I know a number of readers are tired of my writing about climate, so I am instead taking a shot at writing a comprehensive skeptic's argument on Anthropogenic Global Warming. A free pdf will be available for download next week, with a bound copy available for purchase at manufacturing cost.
In the mean time, LuboÅ¡ Motl presents one of the core skeptics arguments, that CO2 heat absorption is a diminishing return relationship to concentration, making frequent predictions of runaway climate scenarios a real head-scratcher.
In terms of numbers, we have already completed 40% of the task to
double the CO2 concentration from 0.028% to 0.056% in the atmosphere.
However, these 40% of the task have already realized about 2/3 of the
warming effect attributable to the CO2 doubling. So regardless of the
sign and magnitude of the feedback effects, you can see that physics
predicts that the greenhouse warming between 2007 and 2100 is predicted
to be one half (1/3 over 2/3) of the warming that we have seen between
the beginning of industrialization and this year. For example, if the
greenhouse warming has been 0.6 Celsius degrees, we will see 0.3
Celsius degrees of extra warming before the carbon dioxide
concentration doubles around 2100.
It's just like when you want
your bedroom to be white. You paint it once, twice, thrice. But when
you're painting it for the sixteenth time, you may start to realize
that the improvement after the sixteenth round is no longer that
If CO2 is not responsible for all the 0.6C of historic warming (a proposition for which there are good arguments) then future warming is even less. Read it all for more detail, or look for my paper next week which covers this topic and many, many others in more depth. There are lots of complications - aerosols, dimming, feedbacks - that are discussed in the paper.