I thought that in addition to the 'bathtub' analogy, she might have also used the 'bedroom wall painting' analogy refering to the relationship between CO2 and temperature - you put the first coat on the wall, noticeable difference, the next coat, some difference, the third coat, a bit more, by the fourth and subsequent coats, you're just adding thickness to the walls but not making any difference. The sublinear climate sensitivity of CO2 is such that additional molecules of CO2 added to the atmosphere will have exponentially reduced effects; CO2 only absorbs radiation within a certain range and can only absorb 100% of that radiation - once you past that point, there is increasingly little effect. Gore's ominous chart showing runaway emissions is just a lttle misleading, no?
Lubos Motl has a great post on this subject.
William Kininmonth also wrote recently:
Start with carbon dioxide. As a greenhouse gas, it is a spent force for climate change; its present concentration is slightly less than 400 parts per million. Calculations show that 66 per cent of the greenhouse effect of CO2 is caused by the first 50ppm. With each doubling of concentration, (from 50 to 100, then to 200 and 400ppm), the incremental advance of the greenhouse effect is reduced.
Even for a further doubling to 800ppm, as projected by 2100 in the case of unabated fossil fuel usage, the increase in the greenhouse effect will only be 10 per cent of the present component attributable to CO2. Overall, CO2 is a relatively minor contributor to the greenhouse effect, which is dominated by the varying water vapour and clouds of the atmosphere.
Increasing the CO2 concentration will have little additional effect.
