

Cows emit 135.6 million metric tons of carbon dioxide equivalent into the atmosphere each year. (photo: The Washington Post)

Frustrated with the Obama administration's foot-dragging over a decision on the Keystone XL pipeline, the Senate this week is considering legislation that would approve the pipeline by making an end-run around the White House. Since we'll be hearing an awful lot about the issue this week, it's worth reviewing exactly what is — and isn't — at stake here.

Opponents of the pipeline often discuss it in near-apocalyptic terms. "The stakes are sky-high," environmentalist Bill McKibben wrote last year. "Whether or not to build the pipeline is a decision with profound physical consequences … everything that reaches the refineries on the Gulf Coast will, sooner or later, spill into the atmosphere in the form of carbon, driving climate change to new heights."

Exactly how much carbon, though? This year the State Department finally wrapped up an exhaustive study of the project's environmental impacts. Among the top-line findings:

From extraction to refining to getting burned as gasoline in your car, oil from the Alberta tar sands "emit[s] an estimated 17 percent more [greenhouse gases] on a lifecycle basis than the average barrel of crude oil refined in the United States in 2005.

At peak capacity, about 830,000 barrels of tar sands oil would flow through the pipeline per day.

According to the Environmental Protection Agency, " The incremental emissions from oil sands crude transported by the Project would therefore be 18.7 million metric tons CO 2 -e (carbon dioxide equivalent) per year when compared to an equal amount of U.S. average crudes, based on the Project's full capacity of 830,000 barrels of oil sands crude per day."

This is the very crux of the issue — that 18.7 million metric tons of additional CO 2 -e, annually. Let's set aside, for the moment, the fact that the tar sands will get developed one way or another, regardless of whether the pipeline gets built. Let's postulate that if we build the Keystone XL pipeline, we will end up with 18.7 million more tons of CO 2 -e in the atmosphere than we would have otherwise. How do we make sense of a number like that?

We can start by putting it in the context of total U.S. CO 2 emissions. According to the Environmental Protection Agency, in 2012 the United States emitted 6.5 billion metric tons of CO 2 equivalent. This means that the annual increase from Keystone would amount to less than three-tenths of one percent of our total annual CO 2 -e emissions — 0.286546 percent, if you want to want to get precise. Here's what that looks like.

That doesn't exactly look like "sky high stakes" to me. One energy analyst equated it to "a rounding error" in a recent New York Times article looking at the effect of Keystone versus broader emissions efforts in the United States. And as I alluded to above, the tar sands are going to get developed — and those 18.7 million tons of carbon released into the atmosphere — regardless of whether Keystone gets built or not.

So, 18.7 million tons sounds like a huge number on its own, but consider that more than 10 times that much CO 2 -e gets released into the atmosphere each year from methane produced by cows. We could say that in terms of overall CO 2 -e emissions, Keystone amounts to a little over one tenth of U.S. cow flatulence.

I don't mean to trivialize global warming as an environmental issue — it is in fact a dead-serious one. But the fact that environmentalists are pouring such a tremendous amount of time and energy into such a tiny slice of the overall carbon pie shows just how low the movement has set its sights in recent years.

You could easily imagine a world in which environmentalists offer to give their blessing to Keystone in return for some modest carbon reductions elsewhere — tighter vehicle fuel-efficiency standards, cleaner coal, a cow-flatulence-reduction initiative. But that is not the world we live in.