Obama reaches deal with China on climate change after months of talks

China and the United States made common cause on Wednesday against the threat of climate change, staking out an ambitious joint plan to curb carbon emissions as a way to spur nations around the world to make their own cuts in greenhouse gases.

The landmark agreement, jointly announced here by President Obama and President Xi Jinping, includes new targets for carbon emissions reductions by the United States and a first-ever commitment by China to stop its emissions from growing by 2030.

Administration officials said the agreement, which was worked out quietly between the United States and China over nine months and included a letter from Mr. Obama to Mr. Xi proposing a joint approach, could galvanize efforts to negotiate a new global climate agreement by 2015.