ethical questions such as "what steps we should take to mitigate the effects of global warming?"

While I don't often say this, that question doesn't strike me as an ethical question. It seems to turn entirely on questions of what steps would be most effective to producing the desired effect.

When primitives performed human sacrifice to ensure the sun will rise tomorrow, they were not mistaken about ethics - they were mistaken about astronomy.

there's no equivalent feedback mechanism for making-the-right-moral-decision

I disagree - it's usually pretty obvious. While I usually prefer not to talk in terms of "right moral decisions", acting in accord with ethics gets you exactly what you'd expect from it. Ethics specifies criteria for determining what one has most reason to do or want. While what that ends up being is still a matter of disagreement, here are a couple of examples:

consequentialist: do whatever maximizes overall net utility. If you do something to make someone feel good, and you make them feel bad instead, you get immediate feedback as direct and profound as catching a baseball.

virtue ethics: act as the good man does. If you go around acting in a vicious manner, it's obvious to all around that you're nothing like a good person.