A common rallying cry against the Keystone XL pipeline is that it would be a climate change disaster.

But a new analysis says that the possible rise in global temperature that would occur from burning Canadian oil sands crude is small in comparison to combusting global reserves of coal or natural gas, and not likely to single-handedly create a climate tipping point. In addition to existing pipelines carrying oil-sands fuel to the United States, Keystone XL would have ferried the crude from Alberta to Texas refineries.

"By themselves the oil sands will not cause a climate catastrophe," said Neil Swart, a doctoral candidate at the School of Earth and Ocean Sciences at the University of Victoria in British Columbia. "The warming that would occur from utilization of the tar sands is not that great."

Swart co-wrote the analysis with Andrew Weaver, a professor in the department, in a Sunday commentary published in Nature Climate Change.

If all of the economically viable fuel in Canada's oil sands patch were burned, the resulting carbon dioxide emissions would spur an average temperature rise of about 0.03 degrees Celsius, or one-thirtieth of what would occur with combusting viable global reserves of coal, they found. The degree of temperature rise from using viable reserves of gas would be roughly six times higher than that from the oil sands, the assessment says.

The projected temperature rise associated with combusting oil sands fuel is about one-seventieth of the 2-degree-Celsius temperature rise above preindustrial levels cited by the international community as necessary to keep climate change in check, the researchers said.

That 0.03 degree rise would come from combusting 170 billion barrels of proven oil reserves in Canada. If the analysis was limited to the 26 billion barrels of Canadian crude currently under "active development," the temperature rise would be "almost undetectable," or around 0.01 degrees, according to Weaver and Swart.

Global commercially viable reserves of coal, by contrast, could cause a temperature rise of about 0.92 degrees if burned, they said.

"It is important to recognize that our estimates do not include greenhouse gases other than carbon dioxide and do not address other potentially deleterious environmental, health and social side effects of oil-sands production," they said.

Jim Hansen: argument is 'fallacious'

Opponents of the oil sands noted that the analysis did not include CO2 emissions associated with extracting and refining the fuel in Canada. That is a key point about the oil sands, they said, since oil sands fuel has a similar emissions profile to traditional oil once it gets burned in vehicles.

Oil sands crude typically is heated out of the ground with natural gas or mined with heavy equipment before being sent to refineries. That production process causes the oil sands region to release more greenhouse gases than traditional oil drilling.

In an emailed statement, NASA climatologist James Hansen said "the argument that the currently known amount of carbon in the tar sands pit is small compared to the total fossil fuels burned in two centuries is fallacious and misleading -- every single source, even Saudi Arabia, is small compared to the total."

"Tar sands size is not fixed and the numbers given are just current guesses. If we once get hooked on tar sands and set up infrastructure, the numbers will grow as mining capabilities increase," he said.

Hansen engaged in civil disobedience at the White House last year with hundreds of activists to protest Keystone XL before the pipeline was denied a permit by the Obama administration. He also has said production of the oil sands -- when combined with other fossil fuels -- would be "game over" for the planet.

Matthew Horne, an analyst at the Pembina Institute, a Canadian environmental think tank, said it was important to consider the industry's impact on Canada's climate goals, beyond comparisons between fuels. Oil sands development threatens Canada's stated target of cutting greenhouse gas emissions 17 percent by 2020, he said.

"Emissions from gas and coal are declining in Canada," he said. Emissions from the oil sands, on the other hand, could triple by 2020, he said.

Swart said he and Weaver did not calculate emissions in the oil sands production process to avoid double counting. The carbon dioxide released from using natural gas in oil sands production, for example, would be included under the study's emission numbers for gas generally.

Even so, the addition of production figures would enlarge the carbon dioxide footprint for the oil sands by about 17 percent, he said. That would still rank the oil sands significantly below coal and gas's CO2 levels, he said.

He said he hoped the results would "provide perspective" for people, but that they also should not be seen as a policy argument, one way or the other. It is relevant to consider how industrialized nations like Canada will influence energy development in countries such as China, in terms of how much coal and conventional gas they use in the future, he said.

Construction of pipelines like Keystone XL "signifies a long-term North American commitment to using fossil fuels generally," he said.