I, a scientist with a PhD in Microbiology and Immunology, was a climate change denialist. Wait, let me add, I was an effective climate change denialist: I would throw on a cloak of anecdotal evidence and biased one-sided skepticism and declare myself a skeptic. Good scientists are skeptics, right? I sallied forth and denied every piece of evidence that was presented to me, for a relatively long time. Details here.