One of the world's top climate scientists has calculated that emissions from Alberta's oilsands are unlikely to make a big difference to global warming and that the real threat to the planet comes from burning coal.

"I was surprised by the results of our analysis," said Andrew Weaver, a University of Victoria climate modeller, who has been a lead author on two reports from the United Nations Intergovernmental Panel on Climate Change.

"I thought it was larger than it was."

In a commentary published Sunday in the prestigious journal Nature, Weaver and colleague Neil Stewart analyze how burning all global stocks of coal, oil and natural gas would affect temperatures. Their analysis breaks out unconventional gas, such as undersea methane hydrates and shale gas produced by fracking, as well as unconventional oil sources including the oilsands.

They found that if all the hydrocarbons in the oilsands were mined and consumed, the carbon dioxide released would raise global temperatures by about .36 C. That's about half the total amount of warming over the last century.

When only commercially viable oilsands deposits are considered, the temperature increase is only .03 C.

In contrast, the paper concludes that burning all the globe's vast coal deposits would create a 15-degree increase in temperature.

Burning all the abundant natural gas would warm the planet by more than three degrees.

Governments around the world have agreed to try to keep warming to two degrees.

"The conventional and unconventional oil is not the problem with global warming," Weaver said. "The problem is coal and unconventional natural gas."

He said his analysis suggests it is an increased dependence on coal — not the oilsands — that governments have to worry about. As well, there's so much gas in the world that it will also cause problems despite the fact it emits less carbon than oil.

"One might argue that the best strategy one might take is to use our oil reserves wisely, but at the same time use them in a way that weans us of our dependence on coal and natural gas," Weaver said. "As we become more and more dependent on these massive reserves, we're less and less likely to wean ourselves away from them."

Burning all the oil in the world would only raise temperatures by less than one degree, the paper concludes.

Weaver's analysis only accounts for emissions from burning the fuel. It doesn't count greenhouse gases released by producing the resource because that would double-count those emissions.

He said his paper is an attempt to bring some perspective to the often-fraught debate over oilsands development, which continues to cause major concerns about the impact on land, air and water. And emissions from producing oilsands crude are making it very tough for Canada to meet its greenhouse gas reduction targets.

"We've heard a lot about how if we burn all the oil in the tarsands it's going to lead to this, that and the other. We thought, 'Well, let's take a look at this. What is the warming potential of this area?' and the numbers are what they are."

He said the real message is that the world has to start limiting its use of fossil fuels.

"This idea that we're going to somehow run out of coal and natural gas and fossil fuels is really misplaced. We'll run out of human ability to live on the planet long before we run out of them.

"I have always said that the tarsands are a symptom of a very big problem. The problem is dependence on fossil fuels."