"On a philosophical note regarding the main topic, I'd be interested in discussing the logic of government forcing an agenda of reduction in energy production (and therefore wealth generation) on the basis of highly uncertain conjectures about the future of the global climate."
I don't think this is a question unique to climate policy. As it pertains to climate, I don't think any government is advocating reduction in energy production at the expense of wealth, they are merely encouraging/funding exploration of alternative energy production. I for one think this is a good thing! Aside from that, all governments must use a crystal ball to some extent when implementing any policies, whether energy related, health, defense, economic, environmental, etc...of course, if you disagree with their predictions and subsequent policies (and live in a theoretical democracy) you can choose not to vote for them next time around, or lobby them in this term to change their policies.
As for rainfall, there is no doubt that x-amount of rain will fall over x-amount of horizontal area, no matter what the slope of the roof (assuming no wind). I can't believe it's even a matter for discussion, though as Rog generously admitted, and I concur, wind can have an effect of a probably very small amount.