Mark Jaccard is professor of sustainable energy at Simon Fraser University. He tweets @MarkJaccard

In 2007, Prime Minister Stephen Harper's government asked me and four other economists if we agreed with its study showing huge costs for Canada to meet its Kyoto commitment to reduce greenhouse gas emissions by 2010. We all publicly agreed, much to the chagrin of the Liberals, NDP and Greens, who argued that Kyoto was still achievable without crashing the economy. It wasn't.

As economists, we knew that the Liberal government of Jean Chrétien should have implemented effective policies right after signing Kyoto in 1997. It takes at least a decade to significantly reduce emissions via energy efficiency, switching to renewables, and perhaps capturing carbon dioxide from coal plants and oil sands. Each year of delay jacks up costs.

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Mr. Harper's government knew this too. Years later, when environment minister Peter Kent formally withdrew Canada from Kyoto, he charged the previous Liberal government with "incompetence" for not enacting necessary policies in time to meet their target.

With the excuse that Kyoto was too expensive, Mr. Harper replaced it with his own emission target for 2020, which he presented in his 2007 policy statement, "Turning the Corner." Two years later, he reconfirmed it alongside U.S. President Barack Obama and other world leaders at the Copenhagen climate conference.

Just like Mr. Chrétien, however, Mr. Harper failed to immediately implement the necessary policies. Canadian emissions have declined slightly, for which he tries to take credit. But analysts agree that the main causes are the 2008 recession, some decline of heavy industry, Ontario's reduction of coal-fired power, and climate policies in British Columbia and Quebec. Mr. Harper's adoption of U.S. vehicle regulations will have a small effect by 2020, not his coal regulations.

But instead of honestly admitting that it won't achieve the 2020 target, the Harper government still pretends that it will. And it won't admit that its vigorous promotion of oil sands and new pipelines, such as Keystone XL and Northern Gateway, is a key factor in Environment Canada's prediction that Canadian emissions in 2020 will exceed the target by at least 20 per cent. Growth in oil sands emissions alone will account for half the overshoot.

Meanwhile, the U.S. will meet a similar 2020 target. And California, with the same population as Canada, will meet a tougher target.

This time, the Harper government has not asked me to comment on the cost of trying at this late date to keep its promise. I doubt it will – at least not before the 2015 election. But as a helpful gesture, I've done the analysis anyway, with a model like Environment Canada's.

My analysis shows that if Mr. Harper had "competently" enacted in 2007 the regulations he promised, the effective price on carbon would have started around $15 per tonne of CO2 in 2008, reaching $100 in 2020. This would not have harmed the Canadian economy. It would have phased-out most coal plants, as Ontario has done. It would have shifted transportation toward natural gas, biofuels and electricity, as is occurring in California. It would have substantially slowed the growth of oil sands, and led to investments in carbon capture, as in Norway. Oil sands jobs would not have grown as rapidly, but would not have declined. And job creation in alternative energy would be substantial, as has occurred with renewables in B.C. and Ontario. There would be no Keystone XL, no Northern Gateway.

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My analysis further shows that were Mr. Harper now to seriously pursue his 2020 promise, he would crash the economy. His frantic regulations would be equivalent to shocking the economy with a CO2 price that quickly escalates to $200 – increasing the price of gasoline by 50 cents a litre. Industrial jobs would be lost. Oil sands production would decrease.

Mr. Harper has admitted that he will do nothing for the climate that might slow the growth of oil sands jobs, as he recently confirmed during the visit of Australian Prime Minister Tony Abbott. Yet he won't admit that this makes his 2020 climate promise false.

Isn't it time we had some honesty in Canada? Climate change is one of the defining issues of our time. We are being horribly let down by the Harper government.

Mark Jaccard is one of eight scientists who published a commentary in Nature in June calling for a moratorium on oil sands development.