Really interesting article in New Scientist about the reasoning behind denialism.
From the article:
"Many denialist movements originate as cynical efforts by corporations to cast doubt on findings that threaten their bottom line. Big Tobacco started it in the 1970s, recruiting scientists willing to produce favourable data and bankrolling ostensibly independent think tanks and bogus grass-roots movements (see "Manufacturing doubt"). One such think tank was The Advancement of Sound Science Coalition (TASSC), set up in 1993 by tobacco company Philip Morris (American Journal of Public Health, vol 91, p 1749). TASSC didn't confine itself to tobacco for long. After getting funds from Exxon, it started casting doubt on climate science."
Both of my parents are climate change deniers and I have had many a heated and irrational (on their side) discussion with them about this. It's almost impossible to point out facts or figures about recent rises in temperature or melting icecaps. They won't hear it and reject the idea outright, claiming that it's a left-wing conspiracy to bring about more government regulations and, ultimately, a one world government. I've recently given up the hope of ever swaying their opinion since you can't use logic to fight those who are completely illogical.
More at the link: Living in Denial