Hawk says:

'If you look at the amount of CO2 in the Earth's atmosphere...then at the amount of CO2 produced by human civilization...and compare it to the overall greenhouse effects of water vapour and a few other secondary greenhouse gases...it's just utterly negligible.'

Time to get the physics out again.

1. There are 380 ppm of CO2 in the earth's atmosphere - and that might not sound a high proportion.

2. But 380 ppm of CO2 evenly mixed in the atmosphere means over 3 trillion tonnes (3 followed by 12 zeros) of the stuff.

3. Now we know that each molecule of CO2 can absorb radiation at a certain frequency (14 micron wavelength) and that water doesn't absorb at that frequency.

4. We also know that radiation has an energy quantitatively linked to its frequency.

5. So its quite easy to calculate how much energy all that CO2 could absorb - its about 6E+20J (followed by 20 zeros) joules for every absorption cycle.

6. And that is getting close to the total heat capacity of the entire atmosphere - if you put an extra 6E+20J into the atmosphere you'd expect to move its temperature.

7. Now there are huge uncertainties when you try to quantify further - how long does it take for an excited molecule of CO2 to lose its heat and how does it do it? How much energy absorbed by CO2 has been re-emitted to from other CO2 molecules? How much energy is absorbed by the ground or lost to space?

8. However, the point is that 380 ppm CO2 is easily enough to have a big potential impact on the temperature of the the earth's atmosphere. And it looks like we're going to increase that by about another 50% over the next 50 years.

The other point is that this analysis doesn't need the complex models and data sets that the climate professionals are grappling with -its quite standard 19th century physics (and some long multiplication) taught me (quite a few years ago) at high school. Happy to give more details for those enthusiastic about big numbers!

(oh and btw great hockey game at the Olympics last night!)
KP