A long-anticipated Senate hearing on the Keystone XL pipeline today became a climate science showdown as a senior Democrat challenged the U.S. Chamber of Commerce's representative to explain her group's stance on humans' role in global warming.

Senate Foreign Relations Chairman Robert Menendez (D-N.J.) repeatedly asked Karen Harbert, president of the chamber's Institute for 21st Century Energy, to position herself on human-caused climate change after she testified before his panel that environmentalists ought to support KXL, given the smaller carbon footprint of oil pipelines relative to crude-by-rail.

Harbert declined to answer directly, telling Menendez that "we believe we should be doing everything within our power to address the environment" before agreeing that "the climate is warming, without a doubt."

When pressed by Menendez on whether man-made emissions are propelling climatic change, she replied: "It is caused by lots of different things. You can't say climate change is only caused by humans."

Most major scientific reports, such as the recent joint analysis by the U.S. National Academy of Sciences and the U.K. Royal Society, have pointed to humans as the major factor behind climate change. Anti-KXL environmental groups have seized on the pipeline's 700,000-plus barrels of carbon-intensive Canadian oil sands crude as a bellwether of the Obama administration's commitment to slowing the impact of greenhouse gases.


"No one said it was all man-made," veteran climatologist James Hansen, formerly of NASA, told Sen. Ron Johnson (R-Wis.) during another combative interlude about climate science. "However, the man-made effect is now dominant."

Today's Foreign Relations hearing became acrimonious even before Menendez gaveled it to a start. Green activists at Friends of the Earth pressed retired Gen. James Jones to state whether the chamber and the American Petroleum Institute are paying him to provide counsel on KXL and other issues in advance of the former Obama national security adviser's pro-pipeline testimony before the panel.

Yet Menendez began his questions by prodding Sierra Club chief Michael Brune to justify the merits of reining in carbon emissions by rejecting KXL, suggesting the senator's skepticism of pipeline critics matches the skepticism he showed toward pipeline supporters. When Harbert declared that "I don't agree" that her business lobby group "lacks a compass on the environment," the senator countered that "I did not say that the U.S. Chamber lacked a compass."

The committee's top Republican, Sen. Bob Corker of Tennessee, sought to lower the room's figurative temperature during his turn to question Hansen, praising the iconic green activist's support for nuclear power expansion as a carbon-free method of power generation.

"And I thought it was going to be contentious on our side of the aisle," Corker quipped, also aligning with Hansen on the merits of climate action via a carbon tax rather than a cap-and-trade system.

Brune responded by offering to work with the Republican on such a tax.

"I wasn't suggesting that, necessarily," Corker replied.

As Menendez's panel convened its hearing, Secretary of State John Kerry was telling his former colleagues in the upper chamber that he would take a "tabula rasa" approach to his national interest review of KXL -- now underway with no required timeline for completion -- following the largely pro-pipeline environmental review that Foggy Bottom released earlier this year.