Perhaps conscious of his legacy, President Barack Obama in his second inaugural address made one of the boldest statements he's made on climate change since his 2008 campaign.
Casting the issue as an obligation not just to Americans, but to "all posterity," the president vowed in his speech that he would respond to would to the threat of climate change in his second administration.
A failure to do so "would betray our children and future generations," he said. "Some may still deny the overwhelming judgment of science, but none can avoid the devastating impact of raging fires, and crippling drought, and more powerful storms."
The White House went as far as to tweet a quote from the climate change portion of his speech, with a photo of the president, First Lady Michelle Obama, and his daughter, Malia, on a hike.
Obama warned that the path toward sustainable energy sources would be "long and sometimes difficult."
"But America cannot resist this transition; we must lead it," he said. "We cannot cede to other nations the technology that will power new jobs and new industries – we must claim its promise. That is how we will maintain our economic vitality and our national treasure – our forests and waterways; our croplands and snowcapped peaks."
He also cast the issue as one of stewardship, not merely science. Leading the charge toward renewable energy "is how we will preserve our planet, commanded to our care by God," he said. "That’s what will lend meaning to the creed our fathers once declared."
What comes next is uncertain, and it's unclear how the administration will move forward to reduce greenhouse gas emissions. Several groups have outlined various approaches the president could take to address climate change.
The biggest step, legislation that would have capped emissions and set up markets to trade pollution credits, failed in 2010 and is unlikely to be resurrected. More likely: Using the Environmental Protection Agency's ability to regulate carbon dioxide emissions and apply it to existing power plants.
The Natural Resources Defense Council has suggested such a plan, which is likely to be challenged by utilities. Other groups, such as the Clean Air Task Force, think the administration could work to curb methane emissions from the pipeline and production system, even as domestic oil and gas production booms.
Some, including the Sierra Club, are urging the administration to reject the Keystone XL pipeline from the Canadian tar sands. Sierra Club President Michael Brune said the organization is "heartened" by Obama's vow in his inaugural address.
"We will work tirelessly to ensure the transition to safe, clean energy sources to fight the most pressing challenge of our time," he said in a statement.
Former EPA Administrator Carol Browner, who served as Obama's climate change advisor, said in a statement that the president "deserves praise for giving the climate crisis such prominence in his inaugural address today."
"He is sending a clear signal that we can expect strong leadership from him in his second term on climate change and clean energy,” she said.