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More specifically, I've seen some discussion of this article:

http://www.realclimate.org/index.php/archives/2006/09/why-greenhouse-gases-heat-the-ocean/

which claims that the observed ocean warming is explained by the ocean skin absorbing long-wavelength radiation. What I am asking is: is this mechanism necessary for ocean warming to occur? My naive understanding was that our increasing the magnitude of the greenhouse effect meant that there was less radiation escapting to space, and therefore the average temperature of the entire ocean+earth+atmosphere system will increase until it reaches a new equilibrium, where outgoing radiation again equals incoming. Is this correct? And if it is, does it not imply that the ocean must also get warmer, simply because it is a thermally coupled part of the entire warming system? I had someone tell me that the a warming atmosphere could not warm the ocean, because the atmosphere has a much lower heat capacity. But it seems to me that the constraint on the final equibilibrium temperature means that all components must warm, no matter how inefficient the means of energy transfer between them. Am I right, or have I misunderstood? To clarify, I'm talking about an idealised earth that actually can reach equilibrium, and I'm ignoring all the complexities of ocean currents and winds etc. I'm just asking about the absolute thermodynamic basics.

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  • $\begingroup$ I think this may belong on another SE. However the ocean is guaranteed to warm in the sense that it will warm at equilibrium (however the system probably never reaches equilibrium, as we know from past, naturally-driven, climate change, but instead oscillates). The interesting and important question is what happens to the ocean when the system is not at equilibrium, since it has enormous thermal capacity compared with the atmosphere, and complicated coupling with it. $\endgroup$ – tfb Apr 17 '17 at 11:36
  • $\begingroup$ Ah ok - maybe the Earth Sciences SE? Yes, I was talking about idealised case where we ignore natural varation and only consider the effect of increasing the greenhouse effect. But it sounds like the answer to the question 'is this mechanism necessary for any ocean warming to occur?' is no. $\endgroup$ – Paul Miller Apr 17 '17 at 11:42
  • $\begingroup$ Yes, I think the Earth Sciences SE might be better (although I don't read it, so I'm not sure). It seems clear to me that the answer is that you don't need a special mechanism as you say, but I'm also aware that this whole thing is complicated (and in particular blundering in with the kind of physicist arrogance that I & lots of physicists have can lead to the wrong answer!) $\endgroup$ – tfb Apr 17 '17 at 14:32
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As the comments suggest this is a subject for earthscience.SE. Here I will say that what warms the earth, and any planet, is primarily the input energy from the sun, primarily because there also exist volcanic energy at some ratio.

If one posits a fixed incoming energy, then the mechanisms of how this energy is distributed, ocean bulk, ocean surface, land , reflection back to space are a matter of a complete dynamic model of a complicated chaotic system.

This article gives an idea of the complexity , the factors that enter to describe a dynamic system.

But it seems to me that the constraint on the final equilibrium temperature means that all components must warm, no matter how inefficient the means of energy transfer between them

Well , a dynamically chaotic system is never at equilibrium . In the sense if one takes average values for everything, there would be an average temperature for the ocean surface and the land masses and the atmosphere , but the ocean would be heated by the direct incoming radiation and not by contact with the atmosphere which would be a smaller contribution, exactly because of heat capacities.

Hotter currents heat the atmosphere as is know by the Gulf stream:

The Gulf Stream, together with its northern extension towards Europe, the North Atlantic Drift, is a powerful, warm, and swift Atlantic ocean current that originates in the Gulf of Mexico and stretches to the tip of Florida, and follows the eastern coastlines of the United States and Newfoundland before crossing the Atlantic Ocean.

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The North Atlantic Current of the Gulf Stream, along with similar warm air currents, helps keep Ireland and the western coast of Great Britain a couple of degrees warmer than the east.[28] However, the difference is most dramatic in the western coastal islands of Scotland

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  • $\begingroup$ Thanks - I have posted on earthscience.SE :) I guess I'm talking more about a simplified model, where the system is roughly near equilibrium, and we then reduce the outgoing radiation via greenhouse gases. In that case, I was thinking that we guaranteed to increase the average temperature until the outgoing radiation again matches, a la Stefan-Boltzmann. And so the ocean must surely get warmer, as it has some kind of thermal coupling to other components, and the average temperature has to reach this new, higher figure? $\endgroup$ – Paul Miller Apr 17 '17 at 14:48

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