The idea that one should obey revelation-based rules obviously was not popular during the Enlightenment, and 18th century thought took two tracks. One was Kant's, which sought to found deontological ethics on reason, and led to the categorical imperatives, the most famous of which is 'Act as though the maxim of your actions could be a general law', or as my mother (knowing nothing of Kant) put it "What would happen if everyone did that?" There are all sorts of criticisms of Kant, and attempt to build on or modify his ideas; my own experience is that raw Kantianism leads to a set of rules that are incredibly strict.
The other great thread is utilitarianism, which essentially says one should act to maximize the overall happiness, or good, or something, of the universe. There are of course all sorts of problems with this too. Is happinees necessarily a good thing? After all, a well-supplied drug addict is happy. How can you define good in utilitarianism in a non-circular way? How do we know if animals are happy, and is their happiness to be given equal weight to ours? If we knew killing a baby Hitler would spare 50 million people, should we kill baby Hitlers? But my own view is we can solve most of these problems sufficiently. The one insurmountable problem, in my view, is the impossibility of the utilitarian calculus. It is simply impossible to forecast the long term results of any action, even to some acceptable degree of probability.
It is probably fair to say most deontologists are on the right, and most utilitarians on the left. The reasons for that are pretty obvious, so I won't belabor them. Because of what I view as the fatal flaw of utilitarianism, I am sort of a half-hearted Kantian, partly by upbringing, partly because I see little practical alternative, being an atheist.
That's all background; here's the point of this post. Climate change is a case study in why the flaws of utilitarianism cause its adherents to become deontologists. Climate change is happening, because we are collectively pumping large amounts of CO2 into the atmosphere. I happen to think the short term consequences of this will be overall benign, but it's hard to say that about the long-term consequences; it will take an awful lot of carbon-dioxide-bestowed goodness to offset drowning the coastal regions of the earth. So what, ethically, should one do?
Oh, oh, I know, says the utilitarian. Institute policies to push us away from fossil fuel use. Stop the atmospheric CO2 increase! Problem is, we can't actually do that. We can reduce our own production of CO2, at some considerable cost to ourselves (a utilitarian evil). But there is no indication enough of the world will do the same. China will say it will, but it won't. India simply refuses. If we lower our consumption of fossil fuels, that will simply increase the supply, lower the price, and incentivize consumption elsewhere. It's depressing but entirely reasonable to predict humans will continue to consume fossil fuels, regardless of long term consequences, until the last readily available fossil fuels are used up. At that point, we are seriously screwed. Another problem with utilitarianism; sometimes you can't do anything to increase the good of the universe.
How does the utilitarian answer that? He/she says we should do it anyway, to show 'leadership'. Maybe if we do the right thing, others will follow. it will at least give us the moral standing to pressure them to follow. I think that's deluded. India has all sorts of good moral arguments why it should continue to grow, and self-interest will cause it to pick its own, over ours
So, in the end, utilitarians are forced to argue that we should limit CO2 production, because it would be good if everyone did it. Kant stirs in his grave and murmurs "By golly, that sounds familiar!" (Auf Deutsch, natürlich). Welcome to the categorical imperatives, boys and girls, and get out your reading glasses. The Critique of Practical Reason is heavy going, but you'll get through it; if everyone did, the world would be a better place.