In his speech on climate in June, President Obama laid out his criteria for approval of the Keystone XL pipeline: "Allowing the Keystone pipeline to be built requires a finding that doing so would be in our nation's interest. And our national interest will be served only if this project does not significantly exacerbate the problem of carbon pollution. The net effects of the pipeline's impact on our climate will be absolutely critical to determining whether this project is allowed to go forward."

Let's parse the two standards: "national interest" and "impact on climate."

There is already a maze of pipelines webbing U.S. soil, with Canadian lines already involved in tar sands oil export from Alberta, including an Enbridge pipeline crossing northern Minnesota and one that risks the vulnerable Straits of Mackinac in Michigan. Both deserve careful scrutiny given Enbridge's poor record of spills and spill management, including the nearly million-gallon spill in the Kalamazoo River in Michigan, and the extra risk involved in transporting tar sands oil.

But the much larger, $7.3 billion Keystone XL pipeline is different in three ways. First, it certainly will carry dilbit, the nasty goop produced from tar sands that requires diluting with other fuels and high-pressure pumping for transport, meaning that if a spill occurs, the results are far more expansive and dangerous.

Second, the pipeline services Gulf Coast refiners, and given the much higher value of oil on the world market vs. the glutted U.S. domestic market, the refined products certainly will be exported, with the paradoxical effect of raising U.S. gasoline prices — hardly in the national interest.

Third, as a new pipeline crossing an international border, Keystone XL requires State Department approval, and the case for approval does not hold up.

The main argument for the pipeline — energy security vs. importing oil from the problematic Middle East and Venezuela — collapses since tar sands oil will be exported and so won't reduce U.S. imports.

Another argument is that Canada is a friendly neighbor. True enough. But one reason Keystone so badly needs to run this export pipeline across American soil is the fierce resistance to it within Canada, from First Nations and many other groups.

Without a new export pipeline, train traffic carrying tar sands oil will certainly increase, with attendant risks such as the recent fiery catastrophe in Quebec. But that is no argument for this pipeline, but rather for more careful regulation of oil freight, dramatically expanding in any case.

But Obama laid down by far the most important measure by which this — and all other future energy infrastructure — must be evaluated: impact on climate. And according to the EPA, emissions from oil sands crude would be 81 percent higher than from regular crude.

Scientists project that the climate future of our state, region and nation will be red hot and ugly if global warming is not stopped and reversed, with a possible increase of 7 or more degrees Fahrenheit this century alone, already the hottest in the temperature record. The Keystone XL pipeline, transporting for export some of the costliest, dirtiest petroleum in the world, is the place to stem that increase.

It's true that slowing any single fossil fuel project, even one as massive as Alberta tar sands development — rightly termed a "carbon bomb" by author Bill McKibben, so far only 3 percent exploited — will not by itself dramatically halt rising global temperatures. But eliminating the biggest fuse to that carbon bomb is a necessary first step.

The Keystone XL permit presents Obama a Rosa Parks moment. A small, seemingly inconsequential decision can influence how the entire world views the oil industry, the way a small, stubborn action on a Montgomery bus changed the nation's tolerance toward Jim Crow. Denying the Keystone XL permit will alert the world that oil no longer rules at any cost when our home planet is in peril.

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James Lenfestey is a former editorial writer with the StarTribune specializing in energy and education.