Try this experiment in your coffee room at work.  Put up a sign that says Did you know it takes over 700 years for a styrofoam cup to breakdown? and put a picture of a coffee mug and a styrofoam cup. 

Watch.  You will see more and more people using mugs.  It may take a few months, but watch and learn.  It really is that simple.

Sometimes a sign is all it takes.