The Keystone XL pipeline, recently approved by the US State Department and awaiting President Obama’s declaration that it is in the “national interest,” will carry oil that is too dirty for the US government to buy — under legislation signed by George W. Bush!

In 2007, President Bush signed into law Section 526 of the Energy Independence and National Security Act of 2007. It prohibits the US government, which is the largest single fuel purchaser in the U.S., from using taxpayer dollars to purchase fuels that have a higher carbon footprint than conventional oil.

This little-known law is significant because Congress crafted it, in part, with the explicit intent to block the US from buying Canadian tar sands oil — considered the dirtiest oil on the planet. With President Obama currently debating whether to authorize the construction of the Keystone Pipeline — which will funnel tar sands oil from Alberta into the the US — and more than 1000 activists arrested in front of the White House last month in protest the pipeline, the issue has moved to the front and center of the climate debate in recent weeks.

According to Congressman Henry Waxman, Chair of the House Energy Committee, the US purchase of tar sands oil would clearly violate Section 526. As he wrote in a letter to the Senate Commerce Committee in 2008, the law “applies to fuels derived from unconventional petroleum sources such as tar sands which produce significantly higher greenhouse gas emissions then are produced by comparable fuel from conventional sources.”

Meanwhile the Canadian government has been working behind the scenes to strike Section 526 from the books to clear the way for tar sands extraction. Using Freedom of Information requests, the Pembina Institute and Climate Action Network Canadian, uncovered a 2008 strategy memo by Canadian Embassy official Hélène Viau, which urged US oil lobbyists to send letters to the U.S. Department of Energy and the Department of State to show “concerns with regard to section 526 and argue that oil sands products should not be targeted by this provision,” and to develop “a comprehensive oil sands advocacy strategy to focus on outreach to allies, influencers, legislators, etc.”

And Big Oil lobby have taken Viau’s suggestions to heart. Matt Fox, senior vice-president of oil sands for ConocoPhillips warned US legislators that Section 526 “could bring [tar sands] development to a screeching halt. You’d have to think twice about oil sands development if your intention was to deliver oil to the lower '48.”

If President Obama elects to unilaterally disregard Section 526, the planet may be doomed. According to Bill McKibben, founder of 350.org and one of the leaders of the Keystone pipeline protests, the burning the recoverable oil in the Alberta tar sands by itself would raise the carbon in the atmosphere by 200 parts per million (ppm). It wasn’t hard to figure out that this would increase the 390 ppm carbon in the atmosphere today by more than half. Indeed, it would increase the gap between the current level and the safe level of 350 ppm five-fold.

The leading NASA climate change specialist James Hansen summed up what’s at stake saying: “If the tar sands are thrown into the mix it is essentially game over” for a viable planet.

While protecting the climate will ultimately require legislation and treaties, in the meantime it is essential to prevent the use of “extreme energy” fuels like the Alberta tar sands oil that will rapidly make climate change far worse.

Congress and President Bush showed wisdom in saying that the US should not and would not buy such oil. President Obama would be wise to find the Keystone XL pipeline — whose only purpose is to bring the world’s dirtiest oil to the US — is not in our national interest.