Singer and Avery suggest that there should be no binding constraints on human emissions of greenhouse gases until three things can be demonstrated:
1. That greenhouse gases are certain to raise global temperatures significantly higher than they rose during previous natural climate warming cycles;
2. That such a warming would severely harm human welfare and nature;
3. That rational human actions could actually forestall whatever warming may occur.
In short, they do not think that the "global warming alarmists", including the IPCC, have been able to meet any of these requirements.
Singer & Avery pull no punches in this book of four parts. The first describes the discovery of the 1,500-year (or, strictly, 1,470 year +/- 500 year) cycle of warming and cooling and the evidence for it both from historical sources and scientific investigation - temperature proxies such as tree rings, marine deposits, habitation patterns, ice cores and sea levels, even stalagmites and fossilised pollen. Temperatures are not yet as warm as they have been in the relatively recent past - long before man was having any significant impact on the atmosphere - when mankind seemed to be thriving. In the second, they rubbish the evidence that human activity, and in particular the production of CO2, is causing any temperature change; they are particularly scornful of computer modelling and the political re-writing of the various IPCC reports. In the third section, they attack what they see as groundless fears about the effects of warming - the sort of thing that Al Gore put into "An Inconvenient Truth". The fourth section concludes by saying that Kyoto is pointless whichever way you look at it, unless you are Putin, looking to be able to sell billions of dollars worth carbon credits (based on Russia's 1990 industrial economy) but not now necessary to Russia or European leaders hoping to restrain the US's faster growing economy.
The 1,470 year temperature cycle was discovered by Willi Dansgaard and Hans Oeschger, and the research independently validated by Claude Lorius, based on ice-core research in the 1980s and 1990s. D, O & L did not explain a causal link more sophisticated than that it was due to the sun, and Singer & Avery credit Henrik Svensmark with identifying the link between solar activity, cosmic rays and cloud formation (as explained in Svensmark's "The Chilling Stars"). This solar cycle is thought to be caused by a combination of two previously identified solar cycles: the 87-year Gleissberg cycle and the 210-year DeVries-Suess cycle, but the theory does not get much more sophisticated than that. In short, there does not yet seem to be a theoretical explanation as to why the sun triggers a 1,470 year cycle, nor why it should be +/- 500 years (which does seem quite a lot to a layman like me), but the cycle is based on a great deal of consistent, and planet-wide, empirical evidence. Singer & Avery cite many sources to show that the Roman and Medieval Warmings and the Dark Ages and C16 - C18 "little " ice ages were planet-wide.
Singer & Avery suggest that it would be prudent to consider that mankind is contributing to the (slightly) warming Earth, but that the vast majority of the relatively mild (but greatly overstated) warming is being caused by solar events completely outwith man's ability to control. This may be just as well, as they are highly sceptical about the practical effectiveness of many so-called alternative energies - although they do not go into detail about the practical problems to the extent, for example, that Booker and North do in "Scared to Death". Even nuclear fission, they think, would only be of temporary help, and in the long term, when fossil fuels run out or we are choose to stop using them, we had better hope that we have cracked nuclear fusion. This, ironically, is the same conclusion reached by James Lovelock of the Gaia theory!
This book is at its best in its detailed statement of facts in support of there being significant natural climate variation, and in pointing out the weaknesses in some of the data presented by global warming alarmists. (Some of the facts, based on historical interpretation, would probably be rejected by scientists as insufficiently quantifiable, but they seemed worthy of conclusion, to me, in support of quantifiable data.) Otherwise, I have to admit, I was a little disappointed by it, because I seemed to have read many of their arguments in greater detail elsewhere: Svensmark on the solar/galactic effect, Bjorn Lomborg on the economic consequences of an over-reaction, Booker and North on the limitations of alternative energies as they currently exist, Patrick Michaels on the reasons why scientists find themselves acting, unscientifically, to support a developing "paradigm".
This book is, nevertheless, 260 tightly-argued pages demonstrating that there is no "global warming consensus" that man made global warming is out of control. If, for example, you are alarmed by the arguments of the "consensus" and wish to explore some of the arguments of the "sceptics" then you could do a lot worse than starting here.