I have trouble taking either statement that seriously.  We do not have a baseline to compare against as there is no spare earth available that is untouched by human hands.<p>The question has to be considered primarily from a qualitative point of view.  The only reason people discuss the science so much is because they lack good instincts about the environment.  It is so easy to believe that humans are an insignificant part of the environment when you entire world is made by man.