First, let's get back to the original statement I made:
"skeptics" claim that the burden of proof is on those who say it will happen on a large scale, despite evidence that it IS happening on a large scale. This has never been the way science works. The burden of proof is on "skeptics" to explain why a reproducible, verifiable model on a small scale won't work on a large scale. They have no evidence, and are quite dishonestly trying to shift the burden of proof back on the scientists, knowing full well that on a large scale it will take a much longer time to acquire the kind of evidence they are seeking.
I was not quite as overly-precise as I needed to be. Note that in the first sentence, I qualified it with "despite evidence that it IS happening on a large scale". I left that qualification out in the remaining text for the sake of brevity. However, the fact that it was the first statement of that paragraph is significant. That's the one you should lend more weight to.
Here's the problem with your argument. It's not that it's incorrect in a general sense, it's that you are applying it to something that I am not trying to say, and are conveniently ignoring the context within which I said it. You are ignoring the very precise opening statement that I made, and cherry picking statements that I made after that, ignoring the previous, carefully chosen parameters that I had made earlier. Do I really need to qualify every single statement, over and over, even after I've already said precisely what I meant, over and over? Do you really think it's efficient for me to have to qualify every single sentence? Yes, there is a burden of proof for both sides, I may have incorrectly implied that only the skeptic needs to meet a burden of proof, but I think that the only people that came away thinking I was saying this were intellectually dishonest hair-splitters. Would any reasonable person come away with the idea that I was arguing that scientists don't have any burden of proof? No. Would it be more precise to say that a larger burden of proof is on those who would like to create multiple complex theories where a single unifying theory would suffice? Yes, it would, but I think most rational people would have figured that out based on what I wrote.
Let's take another example:
We have Newtonian physics and we also have quantum physics. A larger amount of evidence was required for quantum physicists to explain why we needed a new model. While both "sides" have a burden of proof, it takes more proof to explain why we need to complicate our understanding of the world around us. This is because science doesn't just seek to explain things, it seeks to do so in the simplest way possible. (Einstein quote - "Everything Should Be Made as Simple as Possible, But Not Simpler"). When we come up with data that refutes pre-established models, it requires more scrutiny, period, as we don't want to unnecessarily complicate our model by including bad data.
The fact is, scientists are making every reasonable effort that they can to prove this is happening, but it's not reasonable to expect all of this data to be collected before we need to make a decision. In terms of social policy, it's reasonable to think we may have to act much sooner than this.
What AGW advocates are saying is:
1. We have a reproducible model on the small scale
2. We have significant evidence that this model is working on the large scale
What "skeptics" are asserting is:
1. We can't apply the small scale model to the large scale model (they need to prove this, and they have a larger burden of proof to explain why an already established theory should be thrown out)
2. We won't pay attention to evidence that it is happening on a large scale until we can show it happening on a geologically significant time scale, perhaps some time after we go extinct.
In terms of item number one, when we formulate a hypothesis (often described as an "educated guess", in contrast to "completely naive guess that ignores all pre-existing theories") we start with what we already know, and pick a hypothesis that is consistent with what we already know. We don't start with a hypothesis that conflicts with our current understanding unless we have a damn good reason. Then, if the data is consistent with our hypothesis, we accept it. Alternative hypothesis have a larger burden of proof, and in the event that there is an established hypothesis that is consistent with the data, we bias ourselves towards it.
The thing to keep in mind is that "real" scientists ARE skeptics. That is, they apply the same rigorous standards to their own theories that they apply to other's. The armchair "skeptics" are claiming that their own lack of evidence doesn't matter, and that it's up to the other side to keep coming up with more data, which they will of course conveniently ignore. That's not being a "skeptic". That's being a biased, partisan, big business apologist. It's not skepticism if you only scrutinize the other side.