Ice Caps and Water Levels....

[MattRoberts]

Hi People,

 

Apologies if this has been covered before, or is so stupid noone else would have bothered but I've had this thought for ages, accept that I must be wrong somehow, but can't figure out why.....

 

Everyone seems to say, "when the ice caps melt, the water levels will rise, flooding us all."

 

However my theory is that the water level if anything should FALL, or at least stay the same... Based on the following.

 

1) Ice is less dense than water

2) To float a body has to displace it's weight in water.

 

Therefore for a ton of ice to float, it needs to displace a ton of water.... Ice takes up more space than water (so the tip of the iceberg with be out of the water) but when the ice melts it's still only a ton of water, which was displaced by 90% of the iceberg when it was a solid in the first place....

 

So depending on the difference in densities between the two, the water level will fall, IF, enough of the ice is below the water... and will stay the same if "too much" is above water.

 

However I can't see how the water levels would rise, and certainly not by the levels needed to flood my stupid self.

 

The only things I can see ruining my theory is

 

a) The ice caps/sheets aren't actually floating (perhaps self suspending or something)

b) The fact it's salt water, which has some effect on my premises.

 

Anyway, hope i've explained myself well enough and will be interested to see what you think.

 

Kind regards,

 

Matt Roberts

[insane_alien]

the antartic ice sheet isn't floating. theres a whole continent under it. it is this ice sheet that will cause the flooding.

 

you are right in that the arctic icesheet will not cause much rise, though the greenland ice sheets will.

 

also with antatica, when the ice melts and the water runs off, it would cause the land itself to rise up as it is suddenly not under the weight of a few trillion tonnes of ice. this will case further rises in sealevel.

[MattRoberts]

Ok, that would explain it.... I guess I better switch to energy saving lightbulbs after all.

 

 

 

 

Or just buy a boat.

 

Thanks for the prompt reply,

 

Matt

[iNow]

Ok, that would explain it.... I guess I better switch to energy saving lightbulbs after all.

 

 

 

 

Or just buy a boat.

 

Now THAT's funny, Matt.

[Mr Skeptic]

Also, water expands as it warms. If the water in the oceans starts warming, it will increase in volume. The change is miniscule, but the volume is enormous.

[Psycho]

Also, water expands as it warms. If the water in the oceans starts warming, it will increase in volume. The change is miniscule, but the volume is enormous.

 

To add to that, the ice currently reflects more of the light due to its colour (white) where as if it melts the sea which is darker will absorb more of the heat and therefore expand quicker.

[iNow]

Also, water expands as it warms.

 

Okay, I might sound like an idiot (I usually do, anyway... it's never stopped me before), but I thought water expanded when it froze? Wouldn't it need to warm up pretty significantly to "expand" in the sense that you mean?

[Mr Skeptic]

 

When water freezes (at normal pressures) it expands a lot, like 10%. But like anything else, it expands when heated. The highest density and lowest volume is at 4 C, which is why that is the ideal temperature for morgues and refrigerators. I think that the expansion below 4 C is an anomaly as compared to most materials, because of the low density of ice.

[JohnB]

also with antatica, when the ice melts and the water runs off, it would cause the land itself to rise up as it is suddenly not under the weight of a few trillion tonnes of ice. this will case further rises in sealevel.

Ah, but as the sea level rises the crust underneath depresses due to the extra weight causing a) the sea level to drop and b) the land to rise.

 

Just out of curiousity are you predicting 50⁰+ of warming down there? >:DFrom Antarctic Connection, "The annual average temperature is -50°C (-58°F). Winter temperatures drop quickly, then level out. Summer is short, from mid-December to mid-January, however, temperatures can reach a balmy -30°C (-22°F)! "

 

Last I heard, ice doesn't melt below 0⁰C.

 

As I write this the temp at the South Pole Station is -75⁰F. Ah, late summer in the south.

 

Or just buy a boat.

Fella next door is building one. Normally wouldn't worry me, but he's been out collecting animals as well.

[swansont]

Ah, but as the sea level rises the crust underneath depresses due to the extra weight causing a) the sea level to drop and b) the land to rise.

 

Why? If you're looking solely at warming, the mass hasn't changed, just the density. And the expansion increases r, so the weight actually decreases ever-so slightly.

 

And if you are looking at added mass, why would the effect of the crust drop exceed that of the water addition?

[insane_alien]

And if you are looking at added mass, why would the effect of the crust drop exceed that of the water addition?

 

especially when the water is far less dense than the ground(hence the oceans are on the surface)

[Mr Skeptic]

Just out of curiousity are you predicting 50⁰+ of warming down there? >:DFrom Antarctic Connection, "The annual average temperature is -50°C (-58°F). Winter temperatures drop quickly, then level out. Summer is short, from mid-December to mid-January, however, temperatures can reach a balmy -30°C (-22°F)! "

 

Last I heard, ice doesn't melt below 0⁰C.

 

Well, best get better ears then.

[swansont]

Last I heard, ice doesn't melt below 0⁰C.

 

Oh, yeah, how'd I miss that?

 

Freezing point depression. Salt water has a freezing point below 0 ºC.

http://www.scienceforums.net/forum/showthread.php?t=30735

[doG]

One more variable for the mix, the oceans are getting deeper and sea levels are predicted to fall over the next millennia...

[swansont]

One more variable for the mix, the oceans are getting deeper and sea levels are predicted to fall over the next millennia...

 

And the article points out that 1.5 microns a year can be safely ignored in light of other factors.

[SkepticLance]

Current sea level rise is about 3 mm per year, or a little more than the length of the average human foot over 100 years. Unless it increases substantially, not too much flooding in the near future.

 

Most of Antarctica and Greenland have average temperatures well below 0 Celsius. Thus no melting unless temperatures rise A LOT! Melting of sea ice does not count, since it has no effect on sea level.

 

In fact, global warming puts more moisture into the atmosphere, which in theory should lead to more moisture in the winds blowing from the sea over Antarctica and Greenland, leading to more water falling as ice onto the land mass. This would be a sea level lowering mechanism. Again, unless temperatures rise a lot.

 

The current sea level rise appears to be caused by a combination of thermal expansion of water, and the melting of glaciers and ice fields in areas other than Antarctica or Greenland. eg. The Rocky Mountains, the Himalayas, and the Andes etc.

[Edtharan]

Current sea level rise is about 3 mm per year, or a little more than the length of the average human foot over 100 years. Unless it increases substantially, not too much flooding in the near future.

This is what theya re talking about, that sea leve rise will increase substantially.

 

Most of Antarctica and Greenland have average temperatures well below 0 Celsius. Thus no melting unless temperatures rise A LOT! Melting of sea ice does not count, since it has no effect on sea level.

Sea ice doesn't have much impact, but Ice shelves do. In Antarctica these are acting like dams against the flow of Glaciers. If these break apart there will not be much stopping glaciers from flowing into the ocean (and then melting).

 

Also remember it is an average rise in temperature not an equal rise all over the world. Some places will get colder and this allows other places to warm up further than the "average".

 

Just out of curiousity are you predicting 50°+ of warming down there? From Antarctic Connection, "The annual average temperature is -50°C (-58°F). Winter temperatures drop quickly, then level out. Summer is short, from mid-December to mid-January, however, temperatures can reach a balmy -30°C (-22°F)! "

Remember these are average temperatures. It can get warmer than these temperatures. All it would take is more time at higher temperatures and more ice would melt in the summer and less in the winter. Cumulatively this can make a big difference.

 

Besides, there was a time when Antarctica was free of ice and global temperatures were not 50° hotter. So it won't take a rise of 50° (or 30° as a minimum) to melt the ice of Antactica.

 

At the moment because the ice sheets of Antarctica are kilometres thick, it is like being on top of a mountain, so of course the surface temperatures are going to be colder than they would normally have been. Once this ice sheet starts to thin (due to glaciers takeing the ice away, then htis height will be lost and the surface temperature will also go up.

[JohnB]

My post was meant with tongue firmly in cheek.

 

To keep people happy.

And if you are looking at added mass, why would the effect of the crust drop exceed that of the water addition?

It wouldn't, it would just be a very, very tiny mitigating factor.

Freezing point depression. Salt water has a freezing point below 0 ºC.

The Antarctic Continental Ice Sheet is not salt water.

Remember these are average temperatures. It can get warmer than these temperatures. All it would take is more time at higher temperatures and more ice would melt in the summer and less in the winter. Cumulatively this can make a big difference.

True. However the statement I quoted said the midsummer temp was -30. You need a lot of warming to raise this anywhere near melting point.

In Antarctica these are acting like dams against the flow of Glaciers. If these break apart there will not be much stopping glaciers from flowing into the ocean (and then melting).

Also true. I'm just trying to add a touch of reality. The Jakobshavn Glacier is the fastest in the world, moving at (at it's fastest) 9.4 km/year.

 

If we look at Antarctica, assuming a glacier that starts at the south pole and flows to the closest shoreline. The distance (via Google Earth) is 1240km. So if the glacier moved at that speed from day 1 it would take 132 years for the pole ice to reach the shoreline. If it flows toward the Indian Ocean, the distance is closer to 2800 km with a travel time of circa 300 years.

 

Bottom line, the ice isn't going to melt anytime soon.

Besides, there was a time when Antarctica was free of ice and global temperatures were not 50° hotter.

40 million years of continental drift tends to change weather patterns slightly.

[swansont]

The Antarctic Continental Ice Sheet is not salt water.

 

No, but the water surrounding it is, and will freeze at a lower temperature. Consequently, it can melt ice, with which it comes into contact, at a lower temperature.

 

True. However the statement I quoted said the midsummer temp was -30. You need a lot of warming to raise this anywhere near melting point.

 

But I believe that's above the sublimation point, so there can still be loss of mass that increases with increasing temperature.

[Edtharan]

Also true. I'm just trying to add a touch of reality. The Jakobshavn Glacier is the fastest in the world, moving at (at it's fastest) 9.4 km/year.

IF you read that article, then you would have read that coinsiding with an increased speed fo the glacier was an increased thinning of it. This thinning was also putting water into the oceans. Imagine if this were to occure with the antarctic glaciers too. Not only speeding up their decent, but also thinning out.

 

They don't need to melt like ice cubes in a drink, they can thin and water from the thinning ends up in the oceans. It is not melting as such, but it can come from the fact that weather patterns change and less snow gets domped onto the glacier, but it has to get dumped somewhere and this could be in areas where the glaciers aren't forming (which if you think about it, it would have to wouldn't it), or it might be that the ice is ground up more by the fast moving galcier (which would generate some extra heat, but the ground up ice would be more likely to melt due to localised increases in temperatures, or finally due to the fact that salt decreases the mealting point of ice and where the glacier is in the ocean, this would increase the amount of melting there (and if it is ground up then this would occur quicker).

 

This isn't mentioning sublimation. If the atmosphere is dry, even if it is very cold, it can cause the ice to sublime and then this water in the atmosphere will have to be dumped eventually somewhere (and likely no over a glacier forming region, but elsewhere where it will casue increased precipitation and therefore more water getting into the oceans.

 

To put it simply: The way Ice and enter and leave glaciers is complex and not yet completely understood. But there is many ways other than just "melting because of high atmospheric temperatures" that Ice can be removed from a glacier and enter the oceans.

 

In fact even if you just moved the ice in the glaciers without melting it from the land into the oceans, it would cause a rise in ocean levels.

 

You can try this experiemnt yourself. Just get a glass and fill it to the brim with water. then get some ice cubes and gently place them into the water. You will overflow the glass.

 

Yes, when ice is already in the water then when it melts the height will remain the same, but the ice from glaciers is not in the water it is on land. When it moves from the land into the water, it is like placeing an ice cube into that glass of water that was already full to the brim. So melting is not the only problem.

[JohnB]

But I believe that's above the sublimation point, so there can still be loss of mass that increases with increasing temperature.

I agree with your point but couldn't find a definitive value for the sublimation point of ice under those conditions. Would you care to establish an estimate of the loss increase?

 

(As an aside while looking for sublimation point values, I came across this webpage. The spiral troughs at the Martian Pole are amazing.)

No, but the water surrounding it is, and will freeze at a lower temperature. Consequently, it can melt ice, with which it comes into contact, at a lower temperature.

Of course, my point was that the ice has a 2,000 km trip to get to the water first.

IF you read that article, then you would have read that coinsiding with an increased speed fo the glacier was an increased thinning of it. This thinning was also putting water into the oceans. Imagine if this were to occure with the antarctic glaciers too. Not only speeding up their decent, but also thinning out.

True. But the Jacobshavn Glacier is less than 150 km long. Are you going to apply coastal weather conditions to the interior of the continent? Can you provide any evidence to back up the idea?

and then this water in the atmosphere will have to be dumped eventually somewhere (and likely no over a glacier forming region, but elsewhere where it will casue increased precipitation and therefore more water getting into the oceans.

On what basis do you consider this "likely"?

To put it simply: The way Ice and enter and leave glaciers is complex and not yet completely understood. But there is many ways other than just "melting because of high atmospheric temperatures" that Ice can be removed from a glacier and enter the oceans.

Again true.

 

A question. Is the Antarctic cold because there is a lot of ice? or is there a lot of ice because the Antarctic is cold?

 

The crux of my comments is that the Antarctic ice is not going to melt anytime soon, soon in this case being within the next 200 years. To do this would require that all Antarctic glaciers increase speed to 50% higher than the fastest glacier tomorrow and continue at this speed for the next 200 years just to get the current polar ice to the coastline.

 

I'm simply against, as the OP put it, the idea that "when the ice caps melt, the water levels will rise, flooding us all." This is fear mongering pure and simple. It has no basis in reality in way, shape or form.

 

We often say here that Extraordinary claims require extraordinary evidence. You want to claim that the ice cap will melt within 100 years? Fine, but that's one hell of a claim, let's see the evidence.

In fact even if you just moved the ice in the glaciers without melting it from the land into the oceans, it would cause a rise in ocean levels.

And if the moon was a differnt colour and made of different stuff, it would be green cheese. As your fact has no bearing on reality, your point is?

[swansont]

I agree with your point but couldn't find a definitive value for the sublimation point of ice under those conditions. Would you care to establish an estimate of the loss increase?

 

The sublimation temperature of water is around 200 K. At -30 ºC (243 K), the vapor pressure is around a few tens of Pa, and it goes up ~exponentially with temperature, so at 250 K it's 100 Pa.

 

http://www.lsbu.ac.uk/water/images/phase.gif

[JohnB]

Ah, thank you.

 

I should have added.

 

And the loss increase is?

 

I fully accept ice loss due to sublimation, but to have bearing on the current discussion we need a figure for the current rate of loss and an estimate for possible future loss rates. We also need some idea of where the lost water is actually going.

 

Without these three things it's only unfounded supposition and hand waving.

 

Please remember I'm countering the doomsayers and alarmists.

 

Greenland has 2.6 x 10⁶ km³ of ice. To melt in 100 years it has to lose on average 26,000 km³ every year for the next century. From Science Daily, which references a NASA article putting the annual loss at 220 km³ for 2005. At this increased rate it will take 11,818 years for the ice to melt.

 

So the current ice loss rate is 118 times too low for a 100 year disappearance. If the rate of loss increased by 3,000%, 30 x, it would still take 400 years to melt the ice.

 

Estimates are that if the Greenland ice sheet melted, sea levels would rise by 6-7 metres. However at current loss rates it would lose 22,000 km³ in 100 years which would be enough to raise sea levels by less than 6 cm.

 

Compare this to tide times and size from Tilbury at the mouth of the Thames.

Time Type Height (metres)

0117 High 6.3

0748 Low 0.2

1342 High 6.5

1953 Low 0.7

 

These just happened to be the first numbers came across and are from the BBC. As can be seen, 6 cm is not (literally) a drop in the ocean and would have no obvious major effect here.

 

Antarctica has 30 x 10⁶ km³ of ice. Again Science Daily (if anyone has better figures, please let me know) puts the annual loss at a whopping 152 km³. Wow, at that rate the Antarctic will melt in a mere 197,000 years. I'm scared.

 

If people want to talk in mere centuries then they had better show bloody good proof that the rate of ice loss will increase not by 20% or 50%, they need increases in the order of 19,000%.

 

Ain't gonna happen.

[swansont]

Please remember I'm countering the doomsayers and alarmists.

 

Greenland has 2.6 x 10⁶ km³ of ice. To melt in 100 years it has to lose on average 26,000 km³ every year for the next century. From Science Daily, which references a NASA article putting the annual loss at 220 km³ for 2005. At this increased rate it will take 11,818 years for the ice to melt.

 

So the current ice loss rate is 118 times too low for a 100 year disappearance. If the rate of loss increased by 3,000%, 30 x, it would still take 400 years to melt the ice.

 

Estimates are that if the Greenland ice sheet melted, sea levels would rise by 6-7 metres. However at current loss rates it would lose 22,000 km3 in 100 years which would be enough to raise sea levels by less than 6 cm.

 

But that's an exceedingly conservative analysis. The rate has doubled in 10 years, according to your link. But you've assumed the loss rate is constant, which contributes ~0.5 mm per year. Why should it stop increasing? What if it continues along its current trend, or accelerates? Even if the rate increase is linear, it's ~3 cm in 25 years (rather than 50) and more than 20 cm by the end of the century (and 30 cm in 100 years). If it's exponential, it's worse. (This is Greenland alone)

[Edtharan]

On what basis do you consider this "likely"?

Well, how much area is in the glacial feeder zones and how much is outside the feeder zones? Precipitation falling outside the feeder zones will not contribute to adding to the glacier (that is obvious). So if the glacier is loosing mass, then it must be going somewhere else (outside the feeder zones).

 

The crux of my comments is that the Antarctic ice is not going to melt anytime soon, soon in this case being within the next 200 years. To do this would require that all Antarctic glaciers increase speed to 50% higher than the fastest glacier tomorrow and continue at this speed for the next 200 years just to get the current polar ice to the coastline.

It took thousnads, if not millions of years for the ice on Antactica to build up. 200 years is soon. Very soon .

 

Sure it may not be in your life time. But humans will still be around, you decendants would have to deal with it. 200 years might sound a long time, but even within 100 years we will be seeing the effects, and that could be within your own children's life time.

 

Remember that 200 years is to get all the current ice into the ocean. We wouldn't need all of it to start to raise the ocean's height by significant amounts.

 

And if the moon was a differnt colour and made of different stuff, it would be green cheese. As your fact has no bearing on reality, your point is?

My point is that you don't actually have to melt the ice to get the rise in sea levels. Even if the glaciers just increased their speed, putting more ice into the oceas, but not melting you would still get sea level rises.

 

It is not about the rate of melting (so you don't need to increase the temperature to the melting point), it is about the rate of water (as ice or as liquid) entering the oceans.

 

We also need some idea of where the lost water is actually going.

There are only two places wher ethe water can go: Into the atmosphere or falling as prcipitation (rain or snow).

 

If it is staying in the atmosphere, then is bad news. Water vapor is a greenhouse gass. This will therefore lead to an increase in temperatures (and more melting ).

 

If it is falling as precipitations, then (statistically speaking) it will be less likely to fall back onto a glacier (in fact Antactica is one of the dryest continents), so it will be falling else where and not gettign locked up in ice sheets. The only place for it to go then is the lowest points, or the oceans. This is also bad news as this will mean an increase in ocean heights.

 

Another bad thing is that when you get water precipitating out of the atmosphere, it releases energy into the atmosphere. This means higher atmospheric temperatures (again leading to more melting and more water vapor entering the atmosphere), stronger winds, more and more powerful storms, and so on.

 

It is a double whammy. Water vapor increases atmospheric temperatures and precipitation causes increase atmospheric temperatures. Increased atmospheric temperatures causes more water to be evaporated into the atmosphere and so on in the cycle.

 

Greenland has 2.6 x 106 km3 of ice. To melt in 100 years it has to lose on average 26,000 km3 every year for the next century. From Science Daily, which references a NASA article putting the annual loss at 220 km3 for 2005. At this increased rate it will take 11,818 years for the ice to melt.

 

So the current ice loss rate is 118 times too low for a 100 year disappearance. If the rate of loss increased by 3,000%, 30 x, it would still take 400 years to melt the ice.

But for the effects to be felt we don't need a 100% loss of ice. It might take those 11,818 years to loose all of the ice, but even 1% of that amount of ice entering the oceans will cause a significant increase in ocean levels (BTW: 1% of 11,818 years is 118.18 years, or close to 100 years).

 

Lets say that ever 50 years the rate is doubleing (conservitive). Your numbers are at 220km^3 per year.

 

So for the first 50 years this give a total of 11000km^3, but for the next 50 years this gives and extra 22000km^3 and a grand total of 33000km^3.

 

Your link indicated a doubleing ever 10 years. Lets look at that.

So for the first 10 years we have 2,200km^3

The next 10 years (total 20) we have and extra 4,400km^3 (total 6,600km^3)

The next 10 years (total 30) we have and extra 8,800km^3 (total 15,400km^3)

The next 10 years (total 40) we have and extra 17,600km^3 (total 33,000km^3)

The next 10 years (total 50) we have and extra 35,200km^3 (total 68,200km^3)

The next 10 years (total 60) we have and extra 70,400km^3 (total 105,600km^3)

The next 10 years (total 70) we have and extra 140,800km^3 (total 246,400km^3)

The next 10 years (total 80) we have and extra 281,600km^3 (total 528,000km^3)

The next 10 years (total 90) we have and extra 563,200km^3 (total 1,091,200km^3)

The next 10 years (total 100) we have and extra 1,126,400km^3 (total 2,217,600km^3)

 

Or 2.2*10^6 .

 

So, if it continues to double, then yes, in 100 years (or there about) it would all be melted.

 

However, I still don't think it would double for 100 years. It might not get that far, but even if it peaked at around the rate of the 50 year mark, that is still a very significant amount of water (ice or liquid water) that is going to enter the oceans. However, if we continue as normal, then we could be looking at the doubling scenario, or even worse (the rate if increase increases).

 

Antarctica has 30 x 106 km3 of ice. Again Science Daily (if anyone has better figures, please let me know) puts the annual loss at a whopping 152 km3. Wow, at that rate the Antarctic will melt in a mere 197,000 years. I'm scared.

Not if the rate of loss increases, as observations seem to indicate it is doing.

 

20 years ago, the loss was not as big as it is today. 10 years ago it was greater than it was 20 years ago, but still less than to day. Why wouldn't the rate of less be larger in the next 10 years then larger again in 20 years than larger again in 30 yearas and so on?

 

The rate of loss is increaseing (aproximately doubling every 10 years). The cuases of this doubing are still there. They are still causing this doubing. So we can project what this doubling would cause by projecting it into the future.

 

Your extimate has this major flaw. You assume that dispite the fact that loss rates have beeen doubling, future loss rates will occur at todays loss rates.

 

It is a bit like being in a car with you foot planted on the accelerator. You glance at you speedo and see that you are only doing 60km/h and assuming that dispite your foot on the accelerator, you will still only be doing 60km/h in 1 minutes time because you are only doing 60km/h now.