It has been a busy week for the much-delayed Keystone XL oil pipeline. The proposed project, intended to carry heavy crude oil from Canada’s Alberta tar sands to refineries along the U.S. Gulf Coast, won approval on Tuesday from Nebraska Gov. Dave Heineman, after its planned route had been adjusted to address environmental concerns. The following day, 53 senators signed a letter to President Obama urging speedy federal approval. “There’s no reason to deny or further delay this long-studied project,” the senators said.

Let’s hope the president listens. It was also this week that the State Department, which is reviewing the TransCanada Corp. project, announced that it would not reveal its findings until the spring. The department had previously promised an announcement by the end of March.

Environmentalists, who in the past have had Mr. Obama’s ear, continue to voice strong opposition to the Keystone XL project. An anti-pipeline rally is being organized for next month in Washington, D.C.

But the arguments against the pipeline have all but evaporated. The route now largely bypasses the most ecologically sensitive regions. The overall contribution of its activity to global warming is too small to measure. It is time for the project to move forward.

According to the State Department, which has final say because the pipeline crosses the border with Canada, the project must be determined to be “in the national interest.” The department defines that as projects that “facilitate the efficient movement of legitimate goods and travelers across U.S. borders” so long as they are within “the context of appropriate border security, safety, health, and environmental requirements.”

The Keystone XL pipeline, as it is now proposed, certainly meets all of these criteria. The new route, which bypasses the environmentally fragile Sand Hills region of Nebraska, was approved after a report this month by the Nebraska Department of Environmental Quality determined that it will have “minimal environmental impacts” if properly managed.

A study last year by the Congressional Research Service found that the greenhouse-gas emissions from energy produced from Canadian tar-sands oil delivered by the pipeline would increase U.S. annual greenhouse gas emissions by a paltry 0.06%-0.3%. These additional emissions have virtually no impact on the rate of global warming, increasing it by an infinitesimal 0.00001 degrees Celsius per year. This amount is too small to detect, much less to worry about.

The last and perhaps most desperate argument from opponents is that the pipeline will demonstrate the viability of the Canadian tar-sands deposits and unleash an oil rush that will ultimately result in sufficient greenhouse-gas emissions to push global warming beyond some critical limit. This is nonsense.

Any such limit is simply a human construct — the more pessimistic you are, the less global warming you’re willing to tolerate. But everyone can take comfort in new scientific research that revises down the future warming for each unit increase in greenhouse-gas emissions. This means that current estimates of how much warming is locked up in the Canadian tar sands is exaggerated.

Neither are the benefits of tar sands an unproven secret that the Keystone XL pipeline will reveal. The Canadian tar sands — sandy deposits with oil in them — are already an important global oil resource. Production has tripled since the mid-1990s, with most of the oil exported to the U.S. through a network of existing cross-border pipelines.

Keystone XL’s sister pipeline, simply known as Keystone, started delivering oil in 2010 to refineries in Illinois. There are a number of proposals in Canada to develop routes to deliver the tar-sands oil to burgeoning markets in Asia.

The expansion of tar-sands development will happen with or without the approval of Keystone XL. A likely consequence of U.S. rejection of the pipeline would be acceleration of the establishment of an Asian outlet.

Opponents are trying to cast the Keystone XL pipeline as a symbol of the type of energy development that the president — with his newly dusted-off promise for action on climate change — must act to stop. But the symbol we need is of leadership and presidential approval of the pipeline — a sign that substance, rather than style, underlies determinations of “the national interest.”