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Global Warming and sea level rise

Posted: Fri Apr 10, 2009 12:44 am UTC
by Govalant
I was thinking about that physics puzzle where you have a block of ice in a glass filled with water and need to calculate the rise in the water level. If the block of ice isn't touching the bottom and is being held at the top only by buoyancy then the level doesn't change at all.

Then.. is the ice in the poles not being held only by buoyancy? Does it go all the way down to the floor?
Thanks.

Re: Global Warming and sea level rise

Posted: Fri Apr 10, 2009 2:17 am UTC
by gmalivuk
The ice at the north pole is floating, so won't contribute to sea level rise. However, the ice on Greenland, as well as that in Antarctica, is sitting on rock, and so would raise the sea level if it melted. As would all the ice on any glaciers anywhere.

Re: Global Warming and sea level rise

Posted: Fri Apr 10, 2009 3:43 am UTC
by Jack21222
Govalant wrote:I was thinking about that physics puzzle where you have a block of ice in a glass filled with water and need to calculate the rise in the water level. If the block of ice isn't touching the bottom and is being held at the top only by buoyancy then the level doesn't change at all.

Then.. is the ice in the poles not being held only by buoyancy? Does it go all the way down to the floor?
Thanks.


Keep in mind that Antarctica is a continent, which means it's a land mass, not a floating block of ice, as gmalivuk pointed out.

Re: Global Warming and sea level rise

Posted: Fri Apr 10, 2009 4:22 am UTC
by Carnildo
The other thing causing sea-level rise is thermal expansion: as water gets warmer, it expands. At least in the short term, that's what will cause most of the rise.

Re: Global Warming and sea level rise

Posted: Fri Apr 10, 2009 4:21 pm UTC
by gmalivuk
Yeah, thermal expansion of liquid water is completely negligible in a small volume, but when you're talking about a couple miles' depth, the tiny fraction increase works out to quite a bit.

Re: Global Warming and sea level rise

Posted: Fri Apr 10, 2009 6:31 pm UTC
by Velifer
gmalivuk et al. wrote:...warmer...


True, and the bar-napkin calculations are shocking. The oceans are not all one temperature, though. They are stratified, with lots of interesting things going on--upwelling, internal waves, langmuir circulation, Eckman spirals, etc.--and it is likely that the temperature changes will not be uniform over depth, or over any area. So to anyone trying to do the work on what's gonna happen, it gets really complicated.

Unfortunately, this fuels detractors, since not knowing the precise extent is somehow seen to be equivalent with nothing happening at all.

Re: Global Warming and sea level rise

Posted: Fri Apr 10, 2009 9:00 pm UTC
by gmalivuk
Velifer wrote:Unfortunately, this fuels detractors, since not knowing the precise extent is somehow seen to be equivalent with nothing happening at all.

Yeah, that's true of deniers of all kinds.

Not sure whether it was 5 million or 6 million Jews killed in the Holocaust? Then it was likely only 50 or 60.
Not sure whether the Earth is 4.3 or 4.6 billion years old? Then it's probably more around 6000.
Not sure if you've found every single scrap of metal from the plane that hit the Pentagon? Then it must have been a missile.

Re: Global Warming and sea level rise

Posted: Fri Apr 10, 2009 9:53 pm UTC
by miles01110
gmalivuk wrote:Not sure whether it was 5 million or 6 million Jews killed in the Holocaust? Then it was likely only 50 or 60.
Not sure whether the Earth is 4.3 or 4.6 billion years old? Then it's probably more around 6000.
Not sure if you've found every single scrap of metal from the plane that hit the Pentagon? Then it must have been a missile.


Not sure of the exact mechanics behind the big bang? Must have been God.

Re: Global Warming and sea level rise

Posted: Sun Apr 12, 2009 2:49 pm UTC
by zealo
just out of interest, does anyone know of the current IPCC or NAS predictions on sea rise?

Re: Global Warming and sea level rise

Posted: Sun Apr 12, 2009 3:38 pm UTC
by Azrael001
I don't know their predictions, but I did read somewhere that a 3-4 degree (Celsius) increase in the average temperature of Greenland would likely melt the entire ice cap in around 1000 years. I did the calculations, and just that ice cap holds enough water for about 6.5-7m of sea level rise.

Re: Global Warming and sea level rise

Posted: Mon Apr 13, 2009 9:29 pm UTC
by Velifer
zealo wrote:just out of interest, does anyone know of the current IPCC or NAS predictions on sea rise?

As of 2007, the estimate from IPCC was 18-59cm by 2100. I don't know of anything more recent.

Re: Global Warming and sea level rise

Posted: Mon Apr 13, 2009 11:59 pm UTC
by headprogrammingczar
miles01110 wrote:
gmalivuk wrote:Not sure whether it was 5 million or 6 million Jews killed in the Holocaust? Then it was likely only 50 or 60.
Not sure whether the Earth is 4.3 or 4.6 billion years old? Then it's probably more around 6000.
Not sure if you've found every single scrap of metal from the plane that hit the Pentagon? Then it must have been a missile.


Not sure of the exact mechanics behind the big bang? Must have been God.

Be careful. There are people who believe all four of these. Also, it would take a fucking fuckton of energy to globally raise the water temperature by one degree. Napkin calculations bring the total energy required to 325,000,000,000,000,000 Joules, give or take what I approximated for average heat capacity and density of water.

Re: Global Warming and sea level rise

Posted: Tue Apr 14, 2009 12:11 am UTC
by gmalivuk
headprogrammingczar wrote:Also, it would take a fucking fuckton of energy to globally raise the water temperature by one degree.

Yeah, 1.5x1024 calories or 6.3x1024 J, actually.

But when you consider that the sun delivers this much energy every year or so, it's not actually that shocking an amount.

Re: Global Warming and sea level rise

Posted: Tue Apr 14, 2009 12:16 am UTC
by Azrael001
Interestingly enough I am at this very moment working on a model which predicts the amount of energy that hits the earth on a monthly average, for any latitude. I've actually got a spreadsheet with hourly predictions for an entire year for four different areas, but any latitude can be substituted. It even works for some places.

Re: Global Warming and sea level rise

Posted: Tue Apr 14, 2009 1:09 am UTC
by EdgarJPublius
gmalivuk wrote:
headprogrammingczar wrote:Also, it would take a fucking fuckton of energy to globally raise the water temperature by one degree.

Yeah, 1.5x1024 calories or 6.3x1024 J, actually.

But when you consider that the sun delivers this much energy every year or so, it's not actually that shocking an amount.


Yea, the sun would only have to double it's output :shock:

Re: Global Warming and sea level rise

Posted: Tue Apr 14, 2009 2:20 am UTC
by gmalivuk
Um, no, that's not how thermodynamics works. And no one's saying the oceans will rise one degree in a year, anyway.

Re: Global Warming and sea level rise

Posted: Tue Apr 14, 2009 6:45 am UTC
by Tass
I've also heard somewhere that melting the antartic ice would actually shift the earths mass distribution so significantly that the sea level would actually drop in the antarctic region, but rise correspondingly more on the northern hemisphere.

Re: Global Warming and sea level rise

Posted: Tue Apr 14, 2009 6:58 am UTC
by Azrael001
Are you talking about Isostatic Rebound? The Lithosphere gets deformed when there is all that ice on it. When the load leaves, the whole lithosphere under it raises back up. This does cause some loss of elevation in areas just outside of the region that is rising. Antarctica isn't going to melt any time soon though. It's Greenland that's the problem.

Re: Global Warming and sea level rise

Posted: Tue Apr 14, 2009 7:47 am UTC
by miles01110
headprogrammingczar wrote:Be careful. There are people who believe all four of these.


So? That doesn't mean they're correct.

Re: Global Warming and sea level rise

Posted: Tue Apr 14, 2009 10:23 am UTC
by Zamfir
Azrael001 wrote:Are you talking about Isostatic Rebound? The Lithosphere gets deformed when there is all that ice on it. When the load leaves, the whole lithosphere under it raises back up. This does cause some loss of elevation in areas just outside of the region that is rising. Antarctica isn't going to melt any time soon though. It's Greenland that's the problem.


Besides that, there is also simple gravitational attraction. Land and ice masses that are higher than the water level mean there is a bit more attraction locally, and as a result the ocean waters get pulled a bit towards those masses. If you imagine away the ice in Greenland, the water levels in the North Atlantic would drop a bit, and rise in the rest of the world. If instead of imagining it away you distribute it over the earth, the result is rise everywhere, but less in the North Atlantic.

I have heard that this effect is actually pretty significant, but I am not sure how reliable the source was.

Re: Global Warming and sea level rise

Posted: Tue Apr 14, 2009 11:50 am UTC
by Tass
Zamfir wrote:Besides that, there is also simple gravitational attraction. Land and ice masses that are higher than the water level mean there is a bit more attraction locally, and as a result the ocean waters get pulled a bit towards those masses. If you imagine away the ice in Greenland, the water levels in the North Atlantic would drop a bit, and rise in the rest of the world. If instead of imagining it away you distribute it over the earth, the result is rise everywhere, but less in the North Atlantic.

I have heard that this effect is actually pretty significant, but I am not sure how reliable the source was.


That is what I have read.

I think it was from something about a climate congress at Copenhagen University

Re: Global Warming and sea level rise

Posted: Tue Apr 14, 2009 7:40 pm UTC
by EdgarJPublius
gmalivuk wrote:Um, no, that's not how thermodynamics works. And no one's saying the oceans will rise one degree in a year, anyway.


You're right, for solar activity to change the temperature of the oceans by one degree over a year, it would have to more than double it's output for that year to make up for heat absorption by everything else on the planet, and reflection and all the other inefficiencies and barriers to heat transfer between the sun and the oceans.

Tossing around numbers and scenarios like this is fairly dishonest. You're tossing around a multi-meter rise in sea level and then trivializing the amount of energy it would take to accomplish, it's the sort of thing I'd expect to see on Fox news.

Re: Global Warming and sea level rise

Posted: Tue Apr 14, 2009 8:08 pm UTC
by gmalivuk
EdgarJPublius wrote:Tossing around numbers and scenarios like this is fairly dishonest. You're tossing around a multi-meter rise in sea level and then trivializing the amount of energy it would take to accomplish, it's the sort of thing I'd expect to see on Fox news.

Yes, I am trivializing that amount of energy, because if it happens over a century it really isn't that significant a quantity of energy. And no one is talking about it happening in a year, so I'm still not sure why the hell you keep bringing that timeframe up. Besides, even if we did want to accomplish it in a year, the sun would not need to fully double its output to raise oceans by one degree. If some mechanism were to prevent so much energy from being reflected or radiated back out to space (such as a runaway greenhouse effect or something), it wouldn't take nearly as large an increase in solar output to accomplish. Assuming Earth's temperature is approximately constant at the moment, it must be radiating or reflecting away exactly as much energy as the sun is putting into it. Which means that if that reflection and radiation are stopped somehow, and instead that energy is pumped into the oceans (obviously this is not a practical thing to do and I'm not suggesting that it is), it would only take a year at current solar output to increase their temperature by one degree everywhere.

Also, why are you drawing a connection between a one degree temperature increase worldwide, and a multi-meter rise in sea levels? I haven't done any calculating myself, but
Azrael001 wrote:I did the calculations, and just that ice cap [on Greenland] holds enough water for about 6.5-7m of sea level rise.
If that's true, it's something that could in theory be accomplished without raising solar output at all, and without increasing overall ocean temperatures at all. There's enough heat already in and on Earth that some combination of climate change and deliberate human intervention could probably melt Greenland's ice rather quickly (from a global climate perspective).

Re: Global Warming and sea level rise

Posted: Wed Apr 15, 2009 3:00 pm UTC
by Velifer
Azrael001 wrote:Are you talking about Isostatic Rebound?

I'm counting on this. I'm currently at 820ft above msl and rising! Up Canadian Shield! Arise! Let's pump out Lake Erie so we can keep ahead of sea level rise!

Re: Global Warming and sea level rise

Posted: Wed Apr 15, 2009 11:45 pm UTC
by EdgarJPublius
gmalivuk wrote:
EdgarJPublius wrote:Tossing around numbers and scenarios like this is fairly dishonest. You're tossing around a multi-meter rise in sea level and then trivializing the amount of energy it would take to accomplish, it's the sort of thing I'd expect to see on Fox news.

Yes, I am trivializing that amount of energy, because if it happens over a century it really isn't that significant a quantity of energy.


No, it's still pretty significant, between five and ten times the average estimated solar variance over the last two thousand years, a much more reasonable time frame to talk about when discussing such significant oceanic temperature change (thousands of years that is)

And no one is talking about it happening in a year, so I'm still not sure why the hell you keep bringing that timeframe up.
You brought it up first (the sun delivers this much energy every year or so). The kind of temperature change that would have to occur for the average oceanic temperature to rise by a single degree, over one year or a hundred, is very significant and far outstrips even the most extreme worst case scenarios for climate change.

Besides, even if we did want to accomplish it in a year, the sun would not need to fully double its output to raise oceans by one degree. If some mechanism were to prevent so much energy from being reflected or radiated back out to space (such as a runaway greenhouse effect or something), it wouldn't take nearly as large an increase in solar output to accomplish. Assuming Earth's temperature is approximately constant at the moment, it must be radiating or reflecting away exactly as much energy as the sun is putting into it. Which means that if that reflection and radiation are stopped somehow, and instead that energy is pumped into the oceans (obviously this is not a practical thing to do and I'm not suggesting that it is), it would only take a year at current solar output to increase their temperature by one degree everywhere.
If you want to add variables, go for it, just say it up front eh? If we're discussing oceanic temperature in isolation with solar output (without changing reflectivity and whatnot) solar output would need to double over one year (or increase by 1% for a century)

Also, why are you drawing a connection between a one degree temperature increase worldwide, and a multi-meter rise in sea levels? I haven't done any calculating myself, but
Azrael001 wrote:I did the calculations, and just that ice cap [on Greenland] holds enough water for about 6.5-7m of sea level rise.
If that's true, it's something that could in theory be accomplished without raising solar output at all, and without increasing overall ocean temperatures at all. There's enough heat already in and on Earth that some combination of climate change and deliberate human intervention could probably melt Greenland's ice rather quickly (from a global climate perspective).

MeteorSwarms post which brought up the one degree change in oceanic temperature in the first place indicated a multi-meter rise (and then you said, gee, that wouldn't actually take that much energy and my alarmist-sensor went off)

Climate Change Alarmism leads to this kind of stuff being considered practical and necessary and in other ways a not-terrible idea.
And that just leads back to this:
Image
without a much better understanding of global climate than we now possess.

there are plenty of other reasons to worry about oceanic levels rising in relatively small amounts of time than thermal expansion of the oceans. And many more dangerous and important outcomes of such temperature changes than sea levels rising. All of which are already being discussed and used to fuel other alarmist scenarios, we don't need any more.

Re: Global Warming and sea level rise

Posted: Thu Apr 16, 2009 4:21 pm UTC
by gmalivuk
EdgarJPublius wrote:
gmalivuk wrote:Yes, I am trivializing that amount of energy, because if it happens over a century it really isn't that significant a quantity of energy.

No, it's still pretty significant, between five and ten times the average estimated solar variance over the last two thousand years

But it need not come from solar variance alone, or at all. If Earth traps 1% more heat energy than it did before, we'd expect that kind of temperature rise over the course of a century, even if solar activity remains constant.

And no one is talking about it happening in a year, so I'm still not sure why the hell you keep bringing that timeframe up.
You brought it up first (the sun delivers this much energy every year or so).

I just did that to put the quantity of energy into context. As in, sure, that looks like several orders of magnitude more than "a great lot" when you compare it to the kind of energy humans produce, but it only takes a year for the Sun to deliver that much. I never meant to imply that myself or anyone else thought a one-year time scale was relevant to any climate change.

Besides, even if we did want to accomplish it in a year, the sun would not need to fully double its output to raise oceans by one degree. If some mechanism were to prevent so much energy from being reflected or radiated back out to space (such as a runaway greenhouse effect or something), it wouldn't take nearly as large an increase in solar output to accomplish.
If you want to add variables, go for it, just say it up front eh? If we're discussing oceanic temperature in isolation with solar output (without changing reflectivity and whatnot) solar output would need to double over one year (or increase by 1% for a century)

Yes, but, again, I wasn't talking about solar forcing alone raising oceanic temperatures. And I never said I was. Rather, I think that's how you interpreted it because it would be the easiest way to argue with me.

I'm not an AGW denier, which means I don't believe (and never have believed) that any one natural phenomenon (such as a change in solar output) is causing the current warming trend or is likely to do so in the near future. I only mentioned the sun at all to explain why a seemingly large amount of energy wasn't actually all that unimaginable.

Climate Change Alarmism blah blah blah

The climate *is* changing, and only needs to change a little bit more over the course of not-too-long for some pretty bad things to likely start happening. I don't see how it's alarmist to say this, except inasmuch as the truth can sometimes be kind of alarming.

Re: Global Warming and sea level rise

Posted: Thu Apr 16, 2009 9:59 pm UTC
by headprogrammingczar
What he is saying is
Sea levels, sea levels blahblahblah alarmist

He is saying there are more important and immediate ecological concerns than how high up the coast the ocean happens to be, and that more effort should be put to counteracting those than just counting the inches.

Re: Global Warming and sea level rise

Posted: Thu Apr 16, 2009 10:15 pm UTC
by EdgarJPublius
An Alarming truth is not the same as alarmism.

An Alarming truth is that the current Earth warming trend is not likely to reverse itself until after the global climate has changed from what is considered 'normal'.

Alarmism is saying that Human activity has, or is about to, push global climate change over a completely hypothetical 'point of no return' and unless we drastically reduce carbon emissions and maybe put mirrors in space, sea levels will rise several meters in our lifetime.

You're saying that environmental change could plausibly increase the energy absorption of the oceans so that within the next hundred years or so, it will absorb a Fantastically large (yet trivial) amount of energy, raising oceanic temperatures by an unprecedented whole degree, potentially causing multi-meter sea level rises (let alone all the other potential side-effects).

I'm sorry if I don't really see the problem here, you'd have to increase energy absorption by ten to twenty percent to get that effect in that time period, It'd be like covering the oceans with iron filings. the level of change you're talking about, no matter what context you attempt to put it in, is staggeringly huge. not even the worst case for climate change interpreted by the most alarmist environmentalists predict a degree change in the oceanic average temperature in a hundred years, Just a fraction of that kind of change is enough to cause a near-cambrian level extinction event in the oceans (Okay, some alarmists have actually predicted cambrian level extinction events, that's not my point) If this is an even halfway plausible consequence of current climate change, then it's time to pack for Mars 'cause this planet is screwed.

Re: Global Warming and sea level rise

Posted: Wed Apr 22, 2009 7:15 pm UTC
by Tahlas
EdgarJPublius wrote:Alarmism is saying that Human activity has, or is about to, push global climate change over a completely hypothetical 'point of no return' and unless we drastically reduce carbon emissions and maybe put mirrors in space, sea levels will rise several meters in our lifetime.

Only if it isn't true :wink:

there's just been this climate conference in copenhagen, (preparation for the big one later this year). A majority of the participants expected sea level to rise by about one meter by 2050.
A meter might not be that much but it's enough to seriously fuck shit up for a lot of countries and regions.

Re: Global Warming and sea level rise

Posted: Wed Apr 22, 2009 9:33 pm UTC
by headprogrammingczar
A meter increase in sea level corresponds to A LOT MORE than a meter of shore recession, which seriously fucks over people who live on the coast.

Re: Global Warming and sea level rise

Posted: Thu Apr 23, 2009 7:22 am UTC
by Zamfir
headprogrammingczar wrote:A meter increase in sea level corresponds to A LOT MORE than a meter of shore recession, which seriously fucks over people who live on the coast.


The secret Dutch policy on sea-level rise is that it would be awesome, since we are market leaders in levee building.

EDIT: I am partially serious. Dutch building companies love to talk about global warming in their market-forecast presentations.

Re: Global Warming and sea level rise

Posted: Thu Apr 23, 2009 11:40 pm UTC
by EdgarJPublius
Tahlas wrote:
EdgarJPublius wrote:Alarmism is saying that Human activity has, or is about to, push global climate change over a completely hypothetical 'point of no return' and unless we drastically reduce carbon emissions and maybe put mirrors in space, sea levels will rise several meters in our lifetime.

Only if it isn't true :wink:

there's just been this climate conference in copenhagen, (preparation for the big one later this year). A majority of the participants expected sea level to rise by about one meter by 2050.
A meter might not be that much but it's enough to seriously fuck shit up for a lot of countries and regions.


If that's true, then it's already too late to do anything about it. In reality, a speaker at the conference said that a sea level rise of one meter is likely by 2100. Due to limitations on the ability of ice to flow from the climatic snow line to sea level, the maximum predicted sea level rise in this time period is actually about 20cm less than that, most models predict between 10-50cm of sea-level rise over the next century (though the existence of such models should not be taken as evidence of anything more than a preliminary understanding of glacial ice melting, there are still significant questions to be answered which may impact future models)
And, as Zamfir mentioned, it's not like a climate conference in Copenhagen is likely to be highly-unbiased about sea level rise.

Re: Global Warming and sea level rise

Posted: Fri Apr 24, 2009 6:45 am UTC
by Zamfir
EdgarJPublius wrote:And, as Zamfir mentioned, it's not like a climate conference in Copenhagen is likely to be highly-unbiased about sea level rise.


No, I didn't say that at all. A far as I can tell, sea level rise calculations are mainly based on thermal expansion, and those contributions are (relatively!) easy to calculate for a given temperature trajectory. That's why you hear so much about it: they are the least controversial local prediction of the effects of climate change. Whether a certain temperature increase would lead for a given location to more drought, or more storms, or more snow is very hard to say, with very large error margins, so the most you hear about are globally averaged quantities, which have smaller error margins.

But sea level rise has the prediction quality of a global quantity, while it is at the same time precise enough to have an idea of the local effects.

Re: Global Warming and sea level rise

Posted: Fri May 29, 2009 4:30 am UTC
by JonBanes
EdgarJPublius wrote:
gmalivuk wrote:
headprogrammingczar wrote:Also, it would take a fucking fuckton of energy to globally raise the water temperature by one degree.

Yeah, 1.5x1024 calories or 6.3x1024 J, actually.

But when you consider that the sun delivers this much energy every year or so, it's not actually that shocking an amount.


Yea, the sun would only have to double it's output :shock:


or the earth would have to retain twice the heat

Re: Global Warming and sea level rise

Posted: Fri May 29, 2009 11:48 am UTC
by SpitValve
Don't know how accurate it is, but there's a sea level rise google maps thingee.

Apparently despite being on the coast, my home city is hilly enough to mostly survive even an extremely dramatic increase in sea level. (Enough to make me somewhat suspicious of their model...)