Firstly, rational discussion of the climate issue was cut off at the knees from the beginning. This is the observation from the Hartwell paper.

“Climate change was brought to the attention of policy-makers by scientists. From the outset, these scientists also brought their preferred solutions to the table in US Congressional hearings and other policy forums, all bundled. The proposition that ‘science’ somehow dictated particular policy responses, encouraged –indeed instructed – those who found those particular strategies unattractive to argue about the science.

So, a distinctive characteristic of the climate change debate has been of scientists claiming with the authority of their position that their results dictated particular policies; of policy makers claiming that their preferred choices were dictated by science, and both acting as if ‘science’ and ‘policy’ were simply and rigidly linked as if it were a matter of escaping from the path of an oncoming tornado.

In the case of climate modelling, which has been prominent in the public debate, the many and varied ‘projective’ scenarios (that is, explorations of plausible futures using computer models conditioned on a large number of assumptions and simplifications) are sufficient to undergird just about any view of the future that one prefers. But the ‘projective’ models they produce have frequently been conflated implicitly and sometimes wilfully with what politicians really want, namely ‘predictive’ scenarios: that is, precise forecasts of the future.”

Page 18, the Hartwell Paper, 2010
http://eprints.lse.ac.uk/27939/

Secondly, unlike other public policy issues, all the institutions shaping public perception lined up on one side and declared the “Science is settled. No debate is needed, only action.” Government, politicians, academia, media, industry, social activists, NGOs all agreed that the consensus was in and skeptics or dissenters were to be ignored or silenced.

Since beginning to explore the topic of global warming, I would see a news report warning of some impending climate disaster. Using Google News to search for various analyses and perspectives on the subject (be it acidic oceans, extinctions of species, rising sea levels, etc.), I would find dozens or even a hundred articles repeating the same story, the only difference being which headline was the most alarming. There’s always more than one side to any story, but with climate issues you have to dig and seek far and wide to find any views other than the mainstream.

Finally, when people do actually engage the climate issue, the science itself turns out to be immature and conclusions are murky. John Christy explains:
“Why do we argue about climate change?
The reason there is so much contention regarding “global warming” is relatively simple to understand: In climate change science we basically cannot prove anything about how the climate will change as a result of adding extra greenhouse gases to the atmosphere.
So we are left to argue about unprovable claims.”
http://www.centredaily.com/2014/03/20/4093680/john-r-christy-climate-science.html

In conclusion, paraphrasing George Will:

When a politician says, concerning an issue involving science, that the debate is over, you can be sure of two things: The debate is raging, and he is losing.