Click on the audio player above to hear this interview.
When he first ran for president in 2007 and 2008, then-Senator Obama promised action on climate change.
"I've put forward a very substantial proposal to get 80 percent reductions in greenhouse gases by 2050," he told Katie Couric, then with CBS News. "That is going to require that we change how power plants operate; that's going to require that we change fuel efficiency standards."
A number of Obama cheerleaders were disappointed with the president's environmental record in his first term, particularly after what many described as a disastrous deal in Copenhagen, in 2009.
But the deal struck earlier this month in Paris meets at least some of the ambition Obama seemed to promise before he took office. Now comes the hard part: Implementing it.
The Paris climate change agreement is based on voluntary pledges by many different countries to cut carbon emissions. Critics may say this makes the agreement unenforceable, but Jeffrey Sachs, director of the Earth Institute at Columbia University, says that doesn't mean it is doomed to fail.
What you'll learn from this segment:
- Why Sachs believes the Paris agreement is a "diplomatic triumph."
- How nations around the world can meet these voluntary pledges.
- Whether U.S. politicians can find the political will to stick to the agreement.