On 18/11/2015 20:49, mcp wrote:

Of course water vapour has the biggest radiative effect but the amount
of water in the atmosphere is driven by temperature. I love the way
this fact always gets trotted out as if it's some kind of relevation.


Not exactly true though is it?
If water vapour were driven by temp and it is the biggest greenhouse gas
then we would have runaway increases in both.

This indicates that the expected effect of greenhouse gas isn't quite right.

Would you like to inform us of why it doesn't runaway?