Humans are partly responsible. The effluent of many life forms that humans grow & rear for food is partly responsible. Changes to the very matter of earth are partly responsible. How each part may be countered with what mankind has already discovered plus what mankind may discover plus the actual but undiscoverable are all facing us. in other words we don't know.
Part of the story we do know how to fix. So sensible humans take action now. Not sensible humans need to put up or shut up'
This is all one of those things that shouldn't have to be asked.