There are many movies about global warming, which say that melting of all polar ice would cause the whole world to suffer a huge flood. According my research (teachers, TV, Internet) people hold one of these two viewpoints:

  1. There will be a huge flood, because the polar ice has a huge volume.
  2. There won't be any flood, because the volume of polar ice is small compared to the whole world.

Which one is correct, if all the polar ice melts? What would be the approximate sea-level change (in meters), if this were to happen?

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    All ice, or just all polar ice? If the latter, how would Greenland have stayed icy? – EnergyNumbers Apr 30 '14 at 8:07
  • @EnergyNumbers alright , all ice. – Poomrokc The 3years Apr 30 '14 at 10:30
  • There won't be a "flood", because it will happen slowly - over centuries. – naught101 Jul 2 '14 at 7:00
up vote 28 down vote accepted

Using the latest numbers from the 2013 IPCC report (Ch. 4, the Cryosphere), Antarctica contains 58.3 m of sea level equivalent (sle) and Greenland 7.36 m sle. Remaining glaciers provide an additional 0.41 m sle. In total and adding very minor contributions from permafrost etc. the total comes out to approximately 66.1 m sle.

EDIT: Just to be complete: If one by "pole ices" also includes sea or other floating ice apart from glaciers terminating in the sea, the contribution from those components to sea level is zero.

  • Don't forget, there's also second-order effects due to the decrease in Earth's albedo causing decreased reflection. – Snowbody Apr 30 '14 at 21:44
  • Would be very interesting if the reduction in the continents surface area could be calculated too – Ron Harlev Apr 30 '14 at 23:07
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    @Snowbody: once all the ice has melted, how does differing albedo affect sea-level? Do you mean warmer => more water vapour in the atmosphere => less water in the sea, or something else? – user348 May 1 '14 at 8:04
  • How long does all this take? Transporting incredible amounts of heat energy to the poles and injecting it into the ice, a good insulator, so that it melts must be very, very slow. The Netherlands, London, and all the rest will be long gone for other reasons, I imagine, long before it could be completed. – ravenspoint May 1 '14 at 14:57
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    @SteveJessop: I think thermal expansion of the oceans would be the largest secondary component. I don't think the water vapour feedback is understood well enough to even put a sign on its effect on sea level. – naught101 Jul 2 '14 at 7:04

As Peter Jansson explains, sea level rise purely due to melting of land-based global ice works out "to approximately 66.1 m sle."

An issue with respect to sea-level rise that isn't often mentioned (especially not in disaster movies!) is that thermal expansion of the sea - i.e. water expanding as global temperatures rise - will also have a huge effect: see section 3.7 of the IPCC report. The magnitude of this effect is of course dependent on the magnitude of rise in global average temperature.

(I can't comment on @kaberett answer as a guest)

Don't forget the odd effect that as ice melts and the water warms from 0C to 4C, that water will contract slightly, dropping sea level a bit (at least, locally). Once it gets above 4C, it will start expanding again. If the oceans overall cool a bit due to cold meltwater mixing in, they too will contract until they start warming again. Note that this contraction won't save us from a huge rise in sea level in any case, and eventually the meltwater will be mixed in and start warming up beyond 4C, and expand.

  • The maximum density of sea water is not at 4 °C. It depends on the salinity of the water (in most cases larger than 30). At typical salinity, water freezes at about −2 °C. It can be even slightly colder. See Figure 3.1 of Talley et al., 2007 book ( Chapter 3 shows up in Google if you do a search for "maximum density seawater". – arkaia May 2 '14 at 20:33
  • @aretxabaleta Interesting. Would the melting of sea ice in itself have any significant effect on global salinity? (AIUI sea ice has somewhat lower salinity than the oceans, but I don't know whether the magnitude of the difference, and the tonnages of water involved, make it matter?) – Semidiurnal Simon May 4 '14 at 11:39
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    The best way to think about that is that you are adding 66m (total sea ice + everything else) to an average depth of 4267m. Assuming an average salinity of 35 from the ocean and 0 for the melting ice (which is not really the case), then the salinity will drop by around 0.5. – arkaia May 4 '14 at 15:32

While @kaberett's and @Phil Perry's answers are technically true, keep in mind 2 important issues:

  • the oceans are so vast and so deep that it literally takes decades if not centuries for them to warm up or cool down. This is called Thermal Inertia - see a much more in-depth explanation about it. Basically, you'll only see the effect of current rising temperatures when you're too old to give a damn.
  • melting ice from the poles will indeed have a significant impact on sea level, eventually (see the first point above). But that's not the problem. The problem is that the combination of fresh water (from the ice) and salt water (already in the oceans) will completely screw up the very large and very important ocean currents, also known as Thermohaline circulation. Once this happens... well, let's just say living in a smelly swamp will be considered luxury...

The 66 meters calculation seems about right :) .

  • Why would a change in the thermohaline circulation (not certain) be a bigger problem than a sea level rise in the order of decametres? – gerrit Apr 30 '14 at 13:45
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    @gerrit Well, because it would probably come first, way before those decameters. Second... it would be a complete disaster. All weather on Earth will change and become chaotic or shutdown or... something, all species of animals in the oceans would die (except those that live on the surface), plants would die because of extreme weather (so no more oxygen) and change in pH levels of ocean water would cause rise in anaerobic bacteria which cause the atmosphere to fill with hydrogen-sulfide, one of the most toxic things known to man (picture the entire planet smelling like rotten eggs). Soo yeah.. – Radu Murzea Apr 30 '14 at 14:02
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    Although it would be locally problematic, you are exaggerating. All weather is already chaotic. I don't know what you mean by "weather will shutdown". Not all animals in the ocean would die. Not all plants would die. There would still be oxygen. I'm not sure why you think the effects would be as severe as you describe. – gerrit Apr 30 '14 at 14:37
  • People have been predicting Ice Ages and Global Warming as the DOOM TO ALL!!! for years and years. 1970 was all about us heading into an Ice Age: “If present trends continue, the world will be about four degrees colder for the global mean temperature in 1990, but eleven degrees colder by the year 2000…This is about twice what it would take to put us in an ice age.”… ... now it's all about us heading into everything melting. – WernerCD Apr 30 '14 at 14:42
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    @WernerCD: I imagine that the day that I start taking anything from Climate Depot seriously will be the day that the first pig gets its pilot's license. – naught101 Jul 2 '14 at 7:12

As Peter Jansson pointed out, it adds up to 66.1 m of sea level rise. But what does that really mean for us? Here's a nice interactive map tool where you can enter how much the sea level will rise and see what that does to our coast lines. So crank it up to 60m and look around.

Obviously, The Netherlands will disappear almost entirely, as will most of Denmark and major parts of Germany. London will disappear. Most of the capitals in northern Europe will disappear under the sea. Scroll west to the US, and you can see that the entire eastern sea board will be flooded. Washington DC only just, but New York for the most part, and Boston entirely. On the west coast, San Francisco and Los Angeles will be a lot smaller, though parts of them are apparently high enough to survive. And before you think it's only the blue states that take a hit, take a look at Florida and Louisiana. The Mississipi south of Memphis becomes a massive sea inlet. Also, the most densely populated are of China gets flooded up to hundreds of km inland.

Most of the world's major population centers are at or near the coast, and almost all of them will be threatened by this level of sea rise.

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    I object to ideas that The Netherlands will disappear under sea level rise. Most people in The Netherlands already live below sea level, so with any of those tools, it would disappear even with 0 metre sea level rise. Now 60 metre may be hard to build dams against (although in 2000 years, who knows?), but 1 to 2 metre sea level rise should be no fundamental problem in The Netherlands. – gerrit May 1 '14 at 13:39
  • Whatever the Dutch end up doing, it will be a mighty struggle. A near-term 1 or 2 metre rise can be dealt with (at no small cost), but a 60+ metre rise may be too expensive to deal with. They will have to dike in all their rivers, and pump out lots of seepage and precipitation. Like New Orleans, they would end up in a bowl far out to sea. – Phil Perry May 1 '14 at 13:55
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    @gerrit According to an official report from a couple of years ago, up to 2 meters is doable (with serious reinforcement of our current defenses), but beyond that, it quickly becomes unfeasible. I believe the cost of coastal defenses goes up by the square of their height. It's probably the only country in the world that's small and rich enough to try to stay, but 60 meters would just be crazy. Not that relocating 17 million people is an attractive option either. – mcv May 1 '14 at 14:43
  • I wonder about the assumptions in such a report. Technological development on a timescale of hundreds or even 1000+ years is highly speculative. I agree that 60 metre would be crazy (but then again, most of current civilisation would be crazy to someone living 500 years ago). – gerrit May 1 '14 at 14:46
  • That is certainly a good point. Melting all of Antarctica would probably take more than 1000 years (I truly have no idea; I'm sure the data is out there somewhere). Who knows what we can do by that time? I believe the report said up to 2 meters in the next 2 centuries, which I believe means we're still okay for the current worst case projections (though it'll cost a lot). After that? Depends on the state of our economy and technology. – mcv May 1 '14 at 14:49

I had been to a conference at the NY American Museum of Natural History and the guest speaker at the science convention estimates about 220-230 feet (66 - 69 meters).

If the polar ice caps melted, how much would the oceans rise?

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