It's not a discussion that started two weeks ago. In New York in September, both leaders came together and said they wanted to be part of the solution. They didn't need any convincing on the impact that climate change was having on the world.
The breakthrough was the acknowledgement that all countries would have slightly different responsibilities. This notion of differentiation was important. The president acknowledged to the PM, "Your 300 million people who don't have access to electricity deserve that access to energy and in an affordable way. "