A State Department review came out last week, allowing the TransCanada Keystone XL tar sands oil pipeline to clear a key environmental hurdle and sending the project to a 30-day comment period and a review by the secretary of state and other federal agencies. Critics of the 1,179-mile pipeline have vowed to continue the fight against the project.

But while stopping Keystone would benefit the environment on the whole, it isn’t critical to reining in the greenhouse gas emissions that cause climate change.

The more effective tool would be a tough federal rule now in the works that would cut carbon emissions from existing power plants, the nation’s largest source of greenhouse gases. Mainers concerned about the environment should track efforts to craft more stringent carbon standards as closely as the movement to stop the pipeline.

The State Department acknowledges that tar sands-derived oil generates about 17 percent more greenhouse gases than traditional crude. But the agency assumes that Canadian tar sands would be developed regardless of what the United States does. If Keystone isn’t built, the report says, the tar sands oil would be transported by methods that would release more greenhouse gases than a pipeline. So Keystone wouldn’t have a “significant” effect on emissions, whether it’s approved or not, the report says.

That said, there are solid reasons to be concerned about a tar sands oil pipeline. The State Department report suggests spills are inevitable along the Keystone route; Cornell University researchers found that spills are more frequent along pipelines carrying tar sands oil than along pipelines carrying conventional crude. A convincing argument against pipelines, then, can be made based on the potential risks they pose to surrounding communities’ air, water and soil, as the tar sands oil moratorium effort in South Portland has shown.

A 2013 survey of studies by the Congressional Research Service – Congress’ nonpartisan research arm – found that the pipeline would add the equivalent of 0.06 percent to 0.3 percent of U.S. greenhouse gas emissions each year. So there’s a benefit to stopping Keystone, but it’s relatively small.

Meanwhile, federal regulators are scrambling to meet a deadline for creating a rule that, ideally, would have a much bigger impact. The Environmental Protection Agency has until June to submit draft carbon dioxide emissions standards for the 1,500 existing U.S. power plants – the source of about 40 percent of the potent greenhouse gas. Maine stands to benefit from these standards, as we’re on the receiving end of a lot of pollution from Rust Belt plants, particularly coal-fired ones, lowering our air quality, causing asthma and aggravating cases of lung and heart disease.

The anti-Keystone movement has compelled a great deal of attention, but the more meaningful action is taking place in conference rooms where EPA lawyers, economists and engineers are hashing out regulatory details. If the latter drive doesn’t succeed, the former one won’t mean much.