Additional info from The Climate Reality Project
You have probably heard about tar sands quite a bit lately, because it’s the oil that would be carried through America’s heartland by the Keystone XL pipeline. Tar sands (sometimes called oil sands) are a thick combination of clay, water, sand, and bitumen ⎯ a heavy, viscous oil. Unlike conventional oil, bitumen can’t be pumped out from the ground, but has to be mined through strip mining or open-pit mining techniques. About two tons of tar sands are required to produce one barrel of oil. Alberta, Canada, has the world’s largest deposits of tar sands.
Oil is a “hydrocarbon”: a compound made of hydrogen and carbon. But that doesn’t mean every kind of oil has the same chemical composition or physical properties. Sometimes the difference is based on the kind of fossils that make up the oil. (Remember that “fossil fuels” are made out of the remains of ancient plants and animals). Sometimes the difference is based on where the oil is found in the world.
If you look at just the combustion of different types of oil, you’d find they release similar amounts of global warming pollution. That’s because oil is refined into fuels like gasoline according to certain fuel standards. So by the time you burn one source of gasoline in your car, it’s nearly identical to gasoline from other sources. But as it turns out, not every source of oil has the same effect on our climate.
Scientists have a variety of tools to get a more complete picture of the relative climate impact of different sources of oil. For example, “well-to-tank” calculations account for emissions from oil extraction, to oil refining, to the delivery of refined fuel to a gas tank. It’s this well-to-tank calculation that tells us how tar sands oil compares to oil from other sources.
A 2012 report prepared for members of the U.S. Congress estimates that tar sands oil leads to between 70 and 110 percent more well-to-tank emissions than conventional crude. According to this report, allowing the Keystone XL pipeline to be built could increase U.S. greenhouse gas emissions annually by the same amount as building over five additional coal power plants (up to 21 million metric tons of extra carbon pollution). The U.S. Environmental Protection Agency has an even higher estimate for Keystone XL, with well-to-tank emissions 82 percent greater than average U.S. crude (PDF). An analysis by a national laboratory indicates that Canadian tar sands oil was the dirtiest source of all diesel emissions in the U.S. in a given year.
And why is tar sands oil so much dirtier? For one thing, it has less hydrogen, but relatively more carbon, sulfur and heavy metals than most other oils. This means that the oil requires a lot more energy-intensive processing to make it into a commercially viable product in the U.S. What’s more, tar sands oil is on average heavier and more viscous than regular crude oil, so it takes more energy to extract and distribute. The highly disruptive mining processes involved also create a far larger carbon footprint for tar sands oil than regular oil. Tearing up the carbon-rich soil under the boreal forest in Alberta releases carbon pollution equivalent to 37 million new cars on the road initially, and adding 5,200 new cars each year afterward. The strong carbon-trapping nature of the wet soil in the boreal forest makes this disruption even worse for the climate than tearing up similar areas of land in other forests, or simply digging oil wells in the types of dry, arid landscapes where much of the world’s oil comes from.
Regardless of which analysis you pay attention to, the main conclusion is the same: Producing, transporting, and processing tar sands oil is a lot worse for the climate than regular oil.