This is the interesting "logic" you run into debating Climate Change. I got this response discussing how the oceans are more accurately described as a thermal reservoir than a thermal sink. If you consider the oceans to be a thermal sink, you are using a classic Carnot Engine model.
The Carnot engine is a simple two box model, Tsink or Tc (for cold) is one box and Tsource or Th (hot) is the other box. Heat flows from hot to cold and if you have both boxes in a prefectly insulated container, eventually, both boxes would end up at the same temperature Taverage.
Carnot never used a Taverage model, because it is useless, and meaningless, because a flow of energy is needed to perform any work, which is the whole point of an engine. Carnot's concept though was very useful because it estimates efficiency and provides reasonably limits of expectation. Getting more than 50% efficiency requires a bit of creativity like adding a second engine to use the wasted energy of the first. You can keep adding energy until you run out of money, but you will never get 100% efficiency.
The problem with the "logic" is that "warming" is related to Taverage and the oceans viewed as Taverage are reservoirs not sinks. A sink at the same temperature as the source or even a greater temperature than the source, is meaningless in thermodynamics. Carnot's simple two model shows then problem once you add the "effective" radiant energy to the problem.
If Th start at 400 K and Tc starts at 200K, if both boxes contain the same volume the final temperature should be 300 K assuming no energy is lost. Tc would have an effective energy of 1423 Wm-2, Tc and effective energy of 89 Wm-2 which would be an average energy of 667 Wm-2, the average temperature of 300 K should have an average energy of 450 Wm-2, so since we are looking at an unrealistic situation, using average temperature as a metric for a heat engine, as if by magic the "blending" caused the system to "warm". But can this actually happen in a real world situation? You bet your ass.
It is easier to add energy to something that is cold than it is to add energy to something that is hot. Heat "wants" to flow from hot to cold so there is always heat flow unless you dream up some perfect barrier to heat flow or an "ideal" model. You can use "averages" to a point to assume that internal flow is insignificant, but the greater the temperature differences involved the less likely that is a valid assumption. When you use a "sink" model, you are assuming a large difference in temperature so that small variations are insignificant, so as the variations become larger, that assumption is less valid. In climate science "discussions", hopefully not in real climate science, people tend to flip flop between assumptions and have Eureka moments.
So let's just look at the difference is ocean surface temperature by hemisphere. The NH is on average 3 C degrees warmer than the SH, 24.5 C versus 21.5 C for the 45 to 90 higher latitudes. Compared to the Carnot example, this difference is next to nothing, but if the two areas were to magically equalize to the same temperature, there would be about 0.23 Wm-2 of unaccounted for warming which happens to be about 1/3 of the entire energy imbalance of the planet. Since the southern oceans are cooler, they are also easier to warm, nearly all of the current ocean heat uptake just so happens to be in the southern hemisphere. Since the Solar energy varies seasonally and currently the southern hemisphere gets the highest energy, the greater temperature difference would imply a higher heating efficiency. The entire imbalance "could" be due to the planet's current position in the precessional cycle,
Now we know better than that because adding CO2 and other GHGs will produce some warming by providing additional atmospheric insulation for one analogy, but ignoring the potential issues of internal imbalances and unbalanced "external" forcing would just "enhance" the efficiency of CO2 related warming to an unrealistic level. Anthropogenic warming cannot be as large as indicated by simple models. With the exception of online climate "experts", the entire thermodynamic literate world knows this.
So how well do the climate modelers do? The "average" climate model over estimates the temperature of the southern oceans and underestimate the temperature of the northern oceans. That is a pretty good indication the models miss part of the thermodynamics which is a large part of the physics they are supposedly based on.
Now the "typical" online expert wants, equations, a better model or some other definitive "proof" that this is a valid issue, which is simple insane, because the Zeroth Law of Thermodynamics, is a "Law" not a suggestion. It is their job to show they aren't playing fast and loose with the law, not mine.
A great example of how much they are clueless is how they consider internal variability. Internal oscillation or peudo-oscillations are a result of internal temperature gradients which constantly exist. Since winds and currents are parts of these oscillations and winds and currents are drivers of the majority of internal mixing of fluids containing heat energy, they directly impact the "average" energy in the system. Increased variability would be greater mixing which would indicate more heat uptake aka "warming" so assuming the oscillations "average" to zero impact is nuts. You can assume some "average" rate of turbulent mixing, but then you have added another layer of assumptions. Assuming internal oscillations have zero impact on "warming" is just another source of over estimation of CO2 forcing impact.
Now when you consider the oceans as a thermal reservoir, you can start to understand why a volcano can sometimes appear to "cause" warming. If the volcano cause more localized cooling, like in the Arctic, the ocean overturning circulation can increase delivering more energy than normal to a region with extremely old temperatures so there is a maximum impact of the poor choice of ignoring the zeroth law. Whether that "warming" is real or not, depends on the rate of ocean heat uptake, so "surface" warming can be a result of total system heat loss or just a glitch in the validity of a poor choice of metric, "Average Global Surface Temperature." When you use just land temperatures, the situation gets worse because the temperature range for determining "average" gets larger.
Hopefully, this is the last time I have to write a post about something that should be common knowledge, the Zeroth LOT.