I followed almost the same approach in my essay. Causes should not be part of this essay as per heading. Ozone depletion and acid rain are different things although I made a blunder by writing ozone depletion in subheadings of threats. In last, it would be better if you make two different headings for Ways to Counter, 'International Efforts' and 'National level Efforts' and then write subheadings. Anyhow it was a good effort and I hope that we both make it.