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Environmental activists, who have pushed Congress to put a price on carbon, as cap-and-trade would have done, they also now realize that such ends can only come from Mr. Obama’s executive power.

“The most efficient way [to cut greenhouse gas emissions and fight climate change] is to put a price on carbon, but there’s no prospect of Congress taking serious action anytime soon, and the president is right to move forward with the regulatory tools at his disposal,” said Eileen Claussen, president of the Center for Climate and Energy Solutions.

The president also lauded the American natural gas boom, primarily due to the perfection of the drilling technique known as fracking, despite opposition from many in his liberal base.

The rise of natural gas, and the fact that it gradually is displacing coal at power plants across the nation, carbon emissions in the U.S. have fallen dramatically in recent years, even without major climate-change legislation.

“If extracted safely, [natural gas] is the bridge fuel that can power our economy with less of the carbon pollution that causes climate change,” Mr. Obama said.