Despite the clamorous opposition of global warming activists to the proposed Keystone XL pipeline from Canada to the U.S. Gulf Coast, a new environmental study from the State Department says the project will not make carbon pollution worse.

Other major environmental issues about the route and safety of the pipeline had already been largely settled. So the latest finding released late last week as the State Department's "final environmental assessment" of the pipeline should clear the way for overdue approval of the project by Secretary of State John Kerry - and President Barack Obama.

Unfortunately, though, the State Department says Secretary Kerry will take his time reviewing the study, despite urgent pleas for action from the Canadian government. That foot-dragging is not in the national interest.

The pipeline will bring heavy oil extracted from Canadian tar sands to the Gulf Coast for refining.

Tar sands oil creates more carbon-dioxide emissions than normal, and its transportation also involves risks of oil spills.

But if the Keystone project is not built, the oil will be extracted and shipped to refineries here or in the Far East in any event.

So the net environmental impact of denying a permit to build the pipeline is approximately zero.

The findings are a far cry from the declaration by climate change scientist and activist James Hansen that Keystone should be opposed because extracting oil from tar sands would be "game over" for the climate.

Such exaggerations have raised angst among some environmentalists, who are threatening civil disobedience if the pipeline is built.

But overstating the urgency of the case has also undermined attempts to reduce carbon emissions in a reasonable - and economically feasible - manner.

And if that oil is shipped to U.S. refineries by rail as a result, the environmental risks could rise, with rail more subject to accidents and spills than pipelines.

President Obama reportedly fears a backlash from his environmental supporters if he gives the Keystone XL project his blessing.

But as the president noted in his State of the Union address last week, the nation is already making substantial progress toward lower carbon emissions by substituting natural gas for coal in electrical power generation - and can make further progress by using non-polluting renewable sources to generate electricity.

Approving the Keystone XL pipeline will not set back that progress.

But it will reduce the nation's vulnerability to political oil shocks from OPEC and add to the nation's economic output.

The Obama administration should finally give the project a green light.