mlc, my understanding of CO2 forcing is that shown on the radiation spectrum graphs where CO2 abruptly closes the absorption window that would gradually taper off under water vapour alone. However this only curtails heat loss below the temperatures that the window opened by water vapour causes heat to be transmitted rather than being absorbed. CO2 only affects the window on the heat loss side and that is what I consider as forcing... On the other side methane has a small influence that slightly narrows the window on the heat retention side. However, the position of the window with regards to the wavelengths absorbed or transmitted, and the width of the window, is due to the inherent properties of each of the gases and not the quantities.... If you consider Plimer to be all over the place, then perhaps with his understanding of the historical aspect of climate change, it is understandable if one considers how many different forces have come together or opposed each other through the changes to the planets climate, that there would be countless different combinations of events that pulled or pushed the climate through it's various stages. For me it is too simple to say that temperature follows CO2 up and down. It may be good for politicians appealing to the masses, but it is simply too simplistic....I haven't read Plimer's book itself, but have closely followed discussion of it. I attended one of his early book launches and left feeling that he doesn't understand where the IPCC are coming from, nor they, him. I also felt that he didn't understand the questions I put to him, but felt that the points he was making about how the present day changes must be put into perspective with regards to previous changes, were valid points, and still are.
