest concern wouldn't be the rising of the water but the affects the masses would have on the overall force of the tides it would create bigger more unstable waves.

Link to comment
Share on other sites

umm what? if anything large areas of mass blocking waves are disappearing so your the point seems doomed from the start.

 

but adding a dense material to a plate of water doesn't influence the size of waves too much.

 

if i put a stack of pennies inthe plate(about 9 times denser) the water just flows round it. if anything the size of wave decreases.

Link to comment
Share on other sites

  • 1 month later...

I'm new to this forum so please excuse an oft repeated question

 

i understand that when a given mass of ice floats in water it diplaces a similar mass of that water. on melting it will effectively 'occupy' this volume, resulting in no overall change in volume of the water and so no increase in water level

Basic physics I know, and easily demonstrated

Here's the rub

When I consider that mature sea ice is mainly fresh water, and the salinity of sea water means it has a higher density, a smaller volume of sea water will be displaced than in the the freshwater eaxmple.

when the fresh water sea ice melts, it will produce a larger volume of lower density fresh water than the equivelent displaced mass of higher density sea water.

I've done the maths over and over, and checked my facts as much as possible, but every answer i get tells me i'm wrong. I would be really greatfull for an explanation of where I've gone wrong, as its driving me a bit nuts

i noticed a couple of references the idea but no definitive answers

Link to comment
Share on other sites

You're right about density displacement - a large part of the sea level rise comes from the fact that antarctic ice is on land, not water. So it's not like a melting ice cube, but rather dropping a new ice cube into an already-full glass.

Link to comment
Share on other sites

Then how do you explain Pevensey castle, the site of the Battle of Hastings in 1066 ? Just about as far South as you can get in England and originally built by the Romans AD 290 on a peninsula, where the sea once washed against its walls, it is now over a mile inland, and nearby Hailsham at that time also on the coast, is now over 6 miles inland. This would seem to be both inconsistent with the South sinking and sea levels rising over the past 2,000 years !

 

Perhaps it’s also worth mentioning the icecap did in fact extend to the South coast of England where the glaciers carved out the smooth chalk sedimentary rocks now known as the South Downs

That really isn't how the south downs formed at all, they were originally created in a shallow sea 60 million years ago from dead crustatations as all chalk is in a shallow sea over time erosion destroyed the centre of the rock formation separating the north and south downs and leaving a flat clay area known as the wield in the middle.

 

As for Pevensey castle it is obvious what happened there, longshort drift changed the coast line separating the large marsh area from the sea and stopping the tidal effect, the sea only ever got to the castle at high tide anyway it was always that far in land just originally marshland that was flooded by the sea separated it where as now due to this effect no longer happening the land has dried up to form what is most likely fertile farm land.

 

More to the point if the ice caps melt and the heat absorption will be greater increasing the water temperature across the globe which will further increase year on year meaning less snow falls and sea ice forms creating a positive feedback loop. Not to mention the increased probabilities of hurricanes which you would think would make the USA care more.

Link to comment
Share on other sites

  • 2 weeks later...

This only applies to the Arctic Ocean. Since there is no land on the Arctic Ocean, it is just a bunch of ice. Ice expands when it freezes, so when it melts, its volume decreases. They will cancel each other out, so the sea level would stay the same if all of the Arctic ice melted.

 

However, in Antarctica, all of the ice sits on a continent. If the ice melted there, it would flow off the land and cause the oceans to rise.

Link to comment
Share on other sites

This only applies to the Arctic Ocean. Since there is no land on the Arctic Ocean, it is just a bunch of ice. Ice expands when it freezes, so when it melts, its volume decreases. They will cancel each other out, so the sea level would stay the same if all of the Arctic ice melted.

 

However, in Antarctica, all of the ice sits on a continent. If the ice melted there, it would flow off the land and cause the oceans to rise.

 

was it really worth it just to reword that which has already been iterated several times?

Link to comment
Share on other sites

http://www.grida.no/climate/ipcc_tar/wg1/412.htm#tab113

 

Here are the sea level rise equivalents if Greenland and Antarctica ice sheets were to completely melt (calculated with allowance for isostatic rebound and sea water replacing grounded ice, and this therefore is less than the sea level equivalent of the ice volume)

 

Greenland ice sheet: 7.2m

Antarctic ice sheet: 61.1m

Link to comment
Share on other sites

ok, so I may be missing something, but unfortunately I don't know what.

I posted a while back asking for help on the very old question of why melting arctic ice doesn't raise sea levels.

I understand that a given mass of ice displaces its equivelant mass of water, and so when it melts it just 'occuppies the space it made' so no overall change in water volume (and consequently level). This is demonstrated with ice melting in a glass and observing the water level.

BUT

When I sit down and produce calculations , I have the added complication that in the Arctic mature sea ice is fresh water, and the liquid it is displacing is higher density salt water.

 

A 1000kg block of fresh water ice melts to produce a cubic metre of fresh water, but when floating in salt water this block will not displace a cubic metre. The 1000kg of higher density salt water displaced will have a slightly smaller volume. When the ice melts, there should be a cubic metre of melt water trying to fit into the slightly smaller space it displaced due to the differences in density.

 

I could be wrong (very likely - if so its probably due to one of my assumptions), if I'm right is it not mentioned because the effect is so small as to be of no consequence? This is not my field, but I am a teacher and feel I have a duty to understand thiis fully.

 

Sorry for the length of the post, but I simply cannot find an answer to this, hope someone can help.

Link to comment
Share on other sites

the salt doesn't contribute to the volume of the water. it will become more dilute, but this is merely because it has more volume available for it to occupy since it could not travel to the volume taken up by the ice.

 

since the ice has melted there is more fluid volume(but less solid volume)

 

again it all cancels out.

Link to comment
Share on other sites

A 1000kg block of fresh water ice melts to produce a cubic metre of fresh water, but when floating in salt water this block will not displace a cubic metre. The 1000kg of higher density salt water displaced will have a slightly smaller volume. When the ice melts, there should be a cubic metre of melt water trying to fit into the slightly smaller space it displaced due to the differences in density.

 

Yes, you are correct, ice made of fresh water, when melted, will create more water than it originally displaced due to the density difference between fresh water and salt water:

 

http://www.physorg.com/news5619.html

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.