The Obama administration, which supports the end of global warming, has embraced a petroleum project that would help produce oil so bad for the planet that the oil-friendly administration of George W. Bush outlawed its use in the United States.

That’s the political turnabout surrounding the Keystone XL pipeline, which is intended to transport tar-sands oil from Canada across the U.S. to refineries in Texas. Tar sands oil is considered one of the “dirtiest” sources of petroleum on earth, loaded with so much carbon that the extraction and use of the Canadian resource could make it almost impossible to reverse the impact of global warming anytime soon, according to some scientists.

Tar sands oil was essentially outlawed for use in the U.S. when President Bush approved section 526 of the Energy Independence and National Security Act of 2007. Section 526 prohibits the government—the largest fuel purchaser in America—from using taxpayer dollars to purchase fuels that have a higher carbon footprint than conventional oil (namely, tar-sands petroleum).

And yet the Obama administration is seriously considering approval of the Keystone project and allowing the carbon-laden oil to enter the country.

Representative Henry Waxman of California, the ranking Democrat on the House Energy Committee , says the U.S. cannot purchase tar-sands oil without violating Section 526.

The American Petroleum Institute and its allies in Congress have repeatedly tried to repeal section 526. Supporters of the project argue that Keystone won’t violate federal law because the plan is to export the processed tar sands oil to other countries, and not sell it domestically.

-Noel Brinkerhoff