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Electric cars are only as ‘green’ as the fuel used to generate the electricity they consume.JOHANNES EISELE/AFP / Getty Images

On a recent trip to Hawaii, we were surprised when the car service sent a beautiful Tesla Model S to pick us up at the airport. As we drove to our accommodations, the driver waxed enthusiastically about how proud he was to be driving a "zero-emissions" vehicle. This prompted me to ask him a series of questions, starting with what powers the car? When he replied "electricity," I asked how that electricity was generated. Looking up at the windmills spinning on the ridges above us, he said, "Those windmills, I guess."

I informed him that Hawaii's 100-plus windmills generate only 5 per cent of the state's power. The other 95 per cent comes from carbon-emissions-intensive, diesel-fuelled power plants. Then I gave him a short physics lesson explaining the scientific axiom that, each time an energy source is changed to another form, an "efficiency loss" occurs.

The largest loss comes when the diesel is burned in the power plant and the electricity is sent to Tesla's charging station. Once the car is plugged in, the next efficiency loss occurs when the battery charger converts the AC electricity to chemical energy stored in the battery. The final efficiency loss occurs when that chemical energy is converted to DC power and delivered to the electric motors driving the wheels.

Combined, these efficiency losses consume some 75 per cent of the energy originally contained in the diesel fuel, leaving just 25 per cent to power the Tesla.

But what if that diesel fuel was burned in an internal combustion engine? The latest turbo-diesel engines are approaching 50 per cent thermal efficiency, so the car would use only half as much diesel and emit half the emissions.

This anecdote conveys two realities. First, electric cars are only as "green" as the fuel used to generate the electricity they consume. Second, sometimes it's environmentally better to burn the fuel directly in the car rather than the power plant.

How does that first reality apply to electric-car owners across Canada? B.C., Manitoba, Quebec and Newfoundland generate the vast majority of their electricity from hydro, so it's thumbs-up for electric cars there. Coal supplies most of the electricity in Alberta, Saskatchewan, Nova Scotia and PEI, and New Brunswick's electricity is fuelled by a roughly equal mix of hydro, coal, fuel oil and natural gas. So electric cars are not "green" in those five provinces.

Which leaves Ontario, the province that just announced a $7-billion Climate Change Action Plan featuring generous subsidies to promote "an electric car in every driveway." On the surface, the fact that some 80 per cent of Ontario's electricity is generated by hydro and nuclear makes electric cars look green.

But it's not that simple. Those millions of new electric cars will require a massive expansion of Ontario's power systems. So what's really important isn't the current fuel mix, but rather what would fuel all that new electricity.

The action plan makes bold assertions about expanding wind and solar sources, but the governing Liberals' last grand green plan was absolutely disastrous, enriching wind and solar companies with huge subsidies while driving Ontario from one of North America's lowest power-rate jurisdictions to one of the highest. And since wind is unpredictable and Ontario's winter daylight hours are short and summer days often cloudy, essentially all wind and solar must be backed up by more reliable facilities. Billions have already been spent on backup natural gas-fuelled power plants, and many more billions would be required to power all those new electric cars.

That's where we return to the second reality from my Tesla anecdote – sometimes it's environmentally better to burn the fuel directly in the car rather than the power plant, not just in Ontario, but across the country. Even in provinces where electric cars are actually "green," not everyone wants to put up with the so-called "range anxiety" of plug-in cars. Given that the CO2 emissions intensity of natural gas is 25 per cent lower than gasoline or diesel fuel, the emissions reduction from switching a large portion of the country's vehicle fleet to natural gas would be dramatic. Moreover, toxic particulate and nitrogen oxide emissions are eliminated with clean-burning natural gas. What a huge leap forward for meeting Canada's atmospheric-emissions-reduction targets.

The Canadian Natural Gas Vehicle Alliance is working to accomplish this vital objective, and it's far from a pipe dream. Millions of natural gas-powered vehicles are already on the road worldwide.

Rather than byzantine, profoundly flawed and enormously costly schemes like Ontario's Climate Change Action Plan, low-carbon-intensity, clean-burning natural gas offers Canadians the biggest single opportunity to reduce atmospheric emissions.

Gwyn Morgan is the retired founder and CEO of Encana Corp. He has been a director of five global corporations.