How much is moral leadership worth?

We'll never know for sure. What we do know is that the price tag will be steep. Justin Trudeau's new climate deal with the provinces will cost Canadians many, many billions, maybe more. Some will come directly from our pockets in the form of carbon taxes. Some of it will disappear by stealth, swallowed up in complicated cap-and-trade schemes, infrastructure investments, clean-tech subsidies and a whole thicket of new building codes and regulations. No cost-benefit analysis has been provided, or ever will be, because too much is subject to negotiation, and too much is impossible to measure even if you tried.

Mr. Trudeau is not a man to set his sights too low. His goal is to fundamentally change the way Canada produces and consumes energy. But his climate deal is not so much a master plan as a dog's breakfast. The only thing we know for sure is that even if Canada were to miraculously achieve its 2030 target for reductions in carbon emissions, the net impact on global warming would be zero. Sadly, we just don't count. If the coastal populations of the world are destined to drown in iceberg melt, they will anyway.

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I know it's cruel and insensitive to say these things. It's like telling your five-year-old that there's no Santa Claus. So I'm sorry. But the age of climate realism is at hand. Donald Trump is ascending to the White House, which means the age of climate idealism is dead. The news seems not to have arrived in Ottawa, where Mr. Trudeau seems to believe that he can single-handedly rescue the Paris Accord and persuade the rest of the world to do the right thing.

So what can we expect? First, we'll have a federal carbon tax. Carbon taxes are allegedly efficient, transparent and easy to

understand. But this is Canada, so good luck with that. In fact, every province will have a carbon tax equivalent that it will have to hammer out with the feds. Some provinces, such as Ontario and Quebec, won't have a carbon tax at all. They'll have a cap-and-trade scheme, which is basically a black box into which tax dollars disappear. Ontario will collect $8-billion in cap-and-trade revenues over the next few years, mostly by charging more for gas and home heating. But greenhouse gas emissions will barely budge because Ontario will probably wind up buying carbon credits from California. Got it?

Mr. Trudeau assures us that all of this will pay for itself in the long run, because investing in the environment is good for the economy. As Catherine McKenna, his environment minister, said this weekend, "This makes us more competitive, not less." Thanks to subsidies for green industries, Canada will soon be able to supply a massive worldwide demand for clean technology from countries such as China.

Do I hear an echo? In fact, Dalton McGuinty made this exact same promise to Ontarians back in 2009. We would become a clean-tech capital of the world! The government proceeded to waste billions on green schemes that developed power produced at absurdly inflated prices from companies owned by China and Germany. The green-economy boom never did materialize. Hydro rates soared. Now, charities are handing out money to people who can't afford to keep the lights on.

Some day, we will have a better and more honest conversation about global warming. This conversation would allow us to admit that there's a lot we don't know about the future. No, global warming is not a hoax and human activity is certainly involved. But the scientific consensus ends about there. There is no consensus on how much more the Earth will warm or how dangerous it will be, and still less on the best ways to mitigate the risk. There are only predictions, which are all over the map.

The story of how moderate voices in the climate debate have been stifled and censured is one of the more sorry chapters in recent intellectual history. Climate alarmists have done a brilliant job of demonizing anyone who points out that the apocalypse may not be at hand and that climate change may not even be the worst problem we face.

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This doesn't mean we shouldn't have a climate policy, or that we shouldn't aim to cut down on fossil fuels. But perhaps we should be a bit more modest in our aims. It's expensive to be a beacon unto the world. And it's possible the world is moving on.