The National Geographic has a great piece on why so many reasonable people refuse to accept the scientific consensus on issues such as water fluoridation, child immunisation and of course, climate change:
We live in an age when all manner of scientific knowledge—from the safety of fluoride and vaccines to the reality of climate change—faces organized and often furious opposition. Empowered by their own sources of information and their own interpretations of research, doubters have declared war on the consensus of experts.
So why do so many people cling to positions so contrary to science?
...Even when we intellectually accept these precepts of science, we subconsciously cling to our intuitions—what researchers call our naive beliefs...as we become scientifically literate, we repress our naive beliefs but never eliminate them entirely. They lurk in our brains, chirping at us as we try to make sense of the world...
...The “science communication problem,” as it’s blandly called by the scientists who study it, has yielded abundant new research into how people decide what to believe—and why they so often don’t accept the scientific consensus. It’s not that they can’t grasp it, according to Dan Kahan of Yale University. In one study he asked 1,540 Americans, a representative sample, to rate the threat of climate change on a scale of zero to ten. Then he correlated that with the subjects’ science literacy. He found that higher literacy was associated with stronger views—at both ends of the spectrum. Science literacy promoted polarization on climate, not consensus. According to Kahan, that’s because people tend to use scientific knowledge to reinforce beliefs that have already been shaped by their worldview...
There's also a social/peer group dimension:
...Science appeals to our rational brain, but our beliefs are motivated largely by emotion, and the biggest motivation is remaining tight with our peers. “We’re all in high school. We’ve never left high school,” says Marcia McNutt. “People still have a need to fit in, and that need to fit in is so strong that local values and local opinions are always trumping science. And they will continue to trump science, especially when there is no clear downside to ignoring science.”
But this part is not quite right:
Meanwhile the Internet makes it easier than ever for climate skeptics and doubters of all kinds to find their own information and experts. Gone are the days when a small number of powerful institutions—elite universities, encyclopedias, major news organizations, even National Geographic—served as gatekeepers of scientific information. The Internet has democratized information, which is a good thing. But along with cable TV, it has made it possible to live in a “filter bubble” that lets in only the information with which you already agree.
Yes, people live in information bubbles, but they always have — Green Left Weekly has always been purchased mainly by people of the left, and The Spectator by people on the right. We all like to read things that reinforce our prejudices. But, if anything, this bubble is now easier to penetrate, given that contrary information and opinion is a single click away, and mostly free. In the days of the gatekeepers, one would have needed a subscription to break that bubble.