As was pointed out earlier, we're not economists, so we look to other people's analyses for this sort of thing. William Nordhaus, who is a very well-respected Yale University economist, has calculated that an economically optimal carbon price or tax would be about $27 U.S. per metric tonne in 2005, rising to $90 U.S. in 2050. So we're talking carbon tax one way or the other of anywhere from $30 to $90 a tonne, according to some economic analysis. I don't know how the numbers shake out in Canada, but that seems like a reasonable level that starts to get some action. Of course, prices could go much higher after that, depending on how tight we have to push to get further reductions, but those are the kinds of numbers people are throwing around. I don't know what my colleagues are going to come up with shortly on this.
On February 4th, 2008. See this statement in context.