Just how dirty are Canada’s oil sands, anyway?

Once again, Congress is debating whether to approve the Keystone XL pipeline, which would bring oil from Alberta’s tar sands down to the Gulf Coast. Republicans want to fold it into the transportation bill. And scientists like James Hansen warn that harvesting tar sands would be “game over” for the climate.

A cup of heavy oil from Alberta. (TODD KOROL - REUTERS) So let’s get some numbers: What would the actual impact be? The Congressional Research Service just put out a new report that takes stock of various academic studies on the subject. Crude from Alberta’s oil sands is heavier, more viscous, and contains more impurities than other types of oil. So it takes more energy to extract and process. When you consider the entire life cycle — from digging the stuff out of the ground to burning it in your tank — oil from tar sands produces 14 to 20 percent more carbon emissions than other oil the U.S. imports.

Overall, the CRS report estimates, approving the Keystone XL pipeline would be the equivalent of boosting U.S. global-warming emissions by between 0.06 percent and 0.3 percent per year. (That assumes the pipeline spurs additional production in Candada.) At the high end, that’s like putting 4 million extra passenger cars on the road.

That may not, in itself, be “game over” for the climate. Though seeing as how the United States has pledged to cut its carbon emissions 17 percent by 2020, it would also be a slight step in the opposite direction.

There’s also more than just Keystone XL to consider. Canada has big plans to export its oil around the world. Catherine Mann and Stacy Feldman of InsideClimate News recently tried to tally up all the different pipeline projects in the works to transport Alberta’s tar-sands oil abroad. Some of these projects could get bogged down by protests and opposition (or shuttered by the vicissitudes of the market). But there are plans to send 3.1 million barrels per day from Alberta to export markets — essentially five times as much as Keystone XL. Here’s the map:

(Picasa)

There’s something else that could throw a kink in these plans. Many countries are now considering measures to reduce the carbon content of their transportation fuels. The European Union is mulling a law to reduce emission from fuel 20 percent by 2020. It would prove tough for oil from Alberta to qualify, given all the recent studies on the crude’s carbon footprint. And granted, Europe doesn’t currently import crude from Canada, but its law could set precedents elsewhere. California has a similar low-carbon fuel law that’s wending its way through the courts, for instance.

The big challenge for Alberta’s oil industry, then, is to figure out how to reduce the carbon intensity of tar-sands oil. In this InsideClimate interview, Adam Brandt, an engineering professor at Stanford, explains a few possible options, from reducing the amount of steam injected into the oil to using natural gas instead of petroleum coke for extraction and processing. “The hope,” he says, “is that as the science improves, they can continue to reduce these emissions, and reduce this difference between the oil sands and conventional oil.”

Until that happens, Alberta’s vast tar sands are likely to remain the center of controversy. As the CRS report suggests, Keystone itself won’t make the difference between the world making or missing its climate goals. And the United States could still have plenty of other reasons to want Canada’s oil — boosting supplies, for one. Yet the overall carbon impact of tar sands appears to be noticeable enough that it’ll likely remain a part of any debate about tackling global warming.

Update: Sabrina Fang, an analyst with the American Petroleum Institute (which represents the oil industry) takes issue with the CRS report. She stresses some of the uncertainties involved in such analyses, though her most forceful point is that Alberta’s oil sands production is likely to boom in the coming decades regardless of whether the Keystone XL pipeline is approved. For those concerned with the climate aspects of oil sands, that’s probably not the most comforting thought.