Canada’s government, which has threatened a trade war over a proposed European rule to penalize oil-sands crude in a bid to clean up transportation fuels, has a powerful new argument in its favour, as new research shows other energy sources are far more dangerous to the climate.

On Thursday, a committee of the European Union will vote on a proposed fuel-quality directive intended to reduce the carbon footprint of gasoline and diesel on that continent. The directive directly penalizes oil-sands crude for its high-emissions content, using language that oil-sands supporters and others have called “flawed,” “discriminatory” and worse.

If passed, such a directive could set a precedent for other international fuel rules that challenge oil-sands products, a prospect that has deeply alarmed Canada’s political and corporate leadership. Officials have waged a years-long lobbying campaign to have it changed, enlisting the help of European nations with oil-sands interests such as Britain and the Netherlands.

But the EU vote comes against a landscape newly shifted by research showing that on a global scale, oil-sands emissions are not the dark-shirted villain some have made them out to be. That research, published in the journal Nature and co-authored by one of Canada’s most respected climate scientists, throws a wrench into the debate over an energy source whose reputed “dirtiness” has sparked fiery debate around the world. In North America, climate concerns have been at the heart of the concerted environmental movement against Keystone XL and Northern Gateway, a pair of proposed oil-sands pipelines that have struggled against a tide of public opposition.

The research, by University of Victoria scientists Andrew Weaver and Neil Swart, calculates the climate impact of producing the oil sands. Dr. Weaver is an internationally respected scientist who has contributed to United Nations climate-change documents. He and Dr. Swart completed several analyses.

The most important examined the impact of producing the roughly 170 billion barrels of oil-sands crude that the industry currently considers economic to produce. If it’s all hauled out of the ground – a process that will take more than a century, even at the forecast 2020 rate of three million barrels a day – the cumulative global-warming impact is 0.02 to 0.05 degrees Celsius, according to the research.

If every barrel of the oil-sands resource is produced – a near-certain impossibility that would see some 1.8 trillion barrels, seven times the size of Saudi Arabia’s current reserves, brought out – it would raise global temperatures by one-third of a degree.

By comparison, burning all of the world’s enormous coal resources would raise temperatures 15 degrees, while consuming the new global bounty of shale gas would produce a lift of just under 3 degrees. (Using up economically accessible reserves of natural gas and coal will raise temperatures 0.16 and 0.9 degrees, respectively.)

Dr. Weaver set out to crunch the numbers after witnessing the angry rhetoric over the Keystone XL debate in the United States, where environmental groups warned the pipeline was the fuse to a “carbon bomb.” NASA scientist James Hansen has famously said that if the oil sands are fully exploited, it will be “game over” for the climate.

“We’re not giving a get-out-of-jail-free card to the tar-sands industry. This is not the purpose of our study,” Dr. Weaver said. Indeed, he is “absolutely opposed” to the Northern Gateway pipeline on social and ecological grounds, and says policies like the EU fuel directive are “probably the way of the future,” arguing that governments must look for ways to “shift consumer demand away” from hydrocarbons.

The sole act of producing the oil sands for use in Canada and the United States, he notes, will take up three-quarters of North Americans’ per-capita carbon allowance if global warming is to be held at 2 degrees Celsius.

But it’s clear Dr. Weaver’s overall analysis will provide additional lobbying force for Canadians seeking to overturn or change the EU fuel-quality directive, which assigns oil-sands-derived fuel an emissions value 23 per cent higher than fuels from more “conventional” sources. The Canadian government, arguing that the legislation fails to penalize similarly carbon-intensive crudes from Venezuela and California, has threatened legal warfare to overturn the directive.

Last December, Canada’s newly installed ambassador to the EU wrote a letter making clear “that Canada will explore every avenue at its disposal to defend its interests, including at the World Trade Organization.”

The threat, made to EU Commissioner for Climate Action Connie Hedegaard in documents released Monday by the environmental group Friends of the Earth Europe, warned that action will be taken if the directive singles “out oil-sands crude in a discriminatory, arbitrary or unscientific way.”

Travis Davies, a spokesman for the Canadian Association of Petroleum Producers, said it is “important” that analyses like Dr. Weaver’s are being done, since it might help calm “the inflamed rhetoric from the other side.”

Yet what’s also clear is that Dr. Weaver’s work does little to absolve an industry that continues to be Canada’s fastest-growing source of emissions. Oil-sands emissions alone are expected to claw back all of the emissions gains made by moving the country’s electrical supply off coal. Mr. Davies acknowledged that “it doesn’t take any onus off industry to do good work in reducing upstream emissions.”

The intersection of oil-sands development and government policy has also placed Canada in a difficult spot internationally. Even if the new numbers suggest the oil sands are not the most significant international climate scourge, Canada’s opposition to the EU policy threatens to further injure an already-damaged international reputation.

“For 99 per cent of people this looks like Canada opposing environmental policy to protect the oil sands,” said Andrew Leach, a business professor and energy researcher at the University of Alberta.