Lack of understanding may be a part of it but I believe a bigger part of it is his lack of integrity. He could just as well have acknowledged that there are dissenting opinions in the scientific community and disagreed with those opinions. But he didn't because he is so emotionally invested in his cause that he is unwilling to acknowledge anything which threatens his cause no matter how obvious it is.
Case in point, he is unwilling to acknowledge the drivers which caused our planet's climate to fluctuate - prior to industrialization - in the polar regions during interglacial and glacial cycles despite the ice core evidence to the contrary. He is unwilling to discuss the different thresholds for extensive continental glaciation and why they are different. One would think this would be an important part of a climate discussion - and a natural starting point for climate discussions - especially since they are arguing man is driving the planet's climate to a super greenhouse state. If that's the case explain where that threshold is for each polar region and why. Explain how once crossing that threshold orbital cycles will no longer trigger glaciation at either pole.
