The new SEIS will be released as the State Department and the EPA are both in the midst of leadership changes. On Tuesday the Senate voted to confirm John Kerry as Secretary of State, and he could be sworn in as early as next week. EPA Administrator Lisa Jackson is expected to leave her post within the next month, and it's unclear who will succeed her.

Kerry, a five-term Massachusetts senator, is a staunch supporter of climate action. Last week, he told the Senate Foreign Relations Committee that climate change is one of the "life threatening issues" of American foreign policy, but he has not indicated whether he's inclined to approve or reject the pipeline.

According to a State Department spokeswoman, the agency has been working with the EPA on the latest SEIS. But if it turns out that the two agencies can't come to an agreement over the document, the pipeline decision could be moved from the State Department to the White House Council on Environmental Quality, said Murphy, the National Wildlife Federation attorney.

"I'm not aware of an instance where that's occurred, and my belief is there's a strong desire among the agencies to work these things out before that happens," Murphy said. "But if one agency feels strongly about their position and the lead agency is being intransigent, that's certainly something the [other] agency can do."

The EPA had suggested taking the decision to the CEQ after reviewing the State Department's first environmental report in 2010. But the EPA decided against that step when the State Department agreed to work with the EPA to resolve their differences.

Murphy's organization has spent months urging the State Department to conduct a thorough climate analysis in the new SEIS. The Keystone XL "locks us into quite a few years of increased development of tar sands, which scientists have pretty roundly said the world can't afford," he said. "This is really a good opportunity early on in [Obama's second term] to send a strong signal that he's very serious about addressing climate."

On Feb. 17, thousands of Keystone XL opponents will hold a rally in Washington, D.C. to protest the pipeline. It will be the fourth mass action of its kind since 2011, and organizers say 20,000 people have already signed up to attend.

InsideClimate News reporter Maria Gallucci contributed to this report.