A person that grew up around conservative values and who's friends are all conservatives with deeply held beliefs will find it very difficult to reject those beliefs and ideals even when confronted with compelling evidence, as doing so would ostracize them from their group/tribe. To eliminate the feeling of cognitive dissonance, they will rationalize away the contradictory evidence, and actually increase the conviction of their beliefs in doing so. If this is done long enough and often enough, they will have constructed their entire identity around this framework of eliminating the cognitive dissonance, to the point that any attempt to deconstruct these beliefs will essentially be interpreted as an attack on themselves, as they can no longer separate themselves from their beliefs.

In the case of Global Warming, many people have been denying that it exists for so long to maintain their in-group status, that as conditions worsen, they will likely find new and inventive ways to justify the belief that it doesn't exist instead of simply admitting that their previous position was incorrect.

According to the studies into prophetic cults, only 1 out of 12 groups disbanded when their prophecy was proven false, the others found new ways to continue with even deeper convictions. In many ways, conservatism is its own cult, with its own beliefs and convictions. Without adequate education or critical thinking skills to defend against its propaganda, it is almost inevitable that one will fall prey to their designs, and once in, it is very difficult to escape unless one has access to support groups (friends or family) that will accept you after changing your beliefs.

A clear example of disconfirmed expectancy is with Trump supporters. He was heralded as an outsider that would drain the swamp of corruption in our government, but obviously did nothing of the sort. In fact, it only became more and more obvious as time went on that he was an incompetent narcissist that cared nothing for the people who supported him. But people had already put so much of themselves in supporting him, in applying all their ideals to him, that a cult formed around him. Now every accusation, every attempt to discredit, and any evidence showing his own corruption and lack of principles is shown only reinforces the cult's belief that he is their savior, and any talk otherwise will get ejected from the group.

It's very difficult to get people to sever themselves from the people that gives them a feeling of community, family, or friendship, even if that group is ultimately self destructive.