"I would tend to be careful about making far-reaching extremist conclusions, and foisting radical societal change on humanity on the basis of them."
Then why are you in fact not at all careful about just that? For instance, you just said "and given the fact that there is not very much we can do to change the carbon cycle on earth anyway (without total disruption of society)". That's a far-reaching extremist conclusion. A) it's well documented that we have in a very short period of time done just that -"change(d) the carbon cycle on earth". And B) it's not at all hard to imagine very positive ways to change it in the opposite direction w/o total disruption of society. It may not be easy, but otoh, this bullshit about it costing too much is just silly, both because there is cost anyway, and because it is investment that HAS to be done anyway for many reasons.
Choosing to not deal with the evidence for what looks to be catastrophic, that too is a far-reaching extremist conclusion.
And I'll ask again: is there any possible level of human-added CO2 and/or methane and other atmospheric gasses that you, James Wood, would believe could be harmful to human life and welfare? If so, what is that level and how did you arrive at it, and if not, can you give me at least some clue as to why not?
We're all excited, btw, about Nuclear Fusion... and many other technologies. But right now, you simply have FAITH in it. It doesn't take faith to speculate on what increases in human-added greenhouse gasses will do to disrupt society.