WeatherRusty said:
Your description of the atmospheric greenhouse effect is as detailed and well stated as I have come across anywhere. Thank you!
I'm honoured! Thanks.
But the ocean is a source of heat. It radiates in the infrared because of it's temperature. The photosphere of the Sun is not a source of heat by your definition, it radiates only because of it's temperature. The source of energy in both cases comes from the Sun's core where it is generated.
The ocean is not a source of heat. Neither is the photosphere. They are both are in approximate energy balance, giving up only what energy they take in.
Because of its massive heat capacity, the ocean takes longer than the land to respond to changing temperatures. As a result, days are cooler and nights are warmer and there's a large flux of heat into and out of the ocean with the day and night cycle. The actual source of the heat involved is the Sun. This is stored and released within the ocean, but the net shift, in total, is zero.
Actually, that's not quite true. The ocean is at present soaking up a little bit more more heat than it receives, so there's a net effect on the surface of the Earth removing heat energy. It's a flux of energy corresponding to about 1 W/m^2 continuously over the whole surface of the Earth, going from the surface into the ocean. Roughly. It's hard to measure, but recent research is gradually pinning this down.
This is a temporary situation that follows directly from the fact that the ocean is at present warming up. If, for any reason, there is a long term net shift in temperature for the whole planet, then the ocean responds to that more slowly than the land. Until an equilibrium is reached, there will be a net flux of energy from the surface into or out of the ocean, depending on whether the net shift is up or down. This corresponds to warming, or cooling, the ocean to a new equilibrium temperature.
The Earth's surface and hence it's atmosphere are warmer with large bodies of liquid water present than they would be without. Oceans absorb a whole lot more solar energy and dissipate that energy much more slowly than solid land. Is this not essentially the same effect as produced by the atmospheric greenhouse (albeit a different mechanism), slowing the release of accumulated thermal energy to space, in effect concentrating it near Earth's surface thus maintaining a warmer near surface temperature even as the source of energy (solar irradiance) remains approximately constant?
This gets a bit subtle. Yes, there is a small net warming effect for a planet with an ocean, but this not because there's any extra heat going in or out. All that happens is that with an ocean, temperatures become more mild. Without an ocean, the cold parts of a planet would be colder, and the warm parts of a planet would be warmer. But the total energy flow out from the surface remains about the same.
This is where it gets tricky. The energy radiated from a body by virtue of its temperature is proportional to the fourth power of temperature. Hence, if the energy in any out remains precisely the same, but temperatures get smoothed out a bit, then the warm bit reduce by less than the cold bits increase.
This is where the example of the Moon is useful. The average temperature is about -23C. But if we made all the surface the same temperature, the average would be -3C. The total energy radiated back out from the surface would be the same as before; but the dayside would have cooled by 110 degrees, from 107C to -3C and the nightside raised by 150 degrees, from -153C to -3C. The calculations, which have to apply over the whole surface, are in the other thread, which I've linked above.
If the lower troposphere is warmed adiabatically by the raising of the 255K infrared emitting layer due to additional greenhouse gases, over time will this not increase oceanic heat content independent of direct insolation as the atmosphere and oceans exchange energy?
Yes, the ocean will be warmer, and hence it will have a greater "internal energy". In physics, the phrase "internal energy" is preferred to the term "heat content". The term heat is usually reserved for the transfer of internal energy by virtue of temperature difference. This is explained also in the physicsforum glossary.
It may take some time for the ocean to heat up to its new equilibrium temperature, because of the enormous heat capacity. That seems to be what is occurring at present. If we somehow held the atmospheric composition constant, then we should expect surface temperatures to continue increasing until this warming up of the ocean was complete, which would remove the small flux of heat down into the ocean. That is, there's another W/m^2 or so of additional energy which we haven't noticed because it is vanishing into the ocean. It's sometimes called "warming still in the pipeline".
I don't think the word "adiabatically" is appropriate there. A process is "adiabatic" if there's no change in the internal energy content. But with greenhouse warming, the internal energy of a given volume is greater than otherwise, for the atmosphere and for the ocean. It's just a new equilibrium state.
Cheers -- Sylas