I don't think climate change is "unbelievable," but the people saying that it's certain haven't made their case yet.
It's basically educated speculation by people who do not know for certain what the future will bring. Some of the predictions scientists have made in the past about it have failed.
On the other hand, the fact of Adam and Eve having children, and their children having children with each other, is a truth revealed to us from our Creator who knows everything about the past and future, and is not subject to the possibility of error.