President Obama's recent announcement that states will need to cut emissions by 30% by 2030 is a great way to study government. To start with it will take another year to become final. That brings up regulation and their public comment period. Secondly the regulation comes under the auspices of the Clear Air Act. Third, it is up to the states to come up with their own plan - federalism. Fourth, Europe is considering a plan to cut emissions by 43% - international relations and on and on. The video above explains it and here is an article giving more details.