Coal-fired power plants have a significant impact on the environment. The Sierra Club is monitoring the progress of every proposed plant in the U.S. You can see them on this map and follow along.
Another issue you can follow with an online map is the plastic garbage vortex in the Pacific. Project Kaisei is studying it and you can follow their expedition with a Google Earth plugin.
I found both of these on Google Maps Mania which is a site dedicated to presenting all the Google Maps mashups they can find about everything.