Economics of climate change policies (and public choice)

Boudreaux, who I have heard argue that there are almost no externalities in real life (by his definition), claims that there is a problem with the rhetoric used by climate change hawks:

I neither deny that climate change is occurring nor that its occurance [sic] is the result of human activity.  (I’m no natural scientist, so my ability to judge the science is inadequate.)...

So much of the conversation by climate-change hawks takes place as if the demonstration of the existence of a cost is sufficient to prove that that cost must be reduced. And, too, so much of that same conversation takes place as if the political authorities to be charged with reducing this cost will act both wisely and in the public interest.

Both stances are most unscientific.