Obama said the "extremely difficult and complex" talks laid the foundation for international action in the years to come.
"For the first time in history, all of the world's major economies have come together to accept their responsibility to take action on the threat of climate change," Obama said at the White House on Saturday after returning from Copenhagen.
The outcome underscored shortcomings in the chaotic UN process and may pass the initiative in forming world climate policy to the United States and China.
Delegates attend a plenary session at the 2009 United Nations Climate Change Conference in Copenhagen December 19, 2009. [Agencies]
In a stormy overnight session, the talks came to the brink of collapse after Sudan, Nicaragua, Cuba, Venezuela and Bolivia lined up to denounce the US-led plan.
Sources close to the talks told Reuters the Danish hosts and UN lawyers had not obtained formal backing from the conference for a smaller group of leaders and ministers to agree a final text, leading to chaos when this was finally presented to a plenary meeting of all 193 countries.
UN talks are meant to be concluded by unanimity. Under a compromise to avoid collapse, the deal listed the countries that were in favour of the deal and those against.
The conference finally merely "took note" of the new accord.
This gives it the same legal status as if it had been accepted, senior United Nations official Robert Orr said. But it is far from a full endorsement, and it was also condemned by many environmental groups as showing a failure of leadership.