A year ago, President Obama rejected a proposed pipeline to transport oil from Canada to the Gulf of Mexico. The Keystone XL pipeline is touted by oil companies as a way to expand the amount of oil that’s produced from the tar sands in Alberta, but its construction raises concerns about the environmental effects and climate change.

Now, oil company TransCanada has re-proposed the Keystone XL pipeline in two parts. The southern part was approved, and is currently under construction, but the northern part is still under review. I spoke with Susan Casey-Lefkowitz, the director of international programs for the Natural Resources Defense Council, about the project.Listen to the interview.

Casey-Lefkowitz says the oil production in the tar sands is equivalent to strip mining for oil: open pit mines that are energy and water-intensive.

“The tar sands are really the start of the oil industry going after a new form of oil that’s dirtier, it’s more expensive, it’s riskier,” she said. “It used to be considered too expensive and too difficult to get, but right now it’s sort of the new gold rush for the oil industry.”

The resulting bitumen is converted into gasoline and diesel for cars and trucks. But the companies developing the tar sands want access to deep water ports, so they can export the oil overseas. They’ve proposed pipelines to the Gulf of Mexico (the Keystone XL pipeline), as well as routes west through British Columbia and east through the Great Lakes to Portland, Maine. All of those proposals are pending, and Casey-Lefkowitz says the NRDC is seeing public opinion in the U.S. and Canada turn against the pipelines.

“People are concerned really, about two things,” she said. “They’re concerned about what an oil spill of tar sands oil would do to their rivers and aquifers and lakes. And they’re also very concerned about what encouraging expansion of this very dirty and carbon and energy-intensive form of oil will mean for climate change.”

Casey-Lefkowitz says the United States needs to find a way to eventually move off of oil. But even though oil drilling in the Middle East isn’t good for the environment either, she says the real danger of the pipeline is investing billions of dollars in new infrastructure that ties the country to oil.

“Relying on the oil that we currently have under production, but not expanding into these newer and dirtier forms of oil is something that really makes sense right now at a time when we’re trying to develop cleaner forms of energy and fight climate change,” she said.