Monckton’s main argument seems to be represented by the statement that climate sensitivity to CO2 has been overestimated by the IPCC by around 6-7 times, giving exaggerated projections of warming for a business as usual scenario of CO2 emissions. The IPCC range is around 2-6C degrees warming by 2100, and Monckton’s is 0.5C. While he provides some calculations, this view is also supported by a measure of respectable scientific literature.
The view that CO2 sensitivity is being grossly exaggerated is the one that is shared by myself and the likes of Spencer, Shaviv, Lindzen, Douglass and others. The most concise illustration of this is the one produced by Spencer, showing where the various authors lie, relative to the IPCC model projections.
There seems to be a new view being put, given the problems of the ‘gates. Essentially, climate scientists have been right all along that increasing CO2 has a warming effect and that climate sceptics are wrong that CO2 does not produce any warming. First there is the straw man that sceptics don’t admit the possibility of a small effect. Another defense recently appeared on arXiv called “Man made global warming explained – closing the blinds“, by T. Sloan, A.W. Wolfendale. They conclude that:
The International Panel on Climate Change (IPCC), using their more exact models, estimate that doubling the of the CO2 level in the atmosphere will change the mean surface temperature of the Earth by between 2 and 3.5C. Our model predicts a rise of between 1 and 1.5C (see also  who ignore all effects except infra red absorption), again illustrating that something extra is needed beyond the simple absorption of the infra-red radiation.
They then go on to argue that something must be done about even this lower amount of warming. They think the sensitivity can’t be low because the models can’t be explained.
Otherwise we would be relying on an unexpected future cancellation to save us from the possible ravages of climate change induced by ever growing amounts of greenhouse gases in the atmosphere.
The hypothesis took the lowest possible range of carbon dioxide’s known warming effect on climate, multiplied it by the lowest possible effect of the various feedbacks that amplify the warming effect, to give a figure well below that shown by any observation. One of the implications of the hypothesis was that, given what we know about climate, there could not have been ice ages in the past. “The hypothesis is completely inconsistent with the observations,” said Professor Matthew England, the co-director of the Climate Change Research Centre at the University of NSW.
The main difference between the low and high sensitivity results are that one is based in ‘observations’, and the other in models. Belief in low sensitivity is based in preference for ’empiricism’. Most climate scientists OTOH argue our knowledge of radiative properties of CO2 outstrip the information climate measurements can provide, and propose accounts of how this provides additional information about the world (such as produced by models or historical reconstructions of ice ages).
A classic dispute between rationalism and empiricism? I tend to think we do need rational approaches, based in models, but models need to be ruthlessly eliminated by evidence. The good models sit at the intersection of the larger sets of plausible dynamic models, and sets of empirically-fit models. Sure there may be things about low climate sensitivity that cannot currently be explained. The intersection of low sensitivity and high natural variability, as recently described by Spencer, have not been decisively eliminated by observations. The high sensitivity models with low natural variability have.