David Tryse has come up with a series of Google Earth Overlays that highlight various global environmental issues, including deforestation, oil spills, endangered species, biological hotspots, etc. The KML files are downloadable from his web site, and you will need Google Earth to launch them. Take a look! David also hosts a few Google Earth tools on his web site.

More overlays covering a wide variety of issues can be found at the Google Earth Outreach site.