I came across this, very sensible, and rational post in a newsgroup, posted by someone using the name 'Indy Jess John'. I hope he doesn't object to my reposting it here...
'I did a bit of digging a few weeks ago, and I discovered that the global warming claim for CO2 is because it blocks certain wavelengths of infrared from escaping into space. The same source of information also pointed out that water vapour also blocks a range of wavelengths of infrared, spanning and a bit wider than the range that CO2 blocks. There is many times as much water vapour than there is CO2 in the atmosphere. It varies by location from almost zero across the polar ice to maxima over rain forests, but the global average is at least 10 times as much as CO2. So even if the amount of CO2 doubles it would make only an insignificant contribution to global warming yet it would considerably improve crop yields.
The reason why CO2 was made the villain is because humans can do nothing about water vapour but they can be blamed for CO2; and that power allows governments to impose "green" taxes or legislate controls on behaviour and have the mugs who pay for it happy to do so to save the planet.
The initial trigger was a mathematical model which got named the hockey stick graph because it predicted runaway temperature increases in the future and that prediction section looked similar to a hockey stick. The other (attempted to be suppressed by the IPCC but it had been leaked) thing I found out was a doubtful scientist who managed to get some research time on the model discovered that there was a fault in the calculation process and it didn't matter what data he fed in, even different sets of completely random numbers, the output was always exactly the same. The whole global warming fiasco has been based on faulty arithmetic. The IPCC timescale was the change since the Industrial Revolution, so about 200 years or so, which is far too short to recognise that climate changes recur to a pattern. I found a scientific report from 1995, updating previous research in 1969, which shows that the pattern of change since the Industrial Revolution is almost identical to the pattern of change from 8000 years earlier. This is roughly the time when humans migrated from hunter gatherers to a crop growing agrarian existence, so they can't be blamed for global warming.'