Rising Oceans

[Josh]

So, I was watching TV last night and heard something I hadn't considered before regarding global warming, climate change and the following doom of rising oceans when all the ice melts.

Most of the ice is under the water, right? We all hear that if global warming continues then the ice will melt and the seas will rise and we're all going to have to learn to swim. But ...

What happens if you fill a glass with ice cubes and then pour in water to the top (filling in all the gaps)? The ice melts and no water overflows. When water freezes it expands; when it melts it shrinks. So why is there going to be rising waters when the Earth's ice melts?

[cyswxman]

I guess they are figuring on the ice that is existant on land now, though I believe those scenarios are quite exaggerated.

[grant hutchison]

So why is there going to be rising waters when the Earth's ice melts?

The ice that resting on bedrock, as cyswxman says, accounts for most of it. Most of the ice on Earth is tied up in glaciers and ice-caps, after all, not floating around as icebergs. A complete melt of the Antarctic ice-caps would raise the global ocean by a couple of hundred feet, for instance.

Grant Hutchison

[Halcyon Dayz]

The melting of sea-ice will have zero effect on the sea-level.
Archimedes tells us that the iceberg has the same mass as the water
it displaces. Therefor when melted, it's water will have the same volume
as that displacement.

The melting of land-ice however is a different story.
If all land-ice would melt, on Antarctica, Greenland and numerous gletchers,
the sea-level would rise approximately 60 meters.

[astronomo flaquito]

If I remember correctly, sea levels should rise not only due to the melting of continental glaciers, but as well to the expansion of the water as a result of higher temperatures. I understand that water expands as it freezes, but does it not also expand as its temperature rises? I'm not sure, if this is indeed true, that the expected change in sea temperature would be significant enough to make much of a difference in sea level.

[novaderrik]

isn't most of the ice on antarctica and greenland actually below sea level, due to the weight of the ice pushing the land down?
now, don't jump on me too hard if i'm wrong- i just remember hearing that somewhere a long time ago.

[Fram]

I think you're right (certainly for Greenland), but as that ice isn't resting in water (ocean) but on land, the calculation of the rising of the sea level if it would melt is still correct (although if parts would form lakes after melting, that might make a difference).

[Launch window]

A Sea-level rise will affect coastal regions throughout the world, causing flooding, erosion, and saltwater intrusion. NASA’s satellites and others like European envi sats have shown Glaciers melting at alarming rates in areas like Parque Nacional los Glaciares-Argentina Bhutan-Himalaya, Arctic glaciers, glaciers in the Democratic Republic of Congo, Indonesia, Uganda, New Zealand, European Alps, North Patagonia Icefield in Chile... and other places and even the modest sea-level rise seen during the 20th century led to erosion and the loss of 100 sq km of wetlands per year in the U.S. Mississippi River Delta. Most of this liquid water on planet Earth is far too salty for humans, plants or animals to consume. Only about 2.5% of the water on earth is freshwater and Himalayan glaciers that feed seven of the great rivers of Asia and ensure a year-round water supply to 2 billion people are retreating at a startlingly fast rate, the good things is that available information about the climate is not limited to the past century.

[Maha Vailo]

So, how would people adapt to rising sea levels, melting glaciers, erosion, and similar problems in the next hundred years?

- Maha Vailo

[Taks]

So, how would people adapt to rising sea levels, melting glaciers, erosion, and similar problems in the next hundred years?

i would assume they'd be smart enough to not wait till the water was up to their necks, so they would slowly move out of the areas that were impacted by rising sea levels.

a couple points:

1) sea levels are actually dropping in some places. the evidence that sea level change is due to melting ice is thin, pun intended. those that measure sea levels in one place as opposed to every inch of every coastline in the world aren't seeing the whole picture. many changes in sea level are due to the plates rising and sinking, which they are known to do.

2) glaciers have been receding since the last ice age. they've also been growing. they go back and forth with a trend towards recession simply because it is now warmer than it was during the last ice age (kind of a duh there). my point? there's not much we can do about something that was in play before we even had a chance to have an impact.

3) i've done some preliminary studies on the expansion of water theory. there's a few problems with the theory. most of the water on earth is actually near freezing (90% is below the thermocline which ranges from 2 to 4 degrees C). the peak density of water occurs at about 4 degrees C. a 1.6 degree C change in temperature at 4 degree C will result in a 0.001%, or one part per 100,000 change in the density. The water that is below that will change even less, and most of it will actually get denser, i.e. occupy less volume. Even surface water, which would see the largest changes, needs to shift by several degrees to see fractions of a percent change in density. In other words, the math just isn't there to support such conclusions.

taks

[Taks]

btw, the IPCC estimate of contribution to thermal expansion of the water was between 6 and 37 inches. that's 1/2 to 3 feet, not 100 feet. even with the low estimate, i would be prepared to debate the numbers.

70% of all the ice is contained in antarctica, and should it melt we'd see 200 feet or so. of course, the average temperature of antarctica is a balmy -37 degrees C, so melting is not an option (it is growing, actually).

greenland could contribute about 20 feet, but most of greenland is inland ice and not melting (coastal areas are, but they have been for longer than we've been rumored to be causing it).

taks

[jkmccrann]

isn't most of the ice on antarctica and greenland actually below sea level, due to the weight of the ice pushing the land down?
now, don't jump on me too hard if i'm wrong- i just remember hearing that somewhere a long time ago.

I believe that is the case, I've read somewhere that Antartica is actually the highest average elevation continent. IIRC it was stated in the article that the weight of ice on Antarctica depresses the land to such a degree that if it were not there, the land itself would rise between 4 & 6km, which one day it is likely to do given Antarctica is slowly moving north, but we're talking hundreds of millions of years and who knows what else will come into play between now and then.

[ToSeek]

Antarctica is slowly moving north

What other direction could it move?

[Glom]

of course, the average temperature of antarctica is a balmy -37 degrees C, so melting is not an option (it is growing, actually).

Indeed. Even a significant warming will still leave the Antarctic subzero and as such the ice will remain. What will change is that the water holding capacity of the air will increase leading to increased precipitation hence thickening. The Antarctic isn't in danger of melting.

What other direction could it move?

Touche, ToSeek!

[hhEb09'1]

3) i've done some preliminary studies on the expansion of water theory. there's a few problems with the theory. most of the water on earth is actually near freezing (90% is below the thermocline which ranges from 2 to 4 degrees C). the peak density of water occurs at about 4 degrees C. a 1.6 degree C change in temperature at 4 degree C will result in a 0.001%, or one part per 100,000 change in the density. The water that is below that will change even less, and most of it will actually get denser, i.e. occupy less volume. Even surface water, which would see the largest changes, needs to shift by several degrees to see fractions of a percent change in density. In other words, the math just isn't there to support such conclusions.

This Water Density Calculator (for the default salinity) says it would be 3.7 parts per 100,000. If the oceans are on average 2 km deep, then that would be 2 x 3.7 cm rise, or about six inches. That may be where the low estimate comes from.

btw, the IPCC estimate of contribution to thermal expansion of the water was between 6 and 37 inches. that's 1/2 to 3 feet, not 100 feet. even with the low estimate, i would be prepared to debate the numbers.

I dunno...

[jkmccrann]

What other direction could it move?

Good point, I guess I should have specified further, I think its moving North towards Australia/East Asia. But we (Australia) are also moving North, I think we're slated to slam into Indonesia (Java/Bali/Timor/Papua) & PNG in around 200-250million years.

[Jakenorrish]

Indeed. Even a significant warming will still leave the Antarctic subzero and as such the ice will remain. What will change is that the water holding capacity of the air will increase leading to increased precipitation hence thickening. The Antarctic isn't in danger of melting.

The melting of the Arctic is the problem here in the UK. Particularly with the change in atlantic salinity brought on by this melt affecting the water currents which fuel the gulf stream. Despite the fact that global 'warming' is often spoken about, in Northern Europe, we may be facing a temperature drop soon, due to the melting of the arctic ice cap, especially if the reduction in gulf stream currents continues at its present rate.

[jkmccrann]

The melting of the Arctic is the problem here in the UK. Particularly with the change in atlantic salinity brought on by this melt affecting the water currents which fuel the gulf stream. Despite the fact that global 'warming' is often spoken about, in Northern Europe, we may be facing a temperature drop soon, due to the melting of the arctic ice cap, especially if the reduction in gulf stream currents continues at its present rate.

Despite everything else, this is to me probably the most immediate possibility of this whole debate. I hear that this could be a reality in as near as 20-30 years (I don't know if that's accurate but in climate terms it is certainly short-term) Apart from anything else, the geo-political ramifications of a colder Europe (Is it by4-5C?) would be fascinating. An ageing population living in ever colder climes.

[The Supreme Canuck]

If it does come about, I don't think it would be too much of a problem. In economic terms, 20-30 years in an eternity.

[Jakenorrish]

I'm not so sure Canuck, us Brits whinge enough about the weather now, if it gets colder, we'll be even worse!

[The Supreme Canuck]

Meh. You won't like it, but you'll do fine. Fuel costs will rise, but you can deal with it. Canada does. Norway does.

[Jakenorrish]

Not fair. I love the heat. I'll have to move somewhere else. I'm not happy with the prospect of our climate being like Norway's. If I liked it, I'd move there! Don't bring it to me, I didn't ask for it, neither did anybody living in Northern Europe!

[jkmccrann]

Not fair. I love the heat. I'll have to move somewhere else. I'm not happy with the prospect of our climate being like Norway's. If I liked it, I'd move there! Don't bring it to me, I didn't ask for it, neither did anybody living in Northern Europe!

Which is exactly the kind of attitude that feeds back into the geo-political ramifications I was referring to. Not just that people who live in Northern Europe may move away, but also that potential migrants, people from developing countries looking to improve their lot in life, may choose not to migrate there, which given the potential age-crunch coming up and the stagnating economies of much of Europe (UK being the very notable exception), brings interesting geo-political questions.

I agree, in economic terms 20-30 years is a long-time, but a cooling climate will certainly not help deal with any of these questions that Europe faces.

[The Supreme Canuck]

Not fair. I love the heat. I'll have to move somewhere else. I'm not happy with the prospect of our climate being like Norway's. If I liked it, I'd move there! Don't bring it to me, I didn't ask for it, neither did anybody living in Northern Europe!

Actually, you're about as far north as Newfoundland. You'd probably get their climate. My advice? Bundle up.

[Fram]

If the Guld Stream doesn't bring the warm water of the Gulf of Mexico and thereabouts towards Europe and then the cooler water back from Europe towards the Guld, then it will stay there, and while Europe will get cooler, the Guld of Mexico will get warmer. Wouldn't this result in even more and stronger hurricanes, making this years naming until Delta (or has there been an Eta as well?) seem like a mild year? Just a thought...

[Ilya]

This Water Density Calculator (for the default salinity) says it would be 3.7 parts per 100,000. If the oceans are on average 2 km deep, then that would be 2 x 3.7 cm rise, or about six inches. That may be where the low estimate comes from.

That's assuming the entire water column warms up, which is impossible. Water is densest at 4 degrees C, so heating it from above is extremely difficult. Water below 500 meters or so is at unchanging 4 C everywhere, including the tropics. (Of course, farther from equator you reach that temperature at much shallower depth.) So oceans' volume expansion due to global warming will be negligible.

[Taks]

That's assuming the entire water column warms up, which is impossible. Water is densest at 4 degrees C, so heating it from above is extremely difficult. Water below 500 meters or so is at unchanging 4 C everywhere, including the tropics. (Of course, farther from equator you reach that temperature at much shallower depth.) So oceans' volume expansion due to global warming will be negligible.

this was my point. actually, below the thermocline the temperature does drop to about 2C eventually (a sort of slow logarithmic decline). all of the water below 4C will actually get denser if it warms.

btw, 2 x 3.7 cm is 7.4 cm or 3 inches, not 6. this is very easy to debate as unmeasurable for the entire globe (i.e. within the statistical measurement error).

the 1 in 100,000 number i got was about 1 in 100,000 as i stated in my original post. the discrepancy is because i gleaned it off of a graph. the actual number of 3.7 doesn't change my calculations by enough to make a difference. the fact still remains that most of the water in our oceans is below this level... as noted, since much of the water would actually get denser, reducing the level, 3 inches is a bit high...

taks

[jhwegener]

The question about melting ice, and rising sea temperatures raise another question: If it happen, how will it affect the earth? It is truly enormous masses in question, so one may ask if there may be more tectonic activity - more earthquakes and tsunamis. Further: if the frozen layers of earth below tundras melt, one should expect that to destabilise the land too, leading to landslides and perhaps more earthquakes (?)

[archman]

Water is densest at 4 degrees C, so heating it from above is extremely difficult. Water below 500 meters or so is at unchanging 4 C everywhere, including the tropics.

That's an error propagated by some poorly written texts; I've been publicly chastized by a room full of oceanographers for stating almost exactly what you just wrote. I was SO embarrassed!

Freshwater is densest at 4C. Saltwater is not. Deep-sea temperatures vary quite a bit, around six degrees or so. Sometime it's above 4C, more often it's below it. The variation can be really fruity in the low-latitudes due to all the freshwater mixing. That 500m "cutoff" is a gross generalization, too. It can be pretty "toasty" at 500m in the Gulf of Mexico, for instance.

As for increasing global water temperatures, there was a report that came out about five years ago, showing pretty strong evidence for an increase of 0.1C. The oceanographers in my building had to explain to me why 0.1C was such a big deal, something to the effect of "upteen atom bombs" worth of energy dumped into the ocean, as I recall.

I doubt 0.1C would cause much expansion in global water volumes, however.

[Dragon Star]

Edit: Pic or the link is not working, so disreguard...