You’ve literally seen feedbacks sink *more* CO2 in response to increased human emissions.
By the way, the word “feedbacks” is usually not normally used to refer to carbon sinks. I mean, informally if a carbon sink responds to more CO2 by increasing absorption, it’s a “feedback” in layman’s terms, but I don’t think scientists use the word that way. “Feedbacks” normally refers to the indirect effects of CO2 on temperature. (Feedbacks, in this latter sense, have been pretty much confirmed as positive at this point, as predicted by Arrhenius, based on warming since 1950.)
It’s true that carbon sinks have absorbed more CO2 (in kilograms) as the atmospheric concentration of CO2 has risen. This can be explained as increased uptake by the ocean and by vegetation. For instance, solubility of CO2 in water responds linearly to atmospheric CO2 concentration — however, the issue is not a simple one; see below.
do you believe that atmospheric CO2 is driven by dependent variables, or independent variables?
I believe it’s driven by the laws of physics; I don’t follow your abstraction. Shouldn’t the laws of physics be the basis for analysis?
If you’re trying to say that carbon sinks respond in a nonconstant or nonlinear way to increased CO2 concentrations, I think that climate scientists would agree with you — but would say that the nonlinearity is not that strong.
Reviewing your first analogy:
Imagine if we started with a 100 gallon tub that was draining at 1 gallon per minute, and was being filled at 1 gallon per minute. Then we get another hose, and add another 1 gallon per minute. Most rational expectations would be that the tub would fill with water at a net of 1 gallon per minute at that point. Instead, the drain magically opened up in response to the additional hose, and we see only 1 tablespoon per minute of increase. We redouble our efforts, and pump 2 gallons per minute more. Instead of a net 3 gallons per minute gain, we only see 2 tablespoons per minute of increase. At this point, it’s obvious that the drain is dynamically modifying itself in response to additional water input.
An additional hose won’t open the drain “magically”. There must be some physical mechanism. Most likely, if the water level rises sufficiently then the increased water pressure could potentially cause a clog to be pushed through the pipe.
Likewise, to expect the CO2 will “drain out” requires some physical mechanism in the natural environment that would dramatically increase CO2 absorption. The natural world isn’t magic, and as far as I know none of the contrarian climatologists have proposed a mechanism for a large drainage.
Another analogy, perhaps this will break whatever cognitive logjam we have due to preconceptions — fat accumulation. Perhaps you’ve heard of “calories in/calories out”.
Now, one might expect that this is trivially true — you can only get fat if you eat more calories than you expend, and those excess calories get shunted into fat cells. But what if those two variables are dependent? What if, when you have too many calories in, the body finds ways to dump them without accumulating fat? Or the body finds ways to slow down the metabolism to reduce calorie usage?
Again, there must be a physical mechanism for the calories to drain out, and again it’s easy to imagine one. In fact I distinctly remember, when I read some articles saying, “calories in = calories out, therefore the body must burn every calorie that goes in”, I remember thinking “um, couldn’t we just poop them out?” So there’s a variety of ways that could happen — genes turning on, or a natural genetic predisposition to failing to absorb all the carbs, or a complex interaction involving gut bacteria — but it’s obvious that it could happen in principle.
In contrast, after studying climate science for hundreds of hours now, it is not at all obvious that there could be a large unexpected increase in CO2 absorption.
And even if I believed that there could be some large undiscovered carbon sink, there’s a big gulf between that and being convinced that there is one.
Also, logically, uncertainty cuts both ways. If I believed that there could be some large undiscovered carbon sink, then I could also believe that there could be some large undiscovered carbon saturation effect, or even a carbon source.
Let’s consider the ocean, as it’s the biggest thing around. The situation with the oceans is complex, but it’s probably simpler than on land. Solubility of CO2 in water rises with air concentration (linearly) but falls with temperature (roughly linearly). Which effect is stronger, I don’t know personally but it wouldn’t be hard to compute. What makes it harder is that it probably takes many years for the CO2 (carbonic acid) to “saturate” the ocean (reach equilibrium with the air), so at first the air concentration is the dominant factor controlling absorption speed, but after the temperature rises and the deeper waters “fill up” with CO2, the absorption rate should slow down. Next, there are various processes to sequester carbon in the ocean, but how fast are those processes? Again a difficult question, and there are experts that study those processes specifically, so I would defer to them. Have we missed anything? Well, there’s underwater volcanoes, which put out a little CO2.
Anything else? I mean, how much could we possibly have missed? Anybody devoting their life to the study of the ocean could probably come up with a long list of things and be pretty confident about it — but there are many people who have dedicated their life to studying the ocean. I don’t think it’s likely that they all missed some big elephant in the room. And I’m sure if we look at the land we’d find another big group of scientists looking for every possible way that CO2 can get in or out of the air.