WASHINGTON – Environmental advocates told a Senate panel that approval of the Keystone XL pipeline would be “catastrophic,” while supporters argued that energy independence is especially critical as Russia wields a heavier hand in the world.

Lawmakers on the Senate Foreign Relations Committee mainly rehashed many of the same political arguments on the issue. Democrats mostly expressed opinions opposing the pipeline, while Republicans argued the case for building the pipeline is, as Sen. Bob Corker (R-Tenn.) put it, “clear and compelling.”

The proposed 875-mile pipeline would link Morgan, Mont., at the Canadian border to Steele City, Neb., and ultimately link up with other pipelines that would carry the oil from the tar sands of Alberta, Canada, to refineries on the Gulf Coast. It would have a capacity of 830,000 barrels of crude oil from Canada and the Bakken Shale formation in North Dakota and Montana.

Veteran climatologist James Hansen, formerly of NASA’s Goddard Institute for Space Studies, called tar sands the world’s “dirtiest fuel” and said that Keystone would drive further development of the tar sands in Canada.

Michael Brune, executive director of the Sierra Club, said that transporting tar sand oils by rail or through pipelines is not safe, noting that any spill would be “catastrophic.”

“The Keystone XL tar sands pipeline would cut through more than a thousand miles of American farms and ranches, carrying oil that is more toxic, corrosive, difficult to clean up, and more carbon intensive all the way to the Gulf, where most of the oil would be exported,” he said.

Brune cited research by the Intergovernmental Panel on Climate Change (IPCC), advising that in order to keep global warming below 3.6 degrees Fahrenheit the world should not tap into fossil fuel reserves underground, particularly the most carbon-intensive fuel sources, such as the tar sands in Canada.

“The choice is not whether to accept increased risk through rail…or pipeline, but whether to take this oil out of the ground to begin with,” he said.

Supporters of Keystone testifying before the committee framed their national interest argument around energy security and economic opportunity.

Ret. Marine Corps Gen. James L. Jones, president of the Jones Group International, said the energy abundance in Mexico and Canada provides North America with the opportunity to become an “energy hub.”

Jones said the pipeline approval decision would be “a litmus test of whether the United States is serious about national and energy security.”

“Why would the United States spend billions of dollars and place our military personnel at risk to ensure the flow of energy half a world away, but neglect an opportunity to enable the flow of energy in our very own back yard — creating jobs, tax revenue, and greater security?” he said.

Jones said that approving the pipeline would send a message to Russian President Vladimir Putin and other “international bullies” that they cannot use energy security as a weapon.

“Energy scarcity is a potent strategic weapon. The greater the gap between global supply and demand, the more destructive the weapons will become,” Jones said. “If we want to make Mr. Putin’s day and strengthen his hand, we should reject the Keystone. If we want to gain an important measure of national energy security, jobs, tax revenue, and prosperity to advance our work on the spectrum of energy solutions that don’t rely on carbon, it should be approved.”

Karen Harbert, president and CEO of the U.S. Chamber of Commerce’s Institute for 21st Century Energy, said “energy vulnerability equals geopolitical vulnerability” and the question was whether the U.S. will get oil from Canada or other countries that “don’t share our democratic values and principles.”

After committee Chairman Sen. Robert Menendez (D-N.J.) repeatedly pressed Harbert on whether the Chamber of Commerce believes man-made emissions are driving climate change, she replied, “We believe we should be doing everything within our power to address the environment” before agreeing that “the climate is warming, without a doubt.”

She added that climate change is caused by “lots of different things and you cannot say it’s only caused by humans.”

“We have a robust debate going on in this country, as we should, and those that say everything is settled undercut the integrity of science,” she said. “This is an ongoing discussion.”

Hansen told Sen. Ron Johnson (R-Wis.) during another heated exchange about climate change that “no one said it was all man-made.”

“However, the man-made effect is now dominant,” Hansen added.

Johnson, though, said “the science is far from settled.”

The State Department will determine whether the proposed project is in the national interest. The State Department’s review of Keystone’s environmental impact includes whether the pipeline would lead to more carbon-dioxide emissions.

State Secretary John Kerry told a Senate Appropriations subcommittee Thursday that the evaluation should wrap up in 60 days if it continues without delay. Kerry, a longtime environmental advocate, said that he would approach the issue with a clean slate.

“I’m not at liberty to go into my thinking at this point,” he said. “It’s just not appropriate, except to say to you that I am approaching this, you know, tabula rasa. I’m going to look at all the arguments, both sides, all sides, whatever, evaluate them and make the best judgment I can about what is in the national interest.”