Of interest is the diurnal cycle of skin temperature vs. sub-surface temperature. During a sunny day, the skin (the upper less than 1 mm) is much warmer than just below the surface. Which points to solar[sic] IR absorbed at the surface. This has a huge impact on water vapour and (sea) surface air temperature.

You are correct, and there is more to the phenomenon. This is because (in contrast to the atmosphere) the ocean is stable during the day and unstable at night.

During the day, warm water (whether warmed by visible or IR) rises to the top and stays there. At night, the surface water radiates and evaporates, cools, and sinks. This is the main (although not the only) driver of vertical circulation in the upper mixed layer of the ocean (usually ~ 100m).

During the day, then, IR strengthens the vertical thermal stratification in the upper ocean. It leads to higher daytime ocean skin temperatures, particularly in the critical free surface temperature. This leads to increased losses through radiation (radiation increases by T^4). It leads to increased losses through convection (through greater ocean/atmosphere temperature differences and greater instability). It leads to greater evaporative losses (through Clausius-Clapeyron [exponential with T] plus greater wind-driven evaporation [linear with wind speed]).

This means that during the day, the bulk temperature of the mixed layer is immaterial to the rates of radiation, convection, and evaporation. All that matters is the skin temperature. I live, surf, and dive in the deep tropical Pacific. At certain times when the wind and sea are calm, I can be swimming in toasty warm water. But with each stroke of my arms as I paddle, my hands plunge through the surface warmth into much cooler water a half metre down. And during those times, I can feel the extra warmth in the top centimetre. (I imagine I can feel the yet higher free surface temperature, too … but probably that’s just me.)

This means that during the day much more of the absorbed IR is immediately lost, compared to the the visible radiation. Visible radiation is absorbed at depth. It heats the bulk of the mixed layer.

By contrast, IR is absorbed at the very surface. In the tropics much of that IR energy just breaks water molecules loose from the surface. In a funny way, this absorbed radiation should never even be counted in the oceanic energy budget. It is absorbed by a water molecule and breaks it free from the ocean. The energy never heats the ocean in the slightest.

The net daytime result is to ensure that the majority of absorbed IR is immediately returned to the atmosphere.

At night in the ocean, a curious thing happens. It’s kind of an inverse of the way that cumulus clouds form during the day. As daylight fades, at some point the ocean stops being a net absorber of energy. It begins to lose more energy than it is receiving. The surface starts to cool. Due to local inequalities, sinking cells form at intervals. These are akin to the thunderstorms, in that they set up cellular circulation. Cool surface water moves laterally and sinks in vertical columns of cooler water. This is similar to how during the day warm surface air moves laterally and rises in vertical columns of warmer air to begin the day’s mixing.

As occurs during the day, this leads to larger areas of gradually rising water at nighttime, with smaller areas of more rapidly sinking water scattered among them.

During all of this, of course, the free surface of the night-time tropical ocean is both gaining and losing heat through radiation, conduction/convection, and evaporation/condensation. Stronger nighttime IR slows the onset of the night-time circulation. This leaves warmer water on the surface longer, allowing more losses of all types. Stronger nighttime IR also slows the speed of the circulation. This reduces the rate at which cooler water arrives at the surface.

Finally, the tropical cumulus and cumulonimbus (thunderstorm) clouds are much more prevalent during the daytime than the nighttime. By dawn, it is usually clear. Since clouds are the most effective “greenhouse gas” (~ 100% IR absorptivity/emissivity), this leads to much lower downwelling IR levels at night than during the day. Using averages in this regard is very misleading.

What all of that means to me is that the effect of e.g. a 1 w/m2 change in visible energy will be different from the same change in IR.

Given the complexity of all of that, I was very interested in Gavin saying above that:

In a response to one comment, I pointed out that the difference between LW and SW heating of the mixed layer was not a big factor in trying to explain the recent changes in ocean heat content.

Gavin (or anyone), a citation to the comment in question would be great. My take on it is that the situation (ocean/atmosphere interface as affected by day/night/clouds/IR/visible) is too complex and difficult to model for it to be represented in anything like the necessary complexity. I suspect that Gavin might be right, but I’m curious what he’s basing his opinion on.

I think the climate models are meaningless: I have worked with circuit simulators in electronic engineering. These simulations of a simple closed system often dramatically fail to represent reality – and I’ve fooled my self by fudging the component models to make things work as expected. Why do we expect meaning from such a simulation?

To jump from such a simple model to one of an open system – using estimates with unknown error bands expands the old saying of Garbage in – garbage out – to garbage in – mixed in garbage yields garbage out. I suppose skeptics must endeavor to point out the folly of the pursuit – but is it that difficult to see that climate change is unknowable?

There is a famous saying in physics:
“Give me four parameters and I can fit an elephant. Give me five and I can wag its tail”

(The source of the above quote?? Variants of the statement have been attributed to C.F. Gauss, Niels Bohr, Lord Kelvin, Enrico Fermi.)

The next line is from a biology paper unrelated to climate:

When one considers that these models may have parameters that number in the tens to hundreds and are only growing in size, the possibility of generating meaningful computer models is a fantasy.

You cannot neglect 6% errors if you want to make decent calculations. The average inflow of energy to the Earth is about 342 Watts and 6 percent of this amount is almost 20 Watts. Hansen claims that he can determine the “imbalance” (0.8 Watts per meter squared in his case) with accuracy of 0.15 Watts which is 200 times smaller. So be sure that he should rather be careful about the difference between the average distance from the Sun and the maximal distance, for example. There are other reasons why his advertised error margin of 0.15 Watts per meter squared is unrealistic.

One more thing. Imagine that the Earth is a blackbody and you increase the solar radiation by 6 percent. What would it mean for the temperature of the Earth? The radiation emitted by a blackbody – which should agree with the absorbed solar energy – goes like “T to the fourth” where “T” is the temperature in Kelvins. This means that a 6% increase of the radiation means a 1.5% (because of the 4th power) increase of the temperature in Kelvins. Because the room temperature is about 300 Kelvins, 1.5% of this amount is roughly 5 degrees of Kelvin. I suppose that this is too large an error to be neglected.

This was just a very rough global counting. If you want to calculate how various changes – and eccentricity – affects local phenomena such as the Gulf stream, these variations become even more important. If you focus on long-term questions, you are averaging over the year and the eccentricity becomes less important.