US and France Cooperate on Global Climate Change Pact

President Obama and French President Francois Hollande agreed to expand on their work to curb global climate change, ahead of the upcoming United Nations climate summit next year in Paris. The UN is expected to create a global binding agreement to take effect in 2020. 

Why are these two leaders urging other nations to get on board before the summit? 
It would appear that both leaders mean serious business, so they want to make sure everyone else means serious business when the summit arrives. 

In all seriousness, during his State Visit to the US, Hollande said, “How not to mention climate change when France next year will convene and host a conference? It’s not just about hosting a conference and having our hotels full. No, it’s about reaching a global goal, because there is a danger.”

Resources 
Hollande and Obama Push For Global Climate Change Pact - TIME World

Obama, Hollande Cooperate on 2015 Global Climate Change Pact - Environment News Service