Before the Flood: Throughout the whole trailer narrated by DiCaprio, a very strong appeal is made to the emotions of the audience, which is realized through the carefully built structure of it. Firstly, he builds up tension, emphasizes the importance and the urgency of the issue, outlines through both visual and auditory tools that it concerns all of us, and presents data, factual evidence about it.
Secondly, after narrating the sad reality, he expresses the chance for a prospering, hopeful future. His main positive and encouraging message is, that if we act, we solve it, is realized by presenting the opinion of four highly respected, trusted leaders who people listen to.
(1) Ban Ki-Moon [secretary of the United Nations for 9 year] says, that there already are "mass demonstrations", an "unprecedented number of people" are starting to realize this problem and act
(2) Elon Musk [CEO of Tesla and SpaceX] stated, that a "100 Gigafactories would be enough to transition the whole world to sustainable energy" and that this is quite "manageable" with the current technology and resources.
(3) The clip featuring Pope Francis did not use any words nor language, but showed him handing over a gift to DiCaprio, symbolizing the support for this cause
(4) Lastly, the trailer ended with DiCaprio discussing the issue of climate change with Obama, who expressed his thoughts, that "If we keep pushing, there's no reason why we can't solve this problem" and then shook his hand, which created a sense of reassurance, security and hope in the eyes of the audience.