Ice

I spend a lot of time reading climate science blogs. I had a look at Anthony Watts’ site http://wattsupwiththat.com/ this morning. Normally I love reading it, it is one of the few sites that covers climate change issues with an informed rational analysis. Usually it is a breath of fresh air and helps reboot my brain.

This morning it was an awakening from a very different perspective. It wasn’t the core article, which was commenting on the NSF’s decision to fix their claim that sea level would rise because of sea ice melting and cause significant issue for coastal cities. It was the comments afterwards. I learned a lot about the way people think, and how quickly people will accuse each other or being idiots while jumping themselves to the wrong conclusion. I do that often too, so it also made me worry about the quality of my thinking. Do I jump to conclusions too fast too sometimes. Perhaps.

So here in a nutshell is the problem everyone was debating: sea ice melting would cause sea level to rise. True or false. I won’t answer it yet till you get hooked in and even then I’ll do my best to avoid it. You’ll see why.

Some of the early comments looked like teens repeating what they heard in class as gospel truth. Then people gradually got deeper and deeper into the issue. What had started off as people laughing at the NSF for making such a stupid schoolboy error turned out into a debate that showed the fierce complexity of almost anything to do with climate change. Most were being too simplistic and treating everyone else as idiots if they disagreed instead of looking at the problem afresh.

The debate is worth unpeeling, like an onion, to see the many layers of detail involved. Some of the comments showed remarkable lack of thought, other a remarkable level of pedancy, and some raised issues I’d never have thought of in 100 years.

First layer of the debate. Isn’t the NSF stupid? Everyone knows floating ice doesn’t raise water level when it melts. What morons to think it would. Archimedes knew that yonks ago but the NSF is so stupid they didn’t know. There were quite a lot of supporters of that line but I suspect they soon regretted it.

Second layer: Yes, it is true that if you put an ice cube in a glass of fresh water, it will melt into exactly the same volume of water as the cube displaced. Well, almost exactly. But sea water isn’t made of pure water, it is denser. A pure ice iceberg weighing one ton floating in sea water would displace one ton of seawater, but sea water contains lots of salt and is denser than fresh water, so that mass of seawater occupies less volume than fresh water at the same temperature, and the fresh water the ice melts into would take up 2.6% more space. So it isn’t an ice cube melting into a lake of freshwater, it is seawater. If everything else was left simple, sea level would rise. If!

Third layer: It isn’t that simple. The ice berg isn’t pure water, it does contain some salt, about a tenth as much as seawater, though it varies, and that varies with the age of the ice. First-freeze ice contains more than second-freeze ice. And snow landing on the ice is purer still. And the seawater is diluted a bit by recent ice melt, so its density locally isn’t the same as other parts of the sea. And the temperature of the water isn’t the same as elsewhere so the density is different. But it is all one big ocean so which density is the appropriate one? And melting ice dilutes it. But the salt from the rest of the seawater also mixes with the recent melt and concentrates that.

So there are a hundred complicating factors in the equation before you get to any answer worth looking at. The NSF isn’t looking quite so dumb perhaps. Except until you look at the maximum figures involved and find the differences any of this all makes are in the region of a millimetre. So regardless of the fact that there is a finite but hard to calculate rise in sea level due to sea ice melting, the fact that the rise is of the order of a millimetre or two means they were certainly right to retract the part that said it would be significant to cities.

But the onion still isn’t peeled fully. The sea ice formed mostly from sea, so in the long term, its melting would theoretically mean return to the ‘original’ level. But that misses one of the points, because some of the sea ice is old, and some of the time-scales involved are high. So yes it would return, but if there had been loads of sea ice and then there isn’t, there will still be a difference between then and now.

And ice floats, and ice is a different colour to the sea. It therefore affects the average height of the surface, which affects lots of things, such as the rotational angular momentum of the earth, and the gravity distribution, and the area exposed to wind, and the amount of solar energy absorbed and radiated is different at the various parts of the spectrum because of the colour difference. How many layers does this darned onion have? Let’s not forget ocean currents that change local temperatures and salt concentrations, winds that move bergs around and a zillion other factors, right down to where polar bears poo given there are usually no woods nearby.

All of this debate was coloured by endless discussion of the relative temperature-density profile of seawater and fresh water, whether ice should form at the bottom or top of the oceans, and how something can be irrelevant because of its dilution across the whole planet, even while something else of similar magnitude could be central to the debate. There were also numerous references to experiments and hypothetical experiments that would actually prove something totally irrelevant to the central point, things like melting ice cubes in an alcoholic drink. When tiny effects like the differences made by taking into account temperature-dependent salt concentrations are coming into the debate, such school lab experiments are hardly relevant.

Anyway, the NSF retracted, and were right to, but not because of the reason assumed by some of those making comments. Mainly they were right because the effect is too small to be ‘significant’. Sea level would rise a tiny bit, but as to exactly how much, anyone’s guess. The only sensible answer is: not much.

So no panic then. Physics is intact and so is planet Earth for  while longer. But a great many egos damaged I think. Like everything in climate science, it isn’t as simple as it looks.

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