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Thanks for the link. I understand what he's got there, regarding CO₂ solubility, but it has nothing to do with global warming. See, the range of CO₂ concentrations he's got there(200-280ppmv) includes almost no change in heat retention by the gas. So, the temp can't possibly change much, because of atmospheric CO₂. He's got a 10^o temp change there, so all of that must be due to something else. That something is the Sun's output, because that's the only energy source that could possibly cause that temp change. ...if the temp change is real that is. I don't know how they measured that.

"But obviously temperature dependent increases in photosynthesis can't because the observed correlation is defintiely positive and quite high."

The ice core data is independant of that. It's been ignored, as far as I can see.

"That's part of his argument about why CO2 doesn't cause the observed warming."

Nothing he's got there addresses any heat retention mechanism. The paper's oblivious to that. The simple fact that they show the range change as 200-280 ppmv says there's no effect from CO₂

I think you must have misinterpreted what he is saying. His point has nothing to do with variations in CO2 concentration affecting temperature but rather the reverse. So heat retention etc. is irrelevant to his point.

As for how they infer %CO2 and temperature from the ice cores, depth correlates with age, CO2 can be measured directly from gas bubbles in the ice and temperature is inferred from ratios of isotopes. I don't know what the relevant error bars are or how this data matches other historical inferences.

The ice core data is independant of that

What do you mean? You said photosynthesis increases 10% for each 1°C increase. By this I assumed you meant that for each 1°C plants would increase their absorption of CO2 by 10%. Therefore, if this photosynthetic temperature dependence accounts for CO2 temperature dependence, I'd expect to see CO2 concentrations go down as temperatures rise. The Vostok data show the reverse so it seems quite relevant to me. Further, I don't see how to conclude anything other than that photosynthetic temperature dependence doesn't account for the CO2 variations with temperture.

Have I missed something?

Nothing he's got there addresses any heat retention mechanism.

As I've been at pains to make clear, he doesn't mention it because it's not material to his argument. However, as you're evidently using it as an argument *against* CO2 caused temp increases, let's discuss it. I don't think it's directly relevant to pro-GW arguments. As far as I know, no one says that heat being retained in the CO2 accounts for temperature increases. That would be ludicrous because the gas is not insulated from the rest of the atmosphere.