Or just let yourself and the people around you enjoy what time they have left. if everyone is doomed and there is nothing that can be done to change that fact then why complain and preach at people,what good will it do? If as you say it can't be changed so your changing would be pointless then just enjoy the here and now.
Still given that global warming is a contested subject(And anyone who tells you everyone in any field of science agrees on anything and that everyone who doesn't conform is a tool has no idea what they are talking about or how real science works)and what we have been through in the past I think it will take a lot more then that to wipe out us or the planet. Even if these are our last day and there is nothing we can do to change that then why go around pointing fingers instead of enjoying life?
Still I would rather look on the bright side of life.