Environmental challenges fall into the same three categories, and most of what we think about are local environmental problems: air pollution, water pollution, hazardous waste dumps. But there are also regional environmental problems, like acid rain from the Midwest to the Northeast, and from Western Europe to the Arctic, and from the Midwest out the Mississippi into the dead zone of the Gulf of Mexico.
Izazovi očuvanja okoliša mogu se svrstati u iste tri kategorije i većina onih o kojima razmišljamo su lokalni problemi okoliša: zagađenje zraka, zagađenje voda, odlaganje opasnog otpada. No postoje i postoje regionalni problemi očuvanja okoliša, poput kiselih kiša od Srednjeg zapada do Sjeveroistoka, te od Zapadne Europe do Arktika i od Srednjeg zapada niz Mississippi do mrtve zone Meksičkog zaljeva.