Well.... I'm studying for my geological oceanography final, so this will be a justifiable excercise.
> Both claims/objections seem easy to dismiss. IF the
> relationship between human produced emission and CO2
> level in the atmosphere is cumulative i.e. CO2 already
> released stays there for a while, it is obvious that
> short term drops in human produced emissions (e.g.
> during the Great Depression, which Cockburn cites)
> will NOT be followed by drops in the CO2 level in the
> atmosphere. If there is any effect, it will be
> manifested by a slightly slower rate of accumulation
> rather than a drop.
Bingo.
> As to the second objection (based on the mass of water
> on Earth and its CO2 emission), it does not apply if
> the relationship between emissions and warming is
> recursive and non-linear. Recursivity means basically
> a positive feedback, some CO2 emissions produce some
> warming which in turn intensifies future emissions,
> which produce more warming et. Non-linearity means
> that a samll change on the independent variable
> (emissions) may trigger a disproportionally large
> change on the depeneded variable (climate change).
> AFIK, climate models assume recursive and nonlinear
> relationships between human emissions and climate
> change, so Cockburn's argument is a nonsequitur.
That's all more or less true, but could be put somewhat simpler. The argument is that since the ocean contains much more CO2 than the atmosphere, and gasses become less soluble in water with rising temperature, the rising CO2 in the atmosphere is a result of warming oceans, not the cause. Obviously a non-sequitur when you have other sources of atmospheric CO2, and a cause for worry as a potentential positive feedback.
Real Climate examines Cockburn's handywork here: <http://www.realclimate.org/index.php/archives/2007/05/this-week/>
Interestingly, the second point was a point of misrepresentation of oceanographer Carl Wunsch's views on the part of that British TV special:
<http://ocean.mit.edu/~cwunsch/papersonline/responseto_channel4.htm> <http://ocean.mit.edu/~cwunsch/CHANNEL4.html>
[...]
An example where my own discussion was grossly distorted by context: I am� shown explaining that a warming ocean could expel more carbon dioxide than it absorbs -- thus exacerbating the greenhouse gas buildup in the atmosphere and hence worrisome.� It was used in the film, through its context, to imply that CO2 is all natural, coming from the ocean, and that therefore the human element is irrelevant. This use of my remarks, which are literally what I said, comes close to fraud. [...]
-- Andy