Angry old white Australian male and proud of it!, page-50

This my friend is an example of Dunning Kroger effect. It's a cognitive bias that allows the most incompetent in a field to believe they have knowledge disproportionate to their actual knowledge level and be unable to recognise or acknowledge expertise in a given field. It occurs because people who are incompetent in a field do not possess the skills to recognise their own incompetence, or the expertise of the field's elite.

This is how a local labourer (as a random example) can come to the confident conclusion that the doctors are all wrong and smoking doesn't cause cancer, or the scientist are wrong and people don't cause climate change. They way up the evidence they see and come to the conclusion that their knowledge of the issue is as valuable,or more valuable than the knowledge possessed by experts.

To be clear I'm not saying that this makes a person less intelligent. The bias can be present in anyone in fields they lack competence. Their also not generally aware of it because they lack the skills or knowledge to recognise their incompetence. An investor and a climate scientist may have equal intelligence, but when engaging in the other person's area of expertise they don't tend to recognise their own incompetence or the expertise of the other.

Multiply that bias by a few million people, add some self interest in denial and there is the reason we're even having a debate about acting on anthropogenic climate change.