The Alberta tar sands just took another humiliating PR hit. Oil giant Royal Dutch Shell reneged on a legal commitment to reduce carbon emissions for a massive $13.7 billion tar sands expansion down to those of conventional oil.

Now why would Shell do that? Perhaps because it can’t be done.

Tar sands emissions are at least three times those of conventional oil and likely to rise as near-surface deposits are exhausted. So-called carbon capture and storage (CCS) for the tar sands have been panned both by experts and the marketplace. The Alberta and Canadian governments have been told it won’t work but that has not stopped them from plowing $500,000 a year into Washington-based lobbying.

Now comes word that Shell is abandoning a legal commitment that was a condition of their regulatory approval back in 2007. According to Pembina Institute, this backsliding will add an additional 900,000 tonnes of CO2 emissions annually or the equivalent of putting 200,000 more cars on the road.

You can bet that this mess is heading to court. EcoJustice Canada have already filed an affidavit with Alberta’s Energy Resources Conservation Board (ERCB) and the federal government requesting that the approval of the Jackpine Mine and Muskeg River Mine expansion tar sands projects be overturned.

It is interesting that Shell never said how they were planning to cut back all that carbon. They could buy offsets or invest in green energy but the only direct way to reduce tar sands carbon is through highly unproven CCS technology. Shell is one of the few companies that publicly committed to building a pilot facility, though the project seems to be little more than a pamphlet.

That said, their Shell Quest CCS project was projected to reduce carbon emissions by 1.2 million tonnes a year. If that is economically and technically feasible, why did Shell just expose themselves to litigation that could cost them billions?

The CO2 reduction commitments back in 2007 weren’t the usual window dressing. They helped inform the decision by the governments of Alberta and Canada to grant regulatory approval for the projects.

Public interest lawyers are now licking their chops. “We are confident that the ERCB and the Government of Canada will stand by their word and re-evaluate these projects in light of this new evidence by promptly convening public hearings,” said Barry Robinson, a staff lawyer with Ecojustice.

The lipstick is starting to come off the pig. In spite of massive lobbying and PR efforts, the marketplace is clearly not convinced that carbon capture is going to fly at the tar sands – no matter what Washington is being told.

The timing of this flip flop is particularly embarrassing for Ottawa and Alberta given that carbon pricing is moving its way through the US Congress, and the Alberta government just ran a record $4.7 billion deficit as the latest oil boom has gone bust.

This latest development adds further risk to the already unravelling investment market for the diriest oil on Earth.