Is the ocean guaranteed to warm in a warming climate, regardless of whether it absorbs LW radiation?

Question

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 beyond an infinitesimal amount, 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 - as long as there is some means for energy transfer, increasing the overall temperature must increase each of the components. Am I right, or have I misunderstood?

Answer 1

My naive understanding was that our increasing the magnitude of the greenhouse effect meant that there was less radiation escapting to space

That's 100% correct. If we assume constant solar input, there's only two ways the Earth's surface temperature can change. Albedo and Thermal radiation. Greenhouse gas driven climate change means exactly what you said - less heat radiates off Earth into space. Most of this heat goes into the Ocean.

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 beyond an infinitesimal amount, because the atmosphere has a much lower heat capacity.

Your friend is half right, and half wrong. Air has a bit over 1/4th the heat capacity compared to water and it's about 800 times less dense, so he's correct, but it's not that simple.

Sunlight - somewhat counter-intuitively, isn't great at warming oceans because the photons from sunlight are energetic enough to evaporate water molecules into gas molecules. Oceans have low albedo which means they absorb most of the energy from the sunlight, but much of that heat is lost in evaporation by visible light photons. While that has nothing to do with your question, it's worth pointing out that sunlight isn't as good at warming oceans as one might think. (If anyone has one of those solar mirror ovens, I'd be curious to see how well they work on pure water . . . just out of curiosity, evaporation loss vs rate of warming).

The back-radiation from the atmosphere is comparatively much less total solar energy, but oceans are good at absorbing and storing thermal back-radiation reflected back off the greenhouse gas rich atmosphere into the ocean. This is a tiny amount of the total heat Earth gets from sunlight, and the increase of this radiation due to greenhouse gas is a fraction of one percent of solar energy, but it adds up.

One way to explain this is that 85 degree air will warm 80 degree water. That's a thermodynamic law. It just takes a while and because the heat capacity and density of water is much greater, it takes about 4 liters of air to give 1 degree back to warm 1 cc of water 1 degree. But despite the inefficiency, warmer air still transfers heat into colder water. It takes many decades, perhaps centuries, for the oceans to catch up to the warming air, but air, however inefficiently, does warm the oceans.

The quirk in this, is that the oceans, despite warming much more slowly than the air, are still absorbing over 90% of the trapped heat added by the increase in greenhouse gas. It's a matter of scale. Oceans warm slowly because they're enormous and always circulating and it takes much more energy to war them, but they also absorb most of the heat, for the same reason, they're very good at holding heat. Slow to heat up, but also, slow to cool down. That's why bodies of water often feel warm when you go swimming at night.

I should probably add something about increased evaporation in higher air temperature, which effectively cools the oceans and surface air, but also increases the greenhouse effect with an increase in water vapor, but running those numbers is a bit over my pay-grade. The greater efect is the one mentioned above.

Answer 2

That's in a nutshell, simple conduction air to water.

No....it's not so simple.....far from it. In fact, there are several rather complicated processes occurring simultaneously, none of which involve the simple transfer of heat from warm air to cool sea water, as stated by userLTK, above. From Skeptical Science:
How Increasing Carbon Dioxide Heats The Ocean

Sunlight penetrating the surface of the oceans is responsible for warming of the surface layers. Once heated, the ocean surface becomes warmer than the atmosphere above, and because of this heat flows from the warm ocean to the cool atmosphere above.

But really, you should read the entire text for a good explanation of the process that leads to warming seas. Another important resource is found at the Scripps Institution of Oceanography:

Physics of greenhouse effect and convection in warm oceans

On average, convective regions are more humid, trap significantly more longwave radiation, and emit more radiation to the sea surface. The greenhouse effect in regions of convection operates as per classical ideas, that is, as the SST increases, the atmosphere traps the excess longwave energy emitted by the surface and reradiates it locally back to the ocean surface. The important departure from the classical picture is that the net (up minus down) fluxes at the surface and at the top-of-the atmosphere decrease with an increase in SST; that is, the surface and the surface-troposphere column lose the ability to radiate the excess energy to space.

The cause of this super greenhouse effect at the surface is the rapid increase in the lower-troposphere humidity with SST; that of the column is due to a combination of increase in humidity in the entire column and increase in the lapse rate within the lower troposphere. The increase in the vertical distribution of humidity far exceeds that which can be attributed to the temperature dependence of saturation vapor pressure; that is, the tropospheric relative humidity is larger in convective regions.

Answer 3

First we need to see if your question is based on facts. If the only energy in the climate system comes from the sun, what things can increase the energy in the system, other than the sun? The answer is: nothing. To increase temperature you need to increase the intensity of emitted heat where the temperature increase. Since the only source of energy is the sun, how could we increase the intensity anywhere, if not the intensity of solar irradiation is increased? This is a surprising mistake done by the entire climate science. The claim is that increasing the amount of a potent heat absorber would increase the intensity of emitted heat from the surface. If you add a heat absorber that absorbs heat from a body, it cannot cause warming. Often it is claimed to retain, or delay heat loss. But that cannot be true according to thermal physics. Preventing heat loss is exactly what we do by insulating the boundary of the system we want to stay warm. Thermal insulation is a logic simple thing, you can read about it here:

https://en.wikipedia.org/wiki/Thermal_insulation

"Thermal insulation provides a region of insulation in which thermal conduction is reduced or thermal radiation is reflected rather than absorbed by the lower-temperature body."

As you can see, it is without doubt very clearly stated, that preventing heat loss, or retaining heat, is done in the exact opposite way to what the theory of global warming claims. Absorption is what you want to avoid to prevent heat loss. There is a lot of things in the warming science-camp that indicate a lack of physics education in their field of science. Actually, every single argument in the greenhouse theory is a head-on violation of known, proven 100% consensus physics.

So, first of all, according to proven physics, it is highly unlikely that there is a warming climate at all. Secondly, the ocean cannot warm, if the amount of heat from the sun doesn´t increase. And we know that it doesn´t.