Because the end of the world has never happened before, it’s understandable many people have a hard time wrapping their heads around the potential apocalyptic consequences of climate change.

Floods, famines, mass-migrations – it might be a little too Old Testament for many folks to want to think about.

But what about climate deniers? Those people who don’t react with honest skepticism or debate, but vitriol and spleen-venting anger?

Psychologist Linda Buzzell was wondering the same thing. In an interesting post last week on Huffington, she tried to plum the depths of why some people can’t seem to have a civilized conversation about climate science.

She asks: “Why are these folks so desperate and frantic to dispute the current scientific consensus…? And if you disagree, why the need to scream and foam at the mouth?”

As a medical professional, she wonders: “why are the climate change deniers so upset, so shrill, so fearful, loud and angry at those who agree with the international scientific consensus? What’s the psychology behind the screaming? What are the deniers afraid of?”

Maybe it’s just the money talking. As itemized almost daily on this blog, many of the shrill voices in the media seem not to be speaking on their own behalf but punching the clock for Big Oil.

To understand why denial is so important to them, you have to look at the psychology of climate change for the rest of us. A recent report by the American Psychological Association looked at some of the personal brain barriers to recognizing what the scientific community is collectively telling us, and being able to act on it.

“What is unique about current global climate change is the role of human behavior,” said task force chair Janet Swim, PhD, of Pennsylvania State University. “We must look at the reasons people are not acting in order to understand how to get people to act.”

Their research turned up some fascinating findings, particularly on the importance of uncertainty. The researchers looked a recent poll by the Pew Foundation that found the over 75% of respondents believed that climate change was an important issue, but ranked it last in a list of 20 compelling issues including the economy or terrorism.

Why is that? The authors found that even small doubts about the accuracy of science, or the the motivations of researchers can have big impacts on whether individuals feel a personal urgency to act.

Of course this foible of human nature has not been lost on those who manage public opinion for a living. The PR firm Brown and Williamson famously advised their tobacco industry client:

“Doubt is our product, since it is the best means of competing with the ‘body of fact’ that exists in the mind of the general public. It is also the means of establishing a controversy. … Spread doubt over strong scientific evidence and the public won’t know what to believe.”

Likewise, renown Republican spin-doctor Frank Luntz wisely advised the Bush administration:

“The scientific debate is closing [against us] but not yet closed. There is still a window of opportunity to challenge the science. Voters believe that there is no consensus about global warming within the scientific community. Should the public come to believe that the scientific issues are settled, their views about global warming will change accordingly. Therefore, you need to make the lack of scientific certainty a primary issue in the debate.”

The world’s best PR firms can afford a lot of focus groups. Those who working hard on behalf of the fossil fuel industry have correctly advised their clients the best way to prevent the public from demanding action on climate change is to convince them the science is not settled.

And when you try and address that doubt? They get a bit irate.

As a psychologist, Buzzell believes the visceral reaction from many climate deniers has more to do with posturing than pique: “I’m afraid it comes down to politics and the corporations who pay the politicians’ bills. The true fear may be that if reforms happen, the insurance and fossil fuel industries will lose money.”

Climate deniers aren’t crazy, they’re just working.