Pres. Barack Obama vetoed a bill to approve construction of the Keystone XL Pipeline on February 24—not because of climate change, not because of low oil prices and not because of the risks from leaking diluted bitumen from the tar sands. Obama vetoed the pipeline bill "because this act of Congress conflicts with established executive branch procedures." In other words Obama used the third veto of his presidency to preserve the prerogatives of his office, in this case evaluating cross-border pipelines and the ever-vague "national interest."


Veto aside, the Obama administration still might find Keystone XL is in the national interest, once the Department of State completes its six-years-and-counting review. Approval appears to hinge on whether the pipeline is judged to "significantly exacerbate the problem of carbon pollution," as the president put it in a speech in 2013. State has said no it won’t in the past, but the U.S. Environmental Protection Agency, among others, say yes it will.

There is little doubt that oil made from the bitumen stuck to sand buried beneath Alberta is among the dirtiest kinds of oil found on the planet. Interestingly, about the only worse type of petroleum is the heavy crude from Venezuela that refineries on the Texas coast already process—the same facilities that Keystone aims to reach. And that's just the climate accounting, which leaves out very real health impacts on local people and communities as well as the boreal forest, rivers and lakes of Alberta.

There is also little doubt that tar sands oil will find other ways out, whether other pipelines or by truck, railcar or barge. How much or how little depends on future oil price speculation, Canadian geopolitics and the inner machinations of oil companies. But there is little doubt that without Keystone XL, less tar sands oil will find its way out of the ground and, perhaps more importantly, will not be as cheap—and in a time of low oil prices that may prove to be the difference.

Already, projects to mine more tar sands have been put on hold as the global price of oil approaches the cost of producing it from the sands. Canada-based Cenovus Energy as well as petroleum giants Shell, Total and others have all shelved planned developments in Alberta.

Still, the tar sands juggernaut rolls on like the giant trucks used to mine the stuff via existing projects, such as the North Steepbank mine or the Christina Lake Project, to melt out bitumen with steam. The Canadian government has proved more than willing to subsidize development of the oil sands in the face of low oil prices historically. Keystone XL is also just one pipeline and, as the president has also said time and time again, a nation's energy strategy hinges on more than just one pipeline. That goes double for the globe: stopping a coal mine in Australia or limiting U.S. coal exports can do more to slow the rise of atmospheric carbon dioxide than stopping Keystone XL.

The goal is a shift away from more polluting sources of energy—oil, coal and even natural gas—toward those that add less CO2 to the atmosphere like renewables, nuclear or even fossil fuel–fired power plants outfitted with technology to capture and get rid of global warming pollution. Every bit of infrastructure must be accounted for in some kind of global ledger as either adding more or adding less CO2 while in use. Such energy transitions take decades but there are obvious swaps, like substituting anything for coal or using less of the tar sands.

A glimpse of the ultimate challenge can be seen right now, in low oil prices. Low cost encourages more use, which in turn results in more pollution. As alternatives to fossil fuels grow, coal, oil and natural gas will likely become cheaper as demand shrinks, in turn tempting us to burn more again. To prevent catastrophic climate change, that carbon conundrum will need to be solved.