My information is that UK consumes every year so much paper that is equivalent to a forest with the size of Wales.
I understand it's not only books, but an attitude change is needed to move toward electronic formats in all areas in order to bring breakthrough. So reading ebooks should become commonplace in order to help changing behaviours in the office.
As a minimum, we need to make distinction between materials that we read only once (newspapers, reports, novels) and those we refer to again and again (eg. dictionaries, textbooks).
I'm not sure about the direct impact of pbooks on the environment, but I believe that there is a huge indirect effect resulting from positioning paper based reading as the normal, accepted behaviour, whereas ebook enthusiasts are considered nerds, geeks, wierdos, etc. (that's my current experience
) That doesn't do good to the cause of reducing environmental footprint.