Falling oil prices have energized opponents of the proposed Keystone XL pipeline. U.S. benchmark crude has tumbled 10 percent this month, closing at $81.01 a barrel in New York trading last week, and further declines are forecast. At $75, a government analysis said producers may be discouraged from developing Canada ’s oil sands without pipelines like Keystone. “It changes the narrative quite a bit,” Anthony Swift, an international lawyer at the Natural Resources Defense Council in Washington , said of the tumble in crude prices. The pace of oil-sands production is key in the debate over Keystone, a Canada-to-U.S. line TransCanada Corp. (TRP) proposed in September 2008 when oil was more than $100 a barrel. Environmentalists oppose developing oil sands because the process releases more greenhouse gases than other types of crude. President Barack Obama has said he won’t approve the $10 billion project if it would significantly exacerbate […]