what it takes to advocate public policy on "Global Warming"

As an economist or even as a libertarian, there is no necessary problem with public policy to deal with AGW. The conditions? 

If we have 1.) GW; 2.) AGW; and 3.) benefits of AGW greater than its costs, then we have a case of significant negative externalities, violation of property rights, etc. One can then easily make the case for intervention-- on paper. From there, we need public policies that would really work-- benefits > costs; not just in theory but in practice. 

So, for me, none of the first three are slam dunks. And the public policy solutions are far from clear to me. (E.g., what if China does nothing.) That said, IF you're going to do something with the best op to work, it would be a tax on the underlying pollution. Again, the intuition is easy here: the tax should be roughly equal to the social costs created by the pollution (and used to finance solutions to the problems created).