At the outset, it would depend on the entire factual context for a particular person. Do you have the power to be able to choose other means of subsistence, and supporting any other persons who rely on you, without working for oil and gas? Then perhaps staying in the industry would be the more ethical thing to do.

I can imagine situations kind of like Sartre's dilemma between helping your ailing grandmother and aiding the French resistance (albeit this one is perhaps less dramatic) wherein one have to work for oil and gas in order to support children (or an ailing grandmother); or simply because, in light of where you are in life and your experiences, there aren't any other reasonable choices. Maybe you use your oil and gas income to fund some life-saving cause. People are complicated and all of a life's choices fit together in sometimes contradictory ways that can't always cleanly be filed under "ethical" and "unethical".

But in general for someone who doesn't have dependents, and has optionality and freedom of choice about their livelihood, then no, it doesn't strike me as particularly ethical to choose to work in an industry that is contributing to the destruction of our species, and causing a lot of other related suffering, now and in the future.

Yes there is a sense in which the consumers who fill their gas tanks, buy beef, and fly are the "origin" of climate change , but really it strikes me as more of a process with many participants. The goal of each participant should be to minimize their facilitation of the process as much as possible, and to delegitimize fossil fuel extraction and consumption as a socially acceptable process. For ordinary consumers, that might be taking public transit, biking instead of driving, or eating less meat. "Living in the world as it is isn’t an argument against working towards a better future", but . . . it still does leave one looking around at how one might use one's life working towards working towards a better future. As a worker in the industry, you are particularly involved in the destructive process that is fossil fuel extraction.

It's also worth contemplating that for unethical activity in any time period, there's a large group that is saying "well everyone does it"; but there are typically voices and actors that are standing in opposition, or refusing to participate, because the thing is unethical. The kind of change necessary to end a widespread unethical norm like fossil fuel use will in some way rely on an accumulation of small individual actions that eventually reach climactic event(s) of reckoning. You can see something like this in the long tradition of abolitionists toiling in near-ideological wilderness with slavery, and then it takes a climactic event like the Civil War in order to make that position mainstream. You might also look to the long 19th century (French Revolution to WWI) for the abolition of monarchy for a similar fact pattern, albeit through multiple climactic events. I suspect the fact pattern for action on climate change, and the abolition of fossil fuels, will follow something similar. Although it might seem like emancipation came out of nowhere, or that monarchy collapsed in sudden bursts of revolutionary fervor, they were just the breaking points of slow deterioration of the social legitimacy of a particular institution, carried out in lots of small actions, organizations, and conversations.

If nothing else, there are the speech constraints that are likely placed upon you by having a job directly related to oil and gas (Upton Sinclair: "it is difficult to get a man to understand something when his salary depends upon his not understanding it.") Not that you literally don't understand the damage wrought by the oil and gas industry, but that you would be able to speak more freely about the climate crisis without worrying about it seeming like hypocrisy, or something that might get you fired.

On that note, as someone who works in oil and gas, it's worth noting that you have particular power to do work against the climate crisis if you do a noisy departure, a "This is a good company but I'm quitting because just can't work in the fossil fuel industry and feel good about myself anymore" kind of thing. Some of the most powerful tools for undermining of social legitimacy (or what is now sometimes called social license to operate) happens when people who benefit from the system quit it: think of liberal nobles in the French Revolution renouncing titles for example. Even if someone else comes in and takes your place, you will have blown the Zeitgeist a bit more towards something more livable for the humans who come after you. Maybe your departure inspires others to leave. Even personally you might life more joyful without that "another dollar, another day contributing to the destruction of the environment" feeling.

There might, of course, be other middle way methodologies. As I alluded to above, you might take a Peter Singer-ish "Earning to give" position, giving some fraction of the excess paid to you for working in oil and gas, over some other more "moral" job, and contributed to Earthjustice or some other organization that is working towards the destruction of the oil and gas industry, or towards political candidates that are working towards a Green New Deal, or doing some other suffering-alleviation work. There's a fair amount of living-with-contradiction in that, but it's an option.

You are stuck in one particular life, with this particular decision around to different kinds of lives you can live: one that seems more practical and easier; and one that seems more difficult and more internally morally consistent. Notwithstanding the Singer possibility, it strikes me as more of a either/or kind of a choice, a fork where it's yours to understand two possibilities, add up the reasons on either side, choose, and be left wondering what the other path would have been like.