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teal
2014-Jun-02, 08:18 PM
I understand that carbon dioxide is greenhouse gas, it returns heat back to the surface, and back to the surface of the ocean as well. Meaning it will heat up ocean a little bit, as well as it will heat up Earth's surface.

Water vapor is also a greenhouse gas, much more efficient than carbon dioxide, water vapor contributes (on average) 23K to the temperature, CO2 contributes only 3K to the temperature. Meaning water vapor is also heating up Earth's surface and, possibly, ocean surface.

In the model i'm building, i go with simple saturation vapor pressure to estimate amount of water vapor in atmosphere, by doing that i get amount of water vapor in atmosphere similar to the number provided by NASA: http://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html. NASA says, "typically makes up about 1%", my model estimates to 1.5%, which is acceptable for me.

Saturation vapor pressure strongly depends on temperature of water, that is, higher temperature - more vapor. But if water vapor, as a greenhouse gas, returns heat back to the ocean, then more ocean evaporates, more heat it gets back from greenhouse effect, more heat - more it evaporates, and so on.. If i put this kind of feedback loop into my model, then heating effect on the ocean is exponential and, to me, this behavior doesn't seems to be unrealistic.

I'm building a toy model, it doesn't have to be very accurate, but i want it to act realistically. What is important for me is what feedback loop is present in the environment and what is not.

My best guess on the topic is that ocean and water vapor are locked in equilibrium, which saturated vapor pressure basically describes, right? Thus there won't be any greenhouse effect to the ocean surface from water vapor in atmosphere. I mean water vapor will return heat, but this effect is already included into saturated vapor pressure value. Only external heat sources, including effect of other greenhouse gases, are need to be taken into account when estimating amount of water vapor in atmosphere.

To sum up my guess:

* water vapor has greenhouse effect to Earth's surface
* water vapor doesn't have any greenhouse effect to ocean surface temperature (and evaporation)
* carbon dioxide has greenhouse effect on both: Earth's surface and ocean surface temperature
* other greenhouse gases has the same effect as carbon dioxide

But i can't find source confirming this or explaining feedback loop in any details.

Any ideas?

Ara Pacis
2014-Jun-03, 04:50 PM
Are you calculating for water's high specific heat capacity? You can add a lot of heat before increasing its temperature, and the bulk of the ocean, even in the upper mixed layer is fairly cool (well below boiling point). In fact, I recently read that the average temperature of the entire ocean is close to 0C.

Are you just looking at boundary conditions at the ocean's surface? The sea surface mixes down, and infrared radiation may penetrate below the immediate boundary layer.

teal
2014-Jun-03, 05:19 PM
@Ara Pacis
In my model i'm looking at ocean as at black body, in fact, i'm getting its temperature to be 274K (1C) this way, not taking into account greenhouse effect. This somehow matches your reference of ocean temperature being close to 0C, could you please link me to that? It would be interesting for me to read.

I'm looking at ocean surface indeed, i'm mostly interested in ocean-atmosphere interaction and ocean's contribution to atmosphere, since water vapor is the main greenhouse gas - i need to know how much of it would be in atmosphere and how it will influence overall planetary conditions.

My main concern is if should i include feedback from water vapor back to ocean's surface temperature - evaporation rate and amount of water vapor in atmosphere depends on it. I think i don't have to, but i think so because this renders my model's behavior unrealistic (exponential evaporation of ocean). My model is not necessary correct though, so i'm looking for a proper reference which can explain greenhouse feedback to the ocean surface.

profloater
2014-Jun-03, 05:20 PM
I understand that carbon dioxide is greenhouse gas, it returns heat back to the surface, and back to the surface of the ocean as well. Meaning it will heat up ocean a little bit, as well as it will heat up Earth's surface.

Water vapor is also a greenhouse gas, much more efficient than carbon dioxide, water vapor contributes (on average) 23K to the temperature, CO2 contributes only 3K to the temperature. Meaning water vapor is also heating up Earth's surface and, possibly, ocean surface.

In the model i'm building, i go with simple saturation vapor pressure to estimate amount of water vapor in atmosphere, by doing that i get amount of water vapor in atmosphere similar to the number provided by NASA: http://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html. NASA says, "typically makes up about 1%", my model estimates to 1.5%, which is acceptable for me.

Saturation vapor pressure strongly depends on temperature of water, that is, higher temperature - more vapor. But if water vapor, as a greenhouse gas, returns heat back to the ocean, then more ocean evaporates, more heat it gets back from greenhouse effect, more heat - more it evaporates, and so on.. If i put this kind of feedback loop into my model, then heating effect on the ocean is exponential and, to me, this behavior doesn't seems to be unrealistic.

I'm building a toy model, it doesn't have to be very accurate, but i want it to act realistically. What is important for me is what feedback loop is present in the environment and what is not.

My best guess on the topic is that ocean and water vapor are locked in equilibrium, which saturated vapor pressure basically describes, right? Thus there won't be any greenhouse effect to the ocean surface from water vapor in atmosphere. I mean water vapor will return heat, but this effect is already included into saturated vapor pressure value. Only external heat sources, including effect of other greenhouse gases, are need to be taken into account when estimating amount of water vapor in atmosphere.

To sum up my guess:

* water vapor has greenhouse effect to Earth's surface
* water vapor doesn't have any greenhouse effect to ocean surface temperature (and evaporation)
* carbon dioxide has greenhouse effect on both: Earth's surface and ocean surface temperature
* other greenhouse gases has the same effect as carbon dioxide

But i can't find source confirming this or explaining feedback loop in any details.

Any ideas?

My understanding is that wind is the big factor in evaporation because whole droplets get carried way up and the effective surface area is orders of magnitude higher than the water surface area. IIRC there is a fourth power relationship with wind speed. So in the low part of the atmosphere over an ocean there is very significant water mass as droplets in addition to vapour which will be increasing. Then you get to the cloud layer where as you say, the water vapour is many times more significant than CO2, absorbing a very wide section of the EM spectrum. Finally the cloud seeding is affected by micro-organisms in the ocean! This new factor really makes your model difficult because the point at which clouds form is important to the net effect of the clouds. Without the organisms the vapour rises to great height and acts as green house, but low clouds act as reflectors. Thermal action causes winds of course, and the role of water vapour in large clouds, carrying energy (latent heat) rapidly upwards is very important.