Byron asked: "Sam, do you agree that there is a significant body of hard-core deniers who are not open to evidence? I am not saying that every contrarian belongs to this group (nor that pathological behaviour is confined to contrarians), simply that there are powerful economic, ideological and social forces leading many to a place of epistemic closure on this matter. Would you agree?"
My simple answer is 'yes'. Anthropogenic Global Warming (agw) as presented is a major challenge to the status quo, and so all those with interests in preserving the status quo will have a bias to resist the conclusions of agw. These can take many stripes; often, I would accept, there is a reactionary element involved, and there may even be some legacy influence from fossil-fuel providers funding propaganda.
However, it is also true - so it seems to me - that there are hard-core 'affirmers' who are equivalently immune to evidence, and that there are "powerful economic, ideological and social forces leading many to a place of epistemic closure" in favour of the agw hypothesis.
To my mind, agw is a plausible hypothesis with a significant amount of supporting evidence. It is less than certain; most of all, the dire predictions are much less than certain, and I tend to see bad theology in them.
Beyond this, I tend to see Liebig's law as relevant. The dire predictions associated with the IPCC tend to assume, more or less business as usual, ongoing into through the twenty first century. This seems mindless to me. There is not a hope of business being anything like usual for the next fifteen years, let alone the next fifty or hundred. That is seen most explicitly for me in the assumptions employed re: fossil fuel use, but it applies to all the other limits to growth that we are hitting (and Byron has a useful list here). If we take Liebig's law to apply to the world system as a whole (which I think is reasonable) then it seems highly likely to me that a very great number of the measures and results being sought by agw advocates will be imposed upon human society by reality. Our carbon dioxide emissions, and the whole impact of industrialisation upon the ecosphere, will substantially reduce from present levels. I see this as beyond any choice, whether that choice be made by individuals, nations or humanity as a whole. We in the industrial world are going to have to get used to using a great deal less energy, and soon (my wild-assed guess: 50% less energy in 15 years).
Which is why I see agw as a red herring. Although it makes for some dramatic pictures, the science behind agw is less certain than the science behind other ecological concerns (Peak Oil, deforestation, water scarcity etc), and the prognoses from agw are even less certain. Worse than this, they are alarmist and appeal to fear, and that has theological problems too. I simply do not see what is either achieved or achievable by the IPCC and its cohorts. Whereas something like Transition Towns (on the practical side) and the Dark Mountain project (on the human culture side) - these I find exciting, practical and inspiring.