The company building the pipeline, TransCanada, boasts a much sunnier job growth number. They claimed the extension would create "about 20,000 construction and manufacturing jobs" and "generate more than $585 million in new taxes for states and communities along the pipeline route."
Opponents criticized the pipeline because oil from Canada's oil sands region produces between 5 to 30 percent more greenhouse gases than other types of crude.
NASA climate scientist James Hansen painted a dire picture of what tar sands oil means to the climate change battle, describing the pipeline as a "carbon bomb."
"If the tar sands are thrown into the mix, it is essentially game over," Hansen told Reuters. "The principal requirement is that coal emissions must be phased out by 2030 and unconventional fossil fuels, such as tar sands, must be left in the ground."
Extracting the oil sands also uses massive amounts of water and can result in deforestation.
"Tar sands extraction in Canada destroys Boreal forests and wetlands, causes high levels of greenhouse gas pollution and leaves behind immense lakes of toxic waste," noted the National Resources Defense Council.
Supporters claim the pipeline will carry 830,000 barrels a day of oil from Alberta, Canada, to the U.S. Gulf Coast.
American Petroleum Institute spokeswoman Sabrina Fang suggested Keystone XL would "help reduce our dependence on oil from less stable parts of the world."
This assumption is erroneous, opponents stated.
They pointed out that tar sands oil will not necessarily be available for sale in the U.S. It will go to the U.S. Gulf Coast for refining and shipping purposes and then wherever the market demand is greatest.
Activist organization Oil Change International reports energy company Valero "has locked in at least 20 percent of the pipeline's capacity" in accordance with its stated export strategy, and "because its refinery in Port Arthur is within a Foreign Trade Zone, the company will accomplish its export strategy tax free."
Pipeline supporters still tout energy independence as a pressing reason to approve the pipeline.
TransCanada disputed the danger of spills, saying Keystone will "be the newest, strongest and most advanced pipeline in operation in North America" and will use pipe that meets or exceeds U.S. Department of Transportation standards.
It was the spill concern that derailed the project in 2011. The pipeline's original route had it going over Nebraska's environmentally sensitive Sand Hills region, and many state lawmakers opposed it. The concerns allowed Obama to delay his decision, especially as it became a hot-button election issue.
Nebraska's government approved the revised pipeline plan through its state earlier this year.
Supporters of the pipeline pointed out that pipelines already crisscross the nation. More than 2.3 million miles of pipelines existed in 2003 in the U.S., moving natural gas and hazardous materials like petroleum and chemicals, according to the U.S Department of Transportation Pipeline and Hazardous Materials Safety Administration.
Different U.S. government agencies are conflicted about the environmental impact of the Keystone XL.
On March 1, a draft environmental review by the State Department raised no major objections to the pipeline and said other options for transporting the tar sands pose greater climate change danger. Because it is an international project, the State Department is the agency involved in the permitting process.
The State Department's review, which fell short of recommending approval, was criticized by the Environmental Protection Agency in May. The EPA stated the State Department hasn't done a sufficient job of studying the pipeline's environmental impact.
The State Department's study also is based on the assumption that the tar sands would still be exploited if the pipeline falls through, an assumption that some consider debatable.
Even though the final decision has not been made, TransCanada is already seizing land via eminent domain in the pipeline route and starting work on the sites, causing legal skirmishes and acts of civil disobedience.