​On Tuesday, precisely eight years and one month after Stéphane Dion first vowed that a Liberal government would implement a tax on the carbon emissions that contribute to climate change, the Conservative Party warned its supporters the Liberal government is planning to impose "a big new tax on everything."

That much was based on Environment Minister Catherine McKenna's latest expression of fondness for a national price on carbon.

And on Wednesday, in an interview with the CBC's Rosemary Barton, Prime Minister Justin Trudeau did his opponents the favour of confirming his stance that "putting a price on carbon is going to be an essential element" of seriously protecting the environment.

It is almost as if the last eight years, during which no comprehensive program for sufficiently reducing Canada's greenhouse gas emissions was achieved, have only been a mind-numbingly dull and repetitive exercise that shames us as a society.

Which is not to say that nothing has changed.

As Liberal leader in 2008, Stephane Dion proposed implementing a carbon tax. (Chris Wattie/Reuters)

A carbon tax after Dion

Though Dion was pummeled and mocked in 2008, the provinces of Ontario, Quebec and, importantly, Alberta are now committed to broadly pricing carbon (British Columbia introduced its own carbon tax four months before Dion's proposal) and all of the provinces are at least committed to considering "carbon pricing mechanisms" (whatever that means).

The leader of Ontario's Progressives Conservatives, Patrick Brown, is proposing to implement a carbon tax with commensurate cuts to the province's income tax. Michael Chong, a candidate for leader of the federal Conservatives, is proposing the same thing nationally.

And on the same day the federal party was warning darkly of that "big new tax on everything," Mark Cameron, a former policy advisor to Stephen Harper, published a piece entitled "The Conservative Case for a Carbon Tax."

(While the Conservative party argues a carbon tax "will do nothing to actually help the environment," Cameron posits that, "putting a price on negative externalities like pollution and greenhouse gas emissions is often a better and more economically efficient way of discouraging them and reducing emissions than the heavy hand of government regulation.")

Now Trudeau, with the benefit of these last eight years, might do something like what Dion proposed.

A taxing debate about price

Whereas Dion made a "carbon tax" the centrepiece of his party's campaign, Trudeau, a rather more gifted communicator, mused of a "price" among other promises.

"Price" is a catch-all term that could refer to any of a number of policies, a carbon tax, for instance, or cap-and-trade. Jason Kenney, the Conservative now aiming to become premier of Alberta, has described such wording as "Orwellian," but it is also not clear what distinctions are left to be made between pricing mechanisms.

When the Conservatives were opposing Dion's carbon tax, for instance, they were still in favour of putting a price on carbon through a cap-and-trade system. Later, when faced with the NDP's support for cap-and-trade, the Conservatives decided that cap-and-trade and a carbon tax were synonymous and equally ruinous. Then Stephen Harper spoke approvingly of Alberta's carbon levy.

If there is a nuanced argument, perhaps about how the revenues of a price could be used, it has been rather obscured. And all the while, no plan for meeting Canada's reduction commitments has ever been articulated.

Ultimately, the debate seemed to be down to doing something to significantly reduce Canada's GHG emissions versus not.

Any number of economists will argue that putting a price on carbon will reduce emissions at the lowest economic cost — keeping in mind that any policy to reduce GHG emissions will carry some kind of cost — but it is exceedingly easy to argue against anything that can be described as a tax, because no one likes the idea of anything costing more than it already does. And climate change, whatever the very real impacts that are already evident, is still an abstract threat requiring shared global action.

Conservative MP Jason Kenney opposes the Alberta NDP's carbon tax. (The Canadian Press)

Jason Kenney and Brad Wall stand opposed

"I think we need to be mindful of the fact, that we produce, I believe it is, 1.7 per cent of greenhouse gases emitted worldwide," Jason Kenney said earlier this month, a day after announcing his intention to become premier of Alberta.

Kenney objects to Alberta's carbon tax, and on Wednesday he was cheering on Brad Wall as the Saskatchewan premier repeated his objections to a national carbon tax. Wall argues that now is just not the right time for a carbon tax.

There are other potential obstacles to a national deal on carbon emissions — Nova Scotia, for instance, has argued that the increased rates it pays for cleaner electricity amount to a carbon price — but Kenney and Wall have emerged as the loudest voices of outright objection.

Two weeks ago, Kenney did not explain what conclusions might be drawn from his desired mindfulness, but he might not wish to suggest that that 1.7 per cent should be considered in any way insignificant.

Consider, for the sake of comparison, Canada's involvement in the bombing campaign against ISIS in Syria and Iraq, an effort that Kenney was responsible for as defence minister.

For the period in which Canada was involved in that particular campaign, Canadian fighter jets were involved in 2.5 per cent of the international coalition's airstrikes.

That much for a cause that Kenney described as a "moral obligation." And so it is now that Kenney is chided on similar grounds.

"What kind of future does [Jason Kenney] want to leave for our children & grandchildren?" Environment Minister Catherine McKenna tweeted on Monday.

If not a price on carbon, what?

Andrew Leach, the University of Alberta professor who advised Rachel Notley's government on its GHG policy, has also suggested more immediate motivations for acting: the rejection of pipelines like Keystone XL, the possible threats of international standards and environmentally minded shareholder demands on private companies.

Conversely, one might wish to wager that the world is not finally moving towards meaningful action on climate change. That acting to fulfil Canada's international commitments is still not worth the trouble. Or that it somehow still makes sense to wait.

But eight years after Dion's ill-fated Green Shift, the standing proposal is to put a price on carbon. And opponents of the policy might be asked two simple questions.

If not that, what?

If not now, when?