every new molecule of CO2 causes smaller greenhouse effect than the previous molecule: the absorption rate gradually approaches saturation.There had been a response at realclimate.org written by Spencer Weart, a "noted historian of science". Weart joined the discussion thread but declined to offer any substantive responses to criticisms of his argument.
A quote from one of the more technical commentators (Motl attracts 2500 readers a day, and has a very high proportion of professional academics and post docs in his audience):
AGW is like Rasputin. You can stick a knife in it, and drag the entrails out, you can poison it, you can chain up and throw it in the river, and it'll keep on going. If the world temperature started decreasing next year, and continued cooling fo 20 years, they'd concoct some kind of cock-and-bull story about how it's happening, but it's being masked by the aerosols from some factory in far western China.
Meanwhile, looking out of my window, I see cold, wet and stormy weather. It reminds me of 1987.