“Dirty” is a tough label to bear. It’s simple, descriptive and evocative. It sticks.

At least it has for Canada’s oil sands sector, which has been tarred with the “dirty” brush for the products it wrests from beneath the forest of northeastern Alberta.

The industry has struggled mightily to burnish its image with TV commercials and glossy magazine ads. So it was with open arms that it greeted a new scientific report showing that burning billions of barrels of oil sands crude actually has a modest climate impact.

The report, co-authored by respected climate scientist Andrew Weaver and published in the journal Nature, shows that, when it comes to global warming, the oil sands are far from the world’s chief villain – and is being seized upon by Canada’s top industrial political leaders as proof that the oil sands aren’t as dirty as some have made them out to be.

“Hopefully, this will put to rest some of the wild exaggerations and misstatements from too many people who ought to know better,” said Natural Resources Minister Joe Oliver, who plans to incorporate the report’s headline numbers into future speeches.

According to modelling done by Dr. Weaver, if the world burns all of the 170 billion barrels of oil sands reserves, global temperatures would rise by 0.03 degrees Celsius – far less than the nearly one degree of warming induced by burning the world’s coal reserves.

That report comes at a critical time for an industry whose expansion plans are reliant, in part, on new pipelines like Keystone XL and Northern Gateway. Those projects have come under fire for their role in enabling expansion in what critics have called a “carbon bomb.”

Now, oil sands proponents are seizing upon Dr. Weaver’s work to make the case that the oil sands carbon bomb is a modest one. Having new data come from a leading scientist has been manna for government leaders who have struggled with credibility issues as they sought, in recent years, to make similar points.

“It’s important that we have someone that’s independent,” said Diana McQueen, Alberta’s Minister of Environment and Water. “It’s not us having to say it.”

And the new data come as industry and government continue to lose the battle for hearts and minds over the oil sands. Calgary pollster Bruce Cameron points to the “speck” of social media work generated by TransCanada Corp. in the Keystone XL debate, compared to the avalanche of opposition conversation.

“For a country that has trillions on the line [with the oil sands], it seem to me we need to do more to make sure if anybody has factual errors, they’re corrected,” he said.

Dr. Weaver has cautioned about misinterpreting his work as a “get-out-of-jail-free pass” for the oil sands. Indeed, he stands staunchly against Gateway, and supports policy to break fossil fuel dependence.

But his work makes clear that, for a world struggling to manage its carbon output, oil sands are, numerically, not the primary cause for concern. Even if all of the oil sands were produced – a virtual impossibility – the world would see a 0.36-degree rise in temperature – one-eighth the increase possible from burning all of the new supplies of shale gas.

“If people really understood the [world’s] energy [need] scenarios, people would be cheering the oil sands on – even Greenpeace,” said Eric Newell, the former chief executive of Syncrude Canada Ltd. who now chairs Alberta’s Climate Change and Emissions Management Corp. “Although I’m probably not going to live to see that happen.”

It’s clear, even from Greenpeace, that the new figures stand to affect public concern over the oil sands.

“What makes me nervous is that this is really being spun as, ‘We don’t have to worry about the tar sands,’ ” said Mike Hudema, that organization’s climate and energy campaigner. But, he added: “This is not a free pass for the Harper government. Tar sands remain a major issue, and we need to transition from fossil fuels altogether.”

Dr. Weaver’s work is not in dispute – David Barber, another leading climate scientist with the University of Manitoba, called it “very valid” – but other points are. Dr. Barber, for example, said oil sands extraction remains “awfully hard on the environment. There are a lot better places to develop oil.”

But Dr. Weaver’s data fly in the face of other research, which has suggested the impact of producing oil sands will be far more severe.

The differences are driven by a critically important question: How big are the oil sands, really?

The entire oil sands areas contains 1.8 trillion barrels. But much of that can’t be brought out, because it’s either technologically or economically impossible. By today’s best estimate, about 170 billion barrels can be recovered. That number can rise or fall based on crude prices and technological advances; indeed, some believe 400 billion is a more accurate figure. But that’s today’s number, and that’s what Dr. Weaver based his calculations on.

Climate change voices like NASA scientist James Hansen have estimated that fully half of the oil sands will one day be extracted. At a rate of eight million barrels a day – five times today’s oil sands output – it would take 310 years to get out that much oil. Using that number, however, Mr. Hansen argues that exploiting the oil sands will lead to a carbon increase equivalent to all of the coal humanity has burned up to this point, and is tantamount to declaring “game over” for the climate.

According to Mr. Hansen, existing “conventional” fossil fuel resources will generate so much carbon on their own that “unconventional” sources must be left in the ground.

“Preserving creation for future generations is a moral issue as monumental as ending slavery in the 19th century or fighting Nazism in the 20th century,” he has written.

Bill McKibben, the leading climate change voice who first called the oil sands a “carbon bomb,” argues that even if oil sands emissions are smaller than other hydrocarbon sources, they remain dangerous.

“Smoking six packs a day will kill you,” he said. “Smoking 100 packs a day will, yes, kill you more comprehensively. Personally, I tried to raise my daughter not to smoke at all.”