"I had heard the rhetoric, that the tar sands, if it was combusted would sort of lead to game over for the planet Earth," says Weaver, "and I thought it sounded fishy. I thought it would be large, but the numbers came out quite small."

Coal and natural gas more harmful than oil sands

With their model, Weaver and his colleagues found that burning all the viable bitumen from Alberta's oil sands would raise global temperatures by 0.36 degrees Celsius. In contrast, burning the world's coal reserves will raise the temperature by almost 15 degrees, while consuming global natural gas reserves would cause a 3 degree rise.

The results reflect that the world reserves of coal and natural gas are far larger than those of bitumen. However, Weaver cautions that the results should not be taken as an endorsement of oil sands development. He says the message of his study is that the world needs to wean itself off all fossil fuels.

Canada's oil sands, or tar sands as some call them, are the second biggest oil reserves on the planet, with an estimated 170 billion barrels recoverable with current technology.

But the oil is locked in bitumen, a heavy tar-like substance, which is costly to upgrade and refine into usable crude. The process also creates more greenhouse gas emissions than conventional fuel and uses large quantities of water.

The oil sands have been singled out by campaigners in Canada and abroad as a major source of climate change.

Canadian oil producers have reacted positively to the study's conclusion that downplays the importance of oil sands in the global climate change debate. Travis Davies, a spokesman for the Canadian Association of Petroleum Producers, welcomed the study, calling it important and expressing the hope that it might reduce "the inflamed rhetoric from the other side."

'Not a get-out-of jail card': Pembina Institute

However, Ed Whittingham, CEO of the Pembina Institute, a Canadian sustainable energy think-tank, says it would be wrong to read the study as letting the oil sands off the hook for climate change.

"It's a huge mistake to interpret his results as some kind of get-out-of jail free card for the oil sands," Whittingham says. He adds that oil sands development is Canada's largest growing source of greenhouse gas emissions and will likely cause Canada to miss its commitments to meet international reduction targets.

Weaver and Swart's study could also influence a looming trade war between Canada and the European Union. The EU is considering a new fuel quality directive that would designate crude from the oil sands as a source of a high level of greenhouse gas emissions. There is currently no oil from Alberta exported to Europe, but the move is considered symbolic and is potentially inflammatory. Canada's ambassador to the EU has threatened retaliation if oil sands crude is singled out by the EU's fuel quality directive.

External links:

Extract of Andrew Weaver's and Neil Swart's paper