That wasn't my point entirely but admittedly it was a part of it. I have not heard a good reason for why a trace gas has such an effect. Bearing in mind that 0.04% is total CO2 and human produced CO2 is a tiny fraction of that - can't seem to find an agreed on percentage on that one but happy to be enlightened. The other point I was making is that when I have asked that basic question to people who are seemingly frightened of the effects of CO2 I have got massively inflated guesstimates e.g. 50%. I just think if you are going to be scared and try and scare others you should know at least that.