Pipes for Transcanada Corp.'s planned Keystone XL oil pipeline are stacked at a depot in Gascoyne, N.D. The House of Representatives approved the Keystone XL pipeline Friday; the Senate voted against it on Tuesday. Andrew Cullen/Reuters/Landov hide caption

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GOP Rep. Bill Cassidy and Democratic Sen. Mary Landrieu face off in a Dec. 6 Senate runoff. Both are pushing for legislation approving the remaining leg of the Keystone XL pipeline between Alberta, Canada, and Steele City, Neb. Gerald Herbert/AP hide caption

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Pipes for TransCanada's planned Keystone XL pipeline are stored in Gascoyne, N.D. The U.S. House has voted to approve the proposed project, which would allow crude oil to flow from Canada to the Gulf of Mexico. The Senate plans to vote Tuesday on legislation that would greenlight the project. Andrew Cullen/Reuters/Landov hide caption

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Sen. Mary Landrieu, D-La., chair of the Senate energy committee, spoke Wednesday about getting congressional approval for the Canada-to-Texas Keystone XL pipeline. With her is Sen. Joe Manchin, D-W.Va., a member of the committee. J. Scott Applewhite/AP hide caption

itoggle caption J. Scott Applewhite/AP

Democratic U.S. Sen. Mary Landrieu of Louisiana walks through the U.S. Capitol on Wednesday. Congress returned to work following last week's midterm elections break. Landrieu is locked in a runoff with Republican Rep. Bill Cassidy. Mark Wilson/Getty Images hide caption

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Beacon Power President and CEO Barry Brits, at the company's plant in Hazle Township, Pa. He says a loan from the Department of Energy made it possible for his company to develop its flywheel energy storage technology. Jeff Brady/NPR hide caption

itoggle caption Jeff Brady/NPR

Chinese President Xi Jinping and President Obama, seen here during a ceremony at the Great Hall of the People in Beijing, announced pledges to reduce greenhouse gases. HUANG JINGWEN/Xinhua /Landov hide caption

itoggle caption HUANG JINGWEN/Xinhua /Landov