I have enjoyed reading this thread immensely. Most of it is well above my head. Much of it seems to completely disregard previous injunctions not to engage personal asides. And, most of it seems to have nothing at all to do with the original post in regard to the august body of the House of Lords Economic Committee, and a rather old and very conservative ex-Chancellor of the Exchequer. But it's all good stuff, and it is not too difficult to discern the seething passion under the guise of rational scientific debate. The problem with the report of the House of Lords Economic Committee and Nigel Lawson's pronouncements, is that to read these economist's pronouncements in regard to anthropogenic global warming is comically absurd, it produces an effect as bizarre as would be engendered by reading a critique of the Theory of Relativity by a committee of lawyers. For economists to head their second chapter "The Uncertain Science of Climate Change" is not only an obvious ploy to downplay the status of climate change science but, when it comes from representatives of a social science for whom the future always comes as a perpetual surprise, is just a bit rich.
The HLEC considers that not enough emphasis has been placed on the positive aspects of global warming, such as the CO2 fertiliser effect, and its report contains curious debates such as those about the likelihood of people accepting lower wages in remaining areas of clement climates, and the "distinct amenity gains" of Northern Europe. (Of course this latter amenity might be dependent on being able to afford to move to higher ground which, of course, will become rather more expensive, or by living in a house boat - JKM) Equally the paragraphs on "Adaptation vs. Mitigation" contains the same sort of wishful thinking disguised as thoughtful consideration.
In the chapter on "Forecasting Greenhouse Gas Emissions and Temperature Change" this HLEC document may be on safer ground, the high forecasts of the IPCC do seem overgenerous. But in criticising these forecasts, they entirely neglect to acknowledge the fact that these forecasts are not worked out for the benefit of economic planning, but merely for scientific illustration (and are in fact based on projections by their fellow economists of the UN and the World Bank - if the projections are unrealistic this is the fault of economists, not the atmospheric scientists of the IPCC! Typical. I think it was J K Galbraith that said that economic forecasting was only done to make astrology look respectable.) More importantly the lower forecasts, which the HLEC are more happy to accept, are still entirely compatible with major and destructive climate change.
The document then goes on to examine the "Costs of Tackling Climate Change". This is not the place to describe in detail the arguments presented, but when you read such quotes as follow, you get the idea. "the UK research programme (into alternative energy technology) has been "captured" by certain renewable energy interests" and "there is a debatable assumption about the likelihood of passive energy efficiency gains" and "it is better ...... to leave the market to select the technologies" and statements such as "costs of 0.4 to 1.7% of GDP are not trivial" (relative to the possible damage of global warming, I think it is right to say these costs are trivial - what did Hurricane Katrina cost? JKM) and "the UK may have taken unilateral action to no purpose" (like the child protesting to his mother as to why he should clean his bedroom when Tony or George don't have to clean theirs. JKM) and last, but no means least "in terms of percentages of world GNP, damage is relatively low, even for +2.5oC. The damages are not evenly spread. In general, developing countries lose more than developed economies. Some models suggest no real net damage to rich countries" is a classic of blinkered optimism and of an appalling social and moral unconcern for the poor and disposessed in the world. 
In chapter 7, "The IPCC Process", the HLEC take parts of the IPCC reports to task. Whilst I have no doubt that some of the criticisms are valid, and in such a comprehensive document as the IPCC report there are bound to be inaccuracies and mis-statements, the whole tenor of the chapter is to endeavour to cast doubt on the whole report rather than engage in reasoned and appropriate criticism. For instance, the HLEC can't resist taking a dig at "scientific consensus" by quoting Professor Reiter's comment "Consensus is the stuff of politics, not science......" (the quote continues with some reasonable, but entirely irrelevant, observations about science), a professor of tropical diseases making his personal contribution to debunking major scientific agreement on climate change. If I were to hold a glass of water in front of me, and let it go, there would be a very major scientific consensus that the glass will fall to the floor, shatter and loose a good deal of entropy. By what logic, therefore, can Professor Reiter contend that consensus only applies to politics (a naive suggestion in any case, when did politics, or economics for that matter, have a consensus about anything?)But to give some credit to the HLEC, there are at least some important admissions by the HLEC on the likely major detrimental effects of global warming, the need for the public to be informed, the likelihood of the need for major social adjustments, and the urgent need for major investment in research, for example, to the scale of the American endeavours to put a man on on the moon. The summary at the end of their document gives one a quick overview of the points made in the text. However these admissions are not enough to overcome the problems in the report discussed above.
And what to say about Nigel Lawson? He uses so many of the fallacious arguments of the global warming sceptics that one might think he had been reading this site to learn what they are, as you have so thoroughly and clearly debunked them in your pages. This quote says it all "But the real cost of this approach is not so much dearer energy as the reduction in world economic growth. It is far from self-evident, not least for the developing world, that over the next 100 years a poorer but cooler world is to be preferred to a richer but warmer one. And why should the present and next generations sacrifice their living standards in order to benefit more distant generations, who are projected in any event to be considerably better off?" The assumptions underlying these arguments are inane, and the conclusion immoral. To assume that future generations are somehow guaranteed to be better off than we are, whatever we do to the planet, however much poison we pour in to the atmosphere, however much we deplete or damage our water resources, and however quickly we plunder its other irreplaceable assets, is breathtakingly presumptuous and overbearingly arrogant. Perhaps he should have a quiet word to a German citizen who lived in Germany before the Second World War in regard to assumptions about the future. Nigel Lawson's own conclusion, with the alteration of one word, sums it all up nicely: "We appear to have entered a new age of unreason, which threatens to be as environmentally harmful as it is profoundly disquieting. It must not be allowed to prevail".
But the basic problem about the argument "Climate Change vs Economic Cost" is that there can never be any meaningful answer. We are measuring two entirely different things, in other words there is no set of scales, no ruler or set of measurements that can encompass a rational comparison between the two. Climate change is a scientific issue, which will be described and answered by entirely scientific means, economics is a social science which, whilst is uses a good deal of maths and statistics, is basically the study of human behaviour as it impacts on a very narrow field of human existence. Economics is akin to looking at the world through a fixed telescope, it describes in great detail the focus of its attention, but entirely neglects, or is incapable of describing, the vast panorama of human activity and nature that lies outside its narrow field of view. At a fundamental level the two sciences and economics have no common ground. And at a fundamental level, we, as a human species, are going to have to accept the science, which will bear ever more heavily on us, whether we like it or not, and to hell with the economics. After all, the science of global warming is nothing more than the laws of nature. Mankind has no option but to obey the laws of nature. Mankind may temporarily postpone them, like a levee against the floods, but the laws of nature are not to be gainsaid, they will, eventually, have their own way. There are no separate rules for mankind, despite economists' quest to find them. Our choice is not between economics and science, but between a tolerable future, or no future.
(Later, my posting is critiqued, with some fair points. I go on to say at one point that detailed examination of this issue is the "last thing we need" because we are waiting so long to take action already. I accept this was a rhetorical flourish, rather than a reasoned point, and the criticism of this is valid. Of course we need to continue to make a detailed examination, the problem is that this need for more information is a favourite device of global warming deniers on failing to accept that global warming is a problem, or in delaying action in dealing with it even if the problem is admitted.)