US President Barack Obama vowed to make climate change a priority as he was sworn in Monday to a second term, using some of his most forceful language yet despite uncertain political prospects.

In an inaugural address that kept largely to lofty but general prose, Obama zeroed in on the battle against climate change as a specific goal for his presidency's next four years after setbacks in his first mandate.

"We the people still believe that our obligations as Americans are not just to ourselves, but to all posterity. We will respond to the threat of climate change, knowing that the failure to do so would betray our children and future generations," Obama said to applause before a crowd of hundreds of thousands.

Speaking from the steps of the US Capitol where the rival Republican Party controls the House of Representatives, Obama acknowledged the path "will be long and sometimes difficult" but responded directly to climate skeptics.

"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," Obama said.

Describing the transition to green technology as a job creator for the nation, which is the world's largest carbon emitter after China, Obama said: "America cannot resist this transition, we must lead it."

"That's how we will maintain our economic vitality and our national treasure -- our forests and waterways, our croplands and snow-capped peaks.

"That is how we will preserve our planet, commanded to our care by God. That's what will lend meaning to the creed our fathers once declared."

With memories fresh of super-storm Sandy and record-breaking temperatures, Obama has already indicated that climate change would be one of his second term priorities along with reforming the immigration system and tightening gun rules.

But climate legislation faces opposition from many Republicans who contest scientists' view that greenhouse gases such as carbon dioxide are causing climate change and argue that curbing industrial emissions would be too costly.

In a recent opinion article in The Washington Times, Republican Representatives David McKinley and Morgan Griffith accused the administration of "destroying a way of life" in towns that mine coal, the most carbon-intensive major energy source.

Alden Meyer, a veteran watcher of the climate change debate at the Union of Concerned Scientists, called Obama's speech a "clarion call" but acknowledged the difficulties of passing legislation in Congress.

Meyer said it was more likely that Obama would pursue his first-term strategy of taking executive measures, such as tightening emission standards from power plants.

"I don't think given the current divide in the Congress that there is much prospect of action on an economy-wide climate bill in the next year or two, but I think that could shift by the latter part of the president's second term, because clearly public awareness is increasing," Meyer said.

"This is an issue like immigration or gay rights that they can't afford to be on the wrong side of history on," Meyer said of lawmakers.

A plan backed by Obama to start a "cap-and-trade" plan with the first nationwide restrictions on greenhouse gas emissions failed in 2010 in the Senate, even with the president's Democratic Party in control.

The European Union has cap-and-trade systems in place and some experts attribute the lack of US legislation for the slow pace of global talks on a successor to the Kyoto Protocol, with China insisting on clearer commitments.

While the idea is in its infancy, a growing number of US experts have discussed imposing a direct carbon tax similar to one in Australia, which would allow the United States both to reduce emissions and close its yawning debt.

A draft government report recently warned that without action, the United States could face growing storms, fires, droughts, floods and disease and a temperature rise of up to 5.6 degrees Celsius (10 Fahrenheit) later this century.