As many critics have predicted, President Barack Obama on Friday announced that he has rejected the request to expand the Keystone oil pipeline with a second international crossing. The move has been a flash point for critics from the right and left. Mr. Obama’s denial of the proposed pipeline comes as he is seeking to build an ambitious legacy on climate change and comes just ahead of a major UN summit meeting on climate change in Paris in December, when Mr. Obama hopes to help broker a historic agreement committing the world’s nations to enacting new policies to counter global warming.

While the rejection of the pipeline is largely symbolic, Mr. Obama has sought to telegraph to other world leaders that the United States is serious about acting on climate change.

The rejection of a single oil infrastructure project will have little impact on efforts to reduce greenhouse gas pollution, but the pipeline plan gained an outsize profile after environmental activists spent four years marching and rallying against it in front of the White House and across the country.

In announcing the decision (see video) President Obama said the pipeline would not make a meaningful long-term contribution to the economy, would not lower gas prices, and would not enhance energy security.