WASHINGTON - President Barack Obama pledged in his inaugural address Monday to respond to the threat of climate change, saying the "failure to do so would betray our children and future generations."

By singling out climate change for several lines of his speech, he is taking on an issue that he acknowledges was often overlooked during his first term and setting up a confrontation with congressional Republicans who have opposed legislative efforts to curb global warming.

"Some may still deny the overwhelming judgment of science" that global warming exists and has human causes, Obama said, "but none can avoid the devastating impact of raging fires and crippling drought and more powerful storms."

The president has pledged to boost renewable energy sources such as wind and solar power, along with more traditional energy sources such as coal, oil and natural gas.

"The path towards sustainable energy sources will be long and sometimes difficult. But America cannot resist this transition. We must lead it," Obama said.

He said developing new energy technologies will lead to jobs and new industries. "That is how we will preserve our planet," he said.

Environmental groups hailed Obama's new focus on climate change but said the president's words will soon be tested as he decides whether to approve the Keystone XL oil pipeline from Canada.

Obama blocked the pipeline last year, citing uncertainty over the project's route through environmentally sensitive land in Nebraska. The State Department has federal jurisdiction because the $7 billion pipeline begins in Canada.

Republicans and many business groups say the project would help achieve energy independence for North America and create thousands of jobs.

But environmental groups say the pipeline would transport "dirty oil" from tar sands in Alberta, Canada, and produce heat-trapping gases that contribute to global warming. They also worry about a possible spill.

"Starting with rejecting the Keystone XL pipeline, the president must make fighting global warming a central priority," Margie Alt, executive director of Environment America, said Monday.

Alt and other environmental leaders said they are counting on Obama to set tough limits on carbon pollution from coal-fired power plants and to continue federal investments in renewable energy sources such as wind and solar power.

Obama tried and failed in his first term to get a climate change bill through Congress. Some Democratic lawmakers and environmentalists have pushed for a tax on carbon pollution, but White House officials say they have no plan to propose one.

Scott Segal, an energy lobbyist who represents utilities and natural gas drillers, said Obama "missed the opportunity to remind listeners that climate change is an international phenomenon" that will require international solutions.

By imposing "inflexible" national policies to curb climate change, Obama could restrain the U.S. economy without delivering promised solutions, Segal said.