China and the U.S. are responsible for about a third of the world's carbon output, making them the top two greenhouse gas emitters. Their reluctance to pledge to serious cuts has been a major stumbling block to global treaties in the past.
Now the two nations have outlined some of the boldest goals yet to cut emissions and spur green technology.
The plan, announced late Tuesday, follows months of talks and a meeting this week between President Obama and Chinese President Xi Jinping.
This is how the White House put it: "The world’s two largest economies, energy consumers, and carbon emitters are reaching across traditional divides and working together to demonstrate leadership on an issue that affects the entire world."
So far, the proposals have been widely applauded, but observers are cautious.
There is still the question of how it will be put into effect and how domestic policies could hinder reaching the goals.
For more, Take Two is joined by Alex Wang, a professor at UCLA's law school. Wang helped establish the Beijing office for the Natural Resources Defense Council where he was senior attorney.