The US has pledged to tackle climate change by cutting its carbon emissions 26-28% by 2025.
It made the formal offer to the UN as a step towards a global deal in Paris in December. The EU has already promised to cut its emissions by a roughly similar proportion.
Tuesday was the deadline for wealthy nations to make their offers – but some, such as Canada, have failed to submit in time.
The announcement was made on Twitter with the words: "America is taking steps to #ActOnClimate, and the world is joining us" - accompanied by a picture of the President in China.
The US announcement said: "The target is fair and ambitious. 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.
"Achieving the 2025 target will require a further emission reduction of 9-11% beyond our 2020 target compared to the 2005 baseline and a substantial acceleration of the 2005-2020 annual pace of reduction, to 2.3-2.8 percent per year, or an approximate doubling."
Analysts examining the promises made by the first few nations to commit say they are not strong enough to hold global temperature rise to the internationally agreed maximum of 2C.
A major US government website supporting public education on climate science looks likely to be shuttered...
A growing wildfire in Oregon has destroyed multiple homes and prompted evacuation orders in the Columbia...
