BRUNSWICK — Sometimes history is made in our own backyard. That’s happening with South Portland’s fight to block Canadian tar sands, a thick and heavy sludge with major environmental impacts.

The South Portland rebellion began with a ballot referendum and the city’s 2014 Clear Skies Ordinance. The ordinance bans the export of tar sands through South Portland’s harbor, including the installation of two 70-foot combustion stacks to burn off toxic chemicals that help the sludge flow by pipeline. The ordinance also protects Maine, New Hampshire and Vermont from the consequences of a tar sands spill, a risk given the aging 76-year-old Montreal-Portland pipeline. A few weeks ago, a relatively new pipeline failed in South Dakota, spilling 210,000 gallons of tar sands. When it happens, cleanup is expensive; it took over four years and a billion dollars to dredge up the 843,000 gallons of tar sands that burst into Michigan’s Kalamazoo River in 2010.

It’s easy to feel nostalgic about the early days of the Portland Pipe Line Corp. Its pipeline was built during World War II to provide Canada with a safe and efficient means of obtaining critical oil. But Canada has grown into the world’s fourth largest oil exporter. Now the aim is simply to move inland tar sands to ocean tankers bound for international markets. It’s a familiar story – the public bears the climate, environmental and health costs while the big oil companies reap the profits.

The Alberta tar sands aren’t the first time that big energy interests have overreached without environmental due diligence. The Sierra Club battled in the 1960s to stop federal construction of two hydroelectric dams in the heart of the Grand Canyon. These dams would have spoiled the world’s greatest natural cathedral and the raging Colorado River, a symbol of the American West. In 1977, the public protest of nuclear power at Seabrook, New Hampshire, sounded the alarm on President Nixon’s plan to build 1,000 nuclear power plants in the U.S., a tenfold expansion. This resistance helped the country avert more environmental nightmares like Three Mile Island as well as an economic cliff. Indeed, the nation’s largest nuclear plant builder, Westinghouse, just exited the nuclear construction business, declaring bankruptcy in the face of a $10 billion overrun and six-year delay on a Georgia project.

Hindsight is 20/20, but the future is not. That’s why the people of South Portland deserve so much credit for their salient warning about Portland Pipe Line’s misguided proposal.

As the fight has moved from City Hall to the courtroom, we’ve learned that the pipeline reversal project is not economically viable, compounded further by renewed interest in the Keystone XL pipeline, the preferred southern route from Alberta to the Texas coast.

Portland Pipe Line pleaded in court that its financial survival depends on Canadian tar sands. It raises the question: Why is the company putting all of its eggs in one basket and failing to diversify? And why should South Portland and Maine bear the burden of a static company that can’t adjust to emerging markets, including natural gas and renewables?

For constitutional reasons, the case has taken on a life of its own. Portland Pipe Line’s owners, ExxonMobil, Shell and Suncor Energy, can’t let South Portland’s challenge succeed because it would set a precedent favoring home rule and limiting federal pre-emption under the U.S. supremacy clause concerning interstate commerce. A local victory could help communities everywhere defend the health and welfare of citizens and land use decision-making.

A South Portland victory also would send a broader environmental message: that multinational oil companies can no longer escape responsibility for the air pollution and climate change they cause. That would be a powerful market signal to energy investors about the shifting value of cleaner energy sources and technology.

South Portland’s Master Plan envisions a future of vibrant residential neighborhoods, tourism, education, commerce and recreational opportunities. Its success in achieving the vision was recently recognized by National Geographic, which ranked Portland-South Portland among the 25 “happiest” and most livable places in the country.

Why would the business community and residents of South Portland trade such incredible branding by letting the oil companies turn the city into the tar sands capital of the U.S.?

The citizens and elected leaders of South Portland deserve enormous credit for standing up and demonstrating extraordinary political courage. They’re taking on Big Oil, Portland Pipe Line, Canada and Uncle Sam. As Margaret Mead said, “Never doubt that a small group of thoughtful, committed citizens can change the world; indeed, it’s the only thing that ever has.”