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Professor Christopher Kennedy says in a journal that shifting to electric vehicles will only reduce emissions if plants generate low levels of greenhouse gases.

Fernando Morales/The Globe and Mail

It makes environmental sense to switch to electric cars and trains only in regions where electricity comes from clean sources, and a University of Toronto professor has pinpointed where that threshold of cleanliness lies.

Civil engineering professor Christopher Kennedy says in a paper published in the journal Nature Climate Change that shifting to electric vehicles will only reduce emissions if the plants that make the power generate less than 600 tons of greenhouse gases for every gigawatt-hour of electricity.

Canada, overall, is well below that level, at about 200 tons on average, Prof. Kennedy notes, although the level varies dramatically from province to province. Ontario, Quebec and British Columbia, for example, generate very low levels of greenhouses gases from electricity production because they use nuclear and hydro power extensively.

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Alberta and Saskatchewan are over the threshold – at about 750 tons – because they generate considerable amounts of power from coal plants. Consequently, switching to electric cars or trains in those provinces will not help reduce GHG emissions.

"If [we] want to roll out more electric vehicles in Canada, we wouldn't actually want people to drive them in Alberta," Prof. Kennedy said in an interview.

The global average for carbon intensity of electrical production was 536 tons in 2011, but the differences between countries are dramatic. Some countries, such as Iceland, Sweden and Norway, have very low numbers because they use so much hydro and geothermal power.

Others, including big overall emitters such as India, China, Australia, Saudi Arabia and Indonesia, are well above the threshold – all are between 700 and 900 tons – so it makes little sense to switch to electric cars or trains there. In those countries it may actually be more carbon-friendly to fly than to take a high-speed electric train, Prof. Kennedy said.

It is not only in Canada that there are significant regional variations. In the United States, for example, the west coast uses far more renewable electricity than in the Midwest, where coal-powered generation still predominates. India also has huge regional variations.

Coal power plants generally produce about 1,000 ton of greenhouse gases per gigawatt-hour, while hydro and nuclear plants generate close to zero. Natural gas plants are in between at at 600 tons. To make progress, "really it is about getting rid of coal emissions," Prof. Kennedy said.

He noted that the 600-ton threshold is not a precise point for where electricity become "carbon competitive," because there are variations in the efficiency of engines and the characteristics of the power sources that are being displaced. The actual threshold can range from 500 to 700 tons.

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Still, the number is "remarkably consistent" around the world, he said, and it should be used in international policy negotiations concerning carbon emissions. "Countries should be challenging each other to reduce the carbon intensity of the electricity supply, [and this] gives them a benchmark." It is a "not unreasonable ask" to get to the 600-ton level, he said.

While any government considering electrification of transportation should do a detailed life-cycle study to make sure there are benefits, this benchmark provides a rule of thumb that will give them a pretty good idea if it is worthwhile, he said.

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