There's a gap in Leach's otherwise astute assessment of the problem of carbon pricing: He does not expressly consider benefit/cost analysis. Effectiveness/cost analysis is relevant but not the same thing.
While Leach does mention 'benefits' briefly in his segue to political considerations, the distinction between benefit and effectiveness, and the relation to politics should be drawn more explicitly.
Leach aptly discusses effectiveness in terms of CO2 (or equivalent) concentration in the atmosphere. But politics -- especially re Pielke's Iron Law -- ultimately hinge on the perceived value of that effect in relation to the value of the costs imposed to achieve it. Moreover, political metabolism of a carbon tax or other policy measure depends not only on global valuation but on the specific distribution of benefits and costs among particular constituency factions -- geographic, economic, social, cultural, etc. Leach does mention the latter, but does not fully pursue it here.
But it is the uncertainty and distributional variance of benefits and costs that makes contriving an effective carbon tax complex and difficult. While the costs become immediately palpable and measurable, benefits are far fuzzier, distant, and controversial. It's more clear that costs and benefits are prone to be unequally distributed in space and time.
IPCC reports concede that the impacts of AGW -- as best as imperfect computer models can estimate them -- are likely to be beneficial to some people, in some places, at some times, while harmful to others, elsewhere, otherwise. Moreover, the perennial gridlock of UN negotiations aimed at contriving some global regulatory scheme stems from sharp disagreements about who should bear the largest burden of the costs of so-called mitigation. The same conflicts stymie the deliberations of many nations' legislatures.
Pro-growth policies are popular because they offer the prospect of conferring benefits on all or nearly all consitutencies -- as suggested by John Kennedy's aphorism, "A rising tide lifts all boats." Decarbonization policies have been generally unpopular and infeasible because impose onerous costs or negative benefits on too many potent political factions while offering few if any immediate benefits to most.
The best case for a carbon tax is the one made by Pielke, BTI, myself and others. That is: a carbon tax might be politically palatable if it were relatively modest (equivalent to a few cents per gallon of gasoline) and the proceeds targeted on research and development of innovative energy technologies that are relatively free of carbon emissions and cheaper than fossil fuels.
Even so, the growing burdens of aging populations in most of the richer nations (and a number of developing ones as well) make the prospects for additional, sustained fiscal commitments to energy innovation uncertain at best.
An alternative strategy would be to fundamentally transform the mechanics of existing investments in energy research and development to accelerate the pace and impact of innovation. In short, to get more bang for the buck. For more on how to do that, see: http://j.mp/1cqZDHI