What do you mean externalise the cost? What exactly is the cost for pumping CO2 into the air and who is paying it? You still go into these debates with a Pre-biased faith that CO2 and global warming are true, yet nothing has been observed to support it let alone prove it. The governments biggest high profile parrot Tim Flannery has already been PROVEN wrong on a number of these predictions. Again, in supporting a financially unviable technology we are prohibiting the free market from allowing precious resources being diverted to finding a financially viable long term solution. How do you justify that? Edit to If AGW was far more likely than has already be proven AND every single cent of this CO2 tax money was being sent into R&D into a more viable alternative then this tax could be justifiable almost. On both counts we are far from that and any Polly supporting it should be charged with Treason.