@jennifers, I don't have a sensation of heavy emotional struggle right now or a lotta lotta extra cash, but have thought seriously about these same issues for sure. Have been a full time social justice activist at times, worked on issues for years through community organizations, campaigned politically, helped make bits of history. My FIRE was more accidental than my impact, though there was more chance than I want to admit in both paths. Fwiw:
1. Keep going... any confusion or negative feelings are obstructions that need not be permanent. Almost of all of us experience something like them, though, so no shame - they're very common. It'll get better.
2. Hopelessness is the enemy of everything good. Keep going.
3. Great decisions you already made!
4. There are a lot of different paths toward doing something good. One formula is not always better than all of the others, so that if you found it, now you'd have The Right Answer. But there are answers that are better than most because people did some hard work already to develop a very good answer. The suggestions upthread are excellent examples of good answers. It's okay to pick the good answer that suits you. Your money, your time, your brain, your caring can all have some impact in many places, many ways. It's worth searching for high impact examples you can feel good about, just like you would search carefully for a car or bike or apartment or friend. Maybe even a spouse level search, given that you have a large amount of potential largesse. But don't expect perfection, be glad with something good and move forward.
5. Take your time and iterate.
6. Do something. (You're already doing this. Awesome!!!)
7. Fwiw, I think it's good to:
a. Set a minimum, like 10%.
b. Set a maximum, such as "never reduce my stash below what is healthy for me, plus a safety margin"
c. Remember that most accomplishments of the past were done by uncertain people making moves that were doubted by others, and sometimes doubted by themselves. So what you do today can be just as effective as all the doers of the past.
8. Meet other donors, and doers.
9. Donate by character. If you like to diversify, pick three causes. If you like to focus, pick one. If you like to feel caring, take care of the puppies. If you want impact, compare the CharityNavigator vs Givewell approaches and get the opinions of wise people on which is better. You can do this. Keep going!
10. Congratulations on undertaking this.
Re the global warming thing... don't let that stop you. I myself put about 25% of my efforts toward that, but 75% elsewhere (25% US social justice, 25% foreign mostly oriented towards women, 25% personalized giving though I am slack with this because it intimidates me). There's always a looming threat. Do what you can with what you have. We're all in this together, and I thank you.