An excellent technique to get people to perk up and really hit your most important points is to slow down the speech. Slow it down a lot. Take longer pauses in between your words, and put calculated pauses at particular points to help drive home your main ideas one final time. If someone missed the rest of the speech, they should be able to get something just form this. "The fight for climate change (pause ) is a fight (pause) that we must (pause) win. Our children (pause). Our children's children (pause). Demand it." If you've just presented a really grim portrait, or a really technical series of details throughout a speech, the ending can be a great time to lighten things up a bit and end on a positive note. Letting people know that the situation is changeable, and that things aren't quite so bleak can help to get your audience energized. Return to the story of the veteran struggling to find work. With the sorts of infrastructure you're calling for in your speech, maybe he could be working a specific job, and getting into his own house, and even starting to plant a garden in the yard, something he always wanted to do. Dream a little, and let your audience do the same. Repeating a phrase or a couple of lines can be a great way to hammer home a couple of points and let your speech end with a bang. You can repeat whole phrases, or use parallel sentence structure to end your speech with repetition.  "We must do this for our children, we must do this for our neighbors, we must do this for America, we must do this for the world, we must do this for the oceans, we must do this for the forests..." "Politicians can't legislate this. Architects can't build this. Artists can't dream this. Developers can't innovate this. Only you can do this." Persuasive speeches require you to come up with a solution to a particular problem, and an excellent way of ending a speech like this is to let your audience know exactly what they can do, now, to make the kind of change you're talking about. End by projecting a telephone number they can call, or by getting them signed up for a particular mailing list about an issue, or helping them learn to contact their congress person to talk up this issue. Actually pass around a sign-up sheet if necessary. Get them involved. Address the audience specifically. Start using "you" toward the end of the speech, or address an individual in the audience to help bring it home.

Summary:
Slow down the speed of your speech at the end. End on a high note. Try repetition. Use a call to action.