Story highlights Obama will designate the Northeast Canyons and Seamounts Marine National Monument on Thursday

It will protect 4,913 square miles of ocean from commercial activity and development

Washington (CNN) President Barack Obama designated an undersea range of canyons and peaks off the US Eastern seaboard as the country's first Atlantic marine national monument on Thursday.

The move, in the works for more than a year, will further Obama's conservation efforts in the final months of his presidency, an initiative he views as a major component of his environmental legacy.

Speaking at a gathering of conservationists in Washington, Obama warned that rising global temperatures were already leading to extreme tides and increased erosion.

"All those things are happening now," Obama said. "They've been happening for a long time. If we are going to leave our children with oceans like the ones that were left to us, we're going to have to act. We're going to have to act boldly."

The Northeast Canyons and Seamounts Marine National Monument, which Obama created on Thursday, is situated 130 miles southeast of Cape Cod on the southern edge of George's Bank. It will protect 4,913 square miles of ocean from commercial activity and development, the White House said.

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