As the Winter Olympics gear up and athletes tear through snow and ice in their various sports, our minds may not be on climate change. Many have found it strange to read reports of no snow in Vancouver, but we know that because of global warming, future winter Olympic gatherings may never be the same.

Unfortunately, as the excitement of the winter games builds in Canada, that country is also pursuing an energy policy that could have a huge impact on winter sports by accelerating global warming—and the U.S. may soon start taking part.

The Canadian province of Alberta is home to a form of oil that’s considered the dirtiest on earth. It’s called “oil sands,” also known as “tar sands,” and each barrel creates three times the global warming pollution as conventional oil. In fact, oil sands are now Canada’s fastest-growing source of global warming pollution.

Now the Canadian government and the oil industry want to bring tar sands oil into the United States through a vast network of pipelines crossing through Montana, Minnesota, Nebraska, South Dakota, Kansas, Oklahoma, Wisconsin, and Texas.

And it’s not just the threat of climate change bringing less snow. To make matters worse, producing this dirty oil also requires clear-cutting giant swaths of ancient forest and excessive water usage. Producing oil this way leaves behind lakes of toxic waste so large they can be seen from space.

Some companies behind these pipelines are even asking the U.S. government to allow them to operate pipelines above maximum burst pressure and comprised of cheaper, thinner pipe in less-populated areas because potential spills would have less of an impact in these regions.

If we allow this massive project to creep across our border, it will lock America into dependence on yet another foreign source of oil, just as our local, homegrown clean energy industry is beginning to thrive. It would threaten the good, lasting American jobs that wind and solar and efficiency projects create—the kind of jobs that can’t be outsourced.

Some might say that tar sands oil is dirty, destructive, and very expensive, but it’s from our good friend and harmless neighbor to the North, so how bad can it be? And more oil is always good, right?

Wrong. Tar sands don’t enhance energy security just because they come from a friendly neighbor. Continued reliance on oil empowers those countries with the most oil, including Saudi Arabia and Iran. The best investments in energy security are investments in alternatives to oil. Fortunately, those best investments also clean up the local environment, combat global warming, and create home-grown jobs in energy efficiency and renewable energy.

We can’t seriously combat global warming—and save our winters—while getting fuel from the world’s dirtiest source. And the way toward breaking an addiction can’t be to double down on that addiction by finding ever dirtier and more expensive sources. The way to get off oil is to get off oil.

Relying on yet another dirty energy source could put an end to the winters we know and love. Unless we act now to combat climate change, future Winter Olympics could be altered dramatically—whether through using artificial snow or forcing outdoor events to compete indoors.

Americans have a chance to turn things around. Right now, we’re poised to become a leader in the global clean energy economy. One of the most important things we can do to demonstrate that leadership is say no to Canada’s oil sands.

For now, the decision rests with Hillary Clinton. As secretary of state, she must sign off on oil sands pipelines before any of Canada’s dirty oil makes it across our border. By denying these permits, Clinton can signal to the world that we’re serious about fighting global warming and helping American clean energy thrive. If she does, we just might be able to save winter and the games we love.

Carl Pope is Executive Director of the Sierra Club, America's oldest, largest and most influential grassroots environmental organization.

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