Ian has asked "why that one source (Yamal) is so important to your overall belief in this subject".
The short and direct answer is that the Yamal data underlies much of the advocacy surrounding AGW, specifically that it seems to be the major grounds for believing that our present climate is warmer than it was in the Medieval Warm Period (MWP). This is the graph accepted by the IPCC in 1990 to show the change in temperature over the last thousand years. Note that the MWP is warmer than the present.
This was replaced after 1998 with the 'hockey stick':
The principal scientific source for the 'Hockey Stick' relied on data from Yamal (see this wikipedia page for more background).
Now, it could well be the case that even without the Yamal data, the evidence for the late twentieth century being warmer than the MWP is robust. I'm open to that being the case. My concerns are different, because, in the end, I'll believe what scientists tell me on matters of scientific fact (in other words, when they stop using words like 'consensus' and just say 'this is how it is' - after all nobody talks about a consensus when discussing, eg, gravity, or the sun being at the centre of the solar system.)
I think that:
a) the science supporting the AGW hypothesis, and the alarmist predictions built on it, is not as robust as it is claimed to be. I think this because i) the IPCC does not take into account the peaking of fossil fuel resources; ii) the (on-going) Svenmark research exploring solar/cosmic ray influence on climate; and, yes, iii) the sort of arguments that McIntyre makes;
b) in other words, I think that scepticism about AGW is not illegitimate, I believe that it is intellectually respectable;
c) because I think this, I find the attempts to repress debate (either by suppressing the data, eg with Biffra) or by ridiculing, scorning and doubting the moral fibre of sceptics to be distinctly lacking in virtue. If the science is robust then it will stand up to the most virulent of partisan criticism, and will emerge all the stronger for it (this is not to say that some criticism isn't simply partisan and deserving of scorn, only to ask for discrimination);
d) because of the prevalence of c) I have come to see that there are aspects of idolatry involved in the AGW consensus. In particular I believe that many people accept AGW because it fits into a wider picture of belief about what is wrong with the world today. As it happens, I share that wider picture of belief (basically, the 'Limits to Growth' argument), I just don't believe that we can build a better future on the back of c) - that is, I really do believe that it is the truth that sets us free and that fear paralyses us (and I think the AGW consensus is trying to force change by amplifying the fear. I see this as morally wrong and spiritually unsound);
e) my motivation in sharing information like that about Yamal, therefore, is much more to do with wanting to combat that idolatry than wanting to object to the bigger picture, and all that it entails. The difference in personal behaviour required in responding to AGW or responding to Peak Oil is pretty small.
That ended up being less brief than planned. I should add that for some time (eg in my early LUBH talks) I accepted the AGW consensus. Two things started to shift me on it: first the IPCC ignorance of Peak Oil, second reading this book. I became more sceptical the more I studied the question. Now I would class myself as an agnostic/mild sceptic on the specific AGW issue, but definitely a critic on the 'wider aspects' of what is involved.