WASHINGTON (AP) – President Barack Obama is talking about climate change as if it were 2009.

The President, who rarely uttered the words "climate change'' or "global warming'' during the second half of his first term and during his re-election campaign, has re-inserted it boldly back into his lexicon. In his fifth State of the Union address before Congress, Obama sounded like he did in his first, urging lawmakers to limit gases blamed for global warming "for the sake of our children and our future.'' Those words followed his inaugural address, in which he said: "We will respond to the threat of climate change.''

The difference between then and now is that Obama knows Congress is unlikely to agree. He said that if Congress won't act, he will through executive action. The question is, What will he do?

In his toolbox are things as small as requiring appliances to be more efficient and as big as controlling the largest single source of heat-trapping emissions: the carbon pollution from the nation's coal-fired power plants. How boldly will he act in the face of inevitable pushback from industries and the costs of any new regulations to the fragile economy?

Environmentalists already are pressing Obama to kill the proposed Keystone XL oil pipeline from western Canada to refineries on the Texas Gulf Coast as a first public test of his commitment to climate change.

"It's like trying to get to Rome, and there are three or four different roads that get you there,'' said David Doniger, a senior attorney at the Natural Resources Defense Council, an advocacy group.

One of the more expensive options available to Obama is regulating greenhouse gases from the oldest, dirtiest coal plants, which are already struggling to compete with cheap natural gas. Whether operators choose to shut them down or invest in pollution controls, the cost is likely to raise electricity rates. By contrast, moves to boost energy efficiency in buildings and appliances wouldn't cost as much.

David Victor, a professor at the University of California, San Diego, who has written books on climate change policy, said: "We are close to the point where we have done what we can with regulation without exposing the economy to a lot of extra cost.''