First of all, thank you for taking the time to bring up the issue in a constructive fashion. Secondly, thanks for posting many questions, I think I can speak in the name of everyone saying we appreciate the effort on your part.
I'd like to clarify a few things. Each question that has been closed has been closed independently of the others, and independently of the author. I can see why it would look suspicious and that is one reason I flagged the other mods to give an independent look at my actions.
The particular question has multiple problems. The largest problem is that it is unclear. Is it about the research article published in Nature or about the reporting on the Washington Post? My comments about "causation" refer to the latter, where the research is spoken of mostly in terms of "relations" and explicit causation is never really claimed. If the question is about the Nature article I have multiple objections.
If the question is about the Nature article, why did you link the WP article and not the actual Nature one? The WP article is completely irrelevant to the question and yet it is the main source of the claim. The Nature article is not even linked in the question.
We don't allow research level questions. Yours is clearly best answered by an expert on the matter, not by a mere skeptic. Any answer is best evaluated by an expert in the field too.
An article on Nature does not really constitute a notable claim. It might be notable, but it's certainly not a claim in itself. It is a fact that the readership of Nature knows how to read a scientific article and can distinguish something preliminary and unreliable from a large study. The article is evidence, which is the opposite of a claim - it might be weak evidence, but it is honest about what it is, since it contains all the evidence needed, methodology and information needed to replicate the result.
"So is a strong causal link between average temperature and human productivity reasonable or is it an accidental correlation based on other factors?" is a not factual question. Asking whether something is "reasonable" or "accidental" because of unspecified factors is asking for an opinion on a (research level) paper.
"So is a strong causal link between average temperature and human productivity reasonable or is it an accidental correlation based on other factors?" is also a false dichotomy, and it's a leading question. Clearly there could be an unproven causal link, or a weak causal link, etc. The question is leading because it tells users how to answer. This is a fallacy.
"a strong causal link between average temperature and human productivity" is also a straw man, since the authors don't claim such a strong result -- in fact they don't even claim strong predictivity of their model, since they prefix their predictions with "If future adaptation mimics past adaptation..." which is a huge caveat.
The title has a different question from the body of your answer ("Is the optimal temperature for human productivity 13°C?"), which is, by the way, not what the authors are claiming at all. Also, this question is not about the Nature paper at all.
I would have closed the question straight away because of these objections, but I decided to interpret the question in the way most favorable to you, that it was about whether the Washington Post coverage was correct, and that, maybe, it was simply written unclearly. In fact, I modified it in that direction. Once you changed it again and complained about the edit, saying that it was, in fact, about the Nature article, I had no choice but to vote to close.
I am sorry but I find your question not viable as currently written and I stand by my vote.
Take closure as an incentive to improve your question. I honestly don't know how to help you in that because I believe that your question would better be answered by, for example, an expert opinion of a climate scientist than by us looking at other papers.
To answer the other issues which you are raising:
"Are moderators too eager to close questions"?
No and in fact I want to reiterate that the community should do so more than us mods. But claiming that we are "eager" to close is frankly offensive. We don't like to close questions. We'd love to have as many open questions as possible, but the questions we closed are the ones we think that need to be fixed before they are viable. A community that is fearful to close and reopen is unhealthy.
Furthermore closing is not a moderator-only action, it is something that every user with 3,000 rep can (and should) do. I know that mods have a heavy vote, but we are encouraged pretty much constantly (see for example this official response) to not let that influence us too much.
I've had a few questions recently which have been closed very early...
Each question was closed for a specific reason, and the reason is always its content and never its author. I know it is probably not what you meant but it came across as a half accusation of targeting you. This is not the case and I wanted to clarify it.
Some of your questions seem to be problematic, especially because they sometimes can be read as highly opinionated, rhetorical or can be thought to be asked while you already had a strong opinion that ideally would like us to corroborate. This kind of questions tends not to work very well, obviously, and is going to be closed.