I was listening to Green party TD Ciarán Cuffe on Today FM a few weeks ago trying to make the case for Carbon taxes. His case was weakened by his attempt to weasel around the issue of precisely who would be hit by an addition Carbon tax. Despite the cliché, it isn't really possible to hit two birds with the one stone and one major difficulty a leftist environmental party like the Irish Greens are going to have is the fact that Pigovian taxes are not always going to neatly align with taxes aimed at redistributing wealth.
The purpose of a Carbon tax (assuming that the problem I identified below is somehow addressed) is to correct for the fact that the "costs" of emitting carbon dioxide are not internalised - these costs are spread and don't depend on level of use - and therefore provide no incentive to cut back. The only Carbon tax which will work is one which is blind to other considerations and applied equally. It's either meant to tackle carbon or not. The climate doesn't know whether emissions come from an SUV, a Jet plane, an industrial plant in India or some old lady's clapped out diesel boiler.
There is this popular view that the rich and powerful are the greatest "polluters", but what if they weren't? There is no direct relationship between pollution and wealth and no particular reason to believe that the rich emit more than the poor. What if the rich young man in his well insulated home is responsible for considerably less emissions than an elderly woman in a poorly insulated home with that clapped out diesel boiler? The Carbon tax, to work properly, must "punish" her more than him. This is a conclusion the Greens would prefer to shy away from, but there are always going to be cases where the interests of the environment are opposed to the interests of "social justice", and they are going to have to decide whether they are primarily a leftist party or an environmentalist party.