The Greenhouse Effect in a Water World

The natural world is complicated. Therefore, so is the science that tries to understand it.

Complexity, uncertainty, ambiguity are all a part of the story that describes processes that are as extraordinary as they are mundane. While these are the very characteristics of scientific study that motivate professional and amateur alike, they are also the characteristics that give delayers, doubters and liars in the climate debates ample material for confusing and misrepresenting reality.

One such complexity is the interaction of infra-red or long wave radiation (IR or LW), the ocean surface and the atmosphere. This is what gives rise to one of the more esoteric arguments in the climate change denier’s arsenal, the argument that the Greenhouse Effect does not operate over 70% of the earth’s surface, the portion that is covered in ocean rather than land and therefore ocean warming can not be a result of an enhanced GHE from rising CO2. Since ocean heat content is by far the lion’s share of climate system warming…um..Not the IPCC.

The grain of truth in this line of reasoning is that ocean warming is primarily from solar short wave (SW) radiation, the visible light, that freely propogates through the atmosphere and penetrates 10’s of metres into the ocean’s upper layers. This sunlight directly warms the ocean waters just as it directly warms the earth’s surface. Recall now that the greenhouse effect is what happens next: all warm bodies, land and water, emit longwave radiation and these IR photons are trapped and re-radiated by greenhouse gases (H20, CO2, CH4 among others). Roughly half of the energy the surface of the earth tries to send back out to space returns this way. So, the GHE increases down-welling LW but not SW energy. Well, it just so happens that this returning LW energy, unlike its SW cousin, does not penetrate water beyond a few micrometres and therfore it can not directly warm anything but an insignificant portion of the upper ocean layers. No increase in SW radiation, no ocean warming.

To be honest, I am not sure what is so compelling about this argument. Firstly, the climate we inhabit exists in the bottom of the troposphere over land, so while not insignificant, warming of the ocean is not our primary concern. Secondly, energy is not destroyed, so absorbed directly or not, the fact is it is having its escape from the earth’s surface, be it land or water, impeded and this must show up as warming somewhere. Logically, some of it must be finding its way back into ocean water via some means or another. Skin layer water molecules that evaporate rather than allow the IR energy to pass through will immediately or eventually give that heat up again as they condense back to liquid form. This results in warmer air which can transfer its heat via conduction. Admittedly, this is probably a minor factor as the heat capacity of air is so much less than water, but that heat does not just disappear. And finally, whatever is going on, the fact is that the heat content of the upper ocean is rising, as expected in an enhanced greenhouse environment. A truly inquiring mind would search for the mechanism that explains the reality, not declare that reality is impossible so… “drill baby, drill!”

Well, it turns out that reality is possible and is happening for a reason, no matter how complicated or surprising. The reason is that that very thin skin layer of water on top of the ocean surface is a strong controller of the heat flux between atmosphere and ocean. Specifically, the size of the temperature gradient between the surface layer and the bulk temperature of the mixed water below it determines how well heat can propogate through it. Now, there are two possible directions heat might propogate. In polar regions or winter in temperate climates, the air is much colder than the water and so heat will flow out of the ocean, whereas in the tropics or summer temperate climates the air will be warming the ocean, drawing energy out. If increased down welling LW is causing a warming of the skin layer, then in the first situation, where the ocean is warmer than the air, the gradient is increasedreduced and in the second, where the ocean is colder, the gradient is reducedincreased. The larger the temperature gradient, the faster heat will move across it.

This image and caption, taken from a RealClimate article on this subject, shows the relationship we are looking for:
Figure 2: The change in the skin temperature to bulk temperature difference as a function of the net longwave radiation.

Please check out that RC article and the first couple of screens of comments for the rather gory details.

Because of the principal of larger temperature gradients causing faster heat transfer, by warming the skin layer, down welling IR will decrease the heat transfer from warm ocean to cold air and increase the heat transfer from warm air to cool water, both of which effects contribute to warmer upper ocean waters. Ocean waters warmed by the direct sunlight find that, in an enhanced greenhouse environment, more of this heat is retained rather than passed into the atmosphere.

It is a bit of a brain twister, I’ll admit, but it is all consistent with well known physical properties of energy transfer and well established observational evidence of warming upper oceans.

82 thoughts on “The Greenhouse Effect in a Water World

  1. “Thus the net effect is a loss of energy and a cooling of the oceans.”

    Except that a cooler ocean (and since water vapourises at 100C, the vapour IS hotter than the ocean) will condense water vapour out of the air and its deposition will dissipate the latent heat into the water body and warm it.

    And a warming ocean still doesn’t lose more H2O as vapour than it’s increased energy content as heat allows. Therefore the ocean REMAINS warmer, just not as warm as it would without evaporation taking place.

    ‘sfunny how denialists and other half-wits always leave out large sections of inconvenient truth, yet complain bitterly about how AGW hasn’t taken EVERYTHING into account.

    Isn’t it.


  2. “I am sorry but you are not getting the point and I can find no literature that explains how down dwelling LW forces the ocean to warm.”

    It doesn’t force the ocean to warm. It warms the ocean. As in “if the LW downwelling were not there, the ocean would be cooler”. As in “if you walk outside on a cold night with a coat on, you’ll be warmer than you would be in a t-shirt”.

    LW radiation is absorbed by the ocean.

    It warms the ocean.

    A warm ocean emits LW radiation upward.

    That cools the ocean.

    Net cooling is less with the GHG present creating more downwelling LW than without it.

    YOUR persistence seems to be merely a restating of the G&T paper “proving” that there is no greenhouse effect, merely dropping it being impossible on land.


  3. Coby,

    Sorry for the delay, but I have had a bug the last few days and just making it to work is about all I have been up to. I will answer in a day or two.


  4. Just read this (a bit behind, yes), and a few things bothered me, so here’s my non-expert take…

    First, terminology. The literature apparently uses “coolings” and “warmings” to refer to fluxes leaving or entering the system; don’t think of it as temperature change–only the sum of all the relevant energy fluxes corresponds directly to a temperature change. A lot of confusion seems to be about this, and the apparent paradox that the easiest way to shed more energy is by getting hotter.

    So lets follow the energy flux; using the numbers and such from the discussion thread, we have 340 W/m^2 at the top of the atmosphere, with about 170 W/m^2 absorbed at depths typically a few meters in the ocean. This energy is re-radiated as long wave IR, and is almost immediately reabsorbed–water is a greenhouse liquid, so the mean free path for LW is tiny. This is essentially a diffusion problem, where most of the LW goes to heating the water around the absorption depth (which is why the SST is relatively warm). The LW that actually escapes to the atmosphere is emitted near the surface, and its spectrum reflects the temperature of the “skin” and “subskin” SST, not the SST at depth.

    The surface typically radiates 390 W/m^2 of short wavelength IR, of which about 324 W/m^2 returns as back radiation. The 66 W/m^2 difference is the cooling capacity of LW escaping to infinity. Since increasing GHGs increases back radiation, this cooling capacity becomes smaller with increasing GHGs. For the oceans, the back radiation will be absorbed at about the same depth it radiated at–the mean free path doesn’t care about direction–so that part is actually fairly analogous to what happens on the surface of the earth, though the part that determines the effective surface temperature is different, and the equilibrium more complex.

    When the ocean skin loses cooling capacity from LW radiation due to increasing GHGs, it has to offset it, primarily by increasing evaporation, but also by increasing outgoing LW radiation. To do either the skin has to get on average warmer–the molecules that evaporate, the ones that “get away”, are the tail of the kinetic energy distribution; to increase the population in the tail, the entire distribution has to move up. Hot water loses more energy from evaporation than cold does–is that really in dispute? However, increasing the skin temperature decreases the cooling capacity available to the SST, due to reduced heat diffusion rates and reduced convection–so the SST has to get warmer to compensate.


  5. All the peer reviewed papers I can find agree that the net down dwelling longwave radiation on the ocean surface leads to an global average of -66 wm2 which is cooling. (I have no desire to publish a list of papers for those to lazy to do their own research.)–Vernon

    The 66 W/m^2 difference is the cooling capacity of LW escaping to infinity. Since increasing GHGs increases back radiation, this cooling capacity becomes smaller with increasing GHGs. — Dan

    Dan, your post is very dense and I think I get it for the most part, and everyone is using this number as a given and I am willing to accept it. But I genuinely want to get to the bottom of its origin. If its a stupid question I am willing to look stupid.

    The only documentation I have seen of it was in the lecture notes Vernon cited, which were based on a graph of the whole atmospheric-oceanic energy budget from–as far as I could tell–the IPCC Second Assessment Report. It was not referencing outgoing LR radiation from the ocean exclusively–*as far as I could tell*.

    Again if I look dumb, fine. I have no problem admitting when I don’t get something. But where the bloody hell does this –66Wm2 figure come from in the “peer reviewed literature” in the first place?

    If everyone else is floating along fine, my congrats, but it would really anchor my ability to follow this discussion if someone would resolve this for me.

    Humor me, please.

    Happy Independence Day, all.


  6. skip

    As I have been trying to say all along, the link I provided at post #1 (yeah I know – right at the very begining) has all the information on this issue.

    Here’s the link again:

    Click on it, then go to the fourth page (it’s page #118 in the document) and have a look at Figure 3.1. There are all the relevant numbers. You will note that the amount of ingoing and outgoing radiation varies with latitude, and hence the net radiation flux varies with latitude (its positive to about 20 degrees).

    Then, if you are really interested in more info, the source for the data is cited (you know, just like in real science). The source on the figure is Hsiung 1986 – and if you then scroll to the end of the paper you get this:

    Hsiung, J., 1986: Mean surface energy fluxes over the global ocean. J. Geophys. Res., 91, 10,585–10,606.

    If you type that into Google scholar, you get this link:

    So – as I said right at the very beginning of this thread:

    “…If someone truly wants to understand this issue, then this link provides some reasonable reading…”

    Is there anything else I can help with?


  7. Not having a go at you there skip. I tried to point this out to several people who were asking questions and trying to make points on this issue – but I guess the reading of science is not a common trait among many posters around here.


  8. Skip, try this diagram:

    for energy fluxes.


    “only the sum of all the relevant energy fluxes corresponds directly to a temperature change. A lot of confusion seems to be about this”

    Manufactured confusion. Keeping a “debate” alive by “misunderstanding”.

    “The 66 W/m^2 difference is the cooling capacity of LW escaping to infinity.”

    The problem here is that that 66 is just a difference between two radiative components. You’re forgetting the convection and evaporation. They get a look-in too.


  9. Oh, and a short version of the “problem” with that -66W/m^2. See the graph here:

    (note: science of doom has done several posts explaining the graph too)

    Figures in W/m^2

    Solar radiation absorbed by surface: 168
    SW radiation absorbed by surface: 324

    Total absorbed: 168+324 = 492

    SW emitted by surface: 390
    Convection losses by surface: 24
    Evaporation losses by surface: 78

    Total lost: 390+24+78 = 492

    Absorbed = Lost

    No lost “-66W/m^2”


  10. There was some discussion with snowman regarding coral reefs on another thread (I can’t remember which one) before he crawled back under his rock. He spouted the standard denialist dogma about there being no climate change, but if there was it wouldn’t be a problem etc.

    I would like to draw everyone’s attention to probably the scariest paper I have ever read, here:

    The paper is supported by this statement from Dr. Ove Hoegh-Guldberg, one of the authors of the paper and Professor of Marine Studies and Director of the Global Change Institute at the University of Queensland. He is one of the world’s foremost experts on coral reefs. In an article about the state of coral reefs around the world, he stated:

    “…The current distribution of carbonate coral reefs around the world today is associated with concentrations of carbonate ions of 200 µmol per kilogram water or more. In this case, there is a natural gradient towards reduced carbonate ion concentrations and more acidic oceans at higher latitudes. This is primarily due to the fact that cold water can contain a lot more carbon dioxide. The significance of this threshold for carbonate ions is that these are the concentrations that you get in tropical oceans when carbon dioxide increases above 450 ppm. Given that these levels of carbon dioxide in the atmosphere are likely to be associated with at least a 2°C increase in sea temperature, it appears that coral reefs will largely disappear if atmospheric concentrations of carbon dioxide exceed 450 ppm…..”

    Take careful note of that – he is suggesting that even under the conditions that we are currently aiming for to contain climate change – and which we are unlikely to achieve unless things change very quickly – then coral reefs around the world will all but disappear. If this is true – and the work is supported by a number of other studies so it appears to be valid – then the consequences over the next hundred years or so are not just going to be bad, they are going to be unimaginably catastrophic.

    This is not just about tourism and nice places to see, if corals disappear the whole ocean ecosystem will collapse. Think about that for a moment. Then think some more. Then start worrying.


  11. Yup, got my powers mixed up! That should have been 25 billion tons.
    There are a large number of water usage sites which give estimates for various activities:

    Evaporation from reservoirs: 275cubic km/yr
    (275 billion tonnes)
    World industry: 90 cubic km/yr…..90 billion tonnes
    (which includes the world’s 63,590 power stations)
    Agriculture 1870 cubic km/yr ( listed as evapotranspiration as they can’t tell the difference)
    So a reasonable estimate for AWV added to the atmosphere is 2200 billion tonnes a year which otherwise would not be there. Which is a lot more than the CO2 added.


  12. > A study of satellite data on clouds and water vapor indicates that prior predictions of substantial Global Warming are wrong.

    Really? Several other studies show they’re right.

    > The study introduces a new method to diagnose the total radiative feedback parameter.

    So it’s new. Why is it right?

    > A completely independent analysis reveals that there is insignificant net positive feedback.

    Yeah, you’re pretty gullible, aren’t you.


  13. So a reasonable estimate for AWV added to the atmosphere is 2200 billion tonnes a year which otherwise would not be there.

    So before the reservoirs were built and the farms were irrigated it was all just barren desert? What is the mean residence time for water vapour in the atmosphere?


  14. It seems to be a pretty good one, even addressing other posters by name and being borderline on topic.

    If Turing had known how low real human dialogue would sink due to the internet, I think he might have had to devise a better test of AI!


  15. Would it not be better to stop bitching in the last few comments and get back to the main topic of “The Greenhouse Effect in a Water World”


  16. Comments like ‘Yup, got my powers mixed up!’ were in the original, which is why I think it is not a live person.

    Would it not be better to stop bitching in the last few comments and get back to the main topic of “The Greenhouse Effect in a Water World”

    Even if you are talking with a machine?


  17. Yes, Richard Simons, I agree that Comments like ‘Yup, got my powers mixed up!’ were in the original, which is why I think it is not a live person. Would it not be better to stop bitching in the last few comments and get back to the main topic of “The Greenhouse Effect in a Water World” Even if you are talking with a machine? waoooo, good post!

    Hey, it’s fun to imitate a machine imitating a person! I’ll leave the comments but neuter them…


  18. Yeah everyone – stop bitching!

    Miss me while I was away? In case you didn’t, I have been travelling and overseas for the past 5 weeks – as well as being in hospital a few times. But it’s nice to be home.


  19. Not this time skip. We went to Vietnam and Cambodia, as well as doing some diving along the east coast of Australia. And took my wife with me, so I had to be a good boy.

    How was your xmas?


  20. In hospital?

    A few times?

    You really should look after yourself better – rather than getting all those people to wait on you hand and foot.

    Seriously. Hope you’re well and staying well.


  21. Hi Adelady,

    Yes, I was testing the different state health systems across the country by being admitted to hospital. So far SA is coming a distant third behind Qld and NSW. Had my appendix out in Toowoomba and discovered I have cavernomas in my brain in NSW. Maybe that’s my problem.


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