"The question is whether we will move forward together, or split apart," Obama said during the U.N-sponsored summit in Copenhagen. "This is not a perfect agreement, and no country would get everything that it wants."
Leaders have a choice -- embrace the accord, work to refine it and build on its foundation, or delay and retreat to the same divisions that have been argued for years, Obama said.
"There is no time to waste," Obama said. "Now, I believe that it's time for the nations and people of the world to come together behind a common purpose."
"(While) the reality of climate change is not in doubt, our ability to take collective action hangs in the balance," Obama said. "I believe that we can act boldly and decisively, in the face of this common threat."
Months of talks and weeks of negotiations produced three clear elements of a draft accord, Obama said.
First, "all major economies must put forward decisive national actions that will reduce their emissions, and begin to turn the corner on climate change," Obama said, noting many have done so.
Second, transparency is needed to ensure countries are meeting their commitments and to exchange information, he said. Measures to guarantee transparency don't have to be intrusive, but must "ensure that an accord is credible, and that we are living up to our obligations," he said. "For without such accountability, any agreement would be empty words on a page."
Finally, financing must be available to aid developing countries adapt to climate change.
"Mitigation. Transparency. And financing. It is a clear formula -- one that embraces the principle of common but differentiated responses and respective capabilities," Obama said. "And it adds up to a significant accord -- one that takes us farther than we have ever gone before as an international community.
World leaders must look to the future, he said in conclusion and "meet our responsibility to our people, and to the future of our planet."