It seems like academics everywhere are jumping on the bandwagon to review Plimer's new book. It's fun pointing out the errors, but the catalogue of errors might yet be as long as the book itself  ;D

Dr Ian G. Enting of the University of Melbourne has started work on a line by line critique of ‘Heaven + Earth’ — Checking the Claims", listing numerous misrepresentations of the sources cited in the book and other inconsistencies.

http://www.complex.org.au/tiki-download_file.php?fileId=91

It's in pdf format, so the following quote has probably dropped a lot of the formatting:



Quote:

In his efforts to down-play the extent of warming from CO2, and exaggerate the relative role of water vapour, Plimer ends up implicitly attributing so much warming to water vapour, that the planetary temperature in the absence of water vapour would be nearer the temperatures of the outer planets. In some cases the numbers given by Plimer are exaggerated to such an extent as to imply that without water vapour, Earth’s temperature would be below absolute zero—a physical impossibility.  ;D The exaggerations fall into two groups: those that relate to anthropogenic CO2 and those that relate to total CO2. In each case, inconsistency arises when the exaggeration in the relative proportions is combined with values for absolute warming. i: exaggerations concerning anthropogenic CO2: The implications of the claim that CO2 derived from human activity produces 0.1% of global warming is analysed in item 81. ii: exaggerations concerning total CO2: The inconsistency in attributing 18 C of warming to total CO2 [page 366] while stating in the caption of figure 44: About 98% of the greenhouse effect in the atmosphere is due to water vapour, is noted in item 55.

You'd better wash your mouth out with soap muso, that book is the holy grail to many confusionalists some of them are even docile enough to  quote it as a source of scientific fact.

That figure of 98% that you'll see on many dodgy websites was obviously copied from these sites by Plimer without quoting the source - because there is no source :) It's urban legend.

The real figure taken globally is around about 50% percent, but there are other feedbacks apart from water.  

Climate sensitivity for a doubling of CO2 is around 3 degrees C (plus or minus 1.5), of which about 1 degree is due to greenhouse gases including CO2, methane nitrous oxide etc, using the forcing equation, which in itself is basic physics:

dT=[alpha]ln([CO2]/[CO2}orig)/(4[sigma] T^3)
(edit - correction - that's the forcing equation for CO2 only. We generally use the same equation for other gases by expressing them in CO2 equivalents (CO2-e)

Another 1 degree C is due to water feedbacks, and all other feedbacks account for another 1 degree or so. Those 'other' feedbacks include albedo, clouds, lapse rate, arctic methane release and reducing CO2 uptake by the oceans as the pH falls.

Incidentally some denialist  sites quote very low or even negative water feedbacks.  It depends on exactly what they want to argue at the time. It's easier to win an argument when you don't have to stick to the facts.