So... my basic view (and its the correct one, ha ha) is that sea ice is an insulator, not a heat sink. In the winter ice-covered arctic, sea ice sits on top of an ocean whose temperature is about -1.8 oC, whereas the air overhead is about -30 oC (or something, I haven't bothered to check. Cold, anyway). If you cleared the ice away, the ocean would freeze over, of course. Heat conduction through the ice is slow and has more-or-less stopped by the time the ice has got to 1-2m thick (which is why ice thickness doesn't keep going up: the thicker ice comes from ridging). Hence, it acts as an insulator. Insofar as the teleological terms make sense, this is its climatic "function".
Lubos uses the old "google trick" to prove that people think the sea ice is a heat sink: just google "heat sink" "sea ice" he says. But this is a very old trick, and, as ever, throws up piles of hits with "sea ice" and with "heat sink" but no great relation between them. Of the hits, the top one is just the Indie article we're talking about. #'s 2,3 are quoting "The Arctic is the heat sink of the Northern Hemisphere" and *this* is fair enough (because of geometry, the tropics get more heat in, so heat flows from tropics to poles, so the poles are sort-of a heat sink). But thats the whole arctic, not the sea ice.
To point out the obvious, that Lubos seems to have missed: GCMs of course include the latent heat of sea ice in their calculations.
In fact, much of this disagreement rests on arguing about different things. If you are modelling sea ice, then yes of course you need to include the latent heat (if you don't, there is no control at all on whether the ice forms or not). And yes, the latent heat of fusion of a meter or so of ice is significant. But...
Trying to seperate out in more detail the heat capacity/latent heat stuff is more difficult. If you regard the ice as there, then the heat capacity is negligible (looking up the numbers, it seems to be about half that of the same mass/volume of water). If the ice isn't there, then yes its formation will indeed soak up heat. But... taking these fluxes in isolation won't work.
If you want to *store* heat then you clearly can't do that in the ice (since it would melt). And you have to take into account the seasonal cycle. To store it, it has to go into the oceans. And heat storage in the oceans is why the worlds warming is least in the great Southern Ocean around Antarctica and predicted to stay that way for a while.
Summary: calling the sea ice a heat sink, as the Indie does, appears to be a mis-paraphrase of "the *arctic* is a heat sink, which is what people do indeed say. Greg Kuperberg (who seems to do his best over at Lubos's comments) has already pointed this out.
[Update (sorry PF): Brian J points to a nice table from a recent Levitus paper (sorry JA). Then (with large caveats, but emphasising that they are probably overestimating the fusion term) they get for the change in heat storage) 18e22 for the ocean; 6e21 for the atmos (1955-96); misc other terms; 5e19 for the arctic sea ice (1978-96).]
[Update #2: I've struck out the 30m calc. I'm almost sure its out by a factor of 1000... somewhat surprised no-one has ripped it apart yet... I'll check in the morning]
[Update #3: For those of you visiting from Lubos Motls blog, let me point out that his version is seriously misleading and dishonest. The erroneous sentence which he bases his entire post around was struck out before he ever read this; I think he is trying to give the impression that I corrected my post based on his reply; but no. Also, Arun (see comments on this post, about #7) provides a nice link+quotes on the climate role of sea ice.
Meanwhile, for those interested in the status of string theory, this is interesting.]
12 comments:
just found http://www.math.columbia.edu/~woit/wordpress/?p=254 - for a bit of fun.
Does the 18e22 J increase in heat energy in the ocean correspond to about 72 days of solar insolation (for the whole earth)? While all the ice in the Arctic melting represents but about 2 hours of solar insolation for the Arctic ? I don't mean to get you checking my back-of-the-envelope calculations, just trying to get a handle on orders-of-magnitude.
I think what is counterintuitive to many people is that small shifts in global average temperature correspond to large shifts in the terms in an energy balance equation. It is change in energy flows that we experience as change of climate?
Dear William,
let me first start to address your ludicrous comments about the credentials, first pretending that I think that you were just joking. ;-)
The question about the heat capacity of sea ice may be a climate question, which could speculatively put you into advantage, but it is also a question that requires a certain amount of basic intelligence and knowledge of simple physics, which puts me to a better situation. This is my answer to your childish comment that one expects you to be right because you are the climatologist hero. ;-)
Let me emphasize that unlike you I am joking and I certainly don't intend to settle scientific questions by comparing the credentials, and whoever thinks that this is how science should be argued, is dumb. Once again, sorry if it includes you, but you can't be granted an exception.
You were apparently unable to find sources that argue that the sea ice and ice cap is a huge heat sink. So let me do it for you. For example look for "heat sink" at these pages:
here (Antarctic icecap),
this PDF (about icebergs as heat sink that affect temperature), and others.
I did not write that you were a great climate scientist (well, I would not write such a thing about various Manns and Schneiders either). I wrote that you are one of the main people who determine the "consensus"; if you wish, one of the main manipulators. This is based on your realclimate.org, Wikipedia, and USENET activities. In my opinion, these things have a certain impact and help to create certain atmosphere.
While ice is a bad heat conductor, it does not diminish its being a heat sink. In fact, you are confusingly talking about "insulation" when the real mechanism is "regulation". Ice stabilizes the temperatures exactly because it keeps them around 0 Celsius by melting/freezing parts of the ice body.
Of course that storing heat in the form of latent heat means to melt it. ;-) I don't know what you find so paradoxical about it. Or do you really think it is impossible to melt ice?
Let me end up with some more facts showing why the latent heat of the 1-3 meters of sea ice is important to account for thermodynamics in the polar regions.
As you may know, about 90% percent of the ocean is below thermocline (where the temperature drops, towards 0-3 degrees Celsius). The deep ocean does not really circulate well and heat is not exchanged efficiently. Thermocline is something like 100 meters below the surface. When we talk about ocean being a heat sink, it is really the upper 100 meters or so only. Compared to this pretty thin column of water, the large heat capacity of ice simply IS important if there is one.
The latent heat of sea ice is equivalent to a 1 degree temperature change of the circulating part of the ocean, and it's not negligible. Even more importantly, it's really the sea ice that drives the whole circulation process of the oceans whenever the sea ice exists. The circulation is deciding how much of the ocean will exchange heat efficiently. So even for the rest of the ocean, it is sea ice if it exists that decides how strong heat sink the whole ocean is gonna be.
Best
Lubos
Be absolutely sure that your 30 meters should have been 30 millimeters. ;-) Do you now agree that you underestimate the latent heat by three orders of magnitude?
Do you agree that your intuition about the numbers in climate is the same as the intuition of a person who confuses Mount Everest with his house?
Lumo & Belette - I did a few calculations here. Also did a little critique of Lumo's rhetorical style.
A point of rhetoric. Check your numbers and check your logic when you argue with Lumo. Misplace a decimal point and he will deduce that you are 1) Incompetent, 2) Criminal, and 3) A communist.
Lubos - you don't get any points for spotting mistakes I've already corrected. You do, however, get your final warning for impolite language. Really you've had quite enough of these, you're an intelligent person, learn to write politely or learn to cope with your comments being deleted.
CIP - Thanks. Will take a look at your numbers this evening.
Arun - not really sure. Off the top of my head, the heat-content changes correspond to a radiation imbalance of a few w/m2 over the 50 years - there is a good Hansen paper on this. I'm not sure about your counterintuitive point: the shifts in the energy balance are also small, compared to the absolute (up-down-different) fluxes.
Hi Paul, fair comment, thank you. To clarify: my 130-ish was downward longwave (ie, infra-red) not insolation.
As a slight quibble, 2m is probably a fairer value for arctic winter ice, but that still leaves 30-odd W/m2.
To which I would reply, yes, but its still a lot less than if the sfc of the ocean was exposed. From the numbers given, you can't calculate how much less (since the value would go to infinity as the thickness goes to zero, which is physically wrong) so it depends on the sfc wind stress and stuff. I will look out some numbers if I can find them...
http://seis.natsci.csulb.edu/rmorris/seaice/climate.htm
INSULATING PROPERTIES
The insulating properties of sea ice restrict the exchanges of heat, mass, and momentum that occur across the air-sea contact in open ocean conditions. Local and regional oceanographic and atmospheric characteristics are subsequently altered, changing their influences upon the climate.
heat
Sea ice greatly inhibits the radiation of heat from the relatively warm ocean to the cold polar atmosphere. There exists a two orders of magnitude difference between heat released from the open ocean and heat released by an ice-covered ocean [Parkinson, et al.,1987]. Thick sea ice (>1 meter), can prevent better than 95% of the heat loss from an otherwise open ocean. Heat fluxes from the open sea surface range between 100-1000 W/m2 while sea ice thicker than 1 meter limits the heat flux to 5-20 W/m2 [Parkinson lecture, 1998].
Heat transfer is primarily, therefore, an open water phenomenon and the distributions of thin ice, leads, and polynyas have important implications upon regional heat budgets [Gloersen, et al, 1992]. Open water within the ice pack is often the location of very high heat flow. Thermal plumes of warm, moist air from a recurring polynya off of Bennett Island (eastern Arctic Ocean) produce cloud formations that can achieve great heights; some plumes have reached 7 kilometers in altitude [Debneth, 1994] , the height of the polar tropopause.
mass
Ice cover also inhibits direct exchanges of matter between the ocean and atmosphere. It becomes a physical barrier, impeding the normal exchange rates of gases and particulates (like water, oxygen, and salt).
momentum
Momentum exchanges between ocean and atmosphere are also greatly inhibited by the presence of sea ice. Waves, for example, are dampened rapidly by ice floes, creating calm conditions within the ice pack [Parkinson, 1997]. Higher frequency waves are dampened rapidly while only the lowest frequency waves penetrate deeply into the ice pack. Ice-breaking ships can seek safety within the ice cover when encountering stormy seas [Parkinson, 1997]. Ice cover also prevents the wind from generating waves, limiting the transfer of momentum from the atmosphere to the ocean.
Linking to Peter Woit's comments on string theory is a mistake.
It is true that string theory does not yet make any predictions in the traditional scientific sense. It is a very incomplete theory. Even so, as a theoretical inference it is credible. The theory is difficult and it needs time to develop.
Woit's comments on the matter are superficial. (As are mine, but I do my best to listen to real experts.)
As to string theory, I have no real opinion... my base motive for linking to Woit was to wind up Lubos, but I shouldn't do that.
There is a vague analogy here with the GW debate. As a climate modeller, I don't know about string theory and wouldn't know what sources to go to for a reliable picture if I did (and not being impolite, but I *don't*, so please don't make me a list anyone!). It looks like many string theorists dont know where to go to for the basics of climate change (PW). Hence my most recent post.
The best short semi-lay discussion of string theory that I have seen is Witten's article in Physics Today and the AMS Notices. I hope that I am allowed a list of length one. (And whose sole entry is only six pages.)
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