What natural disaster is happening on Earth, that will eventually cause the human race to go extinct?

Cooper is asked by NASA to explore 3 planets in a different galaxy. He is told by Professor Brand that there is a plan A and a Plan B. What does Professor Brand tell Murphy near the end of his life? 

What does the message from the ghost say in Murphy's room.

Cooper tells Murphy that time changes (time dilation) when you are in space and that he will be a different age when he comes back. What does Cooper give his daughter before he leaves for his mission?

Why does Cooper think that going to Edmund's planet instead of Miller's planet is a bad decision? They both are showing great data for humans to survive.

What is Murphy attitude about her father, Cooper, leaving to go on the mission?

Why does Dr. Mann lie about his planet?

When Cooper finds out that he wasn't ever supposed to go back home to Murphy, what does he decide to do.

Who is Murphy's ghost?

How does Cooper communicate to Murphy when he is in the tesseract?

When Cooper finally gets back, how old is he?

Why was the relationship between Murphy and her father, Cooper so important is saving the human race from extinction?

What was one of the important jobs of that time?

Why was NASA being so secretive?

Why did Murphy get in trouble at school?