I'm curious what others think about the climax in The City of Ember. I think it's when Lina and Doon discover the egress from Ember, but I'm being told it's when they actually get out into the open air. I would say the climax comes when they get on the boat and leave on the river. The simple problems they come to, such as the wild river ride and the open room where they find the path are parts of the falling action. The resolution is when they actually arrive in the fresh air and enjoy the light of the world. What do you think?
The definition of a climax is that it is the point at which there is no turning back: the outcome is fixed. Some say it the most emotional or most exhilarating point. While these aspects may come into play in a climax, they are not, by definition, required. A climax may be a decision, a determination, an epiphany. These may be very quiet, unemotional events and yet be the climax.
Having said this, I second your opinion that the point of no return, the point at which the outcome is determined, is when they are clear of Ember and on the journey. I also agree that the things you enumerate are elements of the falling action. Emerging in the light on the hillside is the resolution--though it is a resolution that allows for the sequel!