Photo: David Dodge, The Pembina Institute. More at OilSandsWatch.org

Due to skyrocketing costs, Shell Oil is putting expansion plans in the Canadian tar sands on hold for at least five years. The Globe and Mail reported yesterday that the head of Shell's American operations referred to the tar sands as one of the most expensive oil projects on earth.

The tar sands' high cost isn't only financial. Extracting the thick, dirty crude oil located beneath Alberta's magnificent boreal forests has created an environmental catastrophe. The scar left by tar sands operations on the Canadian wilderness is visible from space. Extracting tar sands oil requires 2.5 to 4 times more water and releases 3 times more global warming pollution than extracting conventional crude oil. And tar sands oil contains a lot more sulfur, nickel, nitrogen, and lead than conventional oil. As a result, when it's processed in refineries, tar sands oil releases far higher levels of toxics into the air.

Earthjustice is challenging the government's approval of two new pipelines—the Alberta Clipper and Keystone XL—that would deliver this dirty tar sands oil from Canada to refineries in the U.S. These expensive projects would lock the U.S. into a dirty energy future at precisely the time we need to transition to clean energy. And Shell's decision to put tar sands expansion on hold is a signal from one of the world's largest oil companies that the additional supply of tar sands oil the pipeline would deliver to U.S. refineries may never even materialize.

The pipeline companies—Enbridge and TransCanada—want us to believe that the oil companies are clamoring for additional pipeline capacity to transport ever-increasing amounts of tar sands crude oil to the U.S. The reality is that this new infrastructure is not only unnecessary; it's also a roadblock to the development of low-carbon alternatives.

Tar sands oil is far too costly for the planet. And if one of the richest companies in the world decides it's too expensive, you can bet it's a bad financial investment, too.

(To see some incredible—and horrifying—images of the Alberta tar sands, check out the photos at Garth Lenz's website.)