Gore likens 'global warming' skeptics to racists, supporters of apartheid and homophobes
They are similar in that they all seek to achieve a sense of their own self-worth and self-righteousness by denying and belittling the worth of others.
People who deny man-made global warming aren't denying it because of anything they actually believe: as most of them are clueless of the facts and don't care. They deny it because they want to deny and belittle the "other guys". In this case they want to deny and belittle people who are logical, reasonable, and well-educated (scientists), so as to make themselves feel superior to and more righteous than them.
It's all about the false pride of the ignoramus. That's what underpins any form of bigotry: racial bigotry, religious bigotry, sexual bigotry, and intellectual bigotry.