The more I listen to federal Liberal politicians talking about climate change, the more worried I become.

Federal Climate Change Minister Catherine McKenna, for example, in her calls for a national carbon price to lower industrial greenhouse gas emissions linked to climate change, doesn’t seem to be aware of two key issues.

The first is that any province imposing a cap-and-trade scheme on emissions — such as Ontario — doesn’t know what its carbon price will be.

The second is that any province imposing a carbon tax — such as Alberta — doesn’t now how much it will lower emissions, if at all.

In cap-and-trade a government can, theoretically, lower emissions to a prescribed level due to the annual cap it places on them.

But it doesn’t know in advance what its carbon price will be — meaning how much revenue it will make — because that’s determined by trading carbon allowances in a speculative carbon stock market, where prices fluctuate.

The Wynne government in Ontario is guessing that when it imposes cap-and-trade next year, the cost of a carbon allowance to emit one tonne of industrial greenhouse gases will start out at $17 to $18, yielding $1.9 billion annually.

But that’s just a guess.

The real-world experience with cap-and-trade in Europe and North America is that the price of carbon allowances regularly crashes due to such factors as economic downturns and legal challenges by opponents.

Wynne has acknowledged she doesn’t know how much money cap-and-trade will raise for her government, paid for by the public in higher retail prices for most goods and services.

By contrast, a carbon tax — such as Alberta is imposing next year — provides a known amount of money to the government because it can determine total emissions and then apply the tax to figure out its annual revenues.

But with a carbon tax, there’s no way to know in advance how effectively it will lower emissions, if at all.

Governments have to guess how high their carbon tax should be to achieve the emission reductions they want, through a trial and error process.

Neither Trudeau nor McKenna has given Canadians any indication of what they want the national carbon price to be, which they warn they may impose on provinces that don’t go along.

Presumably, they want it to be higher than B.C.’s $30-per-tonne, the highest in the country today, because that’s only projected to reduce B.C. emissions by three megatonnes annually by 2020.

Given that Canada has to lower its emissions by a projected 146 megatonnes annually by 2020 to meet what is now Trudeau’s target, the Liberals would have to set a national carbon price somewhere in the range of $150 to $200 per tonne — at least five times the highest price in Canada today.

The problem is unless such a measure is revenue neutral (only B.C.’s carbon tax comes close) this would cause a massive recession because of the huge spike it would prompt in the cost of living for Canadians.

Ironically, a recession would cause Canada’s emissions to drop dramatically.

But deliberately provoking a recession, one hopes, is not Trudeau’s plan for fighting man-made climate change.

On the other hand, Trudeau could always meet Canada’s targets by spending billions of dollars of taxpayers’ money buying carbon allowances on fraud-ridden international carbon markets.

But that’s a worry for another day.