forcing. The existence of the 100-kyr cycle and the synchronism between Northern and South- e r n H e m i s p h e r e c l i m a t e s m a y h a v e t h e i r o r i g i n i n t h e l a r g e g l a c i a l - i n t e r g l a c i a l C O 2 c h a n g e s [Genthon et al., Nature, 329, 414–418 (1987)]. .
This interpretation essentially reflects the mainstream climate science interpretation over the ensuing decades: the climate CO2 connection is that of a feedback loop with CO2 changes am- plifying the effects of changes in insolation due to orbital changes. The reasons for regarding this as a two-way interaction rather than direct causality in either direction are:
Why CO2 changes are not the sole cause of ice ages: i: The gas changes are too small. In preparing the diagram for Twisted... I followed a suggestion from the RealClimate website and plotted the concentration curves in proportion to the expected temperature changes. ii: There are no plausible mechanisms for linking concentrations to orbital changes, except via climate changes over large regions.
Why orbital changes are not the sole cause of ice ages:: iii: The changes in insolation are too small: iv: Many of the insolation changes act with opposite signs in the two hemispheres and so the approximate hemispheric synchronisation is hard to account for except through an amplifying factor (such as greenhouse gas concentrations) that is common to both hemispheres.
Thus having concentration changes lag behind temperature is entirely to be expected under this mainstream view, while the opposite result would have been extremely difficult to account for.
In addition to the reasons noted above: v: the abrupt nature of the deglaciation, unlike the smooth variations in orbital forcing, points to ‘tipping point’ behaviour characteristic of a non-linear coupled system.
l Gore’s book largely ducks the issue and calls the relation complicated.51
Plimer’s overall approach to the IPCC reports is one of “shoot the messenger”. This attack involves extensive misrepresentation of the content of the IPCC reports [items 10, 11, 29, 32, 93, 97, 100, 109, 110, 111, 118].
One aspect of the IPCC reports that Plimer repeatedly misrepresents is the authorship of the chapters. The IPCC’s instructions on how chapters should be cited give a specific definition of authorship, i.e. those who should get the credit (or take the blame) for what is in the chapter and who are responsible for addressing review comments. These are those people listed as ‘lead authors’ and ‘convening lead authors’. These people a characterised by Plimer as scientists and environmental extremists [page 98] without actually naming any people in the latter category.
There have been two errors identified in the 2007 IPCC assessment
an incorrect claim about melting of Himalayan glaciers
51In the interests of precision and ability to check issues, I mainly work with the book version of n Inconvenient ruth. My recollection is that the content of the book (i.e. excluding the preface) and film are very similar apart from the film’s early line I used to be “The next president of the United States”, and, of course, the stunt with the hoist.