I think the real issue here is that you've internalized a scarcity mindset about morality. Like there's a fixed pool of 'virtue' and you're either in it or you're out. And once you've decided your efforts aren't mathematically sufficient, you feel like you might as well give up. But that's not how it actually works.
Listen, I'm not a climate scientist or a philosopher. I'm a regular person who gardens, composts, drives less, tries to be thoughtful about consumption. Not because I believe my composting will stop climate change - I'm not delusional. But because I actually prefer living that way. I like that my hands are in soil. I like knowing where my food comes from. I like not being a passenger in giant traffic jams. I like the person I am when I'm conscious about these things.
That's the real answer to your question. Not 'does my virtue matter for the world' but 'does virtue matter for my own life.' And honestly? It does. Not because I'm saving the planet. But because I'm not constantly at war with myself. I'm not eating food I feel awful about. I'm not driving a car that makes me feel complicit.
Your kid isn't going to remember whether you were perfectly virtuous. But they'll remember whether you lived according to what you said you believed. That actually matters. Not for the world's carbon budget. But for theirs - for what they learn about integrity.