The United States, showing a strong commitment to action on climate change, is formally promising to cut its emissions 26 percent to 28 percent below 2005 levels by 2025.
The U.S. government has made the formal commitment to the United Nations ahead of a global climate summit set for December in Paris.
It made the offer on Tuesday, the deadline for the world's wealthier countries to announce their commitments.
The European Union has already committed to a similar reduction in emissions, and Russia, Norway, Switzerland and Mexico have submitted their plans, but a number of other developed nations, including Canada, made no submission by the deadline.
The U.N. had asked for early commitments to avoid a repeat of the chaotic climate conference in Copenhagen in 2009, generally considered a climate-protecting failure.
China, one of the world's largest carbon emitters, has not made a commitment to the U.N. but is expected to announce a plan to have the country's emissions peak by 2030 while it pursues a goal of producing 20 percent of its energy needs from nuclear power and renewable sources.
India, also a major carbon emitter, has not yet made its commitment.
Jeremy Woods, who heads the Global Calculator project at Imperial College London, said the declarations were "an important first step" but that the world is nowhere near reining in global emissions, with China a particular concern.
"Over the last decade, the EU's emissions have shrunk, the U.S.'s have remained more-or-less stable but China's have risen dramatically from just over 10 percent of global emissions in 2000 to just under 30 percent in 2013," he said. "The world has been going in the opposite direction to that needed to reduce global greenhouse gas emissions."
In a five-page document submitted to the U.N., the U.S. government said it was determined to take strong action on cutting its carbon pollution levels and wanted to send a strong message to the rest of the world.
"The target is fair and ambitious," it said in the document (PDF). "The United States has already undertaken substantial policy action to reduce its emissions. Additional action to achieve the 2025 target represents a substantial acceleration of the current pace of greenhouse gas emission reductions."
President Obama has already set out a number of carbon-reduction actions, including tighter controls on U.S. power plants and greater efficiency standards for vehicles on the country's roads under plans announced in 2013.
Despite the announced commitments, Woods at Imperial College London says he isn't overly optimistic.
"Unless major emitters (governments and businesses alike) can find ways and reasons to dramatically change course we will move into uncharted and dangerous waters very soon," he says.
