If you disbelieve in Global Warming and Climate Change, visit the Arctic.   Then visit the Antarctic. In the Arctic, talk to the people: Yupik, Inuit, Icelander, Norwegian, Finn, Sammi, Swede, Siberian. You'll come away with your mind changed, and will have seen some things that are disappearing.

If you're in the States and can't swing the trips I mentioned, go to Glacier National Park and ask how many glaciers are left there. Or visit Alaska. You don't need a passport to do either or both of these.