Your part is not thinking how to reduce your carbon footprint but organizing with other people and partecipating in collective actions or movements or whatever.
Your small part may be even just donating 10€ to the people needing legal help cause protesting. Or just showing up to a rally. Joining a union…
I think that just liberals think we should all try to reduce our carbon footprint so there is really no need to feel guilty about that on this server ;)