Calum MacLeod and Melanie Eversley

USA TODAY

BEIJING — The United States and China, the world's largest emitters of greenhouse gases, announced new targets Wednesday to cut such emissions in a bid to halt climate change and persuade other nations to take equally ambitious measures ahead of a major climate treaty to be finalized next year.

The two nations have achieved "an historic agreement," President Obama said in a joint news conference here with his Chinese counterpart Xi Jinping on the final day of his three-day China visit. The deal represents "a major milestone in the U.S.-China relationship," said Obama in the Great Hall of the People. "It shows what's possible when we work together on an urgent global challenge."

The United States will double the pace of carbon emission reduction, he said, to 26% to 28% of its 2005 level.

China intends to peak carbon dioxide emissions around 2030, and increase the non-fossil fuel share of all energy to around 20% by 2030, said Obama, in what the White House called the first ever Chinese agreement to set a ceiling on its CO 2 limits.

Republican Party criticism quickly followed, as Sen. Mitch McConnell of Kentucky, the next majority leader, called it "unrealistic." The plan, McConnell said, "would ensure higher utility rates and far fewer jobs."

"Our economy can't take the president's ideological War on Coal that will increase the squeeze on middle-class families and struggling miners," McConnell said.

The use of coal to generate power in U.S. plants has declined, as many utilities have shifted to cheaper natural gas, according to the International Energy Agency.

"This is, in my view, the most important bilateral climate announcement ever," said David Sandalow, formerly a top environmental official at the White House and the Energy Department. "It sends the signal the two largest emitters in the world are working together to address this problem."

Environmental group Greenpeace called for more even extensive action. "Both sides have yet to reach the goal of a truly game-changing climate relationship," said Li Shuo, a climate campaigner at Greenpeace in Beijing. "There is a clear expectation of more ambition from these two economies whose emissions trajectories define the global response to climate change."

The breakthrough on emissions formed the highlight of Obama's trip, only his second to China as president. Monday and Tuesday were mostly spent at a summit of leaders of the Asia-Pacific Economic Cooperation forum (APEC). China successfully pushed for movement toward a regional free trade area plan backed by Beijing, while Obama separately held talks with leaders of countries signed up to a rival plan pushed by Washington. Neither deal is close to conclusion.

Obama said Monday that a new agreement to extend the validity of visas for Chinese visitors, students and business people would greatly benefit jobs and companies in the USA. China promised to make similar visa changes, although doubts remain over how fully reciprocal the initiative will prove. The United States also announced progress on reducing tariffs on technology products, and on a bilateral investment treaty.

Wednesday, Obama and Xi announced plans to have their militaries give each other more guidance about their activities in the Pacific. Many analysts have long feared a collision at sea or in the air could spark conflict. At the press conference, a rare event in China, and not aired on Chinese television, Obama referred to several such issues that continue to trouble the relationship, including human rights, cybersecurity, and maritime disputes, as China's increasingly aggressive stance on territorial claims in the East and South China Seas has upset multiple neighbors.

Obama called for a "level playing field" for U.S. firms in China, who complain about market access barriers and intellectual property theft, but also took time to accentuate the positive. "I believe that President Xi and I have a common understanding on how the relationship between our two countries should move forward," said Obama. "Where we have disagreements, we will be candid about our intentions, and we will work to narrow those differences where possible."

After a state banquet Wednesday lunchtime, and a meeting with China's Premier Li Keqiang, Obama flies to Burma, officially known as Myanmar, for another regional economic summit, focused on southeast Asia. Friday he leaves for the G-20 meeting in Brisbane, Australia, the final stop of his summit-heavy, three-nation trip.

Contributing: Associated Press