Assuming anthropogenic climate change (ACC) is real and happening and harming and killing people (and others of God's creatures), and we are all responsible for the greenhouse gases we emit (and responsible for reducing them in whatever feasible ways we can), how much of a sin would it be to deny ACC is happening, and refuse to do sensible things to reduce one's greenhouse gases in practical and feasible ways?
A related question is how much of a sin is it not only to deny ACC & refuse to reduce one's GHGs in any way, but also campaign vigorously to convince others that ACC is not happening, thereby convincing them not to reduce their GHGs?
I know both these would be wrong (assuming ACC is happening), but are they venial or serious sins? At what point does killing people become a serious sin? 10,000,000 people responsible for killing one person; 1000 people responsible for killing one person, 100 people responsible for killing one person, 10 people responsble for killing one person; or one killing one? Also, the intentionality -- a person not really knowing about his/her contributions to others' deaths (which, it seems, would not be a sin at all); a person not putting forth effort to understand how he/she might be contributing to others' deaths (even though the information is easily available); a person refusing to accept what scientists, popes, and others (who claim ACC is real) say & not caring if he/she is contributing to others' deaths; a person actually knowing ACC is real, but yet campaigning to convince others it is not real?
Is there some point at which it is a more serious sin or less serious sin.
NOTE: This is not for a discussion about whether or not ACC is real, only about whether IF it is real, how much of a sin would it be to deny ACC, refuse to reduce one's contributions to it, and strive to convince others it is not real.