how do you reason about the amount of additional giving necessary to offset any negative societal consequences of the field that you work in?

Or a harder question: should you work in negative fields at all? I'm sympathetic to arguments like early 80k gave that many high-earning jobs we conventionally think of as harmful rarely cause a level of harm in the same ballpark as the amount of benefit you can do via donations, especially after considering replaceability, though some still do very poorly. But I also think there's a strong case for avoiding ones with obvious harm. I also think it's important to consider that people often underestimate the harms of their own employment.

Unfortunately for most jobs, even questionable ones, the social impact is very hard to work out. Take your oil rig example: how much is your marginal contribution to oil production, after considering the oil company's elasticity of rig labor and the elasticity of production? Does cheaper oil displace even more carbon-intensive coal? How likely are extreme climate outcomes? Is the benefit of cheaper energy in lifting people out of poverty enough to make it positive on its own? Making a high-quality impact estimate for a career is a huge amount of work, and there are a lot of potential careers. Overall I like a general rule like "don't do work that is illegal, or that would be illegal if the public knew what you were really doing", but I don't have firm thoughts here.

I'm curious how you manage to maintain motivation in the face of uncertainty about the effectiveness of whatever giving you choose. It seems like the feedback loop of telling whether a donation made a difference in something like global poverty would be on the order of years, whereas the feedback loop of working directly with people in need might be on the order of minutes.

I've generally worked in areas where I can tell if I'm making progress at my job. I have long-term goals, quarterly goals, what I'm trying to do this week, the specific flaky test case I'm trying to fix. I find making that sort of progress very motivating, and while I think it would have been possible to do significantly better I've been happy/fulfilled leaving figuring out how to deploy my money to fund managers.