President Barack Obama’s decision to delay a decision on the Keystone Pipeline is a short-term victory for environmentalists. The long-term prospects are murkier.

Until a few months ago, the pipeline seemed on track for approval. The late intervention of environmentalists who woke up to the potential damage from significantly increased development of the Alberta tar sands changed the picture.

The noted environmentalist Bill McKibben’s description of Keystone as “a 1,700-mile fuse to the biggest carbon bomb on the continent” crystallized the concern that approval would have accelerated the transition to climate instability from the greenhouse effect.

Police arrested thousands of protesters, who changed the political dynamic and focused new attention on the risks associated with the pipeline. Combined with Republican-led concerns about contamination from pipeline leaks in the Nebraska Sand Hills, and possible conflicts of interest in the State Department’s handling of the permit, the late surge succeeded in blocking approval, at least for the time being.

Environmentalists showed that they can still muster passion effectively when the chips are down. The Keystone builder has already committed to changing the route in Nebraska. The State Department will be conducting a fresh environmental review.

Tar sands oil, which would supply the pipeline, represents the endgame for oil production.

Over the past century, we’ve depleted the high-quality, easily accessible oil reserves. What remains are petroleum deposits that require ever more energy to extract and deliver. For the bitumen fields of Alberta this means expending about one-third the amount of energy yield just to get the oil into the pipeline. That makes Alberta oil the dirtiest, most polluting choice currently available.

While environmentalists have won this round, a long-term victory will be more elusive.

First, the president’s decision is only a delay. He or his successor could approve the pipeline in the next couple of years.

Second, stopping energy infrastructure projects because of local objections could thwart long-term improvements to the nation’s electric grid and other investments needed to shift to low-carbon forms of energy.

Third, and most important, a long-term environmental victory will require building on momentum created by the pipeline opposition. The delay provides just a bit more breathing room for a transition to low-carbon energy.

If the United States turns to coal or more oil to substitute for the bitumen that would have flowed from Alberta, then there is no victory. If the Alberta tar sands producers find another way to get comparable quantities of bitumen to market, say through a pipeline to the Pacific, then the carbon bomb has found another fuse. Killing the pipeline is only a victory if it is part of a larger strategy to transform the energy economy away from intensive carbon consumption.

Shifting away from fossil-fuel dependence will require ending carbon subsidies and increasing the price of coal, oil and gas to reflect their true costs.

Unfortunately, that requires some heavy political lifting that environmentalists and the president cannot do on their own. Stopping one pipeline is much easier than building a new framework for energy policy.

Eventually, humans will stop pumping carbon into the atmosphere as remaining fossil fuels become ever more difficult and expensive to extract. However, the sooner we transition away from carbon-based energy, the lesser the damage we will inflict on ourselves and our children through climate change.

A 2011 National Academies of Sciences report finds that the total warming of the atmosphere, and consequent instability of climate, is directly proportional to the carbon we emit. And that level of warming will persist for many hundreds of years.

Perhaps President Obama’s drawing of a line in Alberta’s oil sand will help us avoid that bleakest of all possible futures.

• Fischman is professor and faculty fellow at the Indiana University Maurer School of Law and adjunct professor at the Indiana University School of Public and Environmental Affairs.