Here's video of Dr. James Hansen, climate science expert and former head of the NASA Goddard Institute for Space Studies, testifying yesterday at a U.S. Senate hearing, and explaining why he opposes the Keystone XL pipeline.
It's a question of how much of that tar sands is going to be taken out of the ground. If we build this expensive pipeline, it will facilitate the extraction of much more than if we don't build it. As soon as you put a price on carbon that's significant and rising, one of the first things that falls off the table is tar sands. And Canada knows that, that's why they're so desperate to get the United States to approve this. If we don't approve it, a lot of that tar sands will never be developed. The world is going to realize pretty soon that we've got to limit the amount of carbon we put in the atmosphere. And it's going to have to do that via a price on carbon, and that's going to cause the most carbon-intensive things to get left in the ground, and that includes tar sands.