Accepting the word of an expert, without challenge, is falling for the Appeal To Authority fallacy.
The appeal to authority is a logical fallacy because authorities are not necessarily correct about judgments related to their field of expertise. Though reliable authorities can be correct in judgments related to their area of expertise more often than laypersons, they can still come to the wrong judgments through error, bias, dishonesty, or falling prey to groupthink. Thus, the appeal to authority is not an argument for establishing facts.
Here at Skeptics.SE, we are looking for definitive answers to questions. Wherever possible, our answers should avoid appeals to authority.
Humans have limited mental budgets for establishing the truth of each claim. It is understandable that, for example, a politician will need to delegate the task of finding the truth of each claim to a set of expert advisers, rather than become an expert in every area themselves. That introduces a risk that the expert doesn't do an expert job, but they are more likely to have a correct view (based on their research) than a layperson unfamiliar with the subject.
(From a Bayesian point-of-view, we should spend less of our limited efforts challenging the claims of relevant experts, as it has a lower chance of being fruitful in discovering an error. This attitude does not seem common amongst Skeptics.SE members.)
Occasionally, at Skeptics.SE, we get questions which we can't hope to answer with meta-studies of peer-reviewed experimental evidence, and we are forced to fall back on quotes from authorities - checking that they are indeed experts in the fields under discussion. Of course, answers with empirical data should, in general, be upvoted over appeals to authority.
Before I would comment on postmodernism, social sciences and humanities, I would expect you to be more detailed about your concerns, rather than a broad slur.
In my experience the claims about 90+ percent of relevant experts accepting Climate Change is a refutation of the claim by Climate Change Denialists that the science is very much undecided, and there is a legitimate controversy in the field. It doesn't prove Climate Change, but it reassures the public (and Governments) that the science is much firmer and well-established than sometimes claimed.
I didn't understand your third point at all. It is not hard to find members of the public accusing scientists of greed and bias. Indeed, it is not hard to find examples of bias in science. The important point is that science works towards uncovering the results of bias and overturning them so that, slowly but inevitably, the truth about the world is revealed. (Notably, the biggest source of falsehoods in science being discovered is other scientists.)