What are some problems the earth will face in the future?

I'm doing a speech, and I am thinking of doing it on problems we will have in the future. Some examples would be - population explosion, ozone layer, global warming effects, etc... What I am actually asking is what will the earth face in the future if we don't do anything to stop it. I want the full details, so that people get interested and so that they will want to do something about it. Thnx.