LIMA, Peru — When it comes to global warming, the United States has long been viewed as one of the world’s worst actors. American officials have been booed and hissed during international climate talks, bestowed with mock “Fossil of the Day” awards for resisting treaties, and widely condemned for demanding that other nations cut their fossil fuel emissions while refusing, year after year, to take action at home.

Suddenly, all that has changed.

At the global climate change negotiations now wrapping up in Peru, American negotiators are being met with something wildly unfamiliar: cheers, applause, thanks and praise.

It is an incongruous moment, arriving at a time when so many aspects of American foreign policy are under fire.

But the enthusiastic reception on climate issues comes a month after a historic announcement by the United States and China, the world’s two largest polluters, that they would jointly commit to cut their emissions. Many international negotiators say the deal is the catalyst that could lead to a new global climate change accord that would, for the first time, commit every nation in the world to cutting its own planet-warming emissions.