International environmental groups today released two reports detailing the likely climate costs of the proposed Keystone XL oil pipeline in a last-minute attempt to persuade the Obama administration not to approve it.

Their pitch: Building the proposed pipeline to carry 830,000 barrels of Canadian oil sands oil a day to U.S. refineries will ensure the expansion of some of the highest-carbon fuels now in use while delaying a switch to more climate-friendly alternatives.

"This pipeline is not about a pipeline," Danielle Droitsch, Canada Project director for the Natural Resources Defense Council, said at an unveiling of the reports today at the National Press Club in Washington, D.C. "This is about tar sands development. This is about climate."

A paper released by Oil Change International, an anti-fossil-fuels activist group based in Washington, found that the State Department in its assessment of the proposed pipeline had not considered carbon emissions from U.S. refineries burning petroleum coke from oil sands. The agency had thereby underestimated the greenhouse gas effects of the fuel that would be transported through the pipeline by about 13 percent, the study concludes.

The Canada-based Pembina Institute's report looked at the effect the pipeline would have on the expansion of oil sands development in Canada. The industry already produces 1.8 million barrels a day but is set to produce upward of 5 million a day by 2030, Nathan Lemphers of Pembina told reporters at today's event.

The reports were touted by advocates and lawmakers who hope President Obama will reject a revised proposal for Keystone XL in the next few months. Rep. Henry Waxman (D-Calif.) said in a statement that the reports showed Keystone "is the key that will unlock the tar sands."

"If the pipeline is approved, the world will face millions more tons of carbon pollution each year for decades to come," said Waxman, who serves as top Democrat on the House Energy and Commerce Committee. "After Hurricane Sandy, devastating drought, unprecedented wildfires, and the warmest year on record in the United States, we know that climate change is happening now, we have to fight it now, and we must say no to this pollution pipeline now."

Droitsch said the pipeline decision has become a "primary focus" of environmental and climate change activists.

"The pressure is being felt by the president," she said.

Droitsch noted that the Obama administration had committed to consider all the environmental effects of building the pipeline, and said she therefore expects that the supplemental environmental impact statement being prepared by the State Department will take into account the effects not only of transporting the fuel, but of encouraging its production.

"We don't view this as an inevitable approval," she said, adding that whatever the president decides on Keystone XL, it will go down as part of his legacy on climate change.

Speakers agreed that if the pipeline goes forward, it will serve as a powerful market signal encouraging the oil sands industry to expand. That, in turn, would make it very difficult for the world to keep its postindustrial temperature rise to under 2 degrees Celsius, the threshold at which scientists say the worst effects of climate change can still be avoided.

This is especially true, they said, given the current political situation in Canada, where the Conservative government is allied with the oil sands industry and has taken steps to dismantle environmental rules it views as onerous.

"Because Canada does not have a credible plan for responsibly developing the oil sands, including reducing emissions so Canada can meet its climate commitments, the pipeline should not go ahead," said Lemphers. He touted the need for Canada to promulgate a new greenhouse gas rule for oil and gas production, or to price carbon emissions more broadly.