In 1858, the 18 families who founded my church, Plymouth Congregational in Minneapolis, fired their first minister for not taking a strong enough stand against slavery. Think about that. What possible difference could a few families in a frontier town on the edge of the prairie make in the way half the country did its work: human slavery? Yet seven years later, slavery ended in the U.S.

President Obama's decision on Friday to deny a federal permit for the construction of TransCanada Corp.'s Keystone XL pipeline seems similarly mystifying to many. What's the big deal? The nation is already webbed with oil and gas pipelines. Oil imports from Canada are at an all-time high. Particularly worrying in Minnesota, the rail system is burdened with a growing number of possibly dangerous oil tanker cars — a point reinforced by the recent derailment of ethanol cars near Alma, Wis. Pipelines are generally safer.

But railroads have many uses over time, whereas oil pipelines have only one. When world governments conclude, as they will in less than a month in Paris, that the 150-year hegemony of fossil fuels must end — the modern version of how much of the world does its work — Keystone instantly becomes an anachronism.

Keystone would not, as Obama noted, have any noticeable economic benefit to the U.S., and probably would have a negative impact, since it could actually increase domestic gasoline prices (by opening the glut of oil from Canada and the Bakken now flooding the U.S. market to higher-priced overseas markets).

In the end, the decision was indeed symbolic. This is the first of what must be many decisions not to build permanent infrastructure that serves only fossil-fuel extraction and distribution. Many more difficult decisions lie ahead, from preventing expansion of other cross-border pipelines, stopping coal exports, retiring coal-fired power plants and responding if the Saudis drive up oil prices again.

But when one understands the extremely troubling facts of our dangerously changing climate, which could in the foreseeable future render portions of our own country uninhabitable, coastal cities flooded and the ocean food web damaged beyond repair, one recognizes that — like slavery — it is time to end the era of fossil fuels. Tough decisions need to be made, beginning now, to keep the remaining fossil fuels in the ground.

When hitting your head with a hammer, the first step is to stop hitting. That means stopping new fossil-energy infrastructure and accelerating the transition to the next energy revolution based upon safe, noncarbon renewables and nuclear power.

Obama got it exactly right: It is time to "protect the one planet we've got while we still can. … Not later, not someday; right here, right now."

Finally, Obama's decision could actually save TransCanada's investors money in the end. Because, soon, all investments in tar sands and other oil must become stranded investments, as the Earth turns inevitably toward nonfossil energy — just as America began to turn away from human slavery in Minnesota 157 years ago.

James P. Lenfestey is a former editorial writer for the Star Tribune focusing on energy and education.