It has been proven that global warming is occurring and is having on impact on our biosphere.  There is no argument about this.  However, there is some uncertainty as to the cause.  In a minimum of 4 written pages, discuss the evidence that supports the concept that global warming is due to anthropogenic activities, the evidence that supports the concept that it is a natural perturbation of climatic temperatures, and then indicate which position you feel is correct.  Support your conclusions.  Use at least three references in APA format.