After seven years of debate, the Keystone XL pipeline saga may finally be over.

President Obama announced Friday that he has rejected the proposal, arguing not only that it wouldn't be in the country's best interest, but that it would get in the way of U.S. efforts to rally global support in the struggle against climate change.

"America is now a global leader when it comes to taking serious action to fight climate change, and frankly approving this project would have undercut that leadership," Obama said in a noon press conference.

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First proposed in 2008, the pipeline would have snaked 1,179 miles through North America, linking oil sands in Alberta with refineries and shipping ports on the Texas Coast. It needed approval from the U.S. State Department because it would cross an international border, and on Friday morning Secretary of State John Kerry reported to President Obama that he has determined the project is not in the country's best interest. "I agree with that decision," Obama told reporters.

Supporters argued it would provide an economic boost by creating jobs, although there has been ample debate over how many. TransCanada, the company behind the proposal, has suggested Keystone XL would create 9,000 jobs, while some advocates in the U.S. Congress went even further — Sen. John Barrasso of Wyoming, for one, said earlier this year it would create "42,000 new jobs."

This is murky because some of those jobs aren't really new, and few of them would be permanent. Many critics of the pipeline, like Sen. Chuck Schumer of New York, have argued it would only create a few thousand temporary construction jobs and 35 permanent jobs. The exact number of jobs linked to the project remains debatable, but most experts agree its effect on the U.S. economy would be minimal.

Obama echoed that sentiment Friday, saying the pipeline "would not make a meaningful long-term contribution to our economy" and "would not lower gas prices for American consumers," as some proponents claim. Plus, he added, "shipping dirtier crude oil into our country would not increase America's energy security."

Keystone XL protestProtestors rally against the Keystone XL pipeline in February 2014. (Photo: Steven Lyons/Flickr)

But Keystone XL wasn't rejected just because its economic impact would be too small. The question was whether any economic boost might outweigh the known risks, including the possibility of a spill as well as the long-term commitment to a carbon-heavy fuel source that contributes to climate change. It would have carried not just any oil, but petroleum from Canada's controversial oil sands, the extraction of which produces about 17 percent more greenhouse gases than conventional oil.

Obama rejected Keystone XL once before, in January 2012, although that was prompted by what he called an "arbitrary" deadline set by Congress in an effort to force his hand. The State Department essentially invited TransCanada to submit a new proposal afterward, which it did, and that's the proposal Obama finally rejected Friday. While Obama said at the time his 2012 rejection was "not a judgment on the merits of the pipeline," Friday's announcement sounded very much like it was.

The move drew widespread praise from environmental activists, especially because of the tone it sets ahead of next month's blockbuster climate talks being held in Paris.

"By saying no to the Keystone XL pipeline, the president is demonstrating our nation's leadership on climate action in advance of the international climate negotiations in Paris this December, providing an important boost of momentum," says Sierra Club director Michael Brune. "He is also making good on his promise that the nation will leave dirty fossil fuels in the ground, replacing it with clean energy. Stopping the Keystone XL pipeline is a victory for the planet, for the health and well-being of the communities along the pipeline route, and for future generations to come."

While environmental advocates are cheering the news, many also acknowledge this may not be the final word on Keystone XL. A future president could invite TransCanada to submit a new proposal, and several Republican candidates have made clear they intend to do so, such as Florida Sen. Marco Rubio:

And even if Keystone XL is never built, that won't necessarily mean crude from Canada's oil sands will stay in the ground. The region's oil is already being transported by rail, although the safety of oil trains has been increasingly doubted in recent years amid a series of deadly accidents. Plus, as U.S. officials have noted, moving oil by train is more expensive than pumping it via pipeline, and recent drops in oil prices could curb demand for oil sands if rail remains the best option.

For now, the coalition of activists who spent years fighting Keystone XL are taking a moment to bask in their success. On top of conveying broad opposition to this pipeline, they say they've awakened a latent zeal for environmental issues in American politics. And while those issues are always important, the growing threat of climate change is now raising the stakes to unprecedented heights.

"This is a historic moment, not just for what it means about avoiding the impacts of this disastrous pipeline but for all of those who spoke out for a healthy, livable climate and energy policies that put people and wildlife ahead of pollution and profits," says Valerie Love, a campaigner with the Center for Biological Diversity, in a statement. "President Obama did the right thing, but he didn't do it alone. Millions of Americans made their voices heard, and we'll keep pushing Obama and other political leaders to do what's necessary to avoid climate catastrophe."

Russell McLendon ( @russmclendon ) writes about humans and other wildlife.